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Basic toxicokinetics

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basic toxicokinetics
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: acceptable, well-documented publication and study report which meets basic scientific principles

Data source

Reference Type:
Comparative Metabolism and Toxicokinetics of 14C-Resorcinol Bis-Diphenylphosphate (RDP) in the Rat, Mouse, and Monkey
Ralph I. Freudenthal, Lee J.McDonald, Jodie V. Johnson, David L.McCormick, and Richard T. Henrich
Bibliographic source:
International Journal of Toxicology, 19:233–242, 2000

Materials and methods

Objective of study:
Test guideline
equivalent or similar to
OECD Guideline 417 (Toxicokinetics)
not specified
Principles of method if other than guideline:
Nothing to add in this field.
GLP compliance:
not specified

Test material

Details on test material:
Nonradiolabeled RDP was obtained from Akzo NobelChemicals (Dobbs Ferry, NY).14C-RDP was purchased from DuPont/New England Nuclear (Boston, MA). It had a specific cactivity of 48.6 mCi/mmole. The radiolabeled RDP was repurified prior to use, to achieve a minimum radiochemical purity of
14C-Resorcinol Bis-Diphenylphosphate (RDP)

Test animals

other: mouse,rat,monkey
other: B6C3F1 mice,Sprague-Dawley rats,captive-bred cynomolgus monkeys (Macaca fascicularis)
Details on test animals and environmental conditions:
Maleand female B6C3F1 mice approximately 10 to 12 weeks old, male and female Sprague-Dawley rats approximately 7 to 8 weeks old, and male and female captive-bred cynomolgus monkeys (Macaca fascicularis) were purchased from Charles River Laboratories (Portage, MI). The rats and primates were individually housed whereas the mice were group housed. Animal housing was in accordance with the Guide for the Care and Use of Laboratory Animals published by the National Research Council.
Rats and mice received food and water ad libitum throughout the study. Primates received a specified amount of certified Purina monkey chow (PMI Feeds, St.Louis, MO) per day supplemented with at least one Prima-Treat per day, but water was available ad libitum. To maintain psychological well-being, the primates were offered toys and fresh fruit during the quarantine and study. The rodents were held in quarantine for aminimum of 1 week prior to dosing whereas the primates were quarantined for a minimum of 6 weeks. During the quarantine period, each primate demonstrated three negative
tuberculosis tests, a negative chest x-ray, negative throat and rectal swabs for Klebsiella pneumonia and Shigella, and a negative parasite evaluation of stool samples.

Administration / exposure

Route of administration:
unchanged (no vehicle)
Details on exposure:
The group 1 mice were acclimated in metabolism chambers (Metabowl, Jencons Scienti c, Bedfordshire, England) for 24 hours prior to treatment.After themice received radiolabeled RDP via intravenous injection into the tail vein, groups consisting of fourmice each (same sex)were returned to theMetabowls.Exhaled air from the Metabowls was passed through two CO2 traps to collect any 14 CO2 formed by metabolism of radiolabeled RDP. Urine and feces were collected at 2, 6, 12, and 24 hours and 2, 3, 4, 5, 6, and 7 days after dosing.Group 2 rats were also acclimated in Metabowls prior to treatment. Each rat received a single intravenous injection of radiolabeled RDP into the tail vein and then was individually housed in a Metabowl with expired air collected as described above. Urine and feces samples were collected at 2, 6, 12, and 24 hours and at 2, 3, 4, 5, 6, 7, 8, 10, and 4 days. Group 3 primates were acclimated in restraint chairs for several days prior to treatment. A day before dosing, a Teflon catheter was implanted into the right cephalic vein of each animal. Each primate received a single intravenous injection of radiolabeled RDP via the catheter in the cephalic vein while residing in a primate restraint chair. Urine and feces were separately collected at 2, 6, 12, and 24 hours and at 2, 3, 4, 5, 6, 7, 8, 9, 10, 14, 21, and 28 days after treatment.
Group 4 rats were exposed to 14C-RDP in a Cannon 52-port-flow-past nose-only inhalation exposure chamber (Lab Products, Maywood, NJ). The test atmosphere was generated by aerosolization of radiolabeled RDP using a DeVilbiss nebulizer (DeVilbiss Co., Somerset, PA) and a compressed air source. The nebulizer was adjusted to generate an RDP aerosol with an average particle size of 3 μm (Mass Median Aerodynamic Diameter). Aerosol particle size was monitored with a Mercer cascade impactor (In-Tox Products, Albuquerque, NM). The rats were acclimated in the restraining tubes prior to the initiation of the study. Aerosol mass concentration in the breathing zone of the rats was determined gravimetrically from samples collected
at least once each hour from an unoccupied exposure port. In addition to the gravimetric determinations, a real-time sensor was used as a continuous indicator of short-term changes in exposure concentration. After a 6-hour exposure, the animalswere immediately transferred to Metabowls where they were individually housed. Urine and feces were collected at 12 and 24 hours, and at 2, 3, 4, 5, 6, 7, 8, 9, 10, 14, 21, and 28 days after exposure.
Twenty-four hours prior to dosing, group 5 rats were prepared by shaving an area of the dorsal thoracic surface of the skin (about 20% of the total body surface area) with electric clippers. O-rings were then glued to the shaven areas. A measured dose of radiolabeled RDP was applied to the shaved skin which was then covered by a nonocclusive nylon mesh. The mesh was glued to the o-rings. The treated rats were individually housed in Metabowls. After a 6-hour exposure period, the nylon mesh and o-rings were removed and soaked in ethanol, and the dosed area was washed with a mild soap solution, followed by distilled water. The cotton balls used for the washing were also soaked in ethanol. The ethanol solutions were analyzed to quantify the amount of RDP unabsorbed after 6 hours.After removing the residual unabsorbed dose, the animals were returned to theMetabowls. Urine and feces were collected at 12 and 24 hours, and at 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 21, and 28 days after treatment.
On the day prior to treatment, group 6 primates were anesthetized with Ketamine (Fort Dodge Laboratories, Fort Dodge, IA) and atropine (Elkin-Sinn Inc., Cherry Hill, NJ), and an area of the dorsothoracic region (about 30% of the body surface) was clipped free of hair. The primateswere acclimatedto the restraint chairs for several days prior to dosing. After acclimation, the radiolabeled RDP was spread over a shaved area representing about 20% of the animal’s surface area. After a 6-hour exposure period, the dosed area was repeatedly but gently washed to remove unabsorbed RDP. The washes were later analyzed to quantify the amount of dose that remained unabsorbed at 6-hours. Expired airwas not collected from these animals.Urine
and feces were collected at 2, 6, 12, and 24 hours and at 2, 3, 4, 5, 6, 7, 8, 9, 10, 14, 21, and 28 days after RDP application.
Rats in group 7 were fasted overnight before receiving a single oral (gavage) dose of radiolabeled RDP. Immediately after dosing, the rats were individually housed in Metabowls. Urine and feces collection times were identical to those shown above for the primate dermal group, with additional samples collected at 11, 12, and 13 days after treatment.
Duration and frequency of treatment / exposure:
one exposure and observed 7 days after dosing
Doses / concentrations
Doses / Concentrations:
Target RDP dose (mg/kg):100
Target radioactivity dose ( Ci/animal): 50
No. of animals per sex per dose:
8 per sex per dose
Control animals:
not specified
Positive control:
no data
Details on study design:
Nothing to add in this field.
Details on dosing and sampling:
Collection of Blood Samples for Toxicokinetic
Analysis (Rats)
Blood collection at interim time points was by retro-orbital sinus puncture from animals maintained under light CO2 anesthesia into heparinized capillary tubes. On the last day of collection, blood was collected from rats by cardiac puncture using a heparinized syringe.
Collection of Urine, Feces, and Expired Air (Rats)
Immediately after dosing, the rats were returned to individual Metabowls for collection of urine, feces, and expired air. A flowmeter was connected to the Metabowl and joints, lids, and connectors were sealedwith high vacuum grease. Room air was drawn into the Metabowl using a pump and air exiting from the chamber was passed through two Nilox columns connected in series. Each column contained 400 ml of 4M NaOH that served as the liquid scrubber for the collection of radioactivity in the expired air. The amount of radioactivity in the exhaust air was quantified by taking 10-ml samples of the NaOH from each column for analysis by scintillation counting. After collection, the columns were washed and re lled with fresh NaOH. Urine and
feces were separately collected into flasks immersed in dry ice. At each collection time the wire oors and glass sides of the Metabowls were rinsed and the rinsate combined with the urine samples. Excreta samples were weighed and stored at 20±C until analyzed. New collection jars and fresh dry ice were used for each collection sample.
Collection of Blood, Urine, and Feces (Primates)
Prior to dosing, the primates were restrained in plastic chairs designed for the separation and collection of urine and feces. Teflon catheters were implanted into the right cephalic vein (for intravenous dosing) and the right femoral vein (for blood collection). Samples for metabolismand toxicokinetic end points were collected from the all of the animals. Blood samples were collected using a heparinized syringe. After collection, an aliquot of each sample was transferred to a tared glass centrifuge tube, weighed, and centrifuged to obtain plasma. At each collection time point, urine and feces were collected, weighed, and stored at 20±C until analyzed.
Necropsy and Collection of Tissue Samples (Rats)
In order to characterize the tissue distribution of radiolabe in animals exposed to 14C-RDP, an additional group of two male and two female rats received a single intravenous dose of 14C-RDP. This was followed by collection of urine, feces, and expired air for 14 days. At the end of the collectionperiod the rats were euthanized and a limited necropsy was performed to collect potential target tissues and identify specific storage depots
The brain, mesenteric fat, kidneys, liver, lungs, testes/ovaries and spleen were removed, weighed, and homogenized. Measured aliquots of the tissue homogenates, and of the residua carcass, were solubilized and then the radioactivity therein was quantified by scintillation counting.
Comparative absorption (bioavailability) assessments and toxicokinetic analyses were performed using WinNonlin (Scientific Consulting Inc., Apex,NC) and PKAnalyst (MicroMath Corp., Salt Lake City, UT) for compartmental and noncompartmental toxicokinetic modeling.
Toxicokinetic data were compared using two-tailed t tests (for comparisons between sexes) and univariate analysis of variance (for species and route comparisons). In instances where statistical significance was demonstrated by ANOVA, post hoc comparisons were made using Tukey’s HSD multiple comparison test. A significance level of p < 0.05 was established for all comparisons.

Results and discussion

Preliminary studies:
Other studies within this comprehensive testing program showed a lack of immunotoxicity in the National Toxicology Program Tier I and Tier II screens, no target organ toxicityafter nose-only inhalation at doses as high as 2 mg/l, 6 hours per day for 28 days, no teratogenic activity in rabbits when administered at the limit dose of 1000 mg/kg/day, and no adverse effects on either fertility or reproduction in a multigeneration reproduction study in which rats received the dietary limit dose of 20,000 ppm.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
The RDP, was present in significant amounts only in the feces of animals exposed by inhalation or gavage; this appears to reflect unabsorbed ingested material.Dermal absorption of RDP in the rat was relatively low.
Details on distribution in tissues:
The brain, mesenteric fat, kidneys, liver, lungs, testes/ovaries, and spleen were removed, weighed, and homogenized. Measured aliquots of the tissue homogenates, and of the residual carcass, were solubilized and then the radioactivity therein was quantified by scintillation counting.
At 14 days, the total body burden of radioactivity was less than 4% of the Intravenous administered dose. Approximately 2.0% of the administered radioactivity was seen in the lung, whereas about 1.9% was present in the carcass and other tissues. Other than the lung, no preferential sites of RDP or metabolite deposition were identified.
Details on excretion:
Significant quantitative differences were observed for the radioactivity eliminated in the feces, the primary route of excretion. The largest fraction of the administered dose eliminated in the feces was seen in rats that received RDP via oral dosing. In these animals, approximately 80% of the dose was
excreted during the first day after administration. Fecal excretion of radiolabel by rats exposed to RDP by other routes was considerably slower. Animals that received RDP by the inhalation, intravenous, and dermal routes had 60%, 48%, and 32% of the administered dose in their feces. Regardless of the route of exposure, fecal excretion was at least threefold greater than urinary excretion of total radiolabel. The expired air was aminor route of excretion, regardless of route of dosing. A comparison of the parameters obtained after intravenous injection of RDP to primates and rats showed similar concentration versus time profiles, and both species demonstrated two-compartment toxicokinetics. In both species, the primary route of excretion was via the feces. After dermal exposure, there was significantly less absorption by the primate as compared to the rat.
Major urinary metabolites were identified as resorcinol, resorcinyl glucuronide, and resorcinyl sulfate. A small amount of 14CO2 was expired.
Toxicokinetic parametersopen allclose all
Test no.:
Toxicokinetic parameters:
Cmax: 81.86±22.08 µg equiv/ml (monkey i.v.)
Test no.:
Toxicokinetic parameters:
Tmax: 0.08±0.00 h (monkey i.v.)
Test no.:
Toxicokinetic parameters:
AUC: 1895.0±213 µg equiv × h/ml (monkey i.v.)

Metabolite characterisation studies

Metabolites identified:
Details on metabolites:
HPLC analysis of many fecal samples from rat, mouse, and primate showed that RDP is extensively metabolized and that the same four major metabolites are formed by all three species.
hydroxy-RDP half ester (hydroxy-resorcinol diphenylphosphate),RDP half ester, phenyldihydroxy-RDP,phenylhydroxy-RDP.

Any other information on results incl. tables

TABLE 2Comparison of toxicokinetic parametersa









µg equiv/ml














µg equiv × h/ml
















































aAll values are mean±standard deviation. Route of administration is given in parentheses.

BCould not be accurately determined.

CExpressed as Cl/F,V/F, orVss/F.

Applicant's summary and conclusion

Interpretation of results (migrated information): no bioaccumulation potential based on study results
Tissue accumulation and retention of radioactivity was minimal, indicating complete clearance of the administered dose.
Executive summary:

Both Resorcinol bis-diphenylphosphate (RDP) CAS No. 125997-21-9, 57583-54-7 and Bisphenol A bis-diphenylphosphate (BDP) CAS No. 5945-33-5, 181028-79-5 which may be used to replace the flame retardant decabromodiphenyl ether (Deca-BDE) in electronic enclosures due to lower toxicity effects on human health and large chunks of tonnes are used to produce non-halogenated flame retardants such as Bisarylphosphates. These two substances have the analogous stucture and functional groups which are considered have similar biophysicochemical property and metabolites in both rodent and non-rodent animals, therefore the toxicokinetics model which were contibuted from RDP can be used to elicit a prediction of ADME for BDP.