4,4'-isopropylidenediphenol

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics

Type of information:

other: Data analysis of mice, rats, monkeys, chimpanzees, sheep, dog, piglet and human data.

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Principles of method if other than guideline:

Comprehensive analysis of the available toxicokinetic data for BPA following controlled oral dosing in mice, rats, monkeys, chimpanzees, pigs, sheep, dogs and humans. Extrinsic clearance was calculated and analyzed across species and dose using allometric scaling. After determining the relationship between body weight, apparent clearance and AUC, Human Equivalent Dose Adjustment Factors (HEDf) were determined.

GLP compliance:

no

Conclusions:

The results indicate free BPA clearance is well described using allometric scaling with high correlation coefficients across all species and doses up to 10 mg/kg. The results indicate a human equivalent dose factor (HEDf) of 0.9 is appropriate for extrapolating a point of departure from mice and rats to a human equivalent dose (HED), thereby replacing default uncertainty factors for animal to human toxicokinetics.
The new data from pigs, sheep and dogs are consistent with the broader set of data (Poet & Hays, 2018). This gives additional confidence that Clearance scales across species in a fairly consistent manner and any risk assessments that rely on data from an animal toxicology study should utilize a human equivalent dose (HED) using the following table.

Executive summary:

The results indicate free BPA clearance is well described using allometric scaling with high correlation coefficients across all species and doses up to 10 mg/kg. The results indicate a human equivalent dose factor (HEDf) of 0.9 is appropriate for extrapolating a point of departure from mice and rats to a human equivalent dose (HED), thereby replacing default uncertainty factors for animal to human toxicokinetics.

The new data from pigs, sheep and dogs are consistent with the broader set of data (Poet & Hays, 2018). This gives additional confidence that Clearance scales across species in a fairly consistent manner and any risk assessments that rely on data from an animal toxicology study should utilize a human equivalent dose (HED) using the following table.

Species	Bodyweight [kg]	Predicted Clearance	Predicted AUC^a	HEDf (species/human)
Mouse	0.02	147.2	0.6794	0.9
Rat	0.2	142.2	0.7033	0.9
Dog	17	133.0	0.7517	1.0
Pig	30	131.9	0.7582	1.0
Sheep	59	130.6	0.7659	1.0
Chimpanzee	45	131.1	0.7628	1.0
Human	70	130.2	0.7679	1.0

a - calculated using a dose of 100 µg/kg

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2014 and 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Objective of study:

other: The objective was to examine the absorption, distribution, metabolism and excretion of BPA in humans following dermal admistration.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Deuterated BPA (d6-BPA) was dermally administered to 10 subjects (6 men and 4 women) at a dose of 100 µg/kg over a 12-hour period and blood and urine analysis were conducted from the beginning of dosing through a three- or six-day period. Time-course serum and urine concentrations of total and unconjugated(free) d6-BPA were determined and was used to calculate the terminal half-life and the area under the curve. The protocol (protocol number 12-E-0089; clinicaltrials.gov identifier: NCT01573429), blood, and urine collection method was approved by the NIEHS Institutional Review Board (IRB).

GLP compliance:

not specified

Specific details on test material used for the study:

Deuterated d6-BPA (dimethyl‐d6; 98% isotopic purity and 99% chemical purity; product # 588806-1G) was purchased from Sigma Aldrich (St. Louis, MO) and the corresponding labeled internal standard 13C12-BPA (99%) was obtained from Cambridge Isotope Laboratories, Inc. (Andover, MA).

Radiolabelling:

no

Species:

other: humans

Strain:

other: not applicable

Sex:

male/female

Details on test animals or test system and environmental conditions:

Men and non-pregnant women were recruited by the National Institute of Environmental Health Sciences Clinical Research Unit (NIEHS CRU) in 2014 and 2017 from the Raleigh Durham region of North Carolina using standard flyer advertisements. Criteria included age (25–45), ability to fast overnight, and agreement to avoid conceiving a child and not donate eggs or sperm for six months following their participation.

The average age of male (n = 6) and female (n = 4) volunteers was 33 years (range 25–42) and 31 years (range 26–35), respectively. Half of the subjects were non-Hispanic whites (n = 5;), while the remainder were black or African-American (n = 4) and mixed-race (n = 1). The average BMI of male and female volunteers was 27.2 (22.4–34.2) and 28.7 (21.6–34), respectively. The average body weight of male and female volunteers was 91.2 kg (67.7–124.0) and 80.0 kg (70.0–95.4), respectively. Three of the 10 subjects (two males and one female) participated in both experimental protocols (2014 and 2017) and received a different dosing vehicle (CMC or ethanol) at each visit.

Criteria for exclusion included specified pre-existing health conditions, pregnancy, and use of medications that may affect glucuronidation of BPA. Blood samples used to determine eligibility status was collected at the time of the initial screening visit.

Participant Inclusion Criteria:
• Male or female 25-45 years of age at the time of enrollment
• Able to fast overnight
• Able to understand and provide written informed consent in English
• Able to travel to the NIEHS Clinical Research Unit (CRU) for all required study visits
• Male and females of reproductive age agree to use contraception to avoid conceiving a child and agree not to donate eggs or sperm for six months following their participation in the study

Participant Exclusion Criteria:
• Uncontrolled diabetes:
- Hemoglobin A1C of >6.5% or a fasting blood glucose of >126 mg/dL
• Known liver dysfunction or disease:
-ALT - higher than the normative value or determined abnormal by the PI
- AST – higher than the normative value or determined abnormal by the PI
- ALP – higher than the normative value or determined abnormal by the PI
• Known kidney dysfunction or disease:
- Estimated Glomerular Filtration Rate (eGFR)- <60 ml/min per the MDRD equation
•Clinically relevant anemia as defined as hemoglobin concentration <13 g/dL for males and hemoglobin concentration <11 g/dL for females
• Pregnancy: Positive serum quantitative hCG pregnancy test
• Current lactation
• BMI ≤19 and ≥35
•Medication use: Given the widespread use of medications, it may not be practical to instruct subjects to avoid all medication prior to and during the study. Thus, participant exclusion will be based on use of medications within 48 hours of the exposure and for the 6 days following the exposure that affect glucuronidation of the d-BPA dosage: Salicylic acid, acetaminophen, ibuprofen, naproxen, mefenamic acid, diclofenac, gliclazide carbamazepine, valproic acid, cimetidine, sulfasalazine, amoxicillin and erythromycin (Verner et al. 2010).
• Recent blood donation within the past 8 weeks of the BPA exposure visit (so as not to exceed donation of 10.5 mL/kg or 550 mL over an 8 week period)

BPA Exposure Questionnaire:
Each participant was asked to complete a short questionnaire, to collect demographic information including age, ethnicity (required for NIH human participants reporting) and gender. Information about BPA exposure status at home and at work was collected, including the following:
• Information on activities and practices that may impact oral exposure to BPA (i.e., use of polycarbonate bottles, consumption of canned foods).
• Occupational information (e.g., works in the manufacture of BPA or BPA-containing products such as polycarbonate bottles or epoxy resins, handles cash register receipts, etc.).

Route of administration:

dermal

Vehicle:

other: 0.3% carboxymethylcellulose (6 participants) suspension and 95% ethanol (7 participants)

Details on exposure:

TEST SITE
- Area of exposure: Volar surface of the forearm - 4.91 cm2.
- % coverage: Generally, one application site was used per subject. For the 2014-CMC study arm, two or more application sites were used (with simultaneous application) depending on the subjects weight. This was done because a practice session indicated that larger individuals with correspondingly larger dose formulation volumes would have the solution run off their arms, so the formulation was divided to prevent this runoff.
- Type of wrap if used: The application area(s) were encircled with petroleum jelly and each area was then covered with the Hill Top Chamber (HTC) without a pad covering the area. The chamber was secured with tape to prevent the spreading of the dried d6-BPA layer/film on the skin.

REMOVAL OF TEST SUBSTANCE
- Washing (if done): The HTC was removed and skin was rinsed and/or wiped with rinsates and wipe materials saved for analysis.
- Time after start of exposure:12 h

TEST MATERIAL
- Concentration (if solution): The solution for dermal application (25 mg/mL) was prepared by dissolving a weighed portion of d6-BPA (dimethyl-d6; 98.6% isotopic purity and > 99.7% chemical purity, CDN Isotopes, Pointe-Claire, Quebec) (Twaddle et al., 2010) in USP grade 95% ethanol (Decon Laboratories, King of Prussia, PA) or an aqueous suspension containing 0.3% CMC. The d6-BPA solutions were stored as 0.5 mL individual aliquots in 2-mL tubes and stored frozen at -20 °C until the day before the participant’s dosing visit when they were thawed in the refrigerator. For most participants, the nominal d6-BPA concentration (25 mg/mL) was used to calculate the appropriate amount X (mL) of the dosing solution/suspension from the participant body weight Y (kg) measured on the day of the study and the target dose (100 µg/kg BW) (see below). The d6-BPA dosing concentration was validated for four selected participants using HPLC-MS/MS, and this analytical value was used in the calculation instead of the nominal concentration (e.g., a 70 kg subject will receive an application of 0.28 mL of the dosing solution): X mL (100 g/kg BW) Y kg BW/(25, 000 g/mL dosing solution)

Details on exposure:
Dermal administration started in the morning after a fasting period beginning at midnight on the day of the visit. Locations on the skin of the volar forearm were identified and a circle drawn using a Hill Top® Chamber (Hill Top Research, Inc., Cincinnati, OH) as a template. A pipette with a polypropylene pipet tip was used to apply the d6-BPA solution (ethanol) or suspension (CMC) to the unshaven volar forearm of the participant, choosing an area with the least amount of hair and with no visible scratches or open wounds. For both the CMC and ethanol experiments, the solution was allowed to dry for approximately five minutes, using a gentle stream of air from a hairdryer if needed.
Drying time was noted in the participant’s record. The beginning of application of the d6-BPA solution or suspension was considered to be time zero for data-recording purposes. After the solution dried, the application area(s) was encircled with petroleum jelly and each area was then covered with the Hill Top Chamber (HTC) without a pad covering the area. The chamber provided a viewing window for study staff to monitor for possible skin irritation. The area under the HTC was 4.91 cm2. The chamber was secured with tape to prevent the spreading of the dried d6-BPA layer/film on the skin. At 12 h after the start of administration, the HTC(s) were removed and skin was rinsed and/or wiped with rinsates and wipe materials saved for analysis.

Recovery of unabsorbed d6-BPA after dermal administration:
Following dermal administration and removal of the HTC at 12 hrs, the application area(s) were rinsed with a polypropylene squeeze bottle filled with 95% ethanol to recover unabsorbed d6-BPA for quantification.
A volume of 1–2 mL rinsing solution was squirted on the exposed skin area, and a sponge or gauze was used to wipe the exposed skin with the rinsing solution. For the 2014 protocol using CMC, no wiping material was used. The site rinsate was collected in a specimen cup. The rinsing step was typically repeated several times, and the total volume of site rinsate was recorded. Rinsing of the HTC with ethanol and recording the total volume of HTC rinsate was done similarly. Polypropylene vials with 1–2 mL aliquots of the rinsates were sent for d6-BPA analysis. The HTC and the sponge/gauze were also sent to the analytical lab to recover and determine any residual d6-BPA adsorbed to these materials.

Duration and frequency of treatment / exposure:

12 hour/single dose

Dose / conc.:

100 other: µg/kg bw

No. of animals per sex per dose / concentration:

10 subjects (6 men and 4 women)

Control animals:

no

Details on study design:

2014 Protocol versus 2017 protocol
The target dermal dose of 100 µg/kg was selected in order to match the administered dose used in an oral arm of this study (Thayer et al., 2015). A dermal study was initially conducted in 2014 to evaluate the suitability of the oral study sample collection protocol to evaluate pharmacokinetics following dermal exposure (Fig. 1 – included below in attached background information), and to help select a vehicle to best model the nature of human exposure (i.e., handling thermal paper). More specifically, the 2014 protocol was conducted to verify that detectable levels of d6-BPA could be measured using either a 0.3% aqueous carboxymethylcellulose (CMC) suspension vehicle or a 95% ethanol solution vehicle, and whether follow-up for 3 days after dermal administration was sufficiently long to observe complete (or nearly complete) urinary elimination.
Preliminary results of the 2014 study on four subjects using 0.3% CMC suspension vehicle indicated that a longer follow-up period post-treatment was warranted. The protocol was subsequently amended to allow for extending the follow-up period to six days for subjects participating in the 2017 studies.
The preliminary analysis of the 2014 CMC data also included estimates of free d6-BPA serum concentrations. For the current study, urine and serum samples from the 2014 preliminary analysis were re-analyzed using the method described below to better compare across the 2014 and 2017 experiments.
Analysis of free d6-BPA in serum was limited to samples from the ethanol study arms. This was done to complement the 2014 CMC analysis by expanding the database to include free d6-BPA measurements for the ethanol vehicle, and to focus post-2014 analyses on the vehicle believed to facilitate higher absorption.
The study was designed to evaluate the pharmacokinetics of dermal uptake, which required prolonged exposure at a high surface concentration. Ethanol and CMC vehicles on the forearm are not representative of typical exposures (such as thermal receipts on the hands), and the use of a Hill Top chamber caused occlusive conditions, which likely promoted sweat layer formation on the covered skin. This administration regimen might have enhanced dermal absorption relative to what might be expected following skin contact to thermal receipt paper. The aim was to ensure that dermal uptake would indeed occur so that kinetic parameters can be evaluated and compared against other controlled exposure scenarios.


Pharmacokinetic analysis:
Analyses and data visualizations were performed using the R programming language (R Core Team, 2019). Plots of serum concentrations of total and free d6-BPA at each time point were generated at the individual-level. The terminal half-life in serum (t1/2) was determined for each dataset by fitting an exponential curve, beginning at the peak concentration (typically the 12-hour timepoint). A single terminal phase was observed, and all data from the peak concentration through the end of data collection (3–6 days, depending on the protocol) were fitted to a single exponential curve by least-squares regression of log-transformed concentration vs time. The observed t1/2 represents both serum elimination kinetics and diffusion kinetics of absorption from the dermal compartment (which may be a rate-limiting step). If the absorption process would indeed be the rate-limiting step that governs the disappearance from the body, this kinetics would then be described as a flip-flop situation (Derendorf and Rowland, 2020; Gabrielsson and Weiner, 2016). To estimate the area-under-the-curve from time zero to infinity (AUC0–∞) for serum concentrations, the log-linear trapezoidal rule was applied using t1/2 and the serum concentration at the last time point.

Details on dosing and sampling:

TOXICOKINETIC / PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: Urine and blood
- Time and frequency of sampling: Blood: after the start of administration, blood was collected for 12 h via an indwelling IV cannula/saline lock at: 0, 5, 10, 15, 20, 25, 30, 40, 45, 50, 60, 80 and 100 (± 5 min); 120, 150, 180, 210, 240, 270 and 300 (± 10 min); 330, 360, 390, 420, 480, 540 min (± 15 min); and 720 min (± 20 min). Additional blood samples were collected by peripheral blood draw at 24/48/72 h for all participants remaining in the study, and at 144 h for 2017 participants.
Urine: a fasting urine specimen was collected prior to dosing. Following the start of administration of d6-BPA, participants collected all unscheduled urine voids in separate containers from 0 to 2, 2 to 4, 4 to 8, and 8 to 12 h. Participants of the 2014 protocol performed a 24-hour collection for 3 days post-dose, while 2017 participants performed these collections for 6 days post-dose.


Analytical methods:
Sample preparation and quantification of total and free d6-BPA in urine and serum were based on a previously described method (Thayer et al., 2015; Twaddle et al., 2010) with some modifications. In brief, 13C12-BPA was added to an individual urine or serum sample (0.2 mL) for isotope-dilution high performance liquid chromatography-tandem mass spectrometry (HPLC–MS/MS) analysis. Further details can be found below under attached background material - Analytical method_d6 BPA measurements.pdf.

Type:

absorption

Results:

Total d6-BPA: Cmax (serum) = 3.26 ± 2.31 nM. Free d6-BPA: Cmax (serum) = 0.272 ± 0.141 nM. Combined (2017 and 2014 protocol).

Type:

absorption

Results:

Total d6-BPA: AUC0-∞ (serum) = 95.6 ± 54.4 nM x h. Free d6-BPA:AUC0-∞ (serum) = 7.51 ± 2.69 nM x h. Combined (2017 and 2014 protocol)

Type:

absorption

Results:

Total d6-BPA: % free AUC (serum) = 8.81 ± 1.65 nM. Combined (2017 and 2014 protocol).

Type:

absorption

Results:

Total d6-BPA: t1/2 (serum) = 21.4 ± 9.81 nM. Free d6-BPA: t1/2 (serum) = 17.6 ± 7.69 nM. Combined (2017 and 2014 protocol).

Type:

excretion

Results:

Total d6-BPA: cumulative excreted (urine) = 0.998 µg/kg BW. Combined (2017 and 2014 protocol).

Details on absorption:

A summary of estimated pharmacokinetic parameters is presented in Table 2.

Detectable serum levels of total d6-BPA were observed at 1.4 h after the start of dosing. A maximum serum concentration (Cmax) of 3.26 nM was observed. Free d6-BPA was detectable in serum 2.8 h after start of dermal administration, with Cmax of 0.272 nM.

Based on data collected under the 2017 protocol, detectable serum levels of total d6-BPA were observed at approximately 1.4 h (ranging from 0.6 to 3.7 h) following the start of dermal administration. Detectable free serum d6-BPA appeared approximately 1.8 h (1.5–2.2 h) after the appearance of total d6-BPA at the individual-level, or approximately 2.8 h (2.5–3.1 h) after the start of dermal administration. Serum concentrations of free and total d6-BPA increased rapidly for seven hours. Free d6-BPA was a significantly greater percentage of the total serum BPA, with 10.9% (6.6–17%) at Cmax compared to the 0.39% observed in the oral arm (Thayer et al., 2015). Beginning at approximately seven hours and continuing to 12 h (which corresponds to the cessation of exposure), the concentration of free and total serum d6- BPA plateaued. After cessation of dermal exposure, elimination from the serum was slow, with t1/2 values for free and total BPA estimated to be approximately 15–20 h.

Details on excretion:

Total d6-BPA was detected in the urine at first urinary void for all individuals (within 2 h). Approximately 1% of the target dose was collected in urine by day three post-dose. The concentration of total urinary d6-BPA increased rapidly during 8–12 h and then decreased continuously, beginning around 24 h post-dose. For all individuals, there remained detectable levels of total urinary d6-BPA at the end of the experiment (three days post-dose for the 2014 study participants, and six days post-dose for the 2017 study participants). However, the daily urinary excretion of total d6-BPA was a negligible percent of the dose after about three days. There was high interindividual variability in the cumulative excreted dose (which did not plateau at three days post-dose).

The plateau of serum unconjugated and total d6-BPA indicates that a steady-state between absorption and elimination processes had been reached. Given the serum elimination half-life of ~ 6 h for unconjugated d6-BPA (observed in Thayer et al., 2015), steady-state was achieved faster than expected. If the dermal absorption rate of d6-BPA into blood was constant (as in the case of intravenous infusion), it would take approximately five elimination half-lives (30 h) to reach a quasi-steady state serum concentration of unconjugated d6-BPA (97% of the final level).

Metabolites identified:

not measured

Table 2. Pharmacokinetics parameters for total and free d6-BPA in serum and urine of human subjects administered d6-BPA via 12-hour dermal application.

 

	Serum					Urine
	Cmax (nM)	% free Cmax	AUC0-∞ (nM × h)	% free AUC	t ½ (h)	Cumulative excreted (µg/kg BW)
2017 protocol
Total d6-BPA	2.63 ± 1.69 (5)	9.66 ± 3.39 (3)	72.4 ± 45.7 (4)	8.41 ± 1.67 (2)	20.0 ± 6.84 (4)	1.16 ± 0.572 (4)
Free d6-BPA	0.282 ± 0.0583 (3)	-	8.68 ± 1.35 (2)	-	12.2 ± 5.16 (2)	-
2014 protocol
Total d6-BPA	3.66 ± 2.65 (8)	11.9 ± 4.15 (4)	107 ± 57.4 (8)	9.02 ± 1.85 (4)	22.1 ± 11.4 (8)	0.919 ± 0.554 (8)
Free d6-BPA	0.282 ± 0.0583 (3)	-	8.68 ± 1.35 (2)	-	12.2 ± 5.16 (2)	-
Combined protocol
Total d6-BPA	3.26 ± 2.31 (13)	10.9 ± 3.73 (7)	95.6 ± 54.4 (12)	8.81 ± 1.65 (6)	21.4 ± 9.81 (12)	0.998 ± 0.546 (12)
Free d6-BPA	0.272 ± 0.141 (7)	-	7.51 ± 2.69 (6)	-	17.6 ± 7.69 (6)	-

 

All values shown as mean ± SD (n), where n is the number of datasets used to estimate the parameter. AUC_0-∞ estimated by log-linear trapezoidal rule from time zero to infinity (using t_1/2 and the final serum concentration). C_max was directly obtained from the data for all datasets. t_1/2 estimated for individuals I and G of the 2014 protocol omitted data for t = 12 h, since concentrations increased to t = 24 h. AUC, t_1/2, and cumulative amount excreted could not be estimated for individual D due to early withdrawal from the study. Time to C_max (i.e., t_max) is not applicable because serum concentration increases to C_max during exposure, and predictably declines when exposure is stopped at 720 min. There was no discernable difference between vehicles (CMC or ethanol) given the interindividual variability, and data for free d6-BPA were only analyzed for the ethanol results. A pilot analysis was performed on the 2014 CMC data, which included an estimate of free d6-BPA. These preliminary results are not incorporated in this analysis due to inter-laboratory differences.

Table 3: Plausibility check of the fraction dermally absorbed (Fabs), as obtained by three different approaches, in terms of serum clearance of unconjugated BPA.

Approach	Fabs (%)	Dose D (nmol)	AUC (Nm x h)	CL (L/h)
Recovery of total BPA in urine	1	34,141	7.51	45
Serum AUCs of total BPA after oral and dermal administration	2.2			95.5
Mass-balance consideration based on recovery and unabsorbed BPA	12-29			545-1318

The absolute dose (D, nmol) derives from the per-body-weight dose of 100 µg/kg BW multiplied by a body weight of 80 kg and divided by the molecular mass of 234.32 g/mol for d6-BPA. The assumed body weight is represented for the six subjects from which the estimate for the mean serum AUC of 7.51 nM x h for unconjugated BPA was obtained. The serum clearance for unconjugated BPA (CL) was calculated as: CL = Fabs/100% x D/AUC.

Recovery of unabsorbed d6-BPA after dermal administration

A substantial amount of the applied dose was recovered from the application site at 12 h following dermal administration of d6-BPA in ethanol. For the ethanol experiments under both the 2014 and 2017 protocols, 71–99% of the applied dermal dose remained unabsorbed on the skin or the HTC. This is in good agreement with the experiments using CMC conducted in 2017, which found an unabsorbed dose of 75–79%. For the 2014 CMC data, a lower percentage (19–21%) of the applied dose was recovered. For this dataset, no sponge or gauze was used to wipe the exposed skin of the rinsing solution. This likely had a negative impact on the effectiveness of surface recovery. In all experiments conducted in 2014, the largest proportion of the unabsorbed dose was found on the skin, whereas only a minor portion was recovered from the HTC. The opposite is true for the experiments conducted in 2017, where the largest proportion of the unabsorbed dose was recovered from the Hill Top Chamber (HTC )and a minor portion from the skin rinsate. Multiple differences between the 2014 and 2017 experiments were documented, and these could have contributed to the recovery variations. As noted earlier, there was a lack of skin wiping for the 2014 CMC experiment. In addition, the 2014 CMC study used 2–4 application sites rather than a single application site. Distributing the dermal dose (100 µg/kg BW) across a larger skin surface area would enable the applied BPA to diffuse into a larger portion of skin surface to build up a skin depot. Different nurses implemented the surface and HTC rinsing protocol between 2014 and 2017, which could have also impacted surface recovery. Irrespective of these differences, there was good agreement in the unabsorbed dose (71–88%) across the subjects when excluding the implausible value of 99% from one participant (where 1.4% of the dose was still collected in urine) and excluding the low values from the 2014 study using CMC where no skin wiping was performed.

Estimates of absorbed d6-BPA after dermal administration:

The dermal and HTC recovery mass balance implies that up to 12–29% of the applied dermal dose penetrated the skin over a 12-hour period. This is likely an over-estimate due to the experimental variation in rinsate recovery as well as unaccounted amounts lost to the environment.

The percentage of total d6-BPA recovered in urine was significantly lower (approximately 1% of the target dose). This is likely an under-estimate of total absorbed dose because detectable levels of d6-BPA were measured in urine and serum at the end of the experiment for all individuals. This indicates that not all d6-BPA had been cleared from the subjects at the time the last observations were made. Comparing the average serum AUC for total d6-BPA between Thayer et al. (2015) (where the target oral 100 µg/kg of d6-BPA dose was almost completely absorbed) and the current work, the dermal AUC for a target 100 µg/kg dose was 2.2% of the oral AUC. This may be one estimate for the average percent dose absorbed into systemic circulation following 12-hour dermal application, but there is some uncertainty due to interindividual variability, and oral/dermal toxicokinetic differences. Given the high approximate dermal absorption of up to 12–29% as implied from surface recovery, and the fact that detectable levels were measured in serum at the end of the experiment, it is possible that a portion of the administered dose that penetrated the skin remained in the dermis and epidermis throughout the post-dose period and beyond six days. This depot of d6-BPA in the skin would have continued to diffuse into the blood until depleted or lost by other removal processes (contact with other surfaces, skin washing, and desquamation).

To further reduce the uncertainty surrounding the dermal estimates for the fraction dermally absorbed (Fabs) were used to calculate the serum clearance (CL) of unconjugated BPA for a human subject with a body weight (BW) of 80 kg (Table 3). Apart from Fabs, the absolute dermal dose (D) and the AUC for unconjugated BPA entered into the calculation (Table 3). The calculated serum clearances were then compared with the clearance predicted by allometric scaling based on animal data with intravenous administration of BPA.

The Fabs values derived from the three approaches (1%, 2.2%, and12–29%) translate into serum clearances of 45 L/h, 95.5 L/h, and 545–1318 L/h (Table 3). Allometric scaling approaches predict serum clearances of 140 L/h (=5.264 × BW0.749; Cho et al. (2002)) and 122 L/h (=2.34 × BW0.9014; Collet et al. (2015)), respectively, for an 80-kg human. The Fabs value of 1%, which was obtained by considering the recovery of total BPA in urine, translates into a serum clearance of half that predicted by allometric scaling. The Fabs value of 2.2%, which was calculated from the serum AUCs of total BPA after oral and dermal administration, translates into a serum clearance which is physiologically plausible as it is consistent with allometric scaling estimates. This conclusion holds true even assuming a small portion of the dermally absorbed BPA is metabolized in the skin before reaching systemic circulation.

The Fabs value of 12–29%, which derives from mass-balance considerations based on the recovery of unabsorbed BPA, yields a serum clearance of 545–1318 L/h which is physiologically implausible as it grossly exceeds not only the values predicted by allometric scaling but also the hepatic blood flow (Collet et al., 2015). This strongly suggests that the 12–29%, being the complement of the portion recovered from the application site, was mostly lost to the environment rather than absorbed.

 

 

Executive summary:

Deuterated BPA (d6-BPA) was dermally administered to 10 subjects (6 men and 4 women) at a dose of 100 µg/kg over a 12-hour period and blood and urine analysis were conducted from the beginning of dosing through a three- or six-day period. Detectable serum levels of total d6-BPA were observed at 1.4 h after the start of dosing, and a maximum serum concentration (Cmax) of 3.26 nM was observed. Free d6-BPA was detectable in serum 2.8 h after the start of dermal administration, with Cmax of 0.272 nM. Beginning at approximately seven hours and continuing to 12 h (which corresponds to the cessation of exposure), the concentration of free and total serum d6-BPA plateaued. The terminal half-lives of total d6-BPA and free d6-BPA in the body were 21.4± 9.81 h and 17.6± 7.69 h, respectively. Elimination from the body was rate-limited by kinetics in the dermal compartment. Free d6-BPA was a greater percentage of the area under the curve of total serum BPA (8.81%) compared to the 0.56% observed in our previously published oral study. Recovery of total d6-BPA in urine was < 2% of the applied dose after six days. Analysis of the area under the curve for dermal and oral administration revealed that 2.2% of the dermal dose became systemically available. These data are in line with previous studies indicating how pharmacokinetics of BPA differ following oral and dermal exposures. Dermal exposure resulted in a longer apparent half-life and higher free:total d6-BPA ratio compared to oral. The fraction dermally absorbed (Fabs) value of 12–29%, which was derived from mass-balance considerations based on the recovery of unabsorbed BPA, yields a serum clearance of 545–1318 L/h which is physiologically implausible as it grossly exceeds not only the values predicted by allometric scaling but also the hepatic blood flow. This strongly suggests that the 12–29%, being the complement of the portion recovered from the application site, was mostly lost to the environment rather than absorbed.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted by the National Toxicology Program (Research Triangle Park, NC) with Participation from FDA (Jefferson, AR)

Objective of study:

absorption

excretion

metabolism

toxicokinetics

Qualifier:

no guideline followed

Principles of method if other than guideline:

Six men and eight women were exposed to 100 μg/kg bw of deuterated Bisphenol A (d6-BPA) by oral administration and blood and urine analysis were conducted over a three day period. The use of d6-BPA allowed administered d6-BPA to be distinguished from background native (unlabeled) Bisphenol A. The following parameters are reported: rate of oral absorption, serum elimination, half-life, area under the curve (AUC), urinary excretion, and metabolism to glucuronide and sulfate conjugates."

GLP compliance:

not specified

Radiolabelling:

other: deuterated BPA (d6-BPA)

Species:

human

Strain:

other: Men and non-pregnant women were recruited in 2012–2013 from the Raleigh Durham region of North Carolina, USA.

Sex:

male/female

Route of administration:

other: Subjects were fed a vanilla wafer cookie containing a dose of 100 μg/kg bw of d6-Bisphenol A after fasting starting at 12 midnight on the day of the visit.

Vehicle:

other: A single dosing solution (10 mg/ml) was prepared by dissolving d6-Bisphenol A in absolute ethanol. Aliquots of 0.5 and 1 ml were placed in sealed screw-top glass vials, and stored chilled until just before dosing.

Duration and frequency of treatment / exposure:

Single treatment

Remarks:

Doses / Concentrations:
100 µg/kg

No. of animals per sex per dose / concentration:

six men and eight women

Control animals:

no

Type:

other: Mean serum total (unconjugated and conjugated) d6-BPA Cmax of 1711 nM (390 ng/ml) was observed at Tmax of 1.1 ± 0.50 h.

Results:

Unconjugated d6-BPA appeared in serum within 5–20 min of dosing with a mean Cmax of 6.5 nM (1.5 ng/ml) observed at Tmax of 1.3 ± 0.52 h.

Type:

other: The half-times for terminal elimination of total d6-BPA and unconjugated d6-BPAwere 6.4±2.0 h and 6.2±2.6 h, respectively.

Results:

Recovery of total administered d6-BPA in urine was 84–109%. Most subjects (10 of 14) excreted >90% as metabolites within 24 h.

Metabolites identified:

yes

Details on metabolites:

Main metabolite: Bisphenol A-glucuronide in addition Bisphenol A-sulfate was identified and bis-conjugates.

Mean serum total (unconjugated and conjugated) d6-BPA Cmax of 1711 nM (390 ng/ml) was observed at

Tmax of 1.1 ± 0.50 h. Unconjugated d6-BPA appeared in serum within 5–20 min of dosing with a mean Cmax of

6.5 nM (1.5 ng/ml) observed at Tmax of 1.3 ± 0.52 h. Detectable blood levels of unconjugated or total d6-BPA

were observed at 48 h in some subjects at concentrations near the LOD (0.001–0.002 ng/ml). The half-times

for terminal elimination of total d6-BPA and unconjugated d6-BPAwere 6.4±2.0 h and 6.2±2.6 h, respectively.

Recovery of total administered d6-BPA in urine was 84–109%. Most subjects (10 of 14) excreted >90% as metabolites

within 24 h.

Executive summary:

"Conclusions: Using more sensitive methods, our study expands the findings of other human oral pharmacokinetic studies. Conjugation reactions are rapid and nearly complete with unconjugated Bisphenol A comprising less than 1% of the total d6-Bisphenol A in blood at all times. Elimination of conjugates into urine largely occurs within 24 h."

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Research Conducted at Pacific Northwest National Laboratory (Richland, WA) with Participation from CDC (Atlanta, GA) and FDA (Jefferson, AR) Laboratories; Funded by EPA Grant

Objective of study:

other: Volunteers ingested 100% of one of three specified meals comprising standard grocery store food items for breakfast, lunch, and dinner.

Qualifier:

no guideline available

Principles of method if other than guideline:

In the study, 20 human volunteers ate 3 meals in a day that were enriched in canned foods and beverages to ensure that the participants were exposed to BPA. Based on how much total BPA was found in urine, it was determined that the average exposure for all participants was 21% greater than the 95th percentile exposure determined by CDC’s population-scale urine biomonitoring data.
Blood and urine samples were collected from each participant hourly during the day of the study. The blood samples were analyzed for both free BPA and total BPA, while urine samples were analyzed for total BPA (previous data has shown that free BPA is not commonly found in urine), all with a sensitive analytical method.

GLP compliance:

not specified

Radiolabelling:

no

Species:

human

Strain:

other: Twenty randomly selected healthy adult (age 18–55 years) nonsmoking male (10) or nonpregnant female (10)

Sex:

male/female

Route of administration:

oral: feed

Vehicle:

other: Volunteers ingested 100% of one of three specified meals comprising standard grocery store food items for breakfast, lunch, and dinner.

Duration and frequency of treatment / exposure:

Volunteers ingested 100% of one of three specified meals comprising standard grocery store food items for breakfast, lunch, and dinner.

Remarks:

Doses / Concentrations:
Meals were designed to include the major food groups with the condition that canned meats, fruits, and vegetables—all potential sources of Bisphenol A—were present in each meal.

No. of animals per sex per dose / concentration:

Twenty randomly selected healthy adult (age 18–55 years) nonsmoking (no nicotine product use) male (10) or nonpregnant female (10)

Control animals:

no

Type:

other: Average consumption of BPA, estimated from the urinary excretion of total BPA (TOTBPA=conjugated BPA + BPA), was 0.27 μg/kg body weight (range, 0.03-0.86), 21% greater than the 95th percentile of aggregate exposure in the adult U.S. population.

Results:

Total-Bisphenol A concentrations in serum were below the LOD for 86% of the 320 samples collected and free-Bisphenol A concentrations were determined to be ≤ LOD in all blood samples.

The volunteers’ average consumption of BPA, estimated from the urinary excretion of total BPA (as the sum of conjugated and unconjugated BPA) was 21 µg (range 3.3 to 73 µg). Assuming 100 % absorption and urinary excretion and using individual body weights this is equivalent to an oral exposure of 0.27 μg/kg body weight (bw) (range, 0.03–0.86), 21 % greater than the 95th percentile of aggregate (all routes) daily exposure in the adult US population (0.22 μg/kg bw; equivalent to approximately ~15 µg/person). A serum time course of total BPA was observable only in individuals with exposures 1.3–3.9 times higher than the 95th percentile of aggregate US exposure. Total BPA urine concentration Tmax was 2.75 hours (range, 0.75–5.75 hours) post meal, lagging the serum concentration Tmax by ~1 hour. During these high dietary exposures, total BPA concentrations in serum were below the LOD for 86 % of the 320 samples collected. Unconjugated BPA concentrations were always below the LOD (1.3 nM; 0.3 ng/ml). In six individuals, serum total BPA concentrations could be measured (concentrations up to 5.7 nM; 1.3 ng/ml) and the serum levels found were, on average, 42 times lower than urine concentrations. For these individuals, serum total BPA area under the curve per unit BPA exposure (i.e. normalised to urinary BPA excretion, expressed as g/kg bw) was between 21.5 and 79.0 nM x hr x kg/µg.

Conclusions:

Interpretation of results (migrated information): other: EFSA 2015 concluded on this study: "Overall the CEF Panel notes that this study endorses the view that no unconjugated Bisphenol A in serum and only very low levels of conjugated Bisphenol A can be found in humans at levels of dietary exposure."

Executive summary:

EFSA 2015 concluded on this study: "Overall the CEF Panel notes that this study endorses the view that no unconjugated Bisphenol A in serum and only very low levels of conjugated Bisphenol A can be found in humans at levels of dietary exposure. The study report indicates that exposures to Bisphenol A from retrospectively determined dietary exposure (e.g. from canned foods) is at the most 73 µg person per day (three meals). The exposures were at the high end of the NHANES population-based exposure estimates (spot samples) from the 2005-2006 NHANES biomonitoring report. The study encompasses quite a large group of human volunteers and is very rigorously controlled with respect to possible sample contamination (e.g. plasma samples were analysed in a contra-expertise set-up to identify problems with reproducibility and were further analysed if inexplicable results were obtained to identify possible contamination). A limitation of this study is the lack of data concerning the content of Bisphenol A in the canned food."

Reference 5

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at Pacific Northwest National Laboratory (Richland, WA) with Participation from CDC (Atlanta, GA) and FDA (Jefferson, AR) Laboratories; Funded by EPA Grant

Principles of method if other than guideline:

Serum concentrations of Bisphenol A in humans from 93 published studies were compared.

GLP compliance:

not specified

Species:

human

Strain:

other: not applicable

Sex:

male/female

Route of administration:

other: not applicable

Vehicle:

other: not applicable

Duration and frequency of treatment / exposure:

More than 30,000 individuals in 19 countries across all life stages were included.

Remarks:

Doses / Concentrations:
Studies covering all life stages were included.

No. of animals per sex per dose / concentration:

serum concentrations of Bisphenol A in humans from 93 published studies of more than 30,000 individuals in 19 countries across all life stages.

Control animals:

no

Type:

other: Authors show a convergence of robust methods for measuring or calculating serum concentrations of BPA in humans from 93 published studies of more than 30,000 individuals in 19 countries across all life stages.

Results:

Typical serum BPA concentrations are orders of magnitude lower than levels measurable by modern analytical methods and below concentrations required to occupy more than 0.0009% of Type II Estrogen Binding Sites, GPR30, ERa or ERb receptors.

Type:

other: Occupancies would be higher, but <0.04%, for the highest affinity receptor, ERR-g

"Our results show limited or no potential for estrogenicity in humans, and question reports of measurable Bisphenol A in human serum."

Executive summary:

"Our results show limited or no potential for estrogenicity in humans, and question reports of measurable Bisphenol A in human serum."

Reference 6

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2015

Reliability:

2 (reliable with restrictions)

Objective of study:

absorption

Qualifier:

no guideline followed

Principles of method if other than guideline:

Authors hypothesized that the extensive interaction with the oral mucosa by a liquid matrix, like soup, relative to solid food or capsules, might enhance absorption through non-metabolizing oral cavity tissues in humans, producing higher bioavailability and higher serumBisphenol A concentrations. Concurrent serumand urine concentrations of d6-Bisphenol A, and its glucuronide and sulfate conjugates, were measured over a 24 hour period in 10 adult male volunteers following ingestion of 30 μg d6-Bisphenol A/kg body weight in soup.
The corresponding individual pharmacokinetic data, additional details related to the analytical methods employed and the demographics of the cohort are reported in the Data in Brief article.

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

human

Strain:

other: not applicable

Sex:

male

Route of administration:

other: Volunteers were provided with 12 oz of a commercial tomato soup product prepared using label instructionsthat contained a 30 μg/kg bw dose of deuterium labeled Bisphenol A (d6-BPA) and instructed to ingest the soup in their normal fashion.

Vehicle:

other: commercial tomato soup

Duration and frequency of treatment / exposure:

Single dosing

Remarks:

Doses / Concentrations:
30 μg/kg bw

No. of animals per sex per dose / concentration:

10

Control animals:

no

Type:

absorption

Results:

Absorption of d6-BPA was rapid (t1/2=0.45 h) and elimination of the administered dose was complete 24 h post-ingestion, evidence against any tissue depot for Bisphenol A.

Type:

absorption

Results:

This study confirms that typical exposure to Bisphenol A in food produces picomolar to subpicomolar serum Bisphenol A concentrations in humans, not nM concentrations reported in some biomonitoring studies.

Metabolites identified:

yes

Details on metabolites:

Bisphenol A-glucuronide and Bisphenol A-sulfate

Absorption of d6-BPA was rapid (t1/2=0.45 h) and elimination of the administered dose was complete 24 h post-ingestion, evidence against any tissue depot for BPA. The maximumserum d6-BPA concentrationwas 0.43 nMat 1.6 h after administration and represented b0.3% of total d6-BPA. Pharmacokinetic parameters, pharmacokinetic model simulations, and the significantly faster appearance half-life of d6-BPA-glucuronide compared to d6-BPA (0.29 h vs 0.45 h) were evidence against meaningful absorption of BPA in humans through any non-metabolizing tissue (b1%). This study confirms that typical exposure to BPA in food produces picomolar to subpicomolar serum BPA concentrations in humans, not nM concentrations reported in some biomonitoring studies.

Pharmacokinetic parameters for d6-BPA, its metabolites, and total d6-BPA.

Compound	Elimination T1/2 (h)	Distribution T1/2 (h)	Absorption/Appearance T1/2 (h)	Cmax (nM)	Tmax(h)	AUC0–∞ (nmol × h × L−1)
d6-BPA	5.5 (0.5)	0.87 (0.3)	0.45 (0.03)a	0.43 (0.14)	1.6 (0.17)	2.5 (0.4)
d6-BPAG	7.3 (1.9)	–	0.29 (0.04)	286 (23)	1.2 (0.16)	680 (31)b
d6-BPAS	5.0 (1.5)	–	0.62 (0.13)	18 (1.9)	2.2 (.19)	131 (23)b
Total d6-BPA	7.8 (1.3)	–	0.28 (0.06)	365 (24)	1.1 (0.14)	1057 (47)

Mean and (SEM).

a Statistically different from d6-BPAG.

b Variability in d6-BPAG and d6-BPAS concentrations 11 to 24 h post dosing precluded calculation of an accurate AUC0–∞ for volunteers 8 and 18. Instead, an AUC0–t was calculated directly from the data. The difference between AUC0–t and AUC0–∞ was ~4% in the 8 volunteers where both could be calculated, supporting use of AUC0–t in the two volunteers where AUC0–∞ could not be calculated. Elimination half-lives for d6-BPAG and total d6-BPA were calculated for 8 volunteers, excluding 8 and 18 where there were insufficient data to calculate an elimination half-life. The elimination half-life for d6-BPAS did not include a value from volunteer 8 due to insufficient data.

Conclusions:

Interpretation of results (migrated information): other: We introduce new criteria for identification of contaminated serumsamples: serum Bisphenol A percentages above 1% for typical oral exposure scenarios and above 15% for atypical parenteral exposures; urine: blood ratios of total Bisphenol A less than 20.

Executive summary:

Authors indicate: "We introduce new criteria for identification of contaminated serumsamples: serum BPA percentages above 1% for typical oral exposure scenarios and above 15% for atypical parenteral exposures; urine: blood ratios of total BPA less than 20. Finally, our PBPK model simulations show that even arterial blood concentrations of bioactive BPA reaching tissueswould be below22 pMwhen oral exposures equivalent to the 95% upper percentile total daily exposure occur in a single meal because negligible sublingual absorption through a non-metabolizing tissue is observed (b1%)."

Absorption of d6-BPA was rapid (t1/2=0.45 h) and elimination of the administered dose was complete 24 h post-ingestion, evidence against any tissue depot for BPA. The maximumserum d6-BPA concentrationwas 0.43 nMat 1.6 h after administration and represented b0.3% of total d6-BPA. Pharmacokinetic parameters, pharmacokinetic model simulations, and the significantly faster appearance half-life of d6-BPA-glucuronide compared to d6-BPA (0.29 h vs 0.45 h) were evidence against meaningful absorption of BPA in humans through any non-metabolizing tissue (<1%). This study confirms that typical exposure to BPA in food produces picomolar to subpicomolar serum BPA concentrations in humans, not nM concentrations reported in some biomonitoring studies.

Reference 7

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted in accordance with the highest standards for reducing and monitoring for sample contamination with BPA.

Objective of study:

other: An extensive characterization of human BPA exposure in a cohort of 30 pregnant women

Qualifier:

no guideline available

Principles of method if other than guideline:

An extensive characterization of human BPA exposure in a cohort of 30 pregnant women was conducted while applying best practices for exposure assessment and control and monitoring for BPA contamination. The findings were extended to the general population of pregnant women in North America by comparison of exposures to those reported in two much larger national cohorts. The unique aspects of this study that set it apart
from other BPA biomonitoring studies in humans include simultaneous blood and urine sampling, measurement of total daily exposure, and an environmental/clinical setting without medical intervention beyond venipuncture.
Thirty healthy pregnant women recruited to the study were evaluated for total BPA exposure over a 30-h period comprising one-half day in the field and one day in a clinical setting.

GLP compliance:

not specified

Radiolabelling:

no

Species:

human

Strain:

other: Thirty pregnant volunteers (healthy non smoking females 18-40 years of age, between approximately 15 and 35 weeks of a normal, low-risk pregnancy were recruited for the study from the Salt Lake City, UT metropolitan area.

Sex:

female

Route of administration:

other: total daily exposure, which could include oral and potentially parenteral exposure

Vehicle:

not specified

Details on exposure:

a field exposure period and a clinical exposure period.

Duration and frequency of treatment / exposure:

The field exposure period started with the first morning void on Day 1 and ended with collection of the 0-h urine sample collected upon admittance to the clinic, usually immediately after lunch of the first day. The clinical exposure period started immediately after the 0-h urine sample was collected and completed with the final study urine sample collected ~24 h later.

Remarks:

Doses / Concentrations:
total daily exposures typical of North America, which could include oral and potentially parenteral exposure.

No. of animals per sex per dose / concentration:

Thirty pregnant volunteers (healthy non smoking females 18-40 years of age, between approximately 15 and 35 weeks of a normal, low-risk pregnancy.

Control animals:

other: A 20 member BPA cohort with the highest potential for exposure to BPA was selected based on answers to three screening survey questions designed to assess exposure to BPA by ingestion of canned foods and handling of cash register receipts.

Positive control reference chemical:

A 10 member cohort was selected based on answers to three screening survey questions designed to assess dietary or dietary supplement exposure to soy containing products for complementary assessment of exposures to plant-derived estrogens.

Details on study design:

All urine samples were analyzed for total BPA. Serum BPA levels were assessed in selected samples. LC and tandem MS (LC/MS/MS) were used with on-line switching between an initial restricted access-reversed phase trapping column and a subsequent reversed phase analytical column for the analysis of total and unconjugated native BPA in urine and serum.

Statistics:

Differences between cohort characteristics and BPA exposures between cohorts were evaluated using the T-Test (Microsoft Excel).
Differences in the amount of BPA eliminated between volunteers with measureable BPA and those without measurable BPA were evaluated using the Mann-Whitney Rank Sum test (Sigma Plot 12.5).

Type:

other: Evidence is presented arguing against the hypothesis that some behavioral or physiological aspect of pregnancy could lead to measureable blood concentrations of BPA under total daily exposures typical of North America.

Results:

Serum BPA was below measureable levels except where sample contamination could be confirmed through application of a priori quantitative criteria, and there was no relationship between Total BPA exposure and serum BPA levels.

Urinary total BPA concentrations varied widely within and between volunteers across time. All collection blanks collected concurrently to the urine samples contained no detectable

BPA. Total BPA exposure (mg/kg bw) was higher for the clinical exposure period than for the field exposure period in most volunteers. The average bw-adjusted BPA exposure for the study was not statistically significant between the BPA cohort (Mean, 0.043 mg/kg/day) and the Soy cohort (0.025 mg/kg/day) (Students T-Test, p > 0.07).

Twelve of the 48 analyzed serum samples from 30 volunteers had measurable concentrations of BPA (range 0.25-0.51 ng/ml); however, BPAG and BPAS levels were near or below the limits of detection and unconjugated BPA fractions exceeded 15% (range 55-79%) in all samples with measurable BPA. Three approaches were used to evaluate the possibility that serum samples containing BPA were contaminated. The findings were clear evidence that BPA in serum was the result of contamination in the sample collection processing chain, not actual exposure.

Executive summary:

Thirty healthy pregnant women recruited to the study were evaluated for total BPA exposure over a 30-h period comprising one-half day in the field and one day in a clinical setting. BPA and its metabolites were measured in serum and total BPA was measured in matching urine samples. The mean total exposure was similar to the 50th percentile of exposure for U.S. women and pregnant women in a large North American cohort. Twenty volunteers had total daily exposures equal to or exceeding the U.S. mean, and six volunteers had exposures exceeding the 75th percentile. Women working as cashiers did not have higher total BPA exposure. BPA was detected in some serum samples (0.25 - 0.51 ng/ml), but showed no relationship to total BPA in corresponding urine samples, no relationship to total BPA exposure, and had unconjugated BPA fractions of 60-80%, consistent with established criteria for sample contamination. The authors conclude that typical exposures of North American pregnant women produce internal exposures to BPA in the picomolar range.

Reference 8

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

Lactating Sprague–Dawley dams were treated by daily gavage with 100 μg/kg bw d6-Bisphenol A starting at birth. Conjugated and aglycone forms of Bisphenol A were then measured by using LC/MS/MS in milk from lactating dams on PND 7 and in serum from dams and their pups on PND 10. All samples were collected 1 h after dosing, a time selected to produce nearly maximal levels.

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Route of administration:

oral: gavage

Vehicle:

other: The dosing solution (100g/ml) was prepared by dissolving a weighed portion of d6-BPA in 95% ethanol (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

Lactating Sprague–Dawley dams were treated by daily gavage with d6-Bisphenol A starting at birth.

Remarks:

Doses / Concentrations:
100 μg/kg bw

No. of animals per sex per dose / concentration:

Starting on the day of birth, dams (n = 5) were administered a daily oral dose of d6-BPA (100g/kg bw) and control dams (n = 3) were administered the vehicle (10% ethanol in water).

Control animals:

yes, concurrent vehicle

Type:

other: While aglycone BPA (free-BPA) was detected in all dam serum and milk samples, none was detected in pup serum (<0.2 nM).

Results:

Doses delivered to pups lactationally, estimated from milk concentrations and body weights, were 300-fold lower than the dose administered to the dams.

Type:

other: Serum concentrations of total BPA in pups were 300-fold lower than those in their dams.

Results:

Plasma concentrations of total BPA in PND 10 rat pups were 500-fold lower than peak levels achieved following direct oral delivery of the same dose to the same age pups.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A investigated

While aglycone BPA was detected in all dam serum and milk samples, none was detected in pup serum (<0.2 nM). Doses delivered to pups lactationally, estimated from milk concentrations and body weights, were 300-fold lower than the dose administered to the dams. Similarly, serum concentrations of total BPA in pups were 300-fold lower than those in their dams. Furthermore, plasma concentrations of total BPA in PND 10 rat pups were 500-fold lower than peak levels achieved following direct oral delivery of the same dose to the same age pups. These findings of significant dose attenuation for the active aglycone form of BPA, relative to that of the dam, suggest high potency for toxicological effects derived exclusively from lactational transfer. Alternatively, studies that include lactational exposure and report minimal effects from BPA should consider the possibility that inadequate internal exposures were achieved during the critical postnatal period.

Executive summary:

While aglycone BPA was detected in all dam serum and milk samples, none was detected in pup serum (<0.2 nM). Doses delivered to pups lactationally, estimated from milk concentrations and body weights, were 300-fold lower than the dose administered to the dams. Similarly, serum concentrations of total BPA in pups were 300-fold lower than those in their dams. Furthermore, plasma concentrations of total BPA in PND 10 rat pups were 500-fold lower than peak levels achieved following direct oral delivery of the same dose to the same age pups. These findings of significant dose attenuation for the active aglycone form of BPA, relative to that of the dam, suggest high potency for toxicological effects derived exclusively from lactational transfer. Alternatively, studies that include lactational exposure and report minimal effects from BPA should consider the possibility that inadequate internal exposures were achieved during the critical postnatal period.

Reference 9

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

The study used LC/MS/MS to measure serum pharmacokinetics of unconjugated (active) and conjugated (inactive) Bisphenol A in adult female CD-1 mice following intravenous (IV) injection, which produces higher serum levels by circumventing the processes of absorption from the GI tract and presystemic metabolism that occur after oral administration. Deuterated Bisphenol A (100 μg/kg bw) was used to avoid interference by background contamination from trace amounts of native Bisphenol A. Additionally, the pharmacokinetics of unconjugated Bisphenol A were determined in adipose tissue

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

mouse

Strain:

CD-1

Sex:

female

Route of administration:

intravenous

Vehicle:

other: Dosing solutions (50 g/ml) were prepared by dissolving a weighed portion of d6-BPA in 95% ethanol (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

single dose

Remarks:

Doses / Concentrations:
A dose of 100 g/kg bw was administered by intravenous (IV) injection of an administered volume of 2 l/g body weight

No. of animals per sex per dose / concentration:

n = 60; 6 mice/time point

Control animals:

no

Type:

other: After IV injection, unconjugated BPA rapidly distributed out of the circulation (t1/2 = 0.2 h) and terminal elimination also proceeded rapidly (t1/2 = 0.8 h).

Results:

The levels of unconjugated BPA in mouse adipose tissue rapidly reached a maximal level (0.25 h) that was below the serum maximum at the initial sampling time (0.08 h).

Type:

other: Terminal elimination of unconjugated BPA from adipose tissue (t1/2 = 7.0 h) was similar to that for conjugated BPA in serum (t1/2 = 6.6 h)

Results:

<0.01% of the administered dose remained in adipose tissue after 24 h.

Type:

other: These plasma and tissue kinetics are consistent with rapid equilibria.

Results:

These plasma and tissue kinetics underscore the non-persistent nature of BPA.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A measured

Table 1

Serum and adipose tissue pharmacokinetic parameters for unconjugated and total d6-BPA from adult female CD-1 mice administered a single dose of 100 g/kg bw by IV injection (mean values shown for n = 6 mice per time point).

Route-form	t1/2 elim (h)	t1/2 distribution (h)	AUC0–∞ (nmol × h × L−1)	fb	Vd (L × kg bw−1)	Cltot (L × h−1 × kg bw−1)
Serum – total	6.6	0.2	336	–	–	–
Serum – unconjugated	0.8	0.2	54	0.002	0.51	10
Adipose tissue – unconjugated	7.0	0.07	116	–	–	–

Executive summary:

After IV injection, unconjugated BPA rapidly distributed out of the circulation (t1/2 = 0.2 h) and terminal elimination also proceeded rapidly (t1/2 = 0.8 h). Consistent with the degree of aqueous solubility, lipid/water solubility ratio, and partitioning from blood into adipose tissue in vivo, the levels of unconjugated BPA in mouse adipose tissue rapidly reached a maximal level (0.25 h) that was below the serum maximum at the initial sampling time (0.08 h). Terminal elimination of unconjugated BPA from adipose tissue (t1/2 = 7.0 h) was similar to that for conjugated BPA in serum (t1/2 = 6.6 h) and <0.01% of the administered dose remained in adipose tissue after 24 h. These plasma and tissue kinetics are consistent with rapid equilibria and underscore the non-persistent nature of BPA, particularly when compared with slowly metabolized lipophilic organic pollutants like halogenated dibenzodioxins.

Reference 10

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

Serum pharmacokinetic parameters for unconjugated and total Bisphenol A were investigated in adult CD-1 mice administered a single dose of 100 g/kg bw by gavage (n = 12 per time point).

GLP compliance:

no

Radiolabelling:

other: d6-BPA

Species:

mouse

Strain:

CD-1

Sex:

male/female

Route of administration:

other: gavage and SC injection

Vehicle:

other: Dosing solutions were prepared by dissolving a weighed portion of d6-BPA in 95% ethanol (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

Single dose

Remarks:

Doses / Concentrations:
100 µg/kg/day

No. of animals per sex per dose / concentration:

At each post-dose time point, the group size was 12 pups (6 males and 6 females each)

Control animals:

no

Type:

other: Significant inverse relationships were observed between postnatal age and measures of internal exposures (Cmax) to unconjugated BPA after oral administration.

Results:

Phase II conjugation, area under the time–concentration curve (AUC), and elimination half-time of unconjugated BPA were also inversely related to age.

Type:

other: These results suggest that an adverse effect from BPA observed in rodent models, attributable to exposure during a discrete time period of neonatal development, would be less likely for comparable neonatal primate dosing based on internal dosimetry.

Results:

On the other hand in all adults of all species studied, including humans, a low oral dose of BPA produced similarly small internal exposures for the unconjugated form, reflecting the dominant effect of presystemic Phase II metabolism.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A was investigated

Table 1

Serum pharmacokinetic parameters for unconjugated and total BPA from adult CD-1 mice administered a single dose of 100 g/kg bw by gavage (n = 12 per time point).

Route-form	t1/2Elim (h)	t1/2Distr (h)	AUC0–∞ (nmol h L−1)	Cmax (nM)	Vd/f (L kg−1)	Cltot/f (L h−1 kg−1)
Oral-total	7.8	0.30	247	40 ± 19	19.4	1.7
Oral-unconjugated	0.63	0.11	0.10	0.18 ± 0.31	3485	3861

Table 2

Serum pharmacokinetic parameters for unconjugated and total BPA from neonatal mice administered a single dose of 100 g/kg bw by subcutaneous (SC) injection or gavage (mean ± SD, n = 12).

	PND 3 unconjugated	PND 3 total	PND 10 unconjugated	PND 10 total	PND 21 unconjugated	PND 21 total
t1/2Elim-oral	5.9	18	3.0	7.0	0.20	4.1
t1/2Elim-SC	1.2	11	1.5	6.2	2.3	3.1
AUC0–∞-oral	26	1158	11	689	0.50	176
AUC0–∞-SC	26	865	51	629	27	227
Cmax-oral	34 ± 25	179 ± 66	7.4 ± 3.1	139 ± 39	1.1 ± 1.9	28 ± 12
Cmax-SC	42 ± 23	104 ± 47	68 ± 13	149 ± 31	49 ± 14	86 ± 17

Executive summary:

Significant inverse relationships were observed between postnatal age and measures of internal exposures (Cmax) to unconjugated BPA after oral administration. Phase II conjugation, area under the time–concentration curve (AUC), and elimination half-time of unconjugated BPA were also inversely related to age. In postnatal day (PND) 3 mice, the combination of under-developed Phase II metabolism, rapid absorption, and slow elimination kinetics led to equivalent internal exposures for unconjugated BPA from oral and SC routes; however, maturing metabolic capabilities in PND 10 and older mice, led to large and significant route effects. The significant inverse age-related developmental profiles from PND 3 through adulthood for unconjugated BPA internal exposure metrics from oral administration to CD-1 mice and Sprague-Dawley rats were remarkably similar; however, the developmental profile was quite different for neonatal rhesus monkeys in which small insignificant age-related differences were observed. These results suggest that an adverse effect from BPA observed in rodent models, attributable to exposure during a discrete time period of neonatal development, would be less likely for comparable neonatal primate dosing based on internal dosimetry. On the other hand in all adults of all species studied, including humans, a low oral dose of BPA produced similarly small internal exposures for the unconjugated form, reflecting the dominant effect of presystemic Phase II metabolism.

Reference 11

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Principles of method if other than guideline:

The current study used LC/MS/MS to measure serum pharmacokinetics of aglycone (active) and conjugated (inactive) Bisphenol A in adult and neonatal rhesus monkeys by oral (PND 5, 35, 70) and intravenous injection (PND 77) routes using d6-Bisphenol A to avoid sample contamination.

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

monkey

Strain:

other: rhesus monkeys

Sex:

female

Route of administration:

oral: gavage

Vehicle:

other: Dosing solutions (100 μg/ml) were prepared by dissolving a weighed portion of d6-BPA in DMSO (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

Single oral administration of 100 μg/kg bw

Remarks:

Doses / Concentrations:
A dose of 100 μg/kg bw was administered either intravenously or by gavage (administered volume=1 ml/kg bw) using the same dosing solution. Concentrations of all dosing solutions were verified by LC/MS/MS, and were determined to be stable for at least 2 months at ambient conditions.

No. of animals per sex per dose / concentration:

Four adult female rhesus monkeys were used for the adult experiment.
Male and female neonatal monkeys (n=3 of each sex) were treated orally (PND 5, 35, 70) and by IV injection (PND 77) using identical procedures described above for the adults.

Control animals:

no

Type:

other: The concentration-time profiles observed in adult monkeys following oral administration of 100 μg/kg bw were remarkably similar to those previously reported in human volunteers given a similar dose;

Results:

moreover, minimal pharmacokinetic differences were observed between neonatal and adult monkeys for the receptor-active aglycone form of BPA.

Type:

other: Circulating concentrations of BPA aglycone were quite low following oral administration (< 1% of total), which reflects the redundancy of active UDPglucuronosyl transferase isoforms in both gut and liver.

Results:

No age-related changes were seen in internal exposure for aglycone BPA in monkeys, a result different from developing rats where significant inverse age-related changes, based on immaturity of Phase II metabolism and renal excretion, were reported.

Type:

other: These observations imply that any toxicological effect observed in rats from early postnatal exposures to BPA could over-predict those possible in primates of the same age.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A measured after glucuronidase/sulfatase hydrolysis.

Table 4: Serum pharmacokinetic parameters for aglycone and total BPA from neonatal rhesus monkeys (PND 5–70) administered a single oral dose of 100 μg/kg bw (mean±SD,

n=5–6).

Age-Form              t1/2 Elim (h)               AUC0-∞ (nmol×h×L−1)       Cmax (nM)

PND 5—total       4.6±1.6                     4010±1610                                    690±130

PND 35—total       4.3±1.8                   2250±1500                                   550±230

PND 70—total       2.6±1.6 7                   50±760                                          250±250

PND 5—aglycone       2.0±1.4                     5.7±4.8                                       2.0±2.4

PND 35—aglycone       1.7±1.1                     3.7±2.6                                      1.1±0.88

PND 70—aglycone       1.5±1.2                     3.4±2.8                                    1.5±0.70

Table 3: Serum pharmacokinetic parameters for aglycone and total BPA from neonatal rhesus monkeys (PND 77) administered a single IV dose of 100 μg/kg bw (mean±SD, n=5).

Route-Form      t1/2 Elim (h)a       AUC0-∞ (nmol×h×L−1)              Vd (L×kg−1)              Cltot (L×h−1×kg−1)       f

IV—total              3.6±2.8              1950±880                                           –                                   –                            0.54±0.34

IV—aglycone       0.63±0.18              190±57                                       2.1±0.48                      2.4±0.71                     0.019±0.018

Executive summary:

The concentration-time profiles observed in adult monkeys following oral administration of 100 μg/kg bw were remarkably similar to those previously reported in human volunteers given a similar dose; moreover, minimal pharmacokinetic differences were observed between neonatal and adult monkeys for the receptor-active aglycone form of BPA. Circulating concentrations of BPA aglycone were

quite low following oral administration (b 1% of total), which reflects the redundancy of active UDPglucuronosyl transferase isoforms in both gut and liver. No age-related changes were seen in internal exposure metrics for aglycone BPA in monkeys, a result clearly different from developing rats where significant inverse age-related changes, based on immaturity of Phase II metabolism and renal excretion, were recently reported. These observations imply that any toxicological effect observed in rats from early postnatal exposures to BPA could over-predict those possible in primates of the same age, based on significantly higher internal exposures and overall immaturity at birth.

Reference 12

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

The current study used LC/MS/MS to measure serum pharmacokinetics of aglycone (active) and conjugated (inactive) Bisphenol A in adult and neonatal Sprague-Dawley rats by oral and injection routes. Deuterated Bisphenol A was used to avoid issues of background contamination.

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

other: Dosing solutions (100 μg/ml) were prepared by dissolving a weighed portion of d6-BPA in 95% ethanol or DMSO (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

single oral or IV dosing

Remarks:

Doses / Concentrations:
100 μg/kg bw by intravenous injection or gavage

No. of animals per sex per dose / concentration:

5-7

Control animals:

no

Type:

other: Evidence for enterohepatic recirculation of conjugated, but not aglycone, BPA was observed in adult rats. Significant inverse relationships were observed between postnatal age and measures of internal exposures to aglycone BPA and its elimination.

Results:

In neonatal rats treated orally, internal exposures to aglycone BPA were substantially lower than from subcutaneous injection.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A measured

Table 1: Serum pharmacokinetic parameters for aglycone and total BPA from adult female Sprague-Dawley rats administered a single dose of 100 μg/kg bw by intravenous injection or gavage (mean±SD, n=7 or 5, respectively).

Route–form	t1/2 Elim (h)	t1/2 Abs/Distr (h)	AUC (nmol × h × L−1)	Cmax (nM)	Vd (L × kg−1)	Cltot (L × h−1 × kg−1)	f
IV—total	8.1±6.1	0.69±1.2	890±330	—	—	—	—
IV—aglycone	0.66±0.040	—	95±8.8	—	4.3±0.40	4.5±0.44	—
Oral—total	4.6±1.3	0.65±0.81	680±330	73±29	—	—	0.77±0.47
Oral—aglycone	3.0±3.7	0.85±0.48	2.6±2.1	0.39±0.19	—	—	0.028±0.031

Table 2

Serum pharmacokinetic parameters for aglycone and total BPA from Sprague-Dawley rat pups administered a single dose of 100 μg/kg bw by subcutaneous injection or gavage (mean±SD, n=4).

	PND 3 (aglycone)	PND 3 (total)	PND 10 (aglycone)	PND 10 (total)	PND 21 (aglycone)	PND 21 (total)
t 1/2elim (oral)	8.5	6.7	4.0	4.7	1.9	2.9
t1/2elim (SC)	3.9	4.3	2.3	3.7	3.8	3.4
AUC (oral)	56	4030	21	2410	3.2	833
AUC (SC)	930	23,800	761	28,490	366	9820
Cmax (oral)	29±16	445±230	6.7±3.9	219 ±87	0.70±0.42	182±37
Cmax (SC)	1010±290	5090±1090	634±249	5590±2490	318±43	1940±730

Executive summary:

Evidence for enterohepatic recirculation of conjugated, but not aglycone, BPA was observed in adult rats. Significant inverse relationships were observed between postnatal age and measures of internal exposures to aglycone BPA and its elimination. In neonatal rats treated orally, internal exposures to aglycone BPA were substantially lower than from subcutaneous injection.

Reference 13

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20111

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

Distribution of Bisphenol A was investigated into tissues of adult, neonatal, and fetal rats.

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Route of administration:

oral: gavage

Vehicle:

other: The dosing solution (100g/ml) was prepared by dissolving a weighed portion of d6-BPA in 95% ethanol (10% total volume) before dilution in water.

Duration and frequency of treatment / exposure:

single dose

Remarks:

Doses / Concentrations:
100 μg/kg bw

No. of animals per sex per dose / concentration:

Distribution of bisphenol

Control animals:

yes, concurrent vehicle

Type:

other: In adult female rat tissues, the tissue/serum concentration ratios for aglycone BPA ranged from 0.7 in liver to 5 in adipose tissue, reflecting differences in tissue perfusion, composition, and metabolic capacity.

Results:

Following IV administration to dams, placental transfer was observed for aglycone BPA into fetuses at several gestational days (GD),

Type:

other: Following IV administration fetal/maternal serum ratios of 2.7 at GD 12, 1.2 at GD 16, and 0.4 at GD 20; the corresponding ratios for conjugated BPA were 0.43, 0.65, and 3.7.

Results:

These ratios were within the ranges observed in adult tissues and were not indicative of preferential accumulation of aglycone BPA or hydrolysis of conjugates in fetal tissue in vivo.

Type:

other: Concentrations of aglycone BPA in GD 20 fetal brain were higher than in liver or serum.

Results:

Oral administration of the same dose did not produce measurable levels of aglycone BPA in fetal tissues.

Type:

other: Amniotic fluid consistently contained levels of BPA at or below those in maternal serum.

Results:

Concentrations of aglycone BPA in tissues of neonatal rats decreased with age in a manner consistent with the corresponding circulating levels.

Type:

other: Phase II metabolism of BPA increased with fetal age such that near-term fetus was similar to early post-natal rats.

Results:

These results show that concentrations of aglycone BPA in fetal tissues are similar to those in other maternal and neonatal tissues and that maternal Phase II metabolism are critical in reducing exposures to the fetus.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A investigated

In adult female rat tissues, the tissue/serum concentration ratios for aglycone BPA ranged from 0.7 in liver to 5 in adipose tissue, reflecting differences in tissue perfusion, composition, and metabolic capacity. Following IV administration to dams, placental transfer

was observed for aglycone BPA into fetuses at several gestational days (GD), with fetal/maternal serum ratios of 2.7 at GD 12, 1.2 at GD 16, and 0.4 at GD 20; the corresponding ratios for conjugated BPA were 0.43, 0.65, and 3.7. These ratios were within the ranges observed in adult tissues and were not indicative of preferential accumulation of aglycone BPA or hydrolysis of conjugates in fetal tissue in vivo. Concentrations of aglycone BPA in GD 20 fetal brain were higher than in liver or serum. Oral administration of the same dose did not produce measurable levels of aglycone BPA in fetal tissues. Amniotic fluid consistently contained levels of BPA at or below those in maternal serum. Concentrations of aglycone BPA in tissues of neonatal rats decreased with age in a manner consistent with the corresponding circulating levels. Phase II metabolism of BPA increased with fetal age such that near-term fetus was similar to early post-natal rats. These results show that concentrations of aglycone BPA in fetal tissues are similar to those in other maternal and neonatal tissues and that maternal Phase II metabolism, especially following oral administration, and fetal age are critical in reducing exposures to the fetus.

Executive summary:

In adult female rat tissues, the tissue/serum concentration ratios for aglycone BPA ranged from 0.7 in liver to 5 in adipose tissue, reflecting differences in tissue perfusion, composition, and metabolic capacity. Following IV administration to dams, placental transfer was observed for aglycone BPA into fetuses at several gestational days (GD), with fetal/maternal serum ratios of 2.7 at GD 12, 1.2 at GD 16, and 0.4 at GD 20; the corresponding ratios for conjugated BPA were 0.43, 0.65, and 3.7. These ratios were within the ranges observed in adult tissues and were not indicative of preferential accumulation of aglycone BPA or hydrolysis of conjugates in fetal tissue in vivo. Concentrations of aglycone BPA in GD 20 fetal brain were higher than in liver or serum. Oral administration of the same dose did not produce measurable levels of aglycone BPA in fetal tissues. Amniotic fluid consistently contained levels of BPA at or below those in maternal serum. Concentrations of aglycone BPA in tissues of neonatal rats decreased with age in a manner consistent with the corresponding circulating levels. Phase II metabolism of BPA increased with fetal age such that near-term fetus was similar to early post-natal rats. These results show that concentrations of aglycone BPA in fetal tissues are similar to those in other maternal and neonatal tissues and that maternal Phase II metabolism, especially following oral administration, and fetal age are critical in reducing exposures to the fetus.

Reference 14

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

other: PBPK modelling

Qualifier:

no guideline required

Principles of method if other than guideline:

PBPK model

GLP compliance:

not specified

Radiolabelling:

no

Species:

other: PBPK modelling

Strain:

other: PBPK modelling

Route of administration:

other: oral and IV

Vehicle:

other: PBPK modelling

Duration and frequency of treatment / exposure:

Single dose modelling

Remarks:

Doses / Concentrations:
data with 100 µg/kg/day are used for modelling

No. of animals per sex per dose / concentration:

not applicable

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A

This calibrated PBPK adult monkey model for BPA was then evaluated against published monkey kinetic studies with BPA. Using two versions of the adult monkey model based on monkey BPA kinetic data from Doerge et al. (2010) and Taylor et al. (2011), the aglycone BPA pharmacokinetics were simulated for human oral ingestion of 5 mg d16-BPA per person (Völkel et al., 2002). Völkel et al. were unable to detect the aglycone BPA in plasma, but were able to detect BPA metabolites. These human model predictions of the aglycone BPA in plasma were then compared to previously published PBPK model predictions obtained by simulating the Völkel et al. kinetic study. Our BPA human model, using two parameter sets reflecting two adult monkey studies, both predicted lower aglycone levels in human serum than the previous human BPA PBPK model predictions. BPA was metabolized at all ages of monkey (PND 5 to adult) by the gut wall and liver. However, the hepatic metabolism of BPA and systemic clearance of its phase II metabolites appear to be slower in younger monkeys than adults. The use of the current non-human primate BPA model parameters provides more confidence in predicting the aglycone BPA in serum levels in humans after oral ingestion of BPA.

 

Conclusions:

Interpretation of results (migrated information): other: A physiologically based pharmacokinetic (PBPK) model was developed for Bisphenol A in adult rhesus monkeys using intravenous (iv) and oral bolus doses of 100 μg d6-Bisphenol A/kg (Doerge et al., 2010).

Executive summary:

This calibrated PBPK adult monkey model for BPA was then evaluated against published monkey kinetic studies with BPA. Using two versions of the adult monkey model based on monkey BPA kinetic data from Doerge et al. (2010) and Taylor et al. (2011), the aglycone BPA pharmacokinetics were simulated for human oral ingestion of 5 mg d16-BPA per person (Völkel et al., 2002). Völkel et al. were unable to detect the aglycone BPA in plasma, but were able to detect BPA metabolites. These human model predictions of the aglycone BPA in plasma were then compared to previously published PBPK model predictions obtained by simulating the Völkel et al. kinetic study. Our BPA human model, using two parameter sets reflecting two adult monkey studies, both predicted lower aglycone levels in human serum than the previous human BPA PBPK model predictions. BPA was metabolized at all ages of monkey (PND 5 to adult) by the gut wall and liver. However, the hepatic metabolism of BPA and systemic clearance of its phase II metabolites appear to be slower in younger monkeys than adults. The use of the current non-human primate BPA model parameters provides more confidence in predicting the aglycone BPA in serum levels in humans after oral ingestion of BPA.

 

Reference 15

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

other: PBPK modelling

Qualifier:

no guideline required

Principles of method if other than guideline:

PBPK model

GLP compliance:

not specified

Radiolabelling:

other: PBPK modelling

Species:

other: PBPK modelling

Strain:

not specified

Route of administration:

oral: gavage

Vehicle:

other: PBPK modelling

Duration and frequency of treatment / exposure:

Single exposure

Remarks:

Doses / Concentrations:
100 μg/kg

No. of animals per sex per dose / concentration:

not applicable

Control animals:

no

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total Bisphenol A

The calibrated model predicted the measured serum concentrations of BPA and BPA conjugates after administration of 100 μg/kg of d6-BPA in adult rats (oral gavage and intravenous administration) and postnatal days 3, 10, and 21 pups (oral gavage). The observed age dependent BPA serum concentrations were partially attributed to the immature metabolic capacity of pups. A comparison of the dosimetry of BPA across immature rats and monkeys suggests that dose adjustments would be necessary to extrapolate toxicity studies from neonatal rats to infant humans.

Conclusions:

Interpretation of results (migrated information): other: The calibrated model predicted the measured serum concentrations of BPA and BPA conjugates after administration of 100 μg/kg of d6-BPA in adult rats (oral gavage and intravenous administration) and postnatal days 3, 10, and 21 pups (oral gavage).

Executive summary:

Bisphenol A (BPA) has received considerable attention throughout the last decade due to its widespread use in consumer products. For the first time a physiologically based pharmacokinetic (PBPK) model was developed in neonatal and adult rats to quantitatively evaluate age-dependent pharmacokinetics of BPA and its phase II metabolites. The PBPK model was calibrated in adult rats using studies on BPA metabolism and excretion in the liver and gastrointestinal tract, and pharmacokinetic data with BPA in adult rats. For immature rats the hepatic and gastrointestinal metabolism of BPA was inferred from studies on the maturation of phase II enzymes coupled with serum time course data in pups. The calibrated model predicted the measured serum concentrations of BPA and BPA conjugates after administration of 100 μg/kg of d6-BPA in adult rats (oral gavage and intravenous administration) and postnatal days 3, 10, and 21 pups (oral gavage). The observed age dependent BPA serum concentrations were partially attributed to the immature metabolic capacity of pups. A comparison of the dosimetry of BPA across immature rats and monkeys suggests that dose adjustments would be necessary to extrapolate toxicity studies from neonatal rats to infant humans.

Reference 16

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Qualifier:

no guideline required

Principles of method if other than guideline:

A previously developed physiologically based pharmacokinetic (PBPK) model for Bisphenol A in adult rhesus monkeys was modified to characterize the pharmacokinetics of Bisphenol A and its phase II conjugates in adult humans following oral ingestion. Coupled with in vitro studies on Bisphenol A metabolism in the liver and the small intestine, the PBPK model was parameterized using oral pharmacokinetic data with deuterated-Bisphenol A (d6-BPA) delivered in cookies to adult humans after overnight fasting.

GLP compliance:

not specified

Radiolabelling:

other: PBPK modelling

Species:

other: PBPK modelling

Strain:

other: PBPK modelling

Route of administration:

oral: gavage

Vehicle:

other: PBPK modelling

Duration and frequency of treatment / exposure:

single dose

Remarks:

Doses / Concentrations:
100 µg/kg

No. of animals per sex per dose / concentration:

not applicable

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total-Bisphenol A

The availability of the serum concentration time course of unconjugated d₆-BPA offered direct empirical evidence for the calibration of BPA model parameters. The recalibrated PBPK adult human model for BPA was then evaluated against published human pharmacokinetic studies with BPA. A hypothesis of decreased oral uptake was needed to account for the reduced peak levels observed in adult humans, where d₆-BPA was delivered in soup and food was provided prior to BPA ingestion, suggesting the potential impact of dosing vehicles and/or fasting on BPA disposition. With the incorporation of Monte Carlo analysis, the recalibrated adult human model was used to address the inter-individual variability in the internal dose metrics of BPA for the U.S. general population. Model-predicted peak BPA serum levels were in the range of pM, with 95% of human variability falling within an order of magnitude. This recalibrated PBPK model for BPA in adult humans provides a scientific basis for assessing human exposure to BPA that can serve to minimize uncertainties incurred during extrapolations across doses and species.

In this study, the recalibrated human BPA PBPK model was used to estimate the inter-individual variability of internal dose metrics of BPA for the general population based on the estimated daily intake of BPA in the United States (FDA 2014b; Lakind and Naiman 2008). Model predicted peak serum BPA levels fell within the range of pM, with 95% of human variability ranged within an order of magnitude, suggesting that an

uncertainty factor of less than 10 would be reasonable to account for the inter-individual variability in pharmacokinetics. Also, model predicted internal dose levels of BPA were consistent with those calculated using multiple empirical approaches (Teeguarden et al. 2013), and raised questions concerning the plausibility of a small subset of high serum BPA levels reported in literature.

Conclusions:

Interpretation of results (migrated information): other: A previously developed physiologically based pharmacokinetic (PBPK) model for Bisphenol A in adult rhesus monkeys was modified to characterize the pharmacokinetics of Bisphenol A and its phase II conjugates in adult humans following oral ingestion.

Executive summary:

"A previously developed physiologically based pharmacokinetic (PBPK) model for bisphenol A (BPA) in adult rhesus monkeys was modified to characterize the pharmacokinetics of BPA and its phase II conjugates in adult humans following oral ingestion. Coupled with in vitro studies on BPA metabolism in the liver and the small intestine, the PBPK model was parameterized using oral pharmacokinetic data with deuterated-BPA (d₆-BPA) delivered in cookies to adult humans after overnight fasting. The availability of the serum concentration time course of unconjugated d₆-BPA offered direct empirical evidence for the calibration of BPA model parameters. The recalibrated PBPK adult human model for BPA was then evaluated against published human pharmacokinetic studies with BPA. A hypothesis of decreased oral uptake was needed to account for the reduced peak levels observed in adult humans, where d₆-BPA was delivered in soup and food was provided prior to BPA ingestion, suggesting the potential impact of dosing vehicles and/or fasting on BPA disposition. With the incorporation of Monte Carlo analysis, the recalibrated adult human model was used to address the inter-individual variability in the internal dose metrics of BPA for the U.S. general population. Model-predicted peak BPA serum levels were in the range of pM, with 95% of human variability falling within an order of magnitude. This recalibrated PBPK model for BPA in adult humans provides a scientific basis for assessing human exposure to BPA that can serve to minimize uncertainties incurred during extrapolations across doses and species.

In this study, the recalibrated human BPA PBPK model was used to estimate the inter-individual variability of internal dose metrics of BPA for the general population based on the estimated daily intake of BPA in the United States (FDA 2014b; Lakind and Naiman 2008). Model predicted peak serum BPA levels fell within the range of pM, with 95% of human variability ranged within an order of magnitude, suggesting that an uncertainty factor of less than 10 would be reasonable to account for the inter-individual variability in pharmacokinetics. Also, model predicted internal dose levels of BPA were consistent with those calculated using multiple empirical approaches (Teeguarden et al. 2013), and raised questions concerning the plausibility of a small subset of high serum BPA levels reported in literature."

Reference 17

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2015

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Scientific Committee on Consumer Safety (SCCS). Basic Criteria for the In Vitro Assessment of Dermal Absorption of Cosmetic Ingredients. SCCS/1358/10, 22 June 2010.

GLP compliance:

yes

Radiolabelling:

yes

Species:

human

Strain:

not specified

Sex:

male/female

Type of coverage:

other: in vitro

Vehicle:

other: phosphate buffered saline solution (PBS)

Duration of exposure:

24h

Doses:

300, 60, 12, 2.4mg/l

No. of animals per group:

4 donors

Control animals:

no

Dose:

300 mg/l

Parameter:

percentage

Absorption:

> 2 %

Remarks on result:

other: 24 h

Remarks:

Overall, the majority of the applied radioactivity was associated with epidermis samples (10.66%) compared to dermis (3.28%) and receptor fluid (1.98%) samples.

As part of the safety evaluation of Bisphenol A (BPA), a study was required by the European Chemicals Agency (ECHA) to assess the rate and extent of absorption and metabolism of BPA following topical application to human skin.

 

A recent Community Rolling Action Plan (CoRAP) decision regarding the REACH dossier submission on BPA has required the completion of in vitro dermal penetration studies to provide more information on the dermal exposure pathway. The CoRAP decision noted the need to account for (potential) dermal metabolism of BPA. In order to fulfil this requirement, the study described herein was conducted.

 

The study was conducted according to the OECD principles of Good Laboratory Practice as incorporated into the United Kingdom Statutory Instrument for Good Laboratory Practice and as accepted by Regulatory Authorities throughout the European Union, United States of America (FDA and EPA) and Japan (MHLW, MAFF and METI) and other countries that are signatories to the OECD Mutual Acceptance of Data Agreement. All routine activities performed during the conduct of the study are detailed in Charles River Standard Operating Procedures.

 

The abdominal skin was obtained fresh from surgery from 4 different donors (3 female, 1 male). The metabolic competence for phase I metabolism of the skin was confirmed by assessment of MTT reduction. The mean results are summarised in the following table.

 

	Concentration of MTT Formazan Metabolite (mg/mL)
Donor No.	Viable Skin	Heat Deactivated Skin
Donor 1 (0622)	0.080	0.017
Donor 2 (0659)	0.077	0.023
Donor 3 (0668)	0.088	0.039
Donor 4 (0667)	0.071	0.024

 

The metabolic activity was higher in the viable skin discs than heat deactivated skin discs. It was noted that heat deactivated skin produced MTT formazam. This was potentially due to the incomplete destruction of metabolic activity within the skin by heating or that chemicals within the skin may have been direct MTT reducers. This observation is in line with historic data for this assay within this laboratory. The greater reduction in the viable skin compared with the controlstill demonstrated evidence of active MTT mitochondrial reductase enzymes.

 

For three donors, the metabolism of BPA by human skin disks in vitro was assessed in 12 and 96‑well plates. All samples from both viable and heat deactivated skin samples at 0 h after dosing demonstrated no metabolism. The results from the viable skin samples at 24 h demonstrated that metabolism of BPA was possible in the skin. The level of metabolic transformation was less than 25% in all cases. Metabolites observed in the radio-chromatograms had retention consistent with the BPA-glucuronide and BPA‑sulfate. It was noted that the level of transformation was up to 18% for Donors 2 and 4 for the 24 h heat deactivated skin control samples. These results were unexpected and were potentially due to the incomplete destruction of metabolic activity within the skin from the heating process.

 

Split‑thickness human skin membranes were mounted into flow through diffusion cells (0.64 cm², n=4 per dose) and the receptor fluid was pumped underneath the skin at a flow rate of 0.75 mL/h ± 0.15 mL/h. The skin surface temperature was maintained at 32 °C ± 1 °C throughout the experiment. Electrical resistance barrier integrity test was performed and any skin sample exhibiting a resistance lower than 10.9 kΩ was excluded from subsequent absorption measurements with the exception of two samples (Cell 37 and Cell 40) from Donor 3. The barrier integrity results for Cell 37 and Cell 40 were 5.857 kΩ and 4.960 kΩ, respectively. There was no skin remaining from Donor 3 to replace these cells, therefore, these cells were used on this study. The lower electrical resistance observed in these samples indicates poorer barrier integrity and hence potential for greater absorption therefore, including these samples was the conservative approach for a risk assessment. 

 

For six additional skin samples barrier integrity was also performed at 0 h and 24 h post dose, using the method described above. This assessment was conducted using skin from Donor 2 only. All electrical resistance values at 0 h and 24 h were >10.9 kΩ. This confirmed the chosen receptor fluid did not interfere with the integrity/barrier function of skin.

 

[¹⁴C]‑BPA was incorporated into phosphate buffered saline solution (PBS) to produce four test preparations at final BPA concentrations of ca 300 mg/L, 60 mg/L, 12 mg/L and 2.4 mg/L for Test Preparations 1-4, respectively. The test preparations were applied (10 µL/cm²) to human split‑thickness skin membranes.

 

Percutaneous absorption was assessed by collecting receptor fluid (tissue culture medium (DMEM) containing ethanol (ca 1%, v/v), Uridine 5’‑diphosphoglucuronic acid (UDPGA, 2 mM) and 3’‑phosphoadenosine‑5’‑phosphosulfate (PAPS, 40 µM)) at 0, 1 h and then in two hourly fractions from 2 to 24 h post dose, with the exception that for Donor 1 (0622), where the receptor fluid was collected at 0.5, 1, 2, 4, 6, 8, 10, 12 and 24 h post dose.

 

At 24 h post dose, exposure was terminated with a concentrated commercial handwash soap, rubbed in with a tissue swab, followed by rinsing with a dilute 2% (v/v) soap solution and drying the skin surface with tissue paper (tissue swabs); this process was repeated. The receptor chamber was emptied and rinsed with receptor fluid. The cell was dismantled and the donor chamber and receptor chamber retained separately in the pre‑weighed pots containing ethanol. The skin was removed from the cells and the stratum corneum was removed by tape stripping. The unexposed skin was cut away from the exposed skin. The exposed epidermis was separated from the dermis using a scalpel. Twelve skin samples from each test preparation were solubilised with Solvable^® tissue solubiliser. These samples were analysed by liquid scintillation counting. The remaining solubilised skin samples and receptor fluid samples obtained from four cells from each Donor were analysed by HPLC‑UV.

 

A summary of the mean results is provided in the following table.

 

Test Preparation*	1	2	3	4
Target Concentration (mg/L)	300	60	12	2.4
	(% Applied Dose)
Total Dislodgeable Dose	72.34±5.64	70.91±6.20	71.95±7.98	71.57±9.11
WholeStratum Corneum	10.25±5.44	9.25±4.30	7.31±3.33	7.70±4.92
Total Unabsorbed Dose	82.61±8.37	80.31±6.92	79.33±9.97	79.37±9.91
Epidermis	10.66±6.40	10.45±5.73	10.38±5.36	11.91±4.86
Dermis	3.28±2.44	3.97±1.99	6.19±4.28	4.51±3.73
Total Absorbed Dose	1.98±1.42	1.68±1.20	2.72±1.95	3.62±1.69
Dermal Delivery	15.92±8.14	16.10±7.01	19.28±8.54	20.04±6.24
Mass Balance	98.53±1.99	96.41±1.45	98.62±2.18	99.40±6.54
	ng equiv./cm^2
Total Dislodgeable Dose	2326.98±204.66	452.46±36.03	89.64±9.41	17.96±1.90
WholeStratum Corneum	330.28±177.24	59.08±27.96	9.14±4.28	1.96±1.31
Total Unabsorbed Dose	2657.95±299.42	512.53±41.60	98.88±12.31	19.95±2.31
Epidermis	343.27±209.71	67.14±37.98	12.93±6.71	3.04±1.35
Dermis	104.05±75.82	25.55±13.11	7.76±5.41	1.13±0.92
Total Absorbed Dose	63.27±45.29	10.71±7.84	3.38±2.46	0.91±0.43
Dermal Delivery	510.60±263.45	103.41±46.83	24.07±10.81	5.07±1.70
Mass Balance	3168.54±122.76	615.94±23.90	122.95±2.90	25.02±1.88

 

*Each Test Preparation was applied to a total of 12 samples of skin from 4 donors (3 skin samples per donor). The same donors were used for each test preparation.

 

Total Dislodgeable Dose = skin wash + tissue swabs + pipette tips + donor chamber wash

Unabsorbed Dose = dislodgeable dose + wholestratum corneum (all tape strips+ unexposed skin

Absorbed Dose = receptor fluid + receptor chamber wash + receptor rinse

Dermal Delivery = epidermis + dermis + absorbed dose

Mass balance = dermal delivery + unabsorbed dose

 

[¹⁴C]‑Bisphenol A in Test Preparation 1 (ca 300 mg/L) was applied to human split‑thickness skin in vitro. At 24 h post dose, the mean total dislodgeable dose was 72.34% of the applied dose. The stratum corneum retained a mean of 10.25% of the applied dose, with a mean of 2.46% being removed with the first 2 tape strips. The mean total unabsorbed dose was 82.61% of the applied dose. The total absorbed dose and dermal delivery accounted for a mean of 1.98% and 15.92% of the applied dose, respectively.

 

[¹⁴C]‑Bisphenol A in Test Preparation 2 (ca 60 mg/L) was applied to human split‑thickness skinin vitro. At 24 h post dose, the mean total dislodgeable dose was 70.91% of the applied dose. Thestratum corneumretained a mean of 9.25% of the applied dose, with a mean of 2.27% being removed with the first two tape strips. The total unabsorbed dose accounted for a mean of 80.31% of the applied dose. The absorbed dose and dermal delivery accounted for a mean of 1.68% and 16.10% of the applied dose, respectively.

 

[¹⁴C]‑Bisphenol A in Test Preparation 3 (ca 12 mg/L) was applied to human split‑thickness skin in vitro. At 24 h post dose, the mean total dislodgeable dose was 71.95% of the applied dose. The stratum corneum retained a mean of 7.31% of the applied dose, with a mean of 1.79% being removed with the first two tape strips. The total unabsorbed dose accounted for a mean of 79.33% of the applied dose. The absorbed dose and dermal delivery accounted for a mean of 2.72% and 19.28% of the applied dose, respectively.

 

[¹⁴C]‑Bisphenol A in Test Preparation 4 (ca 2.4 mg/L) was applied to human split‑thickness skin in vitro. At 24 h post dose, the mean total dislodgeable dose was 71.57% of the applied dose. The stratum corneum retained a mean of 7.70% of the applied dose, with a mean of 2.29% being removed with the first two tape strips. The total unabsorbed dose accounted for a mean of 79.37% of the applied dose. The absorbed dose and dermal delivery accounted for a mean of 3.62% and 20.04% of the applied dose, respectively.

 

The dose‑response relationship observed for Test Preparations 1‑4 was linear (R²≥ 0.995). The mean total absorbed dose is between 1.68% and 3.62% of the applied dose and dermal delivery is between 15.92% and 20.04% of the applied dose. Therefore, extrapolation within this dose range is possible for this formulation type. 

 

Metabolism was only investigated for the Test Preparation 1 group (300 mg BPA/L). Metabolism was not investigated in samples dosed with Test Preparations 2‑4 since the levels of radioactivity in these samples were too low to allow detection. From dermal delivery, the majority of the radioactivity was associated with epidermis samples compared to dermis and receptor fluid samples. No metabolism was observed in any of the epidermis samples, However metabolism was observed in dermis and receptor fluid samples (0-14%). The metabolites observed in the radio-chromatograms had retention consistent with the BPA-glucuronide and BPA‑sulfate. The level and distribution of metabolites found in the receptor and dermis samples varied among donors. However, overall the cumulative level of metabolism in the receptor fluid plus dermis was reasonably consistent (12-17%).

 

In conclusion, following topical application of [¹⁴C]‑Bisphenol A in Test Preparation 1, Test Preparation 2, Test Preparation 3 and Test Preparation 4 to fresh human skin in vitro, the mean absorbed dose was 1.98% (63.3 ng equiv./cm²), 1.68% (10.7 ng equiv./cm²), 2.72% (3.38 ng equiv./cm²) and 3.62% (0.91 ng equiv./cm²) of the applied dose, respectively. The mean dermal delivery was 15.92% (511 ng equiv./cm²), 16.10% (103 ng equiv./cm²), 19.28% (24.1 ng equiv./cm²) and 20.04% (5.07 ng equiv./cm²) of the applied dose, respectively. The mean mass balance was 98.53% (3169 ng equiv./cm²), 96.41% (616 ng equiv./cm²), 98.62% (123 ng equiv./cm²) and 99.40% (25.0 ng equiv./cm²) of the applied dose, respectively. 

 

Metabolism was investigated for the Test Preparation 1 group only. Metabolism was not investigated in samples dosed with Test Preparations 2‑4 since the levels of radioactivity in these samples were too low to allow detection. From dermal delivery, the majority of the applied radioactivity was associated with epidermis samples (10.66%) compared to dermis (3.28%) and receptor fluid (1.98%) samples.

 

No metabolism was observed in any of the epidermis samples, however limited levels of metabolism were observed in dermis and receptor fluid samples (0-14%) with formation of BPA-glucuronide and BPA-sulfate identified in supernatant from incubation of viable skin disks for 24 h (<25%). Metabolites with retention consistent with BPA‑glucuronide and BPA-sulfate, and also more polar components, were identified. It might be assumed, but is not analytically verified, that these polar compounds are mixed sulfate/glucuronide bis‑conjugate BPA metabolites.

 

Taking into account the skin disk experiments it can be concluded qualitatively that fresh human skin has some in vitro metabolic capacity but further experiments may be necessary to optimize the experimental conditions to quantify that metabolism.

Executive summary:

The followingdermal absorption rates were reported in this study:

Target Concentration (mg/L)	300	60	12	2.4
	(% Applied Dose)
Total Dislodgeable Dose	72.34 ±5.64	70.91 ±6.20	71.95 ±7.98	71.57 ±9.11
WholeStratum Corneum	10.25 ±5.44	9.25 ±4.30	7.31 ±3.33	7.70 ±4.92
Total Unabsorbed Dose	82.61 ±8.37	80.31 ±6.92	79.33 ±9.97	79.37 ±9.91
Epidermis	10.66 ±6.40	10.45 ±5.73	10.38 ±5.36	11.91 ±4.86
Dermis	3.28 ±2.44	3.97 ±1.99	6.19 ±4.28	4.51 ±3.73
Total Absorbed Dose	1.98 ±1.42	1.68 ±1.20	2.72 ±1.95	3.62 ±1.69
Dermal Delivery	15.92 ±8.14	16.10 ±7.01	19.28 ±8.54	20.04 ±6.24
Mass Balance	98.53 ±1.99	96.41 ±1.45	98.62 ±2.18	99.40 ±6.54

 

There are two guidance documents to calculate the potential dermal absorption based on in vitro data.

a)EFSA Guidance on Dermal Absorption (EFSA Journal 2012. 10, 2665)

EFSA defines absorption= receptor fluid + receptor chamber washes + skin sample (excluding tape strips 1 and 2). The guidance indicates:“There is a general practise within EFSA PRAPeR9 meetings that the first 2 tape strips will represent material that will not become bioavailable due to desquamation. The Panel proposes to follow this approach. Thus, the first 2 tape strips can be excluded when calculating dermal absorption …If there is significant variation between replicates (i.e. the standard deviation is equal to or larger than 25% of the mean of the absorption as defined in section 5.6. and 5.8.) consideration should be given to using a value other than the mean or rejecting the study entirely. The preferred approach would be the addition of a standard deviation to the mean value. that the application site was swabbed to remove the test material before termination of the study.”

 

Applying the EFSA guidance leads to the following potential absorption values;bold values denote value to be used according to the EFSA Guidance.

Test Preparation	Mean Potentially Absorbable Dose	Mean+1SD	SD>25% of mean
300 mg/L	23.70	31.84	Yes
60 mg/L	23.09	29.13	Yes
12 mg/L	24.80	31.79	Yes
2.4 mg/L	25.42	30.79	No

 

b)SCCS Basic Criteria for the in vitro assessment of dermal absorption of cosmetic ingredients (SCCS/1358/1)

 

SCCS defines absorption as follows:“In a classicalin vitrodermal absorption setting, the amounts of penetrated substance(s) found in the receptor fluid are considered to be systemically available.Both the epidermis (except for the stratum corneum) and dermis are considered as a sink, wherefore the amounts found in these tissues are considered as absorbed and are added to those found in the receptor fluid.The amounts that are retained by the stratum corneum at the time of sampling are not considered to be dermally absorbed, and thus they are not expected to contribute to the systemic dose.

…

When studies correspond to all of the basic requirements of the SCCS, themean + 1SDwill be used for the calculation of the MoS… In case of significant deviations from the protocol and/or very high variability, themean + 2SDwill be used as dermal absorption for the calculation of the margin of safety.”

 

Applying the EFSA guidance leads to the following potential absorption values;no clear guidance is given on guideline to define if 1 or 2 SD should be used.

Test Preparation	Mean dermal delivery	Mean+1SD	Mean+2SD
300 mg/L	15.92	24.06	32.20
60 mg/L	16.10	23.11	30.12
12 mg/L	19.28	27.82	36.36
2.4 mg/L	20.04	26.28	31.59

 

Overall, a potentially bioavailable portion of BPA of 30% is taken to derive a corrected dermal starting point for DNEL derivation.

 

 

Potential metabolism was also investigated in this study. No metabolism was observed in any of the epidermis samples, however limited levels of metabolism were observed in dermis and receptor fluid samples (0-14%) with formation of BPA-glucuronide and BPA-sulfate identified in supernatant from incubation of viable skin disks for 24 h (<25%). Metabolites with retention consistent with BPA‑glucuronide and BPA-sulfate, and also more polar components, were identified. It might be assumed, but is not analytically verified, that these polar compounds are mixed sulfate/glucuronide bis‑conjugate BPA metabolites. It can be concluded qualitatively that fresh human skin has somein vitrometabolic capacity but further experiments may be necessary to optimize the experimental conditions to quantify that metabolism.

Overall, as a conservative approach no metabolism was taken into account.

 

Comparison with available in vitro data:

EFSA (2015) summarized the available data as follows“In Demierre et al. (2012), the specific permeation kinetics with an initial high penetration rate and a subsequent low penetration rate are suggestive of effects arising from finite dosing (i.e. partial depletion of the dose on the skin surface) and/or evaporation of the aqueous vehicle (→ reduced hydration of the SC), which both are realistic conditions applicable to consumer exposure. In spite of differences in the diffusion-cell design, skin type, vehicle type and applied dose, the in vitro studies of Marquet et al. (2011), Mørck et al. (2010), and Kaddar et al. (2008) support the percutaneous penetration estimate of 8.6 % of Demierre et al. (2012), although tending to somewhat lower values: a rough calculation based on the comparison of permeability coefficients or the normalization of percutaneous penetration to 24 h incubation yielded estimates of 2.3 % (Marquet et al., 2011) and 6.5 % (Mørck et al., 2010) for human skin, and of 4.1 % (Kaddar et al., 2008) for pig skin.

…

For exposure scenarios with dermal contact to thermal paper, the CEF Panel used a conservative value of 10% dermal absorption. The CEF Panel did not consider skin metabolism (conservative decision). “

 

Comparison of the in vitro data between Mørck et al. (2010), Demierre et al. (2012) and Toner (2015)

Parameter	Mørck et al. (2010)^1	Demierre et al. (2012)^1	This study
Number of skin sections	human skin samples from breast surgery	dorsal part of the upper leg from 2 human cadavers.	abdominal skin obtained fresh from surgery from 4 different donors (3 female, 1 male)
Number of skin sections	11	7	12
Skin viability	non-viable	non-viable	Fresh skin
Skin Section thickness	800–1000 μm	200 μm	350-400 µm
Exposed area	2.12 cm2	0.64 cm2	0.64 cm2
Applied volume	32.6 μl	6 μl	6.4 µl
Applied volume per area	15.4 μl/cm2	9.4 μl/cm2	10 µl/cm2
Applied concentration	3995 mg/l (= 17.5 mM)	194 mg/l	4 different concentrations:300, 60, 12, 2.4 mg/l
Applied surface density	259 μg/cm2	1.82 μg/cm2	3, 0.6, 0.12, 0.04μg/cm2
Applied dose	452 μg	1.16 μg	1.9, 0.4, 0.08, 0.015 µg
Temperature	≈32 °C	30–32 °C	32°C ± 1°C
Method	static Franz diffusion cell OECD TG 428	flow-through Franz cell OECD TG 428	flow-through Franz cell OECD TG 428; SCCS
Skin integrity check	capacitance measurement	permeability coefficient within acceptance range	electrical resistance > 10.9 kΩ
donor solution (vehicle)	0.9% NaCl + 2% EtOH	water	Phosphate buffered saline (PBS)
receptor fluid	physiol. saline + BSA	physiological saline	DMEM;ca1%, v/v) + UDPGA (2 mM) + PAPS (40 µM).
Duration of incubation	48 h	24 h	24 h
Recovery	82.1 %	101.5 ± 1.6 %	96.4 – 99.4 %
Percutaneous penetration	13.0 ± 5.4 %	8.6 ± 2.1 %	1.7 – 3.6 %

  ¹: Information derived from EFSA (2015; page 575-576)

 

Taking into account the above mentioned 10 % dermal penetration taken by EFSA for their dermal risk assessment based on the ca. 10% BPA found in the receptor fluid in the Demierre et al. (2012) study a significantly lower penetration value into the receptor fluid was observed in the in vitro dermal penetration study using viable skin (1.7 – 3.6 %). The approach mentioned in the study request by ECHA to consider the dermis, epidermis (with stratum corneum) and receptor fluid for further calculations lead to substantially higher potential penetration values compared to the EFSA 2015 evaluation of BPA.

Reference 18

Endpoint:

basic toxicokinetics

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2011

Reliability:

2 (reliable with restrictions)

Principles of method if other than guideline:

Authors used physiologically based toxicokinetic modelling to simulate concentrations in blood, in liver and kidney, the target organs exhibiting the lowest no observed adverse effect levels (NOAEL).

GLP compliance:

not specified

Radiolabelling:

other: PB-PK modelling

Species:

human

Route of administration:

dermal

Duration and frequency of treatment / exposure:

single

Remarks:

Doses / Concentrations:
simulated concentrations in blood, liver and kidney after dermal intake of a daily dose of 71 g/day (0.97 g/kg/day)

Cmax and AUC for 24 h in blood, liver and kidney derived from simulated concentrations time profiles after dermal exposure with 71 µg/day (0.97 µg/kg/day). The extent of absorption was varied according to the published numbers (10% (EU, 2003), 13% (Mørck et al., 2010), 46% (Zalko et al., 2011), and 60% (Biedermann et al., 2010)) and after oral exposure with a dose of 0.97 µg/kg/day and 50 µg/kg/day (TDI).

Dermal dose (µg/kg/day)	Absorption through skin (percentage of dose)	Blood		Liver		Kidney
		Cmax (pg/ml)	AUC (pg/ml × h)	Cmax (pg/g)	AUC (pg/g × h)	Cmax (pg/g)	AUC (pg/g × h)
0.97	10	2.5	69.7	0.5	8.4	6.0	94.0
0.97	13	5.8	90.7	0.7	10.9	7.8	122.3
0.97	46	20.5	320.7	2.5	38.7	27.6	433.3
0.97	60	26.7	416.7	3.2	50.3	36.1	563.3
Oral dose (µg/kg/day)	Absorption (percentage of dose)
0.97	90	16.3	64.0	44.7	93.3	22.0	86.3
50	90	841.0	3293.3	2300.0	4800.0	1140.0	4433.3

Conclusions:

Interpretation of results (migrated information): other: physiologically based toxicokinetic modelling

Executive summary:

Authors conclusion: "The results of our paper allow the following conclusions. First dermal exposure may contribute to a relevant extent to the overall internal BPA-exposure. Second, concentrations in blood and in kidney on the one hand and in the liver on the other differ remarkably for BPA if given by the dermal as compared to the oral route due to the high first pass in the liver. Third, even if higher blood concentration of a dose given by the dermal route are taken into consideration, the doses to reach the concentrations reported by most of the authors in the literature are orders of magnitude higher than estimated, based on measurements. Hence, the measured unexpectedly high blood concentrations are thought to be erroneous. Fourth, more data should be made available on the external exposure with BPA by the dermal route. In order to reduce the uncertainty on the extent of absorption, which however does not greatly influence our findings, dermal absorption of BPA should be measured in an in vivo human study using specific analytical methods."

Reference 19

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted at FDA Laboratory in Jefferson, AR

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

The study used LC/MS/MS to measure concurrently the pharmacokinetics of aglycone (active) and conjugated (inactive) deuterated Bisphenol A (d6) in maternal and fetal rhesus monkey serum, amniotic fluid, and placenta following intravenous injection in the dam (100 μg/kg bw).

GLP compliance:

not specified

Radiolabelling:

other: d6-BPA

Species:

monkey

Strain:

other: Pregnant rhesus monkeys (Macaca mulatta) of Chinese origin

Sex:

female

Route of administration:

other: IV injection or gavage

Vehicle:

other: dosing solutions (100 μg/ml) were prepared by dissolving a weighed portion of d6-BPA in 95% ethanol (10% total volume) before dilution in water

Duration and frequency of treatment / exposure:

Single oral dose of 100 µg/kg/day d6-Bisphenol A

Remarks:

Doses / Concentrations:
A total of 5 pregnant monkeys at estimated gestation day 121–139 (normal term=165 days) each received a single oral dose of d6-BPA.

No. of animals per sex per dose / concentration:

A total of 5 pregnant monkeys at estimated gestation day 121–139 (normal term=165 days) each received a single oral dose of 100 µg/kg/day d6-BPA

Control animals:

no

Type:

other: Internal exposures of the fetus to aglycone d6-BPA (serum AUC) were attenuated by maternal, placental, and fetal Phase II metabolism to less than half that in the dam.

Results:

Levels of aglycone and conjugated d6-BPA measured in whole placenta were consistent with a role in metabolic detoxification.

Type:

other: The monotonic elimination of aglycone d6-BPA from the fetal compartment accompanied by persistent conjugate levels provides further evidence arguing against the hypothesis that BPA conjugates are selectively deconjugated by either the placenta or fetus.

Results:

.

Metabolites identified:

yes

Details on metabolites:

free-Bisphenol A and total Bisphenol A investigated

Table 1

Serum pharmacokinetic parameters for aglycone and conjugated BPA from pregnant adult monkeys administered a single IV (n=4) or oral (n=5) dose of 100 μg/kg bw d6-BPA (mean±SD).

Route — form	t1/2 Elim (h)	t1/2 Distr (h)	t1/2 Abs (h)	Cmax (nM)	Tmax (h)	AUC0–∞ (nmol×h×L−1)	Systemic bioavailabilitye
IV — conjugates	5.0±1.1	0.5±0.2	–	–	–	984±261	–
IV — aglycone	2.8±1.1	0.5±0.05	–	–	–	159±62	–
Oral — conjugates	4.3±3.0	0.8±0.3	–	339±252	0.25–0.5	527±341	–
Oral — aglycone	11±3.2	1.3±0.79	0.4±0.2	0.37±0.21	0.25–1	0.76±0.83	0.48%

Table 2

Serum pharmacokinetic parameters for aglycone and conjugated BPA from fetal monkeys following a maternally administered single IV dose of 100 μg/kg bw d6-BPA (mean±SD, n=32).

Form	t1/2 Elim (h)	t1/2 Distr (h)	Cmax (nM)	Tmax (h)	AUC0–8 (nmol×h×L−1)	Fetal/maternal AUC ratio
Conjugated	5.3±2.9	–	657±249	0.25–0.5	4349±1336	4.4±0.84
Aglycone	5.3±3.2	0.2±0.2	92±79	0.08–0.25	68±25	0.45±0.042

Executive summary:

The current study used LC/MS/MS to measure concurrently the pharmacokinetics of aglycone (active) and conjugated (inactive) deuterated BPA (d6) in maternal and fetal rhesus monkey serum, amniotic fluid, and placenta following intravenous injection in the dam (100 μg/kg bw). Internal exposures of the fetus to aglycone d6-BPA (serum AUC) were attenuated by maternal, placental, and fetal Phase II metabolism to less than half that in the dam. Levels of aglycone and conjugated d6-BPA measured in whole placenta were consistent with a role in metabolic detoxification. The monotonic elimination of aglycone d6-BPA from the fetal compartment accompanied by persistent conjugate levels provides further evidence arguing against the hypothesis that BPA conjugates are selectively deconjugated by either the placenta or fetus.

Reference 20

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The analysis has been done under GLP conditions and according to OECD TG 428; Federal Office of Public Health, Division of Chemicals, CH-3003 Berne, Switzerland

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

14C-BPA

Species:

other: Full thickness skin was obtained from 2 human cadavers.

Strain:

other: The samples were taken from the dorsal part of the upper legs.

Sex:

not specified

Vehicle:

water

Duration of exposure:

24 h

Doses:

A homogenous solution of 193.6 mg/L 14C-Bisphenol A has been prepared in H2O (concentration checked by RHPLC). The limit of solubility of Bisphenol A in water has been determined to be approximately 250 mg/L in a previous non-GLP pretest.

No. of animals per group:

Full thickness skin was obtained from 2 human cadavers.

Dose:

193.6 mg/l

Parameter:

percentage

Absorption:

> 9.3 %

Remarks on result:

other: 24 h

Remarks:

This analysis resulted in penetration of 8.6% and a total amount of bio-available Bisphenol A of 9.3% of the dose applied after 24 h incubation under realistic exposure conditions.

Conversion factor human vs. animal skin:

10%

Table 1: Distribution of dose recovered after 24 h incubation [% of dose applied]. The mean results ± SD of the two donors are shown, as well as the limit of quantification (LOQ) in each type of sample.

Fraction	Donor 1 (n = 3)	Donor 2 (n = 4)	Total (n = 7)	LOQ
Skin surface rinse	52.4 ± 2.8	60.3 ± 2.7	56.9 ± 4.9	0.30
Donor cell rinse	0.2 ± 0.0	0.6 ± 0.4	0.5 ± 0.4	0.12
Stratum corneum	41.0 ± 3.9	30.3 ± 3.2	34.9 ± 6.6	0.05
Residual skin membrane	0.5 ± 0.1	0.7 ± 0.3	0.6 ± 0.3	0.03
Receptor fluids	7.8 ± 0.1	9.3 ± 2.7	8.6 ± 2.1	0.09
Total recovery	101.8 ± 2.2	101.3 ± 1.3	101.5 ± 1.6

Executive summary:

Bisphenol A (BPA) is ubiquitous and many exposure scenarios have been described during the last decades. While oral uptake is considered as the major route of exposure, the contribution of skin penetration has been recently discussed. In the present study, the dermal penetration rate of BPA has been determined in human skin in an in vitro test method according to the OECD Test Guideline 428. This analysis resulted in penetration of 8.6% and a total amount of bio-available BPA of 9.3% of the dose applied after 24 h

incubation under realistic exposure conditions. This confirms that the systemic exposure to BPA via the skin contributes in a negligible way to total systemic BPA exposure.

Reference 21

Endpoint:

dermal absorption

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Research Conducted by the National Toxicology Program (Research Triangle Park, NC) with Participation from FDA (Jefferson, AR)

Qualifier:

no guideline required

Principles of method if other than guideline:

Cashiers (n = 77) and non-cashiers (n=25) were recruited from the Raleigh-Durham-Chapel Hill region of North Carolina during 2011-2013. Receipts were analysed for the presence of Bisphenol A or alternatives considered for use in thermal paper. In cashiers, total urine and serum Bisphenol A, BPS, and BPSIP levels in post-shift samples (collected ≤ 2h after completing a shift) were compared with pre-shift samples (collected ≥ 24 hours after a work shift). Urine levels in cashiers were compared to levels from non-cashiers. In cashiers, total urine and serum Bisphenol A, BPS, and BPSIP levels in post-shift samples (collected ≤ 2h after completing a shift) were compared with pre-shift samples (collected ≥ 24 hours after a work shift). Urine levels in cashiers were compared to levels from non-cashiers.

GLP compliance:

not specified

Radiolabelling:

no

Species:

other: humans

Strain:

other: humans

Sex:

male/female

Type of coverage:

other: In cashiers, total urine and serum Bisphenol A, BPS, and BPSIP levels in post-shift samples (collected ≤ 2h after completing a shift) were compared with pre-shift samples (collected ≥ 24 hours after a work shift).

Vehicle:

unchanged (no vehicle)

Duration of exposure:

One work shift

Doses:

Cashiers handling thermo paper were investigated

No. of animals per group:

Cashiers (n = 77) and non-cashiers (n=25) were included.

Control animals:

yes

Conversion factor human vs. animal skin:

Not applicable

Mean urine BPA concentrations in 31 cashiers who handled BPA receipts were as likely to decrease as increase after a shift, but the mean post-shift concentration was significantly higher than in non-cashiers. Only a few cashiers had detectable levels of total BPA in serum.

In the BPA receipt group, most cashiers had pre- and post-shift levels of total serum BPA below the LOD or LOQ (26/33, or 79%, in both pre- and post-shift samples). Contamination was suspected in 5 of the 6 serum samples with BPA above the LOQ in the BPA cashier group based on the sample having a relatively high fraction of total present in unconjugated form (>20%).

Results: Each receipt contained 1-2% by weight of the paper of BPA, BPS, or BPSIP. The post-shift geometric mean total urinary BPS concentration was significantly higher than the pre-shift mean in 33 cashiers who handled receipts containing BPS. Mean urine BPA concentrations in 31 cashiers who handled BPA receipts were as likely to decrease as increase after a shift, but the mean post-shift concentration was significantly higher than in non-cashiers. BPSIP was detected more frequently in urine of cashiers handling BPSIP receipts compared to non-cashiers. Only a few cashiers had detectable levels of total BPA or BPS in serum, whereas BPSIP tended to be detected more frequently.

 

Conclusions: Thermal receipt paper is a potential source of occupational exposure to BPA, BPS, and BPSIP.

Conclusions:

Mean urine Bisphenol A concentrations in 31 cashiers who handled BPA receipts were as likely to decrease as increase after a shift, but the mean post-shift concentration was significantly higher than in non-cashiers.

Executive summary:

Mean urine BPA concentrations in 31 cashiers who handled BPA receipts were as likely to decrease as increase after a shift, but the mean post-shift concentration was significantly higher than in non-cashiers. BPSIP was detected more frequently in urine of cashiers handling BPSIP receipts compared to non-cashiers. Only a few cashiers had detectable levels of total BPA or BPS in serum, whereas BPSIP tended to be detected more frequently.

 

Conclusions: Thermal receipt paper is a potential source of occupational exposure to BPA, BPS, and BPSIP.

Description of key information

Oral:

After oral administration, metabolism and distribution of Bisphenol A is evident to be similar in rodents, monkeys and humans. Bisphenol A is rapidly metabolized by intestinal tissue and the liver to Bisphenol A glucuronide. In humans, the glucuronide is released from the liver into the systemic circulation and cleared rapidly by urinary excretion. In contrast, Bisphenol A glucoronide is primarily eliminated in bile in rodents with some partial urinary excretion. The Bisphenol A glucuronide excreted via the bile in rodents undergoes enterohepatic recirculation after cleavage to Bisphenol A and glucuronic acid by glucuronidase in the intestinal tract. 

Dermal:

The dermal toxicokinetics of Bisphenol A in humans differs from oral toxicokinetics. Recent data indicates the presence of a skin depot of Bisphenol A in humans after dermal administration. From this skin depot a slow release into the circulatory system is observed in parallel to the elimination process indicating a steady-state of dermal absorption and elimination. Although a plausibility check in this study indicates that a dermal absorption of 12-29% is physiologically implausible a dermal absorption rate of 30% as worst case scenario is supposed according to an in vitro percutaneous absorption study. Limited metabolic capacity of human skin was also observed in fresh human skin following dermal Bisphenol A administration, however no metabolism is taken into account as a conservative approach.  

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

100

Absorption rate - dermal (%):

30

Absorption rate - inhalation (%):

100

Additional information

Criteria for IUCLID chapter 7 dossier preparation applied in the dossier update 2021 , the dossier update 2015 and in the initial dossier 2010: 

Dossier Update 2021:

The summaries and conclusions of the initial dossier are included in the endpoint summaries of the update. 

A Literature search is performed to cover literature between the dossier update in 2015 and December 2020. Due to the large data set on Bisphenol A criteria were established, for which studies a robust study entry is included in this dossier update. As in the initial dossier und the dossier update in 2015 key studies are defined as comprehensive studies conducted according to scientifically accepted methods and performed according to or exceeding validated guidelines (e.g. OECD testing guidelines). Supporting studies are defined as comprehensive studies conducted to scientifically accepted methods and performed similar to validated guidelines with only very minor deviations. Studies performed at US federal government laboratories (EPA, FDA, National Toxicology Program, CDC, Pacific Northwest National Laboratory), studies that are part of the CLARITY-BPA program (exploratory studies & Core study) and studies relevant for the risk assessment of BPA are included in this dossier update with robust study entries. All remaining studies published until 2017 were cited in chapters 7.9.3.” specific investigations: other studies” and 7.12. “additional toxicological information”. Studies that do not fall in one of the categories mentioned above and were published after 2017 are not included in the updated dossier. 

  

Dossier update in 2015: 

The summaries and conclusions of the initial dossier are included in the endpoint summaries of the update. 

 A literature search is performed to cover literature between the initial dossier submission (July 2009) and July 2015. As in the initial dossier key studies are defined as comprehensive studies conducted according to scientifically accepted methods and performed according to or exceeding validated guidelines (e.g. OECD testing guidelines). Supporting studies are defined as comprehensive studies conducted to scientifically accepted methods and performed similar to validated guidelines with only very minor deviations. Starting in 2008 and continuing through 2015, researchers at several US federal government laboratories (EPA, FDA, National Toxicology Program, CDC, Pacific Northwest National Laboratory) have been conducting in-depth research to answer key scientific questions and resolve uncertainties about the safety of Bisphenol A. These studies e.g. are included in the updated dossier with robust study entries. 

Recently SCOEL recommendation (2014) and EFSA opinion (2015) became available and for each endpoint their conclusion is cited. 

  

Additional exploratory studies identified during the updated literature search are also cited in chapters 7.9.3.” specific investigations: other studies” and 7.12. “additional toxicological information”. 

 

Initial dossier submitted in 2010: 

Due to the large data set on Bisphenol A, criteria were established to define Key-Studies, Supporting-Studies and additional studies to cover all available data for the human health hazard assessment. In the original dossier submitted in 2010 the human health hazard assessment was based on the initial EU Risk Assessment Report 2003 on Bisphenol A and the EU Risk Assessment Update in 2008. For each endpoint the conclusion of the EU Risk Assessments in 2003 and 2008 are cited and, if available, additional relevant information not evaluated in one of the Risk Assessments is indicated. Key studies were defined as comprehensive studies conducted according to scientifically accepted methods and performed according to or exceeding validated guidelines (e.g. OECD testing guidelines). Supporting studies were defined as comprehensive studies conducted to scientifically accepted methods and performed similar to validated guidelines with only very minor deviations. Additional exploratory studies were cited in chapters 7.9.3.” specific investigations: other studies” and 7.12. “additional toxicological information”.

Discussion on toxicokinetics: 

 

EFSA 2015 Conclusions on toxicokinetics: 

"The kinetic data available indicate species- and life stage-dependent differences. Such variability has to be considered when data of different species are compared. Conjugation to Bisphenol A-glucuronide, which is a biologically inactive form, is the major metabolic pathway of Bisphenol A in humans and animals. A study in humans on high Bisphenol A diets (Teeguarden et al., 2011) showed that unconjugated Bisphenol A in serum was below the LOD of 0.3 ng/ml (= 1.3 nM), confirming under the condition of the study that internal exposure to unconjugated Bisphenol A is low. The percentage of unconjugated Bisphenol A in blood is only a few percent of total Bisphenol A (sum of conjugated and unconjugated Bisphenol A). Based on the analysis of oral (gavage) versus intravenous toxicokinetic data, the oral systemic bioavailability of unconjugated Bisphenol A in rats is 2.8 %, in mice 0.45 % and in monkeys 0.9 % (Doerge et al., 2010a,b, 2011a, b, 2012). The concentrations measured in the animal studies and also in the human study render the relevance of serum or blood concentrations in humans, which were measured and reported by some authors in the literature (see Section 4.6.3 in Part I – Exposure assessment) as rather unplausible. Experimental data on the systemic availability of unconjugated Bisphenol A in humans has until now not been published. From studies on physiologically based pharmacokinetic (PBPK) modelling it can be concluded, that at relevant oral exposures (e.g. < 1 μg/kg bw per day) the maximum serum concentrations (Cmax) of unconjugated Bisphenol A are in the 3.2–160 pg/ml (7–37 pM) range, depending on the model used (Mielke and Gundert-Remy, 2009; Edginton and Ritter, 2009; Fisher et al., 2011; Yang et al., 2013). Bisphenol A does not accumulate in the body even though the concentration of unconjugated Bisphenol A is somewhat higher in fat compared to serum.  

Some new animal data in particular in mice, rats and monkey give more insight into the kinetics of Bisphenol A, in particular into the age-dependent maturation of conjugation reactions. Also, diaplacentar transfer of Bisphenol A has been measured in rat and monkey. Data in rats indicate that in early pregnancy transfer to the fetus might be greater compared to later pregnancy after IV injection exposure of Bisphenol A (fetus/dam concentration ratios: 2.8 at GD 12, 1.2 at GD 16, 0.4 at GD 20). Unconjugated Bisphenol A and Bisphenol A-conjugates are measured in the amniotic fluid of rats and rhesus monkeys at low concentrations. Bisphenol A is found in milk of rat dams exposed to Bisphenol A at a level of 100 ug/kg bw per day in the unconjugated and conjugated forms. The amount delivered to the pups is so small that the concentrations in pup serum are below 0.2 nM (45.6 pg/ml), and therefore pup exposure via lactation is extremely low (1/300 of the maternal dose). These data are in marked contrast to the average concentrations reported for human breast milk (unconjugated Bisphenol A 0.3 ng/ml; total Bisphenol A 1.1 ng/ml )despite the fact that the average human exposure is 1/1000 of the rat exposure exposure (see Chapter 4.6.4. in Part I – Exposure assessment).  

Polymorphisms have been described for the enzymes relevant for the conjugation of Bisphenol A. Since Bisphenol A conjugation can be carried out by several enzymes, a single polymorphism in one gene, resulting in a reduction or loss of enzymatic activity of functional enzymes may result in a change in the plasma levels of unconjugated Bisphenol A. Since Bisphenol A is glucuronidated by two UTGs and is conjugated not only to glucuronides but also to sulphates, it can be assumed that the increase in blood concentration is modest. This assumption has been confirmed also in the PBPK modelling study by Partosch et al. (2013) showing a 4-fold difference in AUC and Cmax between the human PBPK models with the highest and the lowest metabolic activity. This difference in sensitivity of Bisphenol A in the human population is covered by the assessment factors used in the risk assessment of Bisphenol A.  

A solid base of toxicokinetic studies in various laboratory animal species (Doerge et al., 2010a,b,c; 2011a,b; 2012) provide internal dose metrics for neonatal-to-adult stages and for different routes of exposure (oral and intravenous/subcutaneous). Moreover, PBPK models have been developed to predict the internal exposures in laboratory animals and humans in a route-specific manner. Overall, this body of information permits extrapolation to humans and the application of the HED concept for providing HEDF which account for the toxicokinetic portion of the interspecies differences. Multiplying the HEDF by a reference point of a critical toxicity study yields a human-equivalent oral dose that is used for risk assessment. The assessment of the physiological plausibility of the derived HEDF values for adult animals with oral dosing revealed a good agreement of the HEDF for monkeys with the allometric scaling-derived DAF. In rats, the HEDF was 3-times higher than the DAF which can be explained by the effect of enterohepatic recirculation, serving to extent the exposure to Bisphenol A. For mice, the HEDF was 2-times lower than the DAF, which suggests a greater metabolic capacity, serving to reduce the AUC. The Panel noted that due to limitations in the analytical detectability of unconjugated Bisphenol A in mouse serum, the HEDF for mice may be conservative by a factor of 5.  

The available evidence from in vitro skin absorption experiments with human, pig and rat skin and from in vivo studies on dermal absorption in rats suggests a 24-h dermal absorption for human skin of 2.3–8.6%. For exposure scenarios with dermal contact to thermal paper, the CEF Panel decided to use a skin penetration of 10%. The CEF Panel decided not to consider the amount deposited in the stratum corneum as becoming available for systemic uptake for reasons emerging from the PBPK modelling of dermal exposure. The CEF Panel further decided not to consider skin metabolism in dermal exposure scenarios as the available information does not permit to arrive at a reliable estimate of the extent of skin metabolism. Not to consider skin metabolism is a conservative decision. The CEF Panel noted that the assumption of 10% dermal absorption for the hand contact to thermal paper is also a further conservative decision, since the absorption across the skin of the palms can be expected to be lower than in other body parts because of the thicker stratum corneum. For scenarios with aggregated oral and dermal exposures, PBPK modelling was used to estimate the internal dose metrics for unconjugated Bisphenol A and to convert external dermal doses into an equivalent oral doses."  

 

The 2008 updated EU RAR concluded: 

"New information on the toxicokinetics of Bisphenol A in humans and in pregnant and non-pregnant rodents of different ages provides an important contribution to the knowledge of kinetic properties of Bisphenol A. Human studies have demonstrated that at comparable exposure levels the blood concentrations of free Bisphenol A in humans are much lower than those in rodents. In rats, mice, monkeys, and humans, the available evidence suggests that following oral administration, Bisphenol A is rapidly and extensively absorbed from the gastrointestinal tract. For the purposes of risk characterisation, absorption via the oral and inhalation routes will be assumed to be 100%; dermal absorption will be taken to be 10%. A number of studies in rats suggest that Bisphenol A metabolites and free Bisphenol A have a limited distribution to the embryo/foetal or placental compartments following oral administration. Maternal and embryo/foetal exposure to free Bisphenol A did occur, but systemic levels were found to be low due to extensive first-pass metabolism. There are differences between humans and rodents in the distribution of Bisphenol A. After oral administration, Bisphenol A is rapidly metabolised in the gut wall and the liver to Bisphenol A glucuronide. In humans, the glucuronide is released from the liver into the systemic circulation and cleared by urinary excretion. In contrast, Bisphenol A glucuronide is eliminated in bile in rodents and undergoes enterohepatic recirculation after cleavage to Bisphenol A and glucuronic acid by glucuronidase in the intestinal tract."  

 

The 2003 EU RAR concluded: 

"Animal data indicates that absorption of Bisphenol A from the gastrointestinal tract is rapid and extensive following oral administration, although it is not possible to reliably quantify the extent of absorption. Following dermal exposure, available data suggest limited absorption of about 10% of the applied dose. Bisphenol A is removed rapidly from the blood and the data indicate extensive first pass metabolism following absorption from the gastrointestinal tract. In view of this first pass metabolism, the bioavailability of unconjugated Bisphenol A is probably limited following oral exposure to no more than 10 to 20% of the administered dose. The major metabolic pathway in rats involves glucuronide conjugation, with approximately 10% and 20% of the administered dose recovered in urine as the glucuronide metabolite in males and females, respectively. The major route of excretion is via the faeces with the urinary route being of secondary importance. Over seven days post dosing, approximately 80% and 70% of the administered dose was eliminated in the faeces in male and female rats, respectively. The first pass metabolism and extensive and rapid elimination of Bisphenol A suggest that the potential for transfer to the foetus and bioaccumulation may be limited. There are no data on the toxicokinetics of Bisphenol A following inhalation exposure."