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Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1987
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
metabolism
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
not specified
Radiolabelling:
no
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
Fourteen Fischer-344 male rats weighing 307+/-10g. Feed (Purina Rat Chow, Ralston Purina Co., St. Louis, MO) and water were provided ad libitum.
Route of administration:
oral: gavage
Vehicle:
not specified
Details on exposure:
Fourteen Fischer-344 male rats weighing 307±10 g were randomly divided into 2 groups (8 treated, 6 control). Doses (0.8 g/kg) of t-butylcyclohexane or water (0.8 g/kg) were administered by gavage on an every other day regimen for 2 weeks. Feed (Purina Rat Chow, Ralston Purina Co., St. Louis, MO) and water were provided ad libitum and animals were weighed daily.
Duration and frequency of treatment / exposure:
2 weeks
Remarks:
Doses / Concentrations:
0.8 g/kg
No. of animals per sex per dose / concentration:
8 treated, 6 control
Control animals:
yes, concurrent no treatment
Details on study design:
Fourteen Fischer-344 male rats weighing 307±10 g were randomly divided into 2 groups (8 treated, 6 control). Doses (0.8 g/kg) of t-butylcyclohexane or water (0.8 g/kg) were administered by gavage on an every other day regimen for 2 weeks. Feed (Purina Rat Chow, Ralston Purina Co., St. Louis, MO) and water were provided ad libitum and animals were weighed daily. Following the 14-day exposure period, the rats were sacrificed by halothane.
Details on dosing and sampling:
During the first 48 h of the initial dosing period, the rats were placed in metabolism cages and the urine was collected. A 5.0 ml aliquot of each urine sample was adjusted to a pH of 4.0, and 0.2 ml glucuronidase/sulfatase was added. The sample was shaken for 16 h at 37°C, then cooled to room temperature and filtered through a diatomaceous earth column using methylene chloride as the eluent. The methylene chloride extracts of the hydrolyzed rat urine were analyzed on a gas-liquid chromatograph (GC) equipped with a flame ionization detector. A 25 m x 0.2 mm ID carbowax 20 M fused silica column was used with injection port and detector temperatures of 200 and 250°C, respectively. The oven temperature was programmed to rise from 60 to 170° C at a rate of 5°C/mm and helium was used as the carrier gas. Additional metabolite identification was accomplished using a Hewlett-Packard 5985 gas chromatography/mass spectrometer (GS/MS) system. The GC was equipped with a 15 m x 0.2 mm ID DX-4 capillary column and the injection port temperature and the oven temperature were the same as reported above. Helium was the carrier gas. The MS was a quadrupole instrument operated in the electron impact mode with a voltage of 70 eV and an ion source temperature of 200°C.

The relative abundance of the urinary metabolites was found by preparing a standard solution utilizing a weighed amount of each pure compound and dodecane as an internal standard and then comparing the integrated areas of the GC curve with the areas of the CC urinary metabolite curve containing added dodecane.
Metabolites identified:
yes
Details on metabolites:
The majority of the oxidative metabolism of t-butylcyclohexane occurred on the cyclohexane structure. Of the 2 products which were the result of metabolic oxidation of the t-butyl side chain, 2-methyl-2-cyclohexylpropanoic acid was formed in greater abundance.

The metabolic oxidation of the cyclohexane ring of t-butylcyclohexane preferentially occurred at the 4-position. The bulkiness of the t-butyl group apparently inhibited monooxidation at the 2- and 3-positions. Both cis- and trans-4-t-butyl- cyclohexanol are formed with the latter being the overall principle metabolic product. The remaining minor metabolites identified were the result of dioxidation on the cyclohexane ring at the 3-position. The least formed cyclohexanediol was the isomer in which all the ring substituents exist in the equatorial position of the cyclohexane chair conformation of 2- hydroxy-4-t-butylcyclohexanol. 2-Hydroxy-4-t-butylcyclohexanol has the t-butyl and the OH at C1 groups in the equatorial position, while the OH at C2 is in the axial position. The most abundant cyclohexanediol, 2-hydroxy-4-t-butylcyclohexanol, has the OH at C2 and the t-butyl groups in the equatorial positions while the OH at C1 is in the axial position. If one envisions that the starting materials for the cyclohexanediols were the corresponding 4-t-butylcyclohexanols, the small amount of cis-4-t-butylcyclohexanol found may be due to its facile conversion into the 2 most abundant t-butyl-1,2-cyclohexanediols isolated. The large amount of trans-4-t-butylcyclohexadiol found may be a reflection of its easier conjugation with glucuronic acid relative to cis-4-t-butylcyclohexanol. The difficulty in glucuronidation of the cis-4-t-butylcyclohexanol could then, conceivably, result in further hydroxylation to facilitate urinary excretion by creating more polar metabolites (diols).
Conclusions:
Interpretation of results: The major metabolites of t-butylcyclohexane were found to be: trans-4-t-butylcyclohexanol, 2c-hydroxy-4t-t-butylcyclohexanol, 2-methyl-2-cyclohexylpropanoic acid, 2c-hydroxy-4c-t-butylcyclohexanol, 2-methyl-2-cyclohexyl-1,3-propanediol, 2t-hydroxy-4t-t-butylcyclohexanol, and cis -4-t-butylcyclohexanol.
Executive summary:

The major metabolites of t-butylcyclohexane were found to be: trans-4-t-butylcyclohexanol, 2c-hydroxy-4t-t-butylcyclohexanol, 2-methyl-2-cyclohexylpropanoic acid, 2c-hydroxy-4c-t-butylcyclohexanol, 2-methyl-2-cyclohexyl-1,3-propanediol, 2t-hydroxy-4t-t-butylcyclohexanol, and cis -4-t-butylcyclohexanol.

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2007
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: The documentation is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Principles of method if other than guideline:
In vitro metabolic study.
GLP compliance:
not specified
Radiolabelling:
no
Species:
other: in vitro: liver microsomes from adult male F-344 rats
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
in vitro: liver microsomes from adult male F-344 rats
Route of administration:
other: in vitro
Conclusions:
Nonlinear kinetic constants for nonane and decane were V(max) (nmol/mg protein/min) = 7.26 +/- 0.20 and 2.80 +/- 0.35, respectively, and K(M) (micro M) = 294.83 +/- 68.67 and 398.70 +/- 42.70, respectively. Metabolic capacity as assessed by intrinsic clearance (V(max)/K(M)) was approximately four-fold higher for nonane (0.03 +/- 0.005) than for decane (0.007 +/- 0.001). There was no appreciable metabolism of tetradecane even with higher microsomal protein concentration and longer incubation time. These results show a negative correlation between metabolic clearance and chain length of n-alkanes.
Executive summary:

Jet propellant 8 (JP-8) jet fuel is a complex mixture of aromatic and aliphatic hydrocarbons. The aim of this study was to determine in vitro metabolic rate constants for semivolatile n-alkanes, nonane (C9), decane (C10), and tetradecane (C14), by rat liver microsomal oxidation. The metabolism was assessed by measuring the disappearance of parent compound by gas chromatography. Various concentrations of n-alkanes were incubated with liver microsomes from adult male F-344 rats. Nonlinear kinetic constants for nonane and decane were V(max) (nmol/mg protein/min) = 7.26 +/- 0.20 and 2.80 +/- 0.35, respectively, and K(M) (micro M) = 294.83 +/- 68.67 and 398.70 +/- 42.70, respectively. Metabolic capacity as assessed by intrinsic clearance (V(max)/K(M)) was approximately four-fold higher for nonane (0.03 +/- 0.005) than for decane (0.007 +/- 0.001). There was no appreciable metabolism of tetradecane even with higher microsomal protein concentration and longer incubation time. These results show a negative correlation between metabolic clearance and chain length of n-alkanes.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2007
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: The documentation is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
excretion
Qualifier:
no guideline followed
Principles of method if other than guideline:
This paper describes a PBPK model for n-decane. 
GLP compliance:
not specified
Radiolabelling:
not specified
Species:
rat
Strain:
not specified
Sex:
not specified
Route of administration:
inhalation
Vehicle:
unchanged (no vehicle)
Control animals:
no
Metabolites identified:
not specified
Conclusions:
Interpretation of results: low bioaccumulation potential based on study results
Executive summary:

This paper describes a PBPK model for n-decane.  The data show that in rats at exposure levels up to approximately 5000 mg/m3, n-decane is rapidly taken up with near steady state conditions being achieved within 8 hours.  Upon cessation of exposure, blood and brain levels rapidly decline with biological half lives of approximately 2 hours.  In humans, measurements of n-decane in blood and exhaled air show similar uptake and elimination behavior.  These data indicate that n-decane is rapidly metabolized and eliminated and does not bioaccumulate.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2004
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
distribution
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
Principles of method if other than guideline:
Rats were exposed to decane vapors at time-weighted average concentrations of 1200, 781, or 273 ppm in a 32-L leach chamber for 4 h. Time-course samples for 1200 ppm and end-of-exposure samples for 781 and 273 ppm decane exposures were collected from blood, brain, liver, fat, bone marrow, lung, skin, and spleen.
GLP compliance:
not specified
Radiolabelling:
not specified
Species:
rat
Strain:
Fischer 344
Sex:
male
Details on test animals or test system and environmental conditions:
Forty-eight male Fischer 344 rats were purchased from Charles Rivers (Raleigh, NC), weighing between 186 g to 240 g (mean body weight = 211 g). All animals were housed in a controlled environment with a 12-h light/dark cycle at 2 1°C. Purina food and water was available at liberty, except during exposures. Rats were given a minimum acclimation period of 2 wk before experiments were begun. All inhalation exposures commenced between 7 and 8 a.m.
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Details on exposure:
Gas Uptake Chamber: Initially, decane was evaluated in a newly built gas uptake chamber, without rats to determine if gas uptake could be utilized to obtain information on the metabolism of decane. Slight modifications were made to previously described gas uptake exposure systems. Decane was injected into the system through an injection port (10 uL and 5 uL) at the incoming air stream to the 7-L closed system chamber. However, this method was deemed unsuccessful for the analysis of decane metabolism because the atmospheric loss rate of decane to the glass chamber (without an animal) was too great (Figure 1). Pharmacokinetic studies were then carried out in a Leach chamber, which avoids the problem of decane adherence to the glass by generating a constant concentration within the chamber.

Leach Chamber: The exposure chamber consisted of a 32-L battery jar. Two metal bellows pumps were used to create inhalation exposures. A 40/50 Pyrex bubbler containing decane was mixed with ambient room air to achieve a specified vapor concentration of decane over a four-hour exposure period. Flow rates through the bubbler to obtain decane concentrations of 273 to 1200 ppm ranged from 1 L/min to 4L/min. Ambient airflow was mixed with the bubbler flow rate to give a total flow rate of approximately 8 L/min to the chamber. The atmospheric pressure within the battery jar was monitored by a Magnehelic pressure gauge and maintained between 0 and -1 inches of water by adjusting the flow rate into the chamber. The flow rates of the bubbler and exhaust from the Leach chamber were monitored by Gilmont Instruments flow meters. Chamber atmospheric concentrations were monitored in 10-min intervals over the entire exposure duration using an auto sampling valve mounted on the gas chromatograph. Exhaust was monitored to determine chamber concentration by splitting the exhaust flow so a portion of the exhaust was routed to the gas chromatograph. The flow rate of the split from the exhaust to the gas chromatograph was monitored by a Matheson 600 HAl flow meter, Exposure concentrations were calculated as a time-weighted average (TWA) over the 4-h exposure period. Aerosols generated by the bubbler were removed via a glass wool scrubber. Tedlar bags containing 223 to 1337 ppm decane were sampled by the auto sampler of the gas chromatograph to create a calibration curve for the Leach chamber. All stainless steel tubing was 1/4 inch diameter throughout system, except for the 1/8-inch tubing to the gas chromatograph.
Duration and frequency of treatment / exposure:
4 hours
Remarks:
Doses / Concentrations:
1200, 781, or 273 ppm
No. of animals per sex per dose / concentration:
1200 ppm (n = 12 per exposure), 781 ppm (n = 8 per exposure), and 273 ppm (n = 8 per exposure).
Control animals:
no
Positive control reference chemical:
none
Details on study design:
Fischer 344 rats were exposed for 4 h to concentrations of 1200 ppm (n = 12 per exposure), 781 ppm (n = 8 per exposure), and 273 ppm (n = 8per exposure). Decane exposure was started immediately after all rats were place into the Leach chamber. The targeted chamber concentration for decane was obtained within 10-15 min after the bubbler containing decane was turned on. Blood, brain, bone marrow, spleen, liver, lung, perirenal fat, and skin tissues were collected for the 1200 ppm decane exposure immediately after the 4-h exposure up to 24 h post exposure, while only end-of-exposure tissue samples were collected for 781 and 273 ppm decane exposures. Rats for the end-of-exposure sampling were removed from the Leach chamber within 30s after turning off the decane exposure, but maintaining air flow to the Leach chamber. Rats were killed by CO2 intoxication within 2-3 min after removal from the Leach chamber; tissue samples were quickly collected (30 s to 2 min) and placed into 2 mL pre-weighed screw-cap vials (National Scientific Co., Scottsdale, AZ) to be weighed. All samples collected were approximately 0.2 g (except bone marrow, 0.02 mg). Bone marrow was collected last (about 3-4 min after killing the rat) by scrapping the inside of femur bones. Skin samples were collected from the abdomen after clipping the hair. Tissue collection techniques for this study were similar to techniques used by Fisher and colleagues with trichloroethylene, a very volatile chemical (Greenberg et al., 1999). Although some inherent experimental error occurs when collecting tissues for analysis of volatile chemicals such as decane, the experimental error was minimized by taking tissues as quickly as possible by trained necropsy personnel and then placing the tissues in sealed vials.
Metabolites identified:
not specified

Sensitivity analysis for selected decane model parameters at 200 ppm evaluated during exposure (3 h) and postexposure (5-25 h)

  Arterial Blood Concentration    Lung Tissue Concentration   Brain Tissue Concentration
Model parameter 3h 5h 7h   3h 5h 7h   3h 5h 15h 25h
PWB 0.98 2.54 1.98   0.98 2.54 1.98   0.95 1.01 1.12 1.48
PB 0 -0.05 0.03   0 -0.05 0.03   0.36 0.72 3.32 4.06
PL 0 0.9 0.02   0 0.9 0.02   -0.02 0.02 0.02 0.02
PLU 0 0.04 0   1 1.04 1   0 0 0 0
PAF -0.01 0.47 0.66   -0.01 0.47 0.66   -0.01 -0.01 0.05 0.4
PAB 0 0.2 0.1   0 0.2 0.1   0.63 0.28 -2.28 -3.01
PABM -0.01 0.53 0.75   -0.01 0.53 0.75   -0.01 0 0 -0.09
PASK 0 0.62 0.62   0 0.62 0.62   0 0 0.02 -0.01
QPC 0.02 -1.53 -0.98   0.02 -1.53 -0.98   0.05 -0.01 -0.12 -0.48
Body Weight 0.01 -0.89 -1.21   0.01 -0.89 -1.21   -0.62 -0.26 2.24 2.84
VBC 0 -0.12 0.03   0 0.12 0.03   -0.64 -0.28 2.31 3.06
Conclusions:
Interpretation of results: PBPK results - The blood/air partition coefficient value was sensitive for predicting blood, brain, and lung decane concentrations. The lung/blood partition coefficient value was sensitive for predicting lung decane concentration. The blood and lung decane concentrations were sensitive to the bone marrow permeability area cross product, ventilation rate, and body weight. The model-predicted brain concentrations of decane were sensitive to the body weight brain/blood partition coefficient value, the permeability-area cross product for the brain, and the volume of the brain.
Executive summary:

Decane is one of the highest vapor phase constituents of jet propellent-8 (JP-8), was selected to represent the semi-volatile fraction for the initial development of a physiologically based pharmacokinetic (PBPK) model for JP-8. Rats were exposed to decane vapors at time-weighted average concentrations of 1200, 781, or 273 ppm in a 32-L leach chamber for 4 h. Time-course samples for 1200 ppm and end-of-exposure samples for 781 and 273 ppm decane exposures were collected from blood, brain, liver, fat, bone marrow, lung, skin, and spleen. The pharmacokinetics of decane could not be described by flow-limited assumptions and measured in vitro tissue/air partition coefficients. A refined PBPK model for decane was then developed using flow-limited (liver and lung) and diffusion-limited (brain, bone marrow, fat, skin, and spleen) equations to describe the uptake and clearance of decane in the blood and tissues. Partition coefficient values for blood/air and tissue/blood were estimated by fitting end-of-exposure pharmacokinetic data and assumed to reflect the available decane for rapid exchange with blood. PBPK model predictions were adequate in describing the tissues and blood kinetics. For model validation, the refined PBPK model for decane had mixed successes at predicting tissue and blood concentrations for lower concentrations of decane vapor, suggesting that further improvements in the model may be necessary to extrapolate to lower concentrations.

The blood/air partition coefficient value was sensitive for predicting blood, brain, and lung decane concentrations. The lung/blood partition coefficient value was sensitive for predicting lung decane concentration. The blood and lung decane concentrations were sensitive to the bone marrow permeability area cross product, ventilation rate, and body weight. The model-predicted brain concentrations of decane were sensitive to the body weight brain/blood partition coefficient value, the permeability-area cross product for the brain, and the volume of the brain.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1999
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
distribution
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
not specified
Radiolabelling:
no
Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Mollegaard Breeding Center
- Age at study initiation: 3 months

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 55 +/- 5
- Air changes (per hr): 8
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Duration and frequency of treatment / exposure:
6hr/day; 5 days/week for 1, 2, or 3 weeks
Remarks:
Doses / Concentrations:
0, 400ppm, and 800ppm (2.29 mg/L and 4.58 mg/L, respectively)
Control animals:
yes, concurrent no treatment
Metabolites identified:
not measured
Conclusions:
Interpretation of results: n-nonane, n-decane, and n-undecane preferentially accumulate in the fat tissue over brain or blood tissue
Executive summary:

This study investigated tissue disposition of dearomatised white spirit. Male rats were exposed by inhalation to 0, 400 (2.29 mg/1), or 800 ppm (4.58 mg/l) of dearomatised white spirit, 6 hr/day, 5 days/week up to 3 weeks. Five rats from each group were sacrificed immediately after the exposure for 1, 2, or 3 weeks and 2, 4, 6, or 24 hr after the end of 3 weeks' exposure. After 3 weeks of exposure the concentration of total white spirit was 1.5 and 5.6 mg/kg in blood; 7.1 and 17.1 mg/kg in brain; 432 and 1452 mg/kg in fat tissue at the exposure levels of 400 and 800 ppm, respectively. The concentrations of n-nonane, n-decane, n-undecane, and total white spirit in blood and brain were not affected by the duration of exposure. Two hours after the end of exposure the n-decane concentration decreased to about 25% in blood and 50% in brain. A similar pattern of elimination was also observed for n-nonane, n-undecane and total white spirit in blood and brain. In fat tissue the concentrations of n-nonane, n-decane, n-undecane, and total white spirit increased during the 3 weeks of exposure. Post-exposure decay in blood could be separated into two phases with half-lives of approximately 1 and 8 hr for n-nonane, n-decane, and n-undecane. In brain tissue two slopes with half-lives of 2 and 15 hr were identified. In fat tissue, only one slope with half-life of about 30 hr was identified.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1993
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
toxicokinetics
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
not specified
Radiolabelling:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals or test system and environmental conditions:
Male Sprague-Dawley rats were obtained from Mollegaard A/S, LI. Skensved, Denmark. The animals were acclimatized for 4 to 6 days before the start of exposure. The number of animals in each cage was 4 with a maximum of 4 cages in each inhalation chamber. Food and water were given ad libitum except during exposure. At the start of each experiment the weight of the animals ranged from 150 to 200 g.
Route of administration:
inhalation
Vehicle:
unchanged (no vehicle)
Details on exposure:
Dynamic exposure of the animals was performed in conically shaped 0.7 mt steel chambers with glass front door and walls as described previously (Walseth & Nilsen 1984). During exposure, temperature and humidity were kept within the limits of 23±1° and 70 ± 20% RH, respectively. The aimed concentration of 100 ppm was maintained by mixing a controlled stream of air saturated with the test substance under a constant temp and flow.
Duration and frequency of treatment / exposure:
single hydrocarbons for 3 days, 12 hr/day
Remarks:
Doses / Concentrations:
100 ppm for each test substance
Control animals:
no
Details on study design:
Animals were exposed to individual hydrocarbons in 6 separate experiments with equal design except for the choice of test substance. The aimed concentration of each test substance was 100ppm. All exposures were performed at daytime for 12 hr per day (8 a.m to 8 p.m) for 3 consecutive days. Light/dark cycles of 14 hr light (7 a.m. to 9 p.m.) and 10 hr dark (9 p.m. to 7 a.m.) were kept constant during acclimatization and exposure. The concentration of hydrocarbons was measured in blood, brain, liver, kidney and perirenal fat immediately after 12 hr exposure on days 1, 2 and 3 of the exposure period, and 12 hr after cessation of the last exposure. The animals were, one by one, removed from the chamber and subsequently killed by decapitation. A standardized procedure made it possible to obtain blood and organ samples within 3 min after the removal of an animal from the chamber.

Determination of hydrocarbon concentration in biological material.
The concentration in blood, brain, and perirenal fat was determined by head space gas chromatography. Two mL of blood or organ homogenate was equilibrated in 15 mL head space vials for 1h at 37 or 60 degrees together with calibration samples and blanks. A gas chromatograph (FID) was used to determine concentrations.
Metabolites identified:
not measured

Table 1 - Biological concentrations of individual hydrocarbons (umol/kg) (Rec = 12 hours after last exposure)

    Iso-alkanes(umol/kg)
    C8 C9 C10
Blood Day 1 3.1 3.3 5.5
  Day 2 3.2 3.4 5
  Day 3 2.9 3.3 6.8
  Rec ND ND ND
         
Brain Day 1 20 32 73.9
  Day 2 22.9 33.9 59.4
  Day 3 24.8 27.9 61.4
  Rec ND ND ND
         
Liver Day 1 10.7 18.4 38.7
  Day 2 10.6 18.7 26.2
  Day 3 9.4 17.3 35
  Rec ND ND ND
         
Kidney Day 1 33.5 38.3 45
  Day 2 42.2 44.2 40.9
  Day 3 44.6 34.7 47.4
  Rec ND 0.8 ND
         
Fat Day 1 175 272 530
  Day 2 221 417 622
  Day 3 200 390 901
  Rec 96 264 446
Conclusions:
Interpretation of results: low bioaccumulation potential based on study results
The concentration of iso-alkanes in blood, brain, liver and fat increased with increasing number of carbon atoms. The C9 and C10 iso-alkanes showed increasing concentration in fat during the exposure period and high concentrations 12 hr after cessation of exposure.
Executive summary:

The toxicokinetic properties of C8 and C10 iso-alkanes have been investigated in rats during inhalation of 100 ppm of the single hydrocarbons for 3 days, 12 hr/day. The concentration of hydrocarbon was measured in blood, brain, liver, kidneys and perirenal fat at days 1, 2 and 3, immediately after exposure and 12 hr after exposure on day 3. The concentration of iso-alkanes in blood, brain, liver and fat increased with increasing number of carbon atoms. The C9 and C10 iso-alkanes showed increasing concentration in fat during the exposure period and high concentrations 12 hr after cessation of exposure.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1990
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: The documentation is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
metabolism
Qualifier:
no guideline followed
Principles of method if other than guideline:
The concentrations of the C9 hydrocarbons n-nonane, 1,2,4-trimethylbenzene and 1,2,4-trimethylcyclohexane were measured in rat blood, brain and perirenal fat after exposures to 1000 ppm of the individual compounds.
GLP compliance:
not specified
Radiolabelling:
not specified
Species:
rat
Strain:
not specified
Sex:
not specified
Route of administration:
inhalation
Vehicle:
unchanged (no vehicle)
Control animals:
no
Metabolites identified:
not specified
Conclusions:
The relative concentrations of hydrocarbons in each organ were; brain: n-nonane > trimethylcyclohexane > trimethylbenzene, blood: trimethylbenzene > n-nonane > trimethylcyclohexane and perirenal fat: trimethylbenzene > n-nonane > trimethylcyclohexane, showing the widely different distribution properties of the different hydrocarbons. Brain/blood ratios of 11.4, 2.0 and 11.4, and fat/blood ratios of 113, 63 and 135 were found for n-nonane, trimethylbenzene and trimethylcyclohexane, respectively. A marked decrease in biological concentrations of trimethylbenzene and trimethylcyclohexane during the initial phase of exposure indicate that these hydrocarbons are capable of inducing their own metabolic conversion resulting in lower steady state levels.
Executive summary:

The concentrations of the C9 hydrocarbons n-nonane, 1,2,4-trimethylbenzene and 1,2,4-trimethylcyclohexane were measured in rat blood, brain and perirenal fat after exposures to 1000 ppm of the individual compounds. Measurements were made by head space gas chromatography at the end of 12 hr exposures on days 1, 3, 7, 10 and 14 of the exposure periods. The relative concentrations of hydrocarbons in each organ were; brain: n-nonane > trimethylcyclohexane > trimethylbenzene, blood: trimethylbenzene > n-nonane > trimethylcyclohexane and perirenal fat: trimethylbenzene > n-nonane > trimethylcyclohexane, showing the widely different distribution properties of the different hydrocarbons. Brain/blood ratios of 11.4, 2.0 and 11.4, and fat/blood ratios of 113, 63 and 135 were found for n-nonane, trimethylbenzene and trimethylcyclohexane, respectively. A marked decrease in biological concentrations of trimethylbenzene and trimethylcyclohexane during the initial phase of exposure indicate that these hydrocarbons are capable of inducing their own metabolic conversion resulting in lower steady state levels.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1988
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: The documentation is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
GLP compliance:
not specified
Radiolabelling:
not specified
Metabolites identified:
not specified
Executive summary:

Toxicity:  nC9 was acutely toxic by inhalation with an LC50 value of 4467 + 189 ppm (approximately 23.5 mg/l).  Signs of acute central nervous system depression were reported, but dose-response relationships were not provided.  Higher molecular weight n-alkanes (C10, C11, C12, C13) were not acutely toxic at saturated vapor concentrations, nor was there evidence of acute central nervous system effects.  Accordingly, for n-alkanes >nC9, it is not possible to achieve vapor concentrations (at 21.6 degree C) which produce biological effects under acute conditions.

Toxicokinetics – Inhaled alkanes nC9-nC13 are taken up into the blood and brain.  However, uptake into both blood and brain decreases with increasing carbon number.  In part this is because the vapor concentrations are reduced at increasing carbon number.  However, there is also a corresponding reduction in the blood/air and brain/air ratios with increasing carbon numbers.  Thus the efficiency of uptake into both blood and brain also decreases with increasing carbon number.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1975
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
Fifteen healthy male subjects were exposed to 1,250 and 2,500 mg/m3 of white spirit in inspiratory air during rest and excercise on a bicycle ergometer. The pulmonary ventilation, the cardiac output, and the concentration of white spirit (subdivided into aromatic and aliphatic components) in alveolar air, arterial blood, and venous blood were determined during and after exposure.
GLP compliance:
not specified
Radiolabelling:
no
Species:
human
Strain:
not specified
Sex:
male
Route of administration:
inhalation
Vehicle:
unchanged (no vehicle)
Details on exposure:
The vapor was produced as follows: Compressed air was passed through a charcoal filter to two rotameters connected in parallel, both supplied with valves for the regulation of air flow. Air from one rotameter passed through a glass tube which was partially located in a tube heater whose output could be regulated with a rotary transformer. With an infusion, adjustable for different piston speeds for 5 or 50 ml syringes, solvent could be injected into the warm zone of the glass tube where it was vaporized in the air passing through the tube. The air passing the rotameters was mixed in a closed vessel and passed via a tube to the bottom of a cylinder from which inspiratory air was drawn into the breathing valve with the aid of a metal tube. Air containing white spirit was supplied to the cylinder at a rate of about 60 L/min. This volume was never less than a subject’s pulmonary ventilation.
Remarks:
Doses / Concentrations:
0, 1250, and 2,500 mg/m3
Control animals:
no
Details on study design:
The trials started with the introduction of catheters into a brachial artery and a medial cubital vein. Exposure then took place at rest and during submaximal exercise on a bicycle ergometer. Each exposure period comprised 30 minutes, and each subject was exposed for four periods at each session.

Five subjects were exposed to both approximately 1,250 and 2,500 mg/ms of white spirit in inspiratory air at rest (30 + 30 min) and during exercise (30 + 30 min) at an intensity of 50 W (300 kpm/ min). Fifty watts corresponds to about the intensity found in light physical vocational work.

Four subjects were exposed to approximately 1,250 mg/m3 of white spirit in inspiratory air during rest (30 min) and during exercise (30 + 30 + 30 min) at intensities of ~50 W (300 kpm/min), 100 W (600 kpm/min), and 150 W (900 kpm/min).

Two subjects were exposed to approximately 2,500 mg/m3 of white spirit in ordinary air and to approximately 2,500 mg/m3 in an air mixture consisting of 21% oxygen, 4% carbon dioxide, and 75% nitrogen during rest (30 + 30 min) and during exercise (30 + 30 min) at an intensity of 50 W (300 kpm/min).

Two subjects were exposed to 1,250 mg/m3 of white spirit in inspiratory air during rest (30 min) and during exercise (30 + 30 + 30 mm) at an intensity of 100W (600 kpm/min).

Two subjects were exposed to approximately 1,000, 1,250, 1,500, and 2,000 mg/m3 of white spirit in inspiratory air at rest (30 + 30 + 30 + 30 mm).

Alveolar air samples were collected in a glass syringe from a breathing valve during exposure and in glass tubes after exposure. Arterial and venous blood samples were taken from the catheters and collected in 15 mL glass bottles. The mean value of the last two determinations in each exposure period was used for the concentration in alveolar air and for the aliphatic components in blood. However, for the aromatic concentration in blood the final value was stated when it was also the highest value, as was almost always the case. Otherwise, the mean value of the last two values was stated.

Heart rate was determined using ECG recordings. The mean value of the three final determinations in each exposure period was used. Blood samples for lactic acid assay were taken at the end of each exercise period. The oxygen uptake and the volumes of expiratory and alveolar air were determined with the Douglas bag method after about 20 minutes of each exposure period. Cardiac output was determined for six subjects. A double determination was made during rest prior to exposure after about 20 minutes during each exposure period both during rest and exercise. The mean value was used.

The volume of expiratory air continuously measured in bags for four subjects throughout entire exposure i.e., for 2 hours, and the air’s white spirit content was assayed. The volume of inspiratory air was taken as being the same as the volume of expiratory air (no more than 1% error), and the uptake of white spirit divided into the two components, was calculated as the difference between insiratory and expiratory air. The measurements were taken from two subjects exposed to 1,250 and 2,500 mg/m3 of white spirit during rest and during exercise at an intensity of 50 W (300 kpm/min) and using two subjects exposed at rest to 1,000, 1,250, 1,500 and 2,000 mg/m3.

After four completed periods of exposure the concentration of white spirit in the form of aliphatic and aromatic components in alveolar air and blood was followed until their levels were under the limit of detection, which was generally after 1 more hour. The exact times for samplings are shown in the figures total amounts in inspiratory and expiratory.
Details on dosing and sampling:
Respiratory volumes, blood lactate, heart rate were determined according to the methods described in the authors’ previous study on toluene. The oxygen and carbon dioxide contents of expiratory air were determined using an oxygen analyzer and a carbon dioxide analyzer, respectively and oxygen uptake was calculated.

Respiratory rate was recorded with the aid of a heat receptor located in the breathing valve, and tidal air was calculated. Dead space in subjects, including the valve, was estimated at 150 cm3, and alveolar ventilation was calculated. No correction was made for any larger dead space during exercise, since differences are small at the measured ventilations. Cardiac output was determined by using the dye dilution technique. The blood loss (approximately 100 ml) in conjunction with these measurements, including the loss arising in blood sampling, had no effect on results.

The white spirit content in blood was determined with a head space method and a gas chromatograph fitted with a stainless steel column.
Preliminary studies:
Pulmonary ventilation and blood circulation. During exercise three subjects displayed occasional atrial premature beats in their ECGs of the same type as during rest. One subject developed atrial premature beats exclusively in conjunction with exposure. One subject displayed gradual flattening and, ultimately, inversion of the T wave during exposure indicating possible action on the myocardium. This subject displayed no other changes. He had no subjective symptoms and the ECG picture had normalized at the time of a check made a few days later in conjunction with exercise.

Values for alveolar ventilation, oxygen uptake, and heart rate at rest were of a normal magnitude. At 100 W (600 kpm/min) and 150 W (900 kpm/min), a mean increase in heart rate for four people of 6 and 10 beats/mm, respectively, and a mean increase in oxygen uptake of 0.15 and 0.20 L/min, respectively, often takes place in conjunction with exercise lasting for 30 minutes and was therefore probably not ascribable to exposure.

No differences were noted in heart rate, alveolar ventilation, or oxygen uptake either at rest or during exercise at an intensity of 50 W during exposure to 1250 mg/m3 and 2500 mg/m3.

At a work intensity of 50 W the subjects utilized an average of 27% of their maximal aerobic work power (max VO2), at 100 W approximately 46%, and at 150 W 65 %. Lactate concentration in blood indicated that work loads of 50 and 100 W may be regarded as relatively light exercise and 150 W as moderately heavy exercise.

Cardiac output was normal at rest and increased in an ordinary manner as work increased, both when exposed to 1250 mg/m3 and to 2500 mg/m3.

In two subjects the alveolar ventilation increased from approximately 7 to 20 L/min at rest and from 23 to 49 L /min during cycling at an intensity of 50 W when pulmonary ventilation was increased through the addition of 4% carbon dioxide. There was no corresponding increase in heart rate, although there was a slight increase in oxygen uptake and cardiac output at a work intensity of 50 W. Thus as blood circulation remained almost unchanged pulmonary, ventilation increased sharply.

Alveolar air and arterial blood concentrations during exposure.

After a 30-minute exposure at rest to approximately 1040 mg/m3 of the aliphatic component in white spirit, the concentration in alveolar air amounted to 255 mg/m3 (~25% of the concentration in the inspiratory air). The corresponding arterial blood concentration was approximately 1.7 mg/kg. When alveolar ventilation tripled during 50 W exercise, the alveolar concentration increased to about 515 mg/m3 (~50% of the concentration in inspiratory air), whereas the arterial concentration rose to 3.5 mg/kg. In exposure at rest to approximately 2075 mg/m3 of the aliphatic component, the concentrations in both alveolar air and arterial blood about doubled those of the lower level of exposure. Alveolar air and arterial blood concentrations in exercise at 50 W approximately doubled those of the resting level, just as in exposure to the lower exposure level.

When exercise intensity was increased successively with an attendant increase in alveolar ventilation to nearly 60 L/mm at 150 W, the alveolar concentration rose stepwise to about 60% of the concentration in inspiratory air. The corresponding arterial concentration was about twice as great as at 50 W.

When alveolar ventilation at rest was increased by adding 4% carbon dioxide to inspiratory air, the alveolar concentration rose from about 20% (two subjects) to about 40% of the level in inspiratory air. During work at an intensity of 50 W, and after the addition of 4% carbon dioxide, the alveolar concentration rose from about 50 to 60% of the level in inspiratory air. The increase in concentration corresponded to the increase obtained through increased alveolar ventilation during exercise while breathing white spirit vapors in ordinary air. Generally speaking, the arterial concentrations paralleled the changes in the composition of alveolar air.

During these different types of experiments, there was a tendency, at least in some subjects, for the increase in alveolar and arterial concentration to slow down towards the end of each period. This leveling-off became more apparent during protracted exposure (90 mm) at a constant exercise intensity of 100 W.

Uptake in the organism.
The total uptake of aliphatic components in the organism was obtained in experiments with continuous measurement of the amounts in inspiratory and expiratory air. The uptakes amounted to 59, 53, 47, and 46 % of the total amount of aliphatic components supplied during four resting exposure periods. The uptake was accordingly greater at the start than at the end of the 2 hours of exposure. Uptake averaged 50% for the aliphatic components.

For exposures conducted during two resting periods, an uptake of about 63% was obtained for the aliphatic components. During 50 W of exercise, the uptake amounted to about 39% for the aliphatic components. Thus, the uptake declined in percentage during exercise, especially for the aliphatic components. However, the total uptake, measured in milligrams per period of exposure, was slightly greater during exercise than at rest for both the aliphatic components.
Conclusions:
Interpretation of results: low bioaccumulation potential based on study results
Executive summary:

Fifteen healthy male subjects were exposed to 1250 and 2500 mg/m3 of white spirit in inspiratory air during rest and exercise on a bicycle ergometer. The white spirit contained approximately 83% aliphatic components. The duration of each exposure period was 30 minutes. The pulmonary ventilation, the cardiac output, and the concentration of white spirit (subdivided into aromatic and aliphatic components) in alveolar air, arterial blood, and venous blood were determined during and after exposure. The concentration of aliphatic components in alveolar air tended to level off towards the close of each period. The resting level of the aliphatic components increased approximately 2.5 times during exercise with increased intensities. The concentration of aliphatic components in arterial and venous blood increased at the start of each exposure period but tended to level off towards the close of the period. The resting value increased fourfold in work at the highest intensity. Pulmonary ventilation appeared to be more important to uptake in arterial blood than to circulation. Measurement of the concentration of white spirit in venous or arterial capillary blood is suggested as a biological check on exposure.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1970
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Objective of study:
absorption
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
not specified
Radiolabelling:
yes
Remarks:
n[I-14C] Hexadecane
Species:
rat
Strain:
Crj: CD(SD)
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Labs
- Weight: 180 -300g
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
Route of administration:
oral: gavage
Vehicle:
unchanged (no vehicle)
Details on exposure:
The test material was administered as a single, 320 mg/kg dose.
Duration and frequency of treatment / exposure:
single dose
Remarks:
Doses / Concentrations:
320 mg/kg
Control animals:
no
Details on study design:
Gas Chromatography was used to measure relative peak areas, which were closely proportional to mole percentages for the hydrocarbons used in the study.

Squalane as a marker for balance studies. 96-100% of squalane fed to rats could be recovered in feces collected for 4 days following administration. Squalane was used to compare test material to squalane.

Balance Studies. The test materials were administered and feces were collected twice a day and stored in chloroform until excretion of the hydrocarbon ceased (72-96h). The percentage of each hydrocarbon retained by the animals was considered to be 100% minus the percentage excreted and was calculated from the formula R = [(A/S)D –(A/S)D] X100%; where R= percentage retained, A/S =molar ratio of test hydrocarbon to squalane, D = diet, F=Feces.

Recirculation in the bile. Bile was collected continuously for 7 hours after subcutaneous injection of 5 mg of [I-14C] Hexadecane (5uCi) in 100 uL of corn oil or i.v. injection (leg vein) of 0.1 mL of rat serum saturated with [I-14C] Hexadecane (0.1 uCi). The bile, collected over 15 min intervals, was assayed both for total 14C content and content of 14C in the hydrocarbon fraction after chromatography on Florisil. Aliquots of bile were saponified, and the saponifable lipids (fatty acids and bile acids) were assayed for 14C. Cholesterol was isolated by preparative thin-layer chromatography in hexane-diethyl ether-acetic acid (85:15:1, by vol).

Action of Bacteria. Two experiments were performed to examine bacterial action. Rats were fed for 5 days on a diet consisting on 1) rodent chow, or 2) rodent chow + 1.0% chlortetracycline, or 3) rodent chow + 0.5% sulfanilamide and 0.1% streptomycin. A mixture of squalane, n-hexadecane, pristine, and pentadecylcyclohexane was administered as in the balance studies. Rats were returned to a diet of just rodent chow for 72 hours. The R values for the 3 test hydrocarbons were determined for each group of rats and compared.

The second experiment utilized fresh feces mixed with [I-14C] Hexadecane (5uCi) per 5 g of feces. The percentages of 14C converted to fatty acid over periods up to 72 h were estimated by saponification of the extracts and assay of the saponifiable and nonsaponifiable fractions for radioactivity.

Site of Absorption. Rats were anaesthetized with pentobarbital and injected with 0.1 mL of hydrocarbon emulsion containing [I-14C] Hexadecane (5uCi) each. The emulsion was injected either 1) in the stomach, which was tied off with a suture at the duodenum, 2) into the duodenum with the small intestine tied off at stomach and caecum, 3) into the caecum tied off both at ileum and colon, and 4) into the colon tied off at the caecum. Blood was collected at intervals from the tail vein, and its content of 14C taken to be a relative measure of absorption from the various gastrointestinal sites.

Absorption from the small intestine was examined in more detail using everted sacs (3 cm) of duodenum, jejunum, and ileum. Samples of serosal medium were taken through Teflon tubes attached to syringes and assayed for total radioactivity at hourly intervals. After 3-h incubation, the sacs were rinsed in saline, then hexane, and extracted with chloroform-methanol (2:1, v/v) to determine the amounts of radioactivity taken up by the tissue. The control was the sacs of all three intestinal regions were incubated simultaneously in the same beaker of mucosal medium.

Lymph v. Portal Circulation. Rats were anaesthetized with pentobarbital and 0.2 mL aliquots of hydrocarbon emulsion containing 10 uCi of n-[I-14C] Hexadecane each were injected into the duodena. Each duodenum was tied off between the puncture and the previous location of the tip of the syringe needle to avoid leakage. Samples of thoracic lymph (20 uL), blood from the portal vein (0.5 mL) and blood from the heart (0.5 mL) were taken at interval up to 1 h after injection of the emulsion. Each sample was assayed from radioactivity and the disint/min per mL compared. A higher concentration reflects absorption of hydrocarbon or its metabolic products directly from the intestines into the portal circulation.
Details on absorption:
The percentage retention of n-alkanes showed an inverse linear relationship to chain length that was describable by the regression line: (percentage retained) = 115.9 – 3.94 * (number of carbon atoms). This line had a correlation coefficient of -0.995, standard error of estimate Sy * x= 3.30, t = 30.85 and P < 0.001. Paraffin having more than 29 carbon atoms thus would not be absorbed to a significant extent under these conditions.

Gas Chromatography was used to measure relative peak areas, which were closely proportional to mole percentages for the hydrocarbons used in the study.

Radioactivity was detected in the bile within 15 min after subcutaneous of i.v. injection of n-[I-14C]hexadecane. The peak concentration of radioactiviy was reached within 45-60 min, but no radioactivity could be detected after 7 hours. The relative amount of radioactivity associated with water-soluble materials varied from 40 to 60% of the total during the 7h period, but the distribution of 14C among lipid fractions was not significantly variable, 90 +/- 1% being in saponifiable lipids (fatty acids and bile acids), 10 +/- 1% in cholesterol. Recirculation of intact hydrocarbon in the bile would not be expected to influence the results of the balance studies. Treatment with antibiotics reduced the retention of the hydrocarbons tested. The small intestine was determined to be the major site of paraffin absorption, with the all portions of the small intestine equally competent. The concentrations of 14C in thoracic lymph, portal blood, and blood from the heart of rats injected intraduodenally with labeled hydrocarbon emulsion are shown in Table 1 below. No microbial degregation was noted.
Metabolites identified:
no

Source Disint./min per uL serosal medium Disint./min x 10^-5 in tissues after 3h Total uptake (Disint./min x 10^-5)
  1h 2h 3h
           
Duodenum 129 308 452 1.014 1.47
Jejunum 48 117 172 1.329 1.5
Ileum 25 61 89 1.718 1.81
Conclusions:
Interpretation of results: low bioaccumulation potential based on study results
Executive summary:

The percentage retention of n-alkanes showed an inverse linear relationship to chain length that was describable by the regression line: (percentage retained) = 115.9 – 3.94 * (number of carbon atoms). This line had a correlation coefficient of -0.995, standard error of estimate Sy * x= 3.30, t = 30.85 and P < 0.001. Paraffin having more than 29 carbon atoms thus would not be absorbed to a significant extent under these conditions.

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2006
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles: non-GLP. Source of data is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Principles of method if other than guideline:
The purpose of this study was to investigate the absorption and penetration of aromatic and aliphatic components of JP-8 in humans. A surface area of 20 cm2 was delineated on the forearms of human volunteers and 1 mL of JP-8 was applied to the skin. Tape-strip samples were collected 30 min after application. Blood samples were taken before exposure (t = 0 h), after exposure (t = 0.5 h), and every 0.5 h for up to 4 h past exposure.
GLP compliance:
no
Species:
human
Sex:
male/female
Details on test animals or test system and environmental conditions:
Study volunteers
Ten healthy adult volunteers (five males and five nonpregnant females) with no occupational exposure to jet fuel were recruited for participation. No restrictions on age, race, gender, or skin type were applied other than that the group was to be equally divided between males and females. If volunteers had a history of cardiovascular disease or atopic dermatitis, were current smokers, or were on prescription medication for a current or chronic illness, they were excluded from the study. Volunteers were not permitted to drink any alcoholic beverages 24 h before or during the experiment. Individuals occupationally exposed to compounds chosen to represent JP-8 were also excluded (e.g., auto mechanics). Approval for this study was obtained from the Office of Human Research Ethics (School of Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC). Informed consent was received from all study volunteers.
Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Duration of exposure:
0.5 h exposure period
Doses:
1 mL JP-8
No. of animals per group:
10 subjects; 5 males, 5 nonpregnant females
Details on study design:
The volunteer’s forearms were examined for obvious skin defects (abrasions, inflammation) that could enhance or impair the penetration of JP-8. After the volunteer was seated comfortably, one forearm was placed palm up inside the exposure chamber , and two aluminum application wells (10 cm2 per well) were pressed against the skin to prevent JP-8 from spreading during the experiment. The exposure chamber was sealed for the duration of the experiment (0.5 h).

The volume of JP-8 to be applied to the skin in order to have sufficient concentrations in blood was estimated using the limit of detection (LOD) of a published analytical method and estimates of permeability coefficients from an in vitro study (McDougal et al., 2000; Waidyanatha et al., 2003). Although the method by Waidyanatha et al. (2003) was developed for the analysis of naphthalene in urine, a similar LOD (5.0×l0−4 ng/ml) was assumed to apply for blood samples. Three times the LOD was assumed to be adequate for detection in blood.. It was determined, using a permeability coefficient of 5.1×10−4 cm/h, that 1ml of JP-8 should produce measurable blood concentrations. Neat JP-8 was applied to the volar forearm using a 0.5 ml gas-tight syringe through two openings on top of the exposure chamber; 0.5 ml was applied to each of two wells for a total of 1.0 ml JP-8 on an area of 20 cm2. Upon application, the openings were sealed to prevent loss from the chamber.

At the end of the 0.5 h exposure period, the two exposed skin sites were wiped with a gauze pad and tape-stripped as many as 10 times. Tape-stripping has also been used in dermatopharmacokinetic studies of therapeutic agents. Tape strips were placed in 10 ml of acetone containing 1 µg/ml of internal standards (naphthalene-d8). All tape-strip samples were stored in 20 ml vials and refrigerated at 4 ◦C. Blood samples were drawn from the unexposed arm at baseline, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, and 3.5 h and collected in 6ml test tubes containing sodium heparin. The blood samples were stored at −80 ◦C until analysis.


Tape-strip samples were analyzed by gas chromatography mass spectrometry (GC–MS). Blood samples were analyzed using head-space solid-phase microextraction (HS-SPME) and the GC-MS system used to analyze the tape-strip samples.

Data Analysis
Exploratory analyses of skin and blood concentrations of JP-8 components were conducted using descriptive statistics. The skin and blood concentrations were plotted as functions of time. The first tape strip was not included in these plots because of potential residual contamination from the dose applied to the skin (Shah et al., 1998). The volume of blood was estimated using allometric relationships (Davies and Morris, 1993). The equation is Volume of blood (Vb) = 72.447×(body weight in kg)^1.007. Vb was used to estimate the total mass of naphthalene, 1-methyl naphthalene, 2-methyl naphthalene, decane, undecane, and dodecane in the blood of each volunteer. The steady state flux (J, µg/cm2/h) was estimated from the slope of the linear portion of the cumulative mass per cm2 versus time curve. The slope of the curve during the uptake period (i.e., exposure duration) was estimated for each subject. The permeability coefficient (Kp, cm/h) was estimated by dividing the flux by the concentration of the chemical (CJP-8, µg/cm3) in the 1ml of JP-8 that was applied to the skin (McDougal and Boeniger, 2002): Kp = J/CJP-8.
Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Conclusions:
The permeability coefficients (cm/h) of aromatic and aliphatic hydrocarbons were determined to be: Naphthalene 5.3E−05; 1-Methyl naphthalene 2.9E−05; 2-Methyl naphthalene 3.2E−05; Decane 6.5E−06; Undecane 4.5E−07; Dodecane 1.6E−06.
Executive summary:

Chemicals placed on the skin undergo absorption into the stratum corneum and evaporation from the surface of the skin. After absorption, the chemicals may be stored in deeper layers of the stratum corneum or in the viable epidermis, or they may penetrate into the dermis for eventual movement into the systemic circulation. Some absorbed compound may also transfer back to the skin surface and evaporate into the surrounding air.

 

The results are similar to in vitro studies that use diffusion cells and pig skin. The tape-strip data showed evidence of absorption of naphthalene, 1-methyl naphthalene, 2-methyl naphthalene, decane, undecane, and dodecane, although decane seemed to disappear faster from the surface of the stratum corneum. It is estimated that aromatic components of JP-8 penetrate faster than the aliphatic components. The flux of the aliphatic components is greater than the flux of the aromatic components because the concentration of the aliphatics in JP-8 is more than an order of magnitude greater than the concentration of the aromatics. Our overall estimates of the apparent Kp were smaller than the in vitro estimates.

 

Consequently, the study shows that permeability coefficients estimated in vitro may overestimate the internal dose of various components of JP-8. The results of the study need to be interpreted with caution because in vitro systems do not account for distribution and clearance mechanisms, i.e., processes such as uptake into peripheral tissues, binding to proteins, metabolism, and exhalation are not incorporated in diffusion-cell experiments.

 

The permeability coefficients (cm/h) of aromatic and aliphatic hydrocarbons were determined to be: Naphthalene 5.3E−05; 1-Methyl naphthalene 2.9E−05; 2-Methyl naphthalene 3.2E−05; Decane 6.5E−06; Undecane 4.5E−07; Dodecane 1.6E−06.

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2003
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles: non-GLP. Source of data is from secondary literature.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Principles of method if other than guideline:
Three aliphatic (dodecane, tridecane, and tetradecane) chemicals, major components of JP-8, were investigated for changes in skin lipid and protein biophysics, and macroscopic barrier perturbation from dermal exposure. Percutaneous absorption was examined in vitro using porcine ears (Yorkshire marine pigs, male). Fourier transform infrared (FTIR) spectroscopy was employed to investigate the biophysical changes in stratum corneum (SC) lipid and protein. FTIR results showed that all of the above five components of JP-8 significantly (P< 0.05) extracted SC lipid and protein. Macroscopic barrier perturbation was determined by measuring the rate of transepidermal water loss (TEWL).
GLP compliance:
not specified
Radiolabelling:
yes
Species:
pig
Strain:
other: in vitro: from Yorkshire marine pigs
Sex:
male
Type of coverage:
other: in vitro
Details on study design:
Model System
Porcine ears (Yorkshire marine pigs, male) were obtained. The external/dorsal skin was dermatomed to 0.5 mm thickness and used in the in vitro percutaneous absorption and TEWL studies. The method of Kligman and Christophers was used to separate epidermis from whole skin to produce the stratum corneum (SC).

In vitro percutaneous absorption
Franz diffusion cells were used in the in vitro percutaneous absorption studies. The dermatomed skin was sandwiched between the cells with the epidermis facing the donor compartment. The maximum capacities of the donor and receiver compartments were 1 and 5 ml, respectively, and the effective diffusion area was 0.785 cm2. The donor compartment contained 4 mCi of radiolabeled test chemicals in 1 ml of JP-8 and the receiver compartment was filled with 5 ml of PBS, pH 7.4 containing 0.1% formaldehyde and 0.2% Tween 80 to act as preservative and solubilizer, respectively. The donor compartment was fitted to minimize evaporation of volatile test chemical. The cells were maintained at 37oC. At appropriate times, 1 ml samples were withdrawn from the receiver compartment and transferred to scintillation vials. The samples were assayed by liquid scintillation counting. The instrument was programmed to give counts for 10 min. Net dpm was obtained by subtracting background dpm measured in the control samples. All experiments were performed in replicates of six, and the results were expressed as the mean +/-S.D. (n = 6).

Binding of chemicals
SC was pulverized in a mortar with a pestle. Ten milligrams of pulverized SC was mixed by vortexing for 5 min with 1 ml of JP-8 containing 4 mCi of the test chemical. The mixture was shaken for 10 h at 37 8C. Since the lag time of these chemicals for attaining steady state transport was well below 2 h, 10 h contact time was considered adequate for reaching equilibrium. After 10 h of contact time, the mixture was separated by centrifugation, and the supernatant was removed. The sediment was resuspended three times in JP-8 to remove chemical adsorbed on the surface. The amount of radioactivity in the supernatants was determined by liquid scintillation counting. The amount of chemical that bound to the SC was obtained by subtracting the amount of chemical recovered in supernatants from the amount of chemical originally added. Six sets of experiments were performed for each chemical.

Biophysical properties of SC lipids and proteins by FTIR
The SC samples were treated for 24 h by applying 500ml of chemical on 10 cm2 area of SC in a closed petridishes. The samples were vacuum-dried (650 mmHg) at 21oC for 3 days and stored in a desiccator to evaporate JP-8 (Yamane et al., 1995). The treated SC was then subjected to FTIR spectroscopy. Attention was focused on characterizing the occurrence of peaks near 2850 and 2920 per cm, which were due to the symmetric and asymmetric C-H stretching, respectively. Strong amide absorbance occurred in the region of 1500-1700 per cm due to C-O stretching and N-H bending. The decrease in peak heights and areas of methylene and amide absorbances is related to the SC lipid and protein extraction, respectively. For each SC sample, peak height and area were measured before and after the chemical treatment. This experimental strategy allowed each sample to serve as its own control.

In vitro transepidermal water loss (TEWL) through skin
Franz diffusion cells were used for in vitro TEWL studies. The dermatomed skin was treated with chemical in a manner similar to the SC for FTIR studies. The treated dermatomed skin was then sandwiched between the diffusion cells with the SC side up and the dermal side exposed to the receiver compartment containing isotonic saline (0.9% sodium chloride solution). Holding the probe over the donor cell opening until a stable TEWL value was achieved performed TEWL measurement. The experiments were performed in a room with an ambient temperature between 20 and 26 oC and relative humidity between 30 and 45%. In all the cases, six replicates of experiments were performed and the results expressed as the mean +/- S.D. (n=6). Experiments were performed in the same manner without chemical treatment of the dermatomed skin to serve as control.

Data analysis
The chemical concentration was corrected for sampling effects (Hayton and Chen, 1982): The permeability coefficient (Kp) was calculated as (Scheuplein, 1978): The binding of chemicals to the SC (P) was calculated as (Zhao and Singh, 2000). Statistical comparisons were made using the Student’s t -test and analysis of variance (ANOVA). The level of significance was taken as P< 0.05.
Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined

RESULTS

Binding to the stratum corneum can be determined by calculating the Log PC (octanol/water) values. There is an increase in binding of the aliphatic JP-8 components to with increasing Log PC value. Log PC values are 8.76 +/- 0.74, 13.15 +/- 1.05, 15.85 +/- 1.36 for dodecane (DOD), tridecane (TRI), and tetradecane (TET), respectively.

The flux (JSS), values were determined to be (mean) 1.94, 13.80, and 1.40 (nmol/cm2 per h)*10E-2 for DOD, TRI, and TET, respectively. The diffusion coefficient values were determined to be (0.21 +/- 0.02)E-6, (6.84 +/- 0.57)E-6,  and (0.20 +/- 0.04)E-6 cm2/h for DOD, TRI, TET, respectively. The lag time, values were determined to be (mean) 1.33, 0.89, and 1.63 hours for DOD, TRI, and TET, respectively. FTIR results suggest that all of the test chemicals significantly (P<0.05) extracted SC lipid and protein in comparison to control. TRI exhibited greater extraction of the SC lipid and protein as well as greater transport through the skin than other chemicals.

 

The TEWL values through control and chemically treated porcine skin. All of the test chemicals caused significant (P/0.05) increase in TEWL in comparison to control. TRI produced larger increase in TEWL (29.22 +/- 0.99 g/m2 per h) followed by DOD (15.15 +/- 1.34 g/m2 per h), and TET (11.64 +/- 1.42 g/m2 per h).

Conclusions:
Retention in the stratum corneum can be determined by calculating the Log PC (octanol/water) values. There is an increase in the retention of the aliphatic JP-8 components to with increasing Log PC value. Log PC values are 8.76 +/- 0.74, 13.15 +/- 1.05, 15.85 +/- 1.36 for dodecane (DOD), tridecane (TRI), and tetradecane (TET), respectively.

The flux, JSS (nmol/cm2 per h)*10E-2, values were determined to be 1.94 +/- 0.39, 13.80 +/- 0.82, and 1.40 +/- 0.20 for DOD, TRI, and TET, respectively. The permeability coefficients, Kp (cm/h)*10E-4, were 0.37 +/- 0.13, 18.46 +/- 1.50, 0.64 +/- 0.20 for DOD, TRI, and TET, respectively. The diffusion coefficient values, D (cm/h)*10E-6, were determined to be 0.21 +/- 0.02, 6.84 +/- 0.57, and 0.20 +/- 0.04 for DOD, TRI, TET, respectively. The lag time (hours) was determined to be 1.33 +/- 0.07, 0.89 +/- 0.17, and 1.62 +/- 0.34 hours for DOD, TRI, and TET, respectively. FTIR results suggest that all of the test chemicals significantly (P<0.05) extracted SC lipid and protein in comparison to control. TRI exhibited greater extraction of the SC lipid and protein as well as greater transport through the skin than other chemicals.
Executive summary:

Three aliphatic (dodecane, tridecane, and tetradecane) chemicals, major components of JP-8, were investigated for changes in skin lipid and protein biophysics, and macroscopic barrier perturbation from dermal exposure. Percutaneous absorption was examined in vitro using porcine ears (marine pigs, male).  Fourier transform infrared (FTIR) spectroscopy was employed to investigate the biophysical changes in stratum corneum (SC) lipid and protein. FTIR results showed that all of the tested components of JP-8 significantly (P < 0.05) extracted SC lipid and protein.

Retention in the stratum corneum can be determined by calculating the Log PC (octanol/water) values. There is an increase in the retention of the aliphatic JP-8 components to with increasing Log PC value. Log PC values are 8.76 +/- 0.74, 13.15 +/- 1.05, 15.85 +/- 1.36 for dodecane (DOD), tridecane (TRI), and tetradecane (TET), respectively.

 

The flux, JSS (nmol/cm2 per h)*10E-2, values were determined to be 1.94 +/- 0.39, 13.80 +/- 0.82, and 1.40 +/- 0.20 for DOD, TRI, and TET, respectively. The permeability coefficients, Kp (cm/h)*10E-4, were 0.37 +/- 0.13, 18.46 +/- 1.50, 0.64 +/- 0.20 for DOD, TRI, and TET, respectively. The diffusion coefficient values, D (cm/h)*10E-6, were determined to be 0.21 +/- 0.02, 6.84 +/- 0.57, and 0.20 +/- 0.04 for DOD, TRI, TET, respectively. The lag time (hours) was determined to be 1.33 +/- 0.07, 0.89 +/- 0.17, and 1.62 +/- 0.34 hours for DOD, TRI, and TET, respectively. FTIR results suggest that all of the test chemicals significantly (P<0.05) extracted SC lipid and protein in comparison to control. TRI exhibited greater extraction of the SC lipid and protein as well as greater transport through the skin than other chemicals.

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1999
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Principles of method if other than guideline:
In vitro isolated perfused porcine skin flap (IPPSF) Studies.
GLP compliance:
not specified
Radiolabelling:
yes
Remarks:
14C-naphthalene, 3H-dodecane, 14C- hexadecane
Species:
pig
Strain:
not specified
Sex:
not specified
Details on test animals or test system and environmental conditions:
in vitro experiment
Type of coverage:
open
Vehicle:
unchanged (no vehicle)
Duration of exposure:
5 hours; 4 trials
Doses:
25 uL of Jet fuel with radio labeled tracers
Control animals:
no
Details on study design:
In vitro isolated perfused porcine skin flap (IPPSF) Studies.
In these studies, jet fuel mixtures were applied non-occluded to mimic field exposure conditions, and experiments were conducted for a total of 5 h in IPPSFs with 4 replicates per treatment condition. A 1 x 5 cm dosing area was drawn on the surface of the skin flap with a surgery marker. A dose, containing 25 uLof the specified jet fuel containing approximately 2 uCi of 14C-naphthalene plus 10 uCi of 3H-dodecane and 14C- hexadecane was applied directly to the surface of the skin flap. The specific activities of the marker compounds were sufficient that the added radiolabeled compounds had little effect on the final concentration of naphthalene (1.21% instead of 1.1%) and dodecane (4.701% instead of 4.7%). Single label studies were initially conducted and compared to the dual-label results to test whether using this dual-label experimental design had any effect on marker absorption. No effect was detected.
Perfusate samples (3 ml) were collected every 5 mm for the first 40 mm. then every 10 mm until 1.5 h. and then every 15 mm until termination at 5 h. At termination, several samples were taken for mass balance of the marker compounds. The surface of the dose area was swabbed twice with a 1% soap solution and gauze, and then 12 stratum corneum tape strips were collected using cellophane tape (3M Corporation, Minneapolis. MN). The entire dose area was removed. A 1x 1 cm core of the dose area was removed and frozen for subsequent depth of penetration studies. This consisted of laying the core sample epidermal side down in an aluminum foil boat and embedding in Tissue-Tek OCT compound (Miles. Inc., Elkhart, IN), snap freezing in liquid nitrogen, followed by sectioning (40 zm) on a Reichart-Jung Model 1800 Cryocut (Warner Lambert, Buffalo, NY). The remaining dosed area as well as the surrounding skin was separated from the fat and held for analysis. All samples (including swabs, tape strips, core sections, skin, fat, mass balance samples, etc.) were dissolved separately in Soluene. A representative volume of each sample was oxidized completely via a Packard Model 307 Tissue Oxidizer. The 3H and 14C samples were counted separately on a Packard Model 1900TR TriCarb Scintillation Counter.

Data analysis. Data was entered into a custom IPPSF database and the resulting analysis reported. Since all experiments were conducted using the identical marker doses across all fuels, and the absolute concentrations of these marker compounds were similar, these results are expressed as percentage applied dose to give a representative assessment of the absorption and cutaneous penetration of a complex mixture such as jet fuel. This is appropriate since the absolute concentrations of jet fuel hydrocarbons are not fixed across all fuels due to differences that arise from the natural sources of the petroleum and different refining processes. Area under the curve (AUC) in the perfusate was calculated using the trapezoidal method. Peak flux was the maximum flux (% dose/mm) observed at any one time point.

The experimental compartments which were analyzed in these studies used the following definitions: (1) Surface is the residue removed by washing the surface of the IPPSF at termination of the experiment plus the residues remaining in the dosing template. (2) Stratum corneum is the residue extracted from the outermost stratum corneum via 12 tape strips at the termination of the experiment. (3) Dosed skin is the residue that remained in the dosed skin plus the depth of penetration core taken at termination. (4) Absorption is the cumulative amount of the marker compound collected in the effluent over the course of the 5-h experiment. (5) Fat is the residue remaining in the fat when it was separated from the dermis at the end of the experiment. (6) Penetration is the summation of the label in the effluent plus skin plus fat, but not stratum corneum nor surface. (7) Evaporative loss is that label which was lost to evaporation. Our previous studies in the IPPSF indicated that the penetration estimate is the best empirical correlate to predict eventual in vivo absorption in humans.

Statistical significance of absorption and penetration parameters were determined using ANOVA or by a priori-defined orthogonal contrasts where appropriate at the 0.05 level of significance. A least significance difference (LSD) procedure was used for multiple comparisons on overall tissue disposition.
Details on in vitro test system (if applicable):
A 1 x 5 cm dosing area was drawn on the surface of the skin flap with a surgery marker. A dose, containing 25 uL of the specified jet fuel containing approximately 2 uCi of 14C-naphthalene plus 10 uCi of 3H-dodecane and 14C- hexadecane was applied directly to the surface of the skin flap. Perfusate samples (3 ml) were collected every 5 mm for the first 40 mm. then every 10 mm until 1.5 h. and then every 15 mm until termination at 5 h. At termination, several samples were taken for mass balance of the marker compounds. The surface of the dose area was swabbed twice with a 1% soap solution and gauze, and then 12 stratum corneum tape strips were collected using cellophane tape (3M Corporation, Minneapolis. MN). The entire dose area was removed. A 1x 1 cm core of the dose area was removed and frozen for subsequent depth of penetration studies. This consisted of laying the core sample epidermal side down in an aluminum foil boat and embedding in Tissue-Tek OCT compound (Miles. Inc., Elkhart, IN), snap freezing in liquid nitrogen, followed by sectioning (40 zm) on a Reichart-Jung Model 1800 Cryocut (Warner Lambert, Buffalo, NY). The remaining dosed area as well as the surrounding skin was separated from the fat and held for analysis.
Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Conclusions:
Within JP-8, the rank order of absorption for all marker components was (mean +/- SEM; % dose) naphthalene (1.17 +/- 0.07)> dodecane (0.63 +/- 0.04) > hexadecane (0.18 +/- 0.08).  The area under the curve (AUC) was determined to be (mean +/- SEM; % dose-h/mL): naphthalene (0.0199 +/- 0.0020)> dodecane (0.0107 +/- 0.0009) > hexadecane (0.0017 +/- 0.0003). In contrast, deposition within dosed skin showed the reverse pattern.
Executive summary:

The purpose of these studies was to assess the percutaneous absorption and cutaneous disposition of topically applied (25 uL/5 cm2) neat Jet-A, JP-8, and JP-8(100) jet fuels by monitoring the absorptive flux of the marker components 14C naphthalene and 4H dodecane simultaneously applied non-occluded to isolated perfused porcine skin flaps (IPPSF) (a = 4). Absorption of 14C hexadecane was estimated from JP-8 fuel. Absorption and disposition of naphthalene and dodecane were also monitored using a nonvolatile JP-8 fraction reflecting exposure to residual fuel that might occur 24 h after a jet fuel spill. In all studies, perfusate, stratum corneum, and skin concentrations were measured over 5 h. Naphthalene absorption had a clear peak absorptive flux at less than 1 h, while dodecane and hexadecane had prolonged, albeit significantly lower, absorption flux profiles. Within JP-8, the rank order of absorption for all marker components was (mean +/- SEM; % dose) naphthalene (1.17 +/- 0.07)> dodecane (0.63 +/- 0.04) > hexadecane (0.18 +/- 0.08).  The area under the curve (AUC) was determined to be (mean +/- SEM; % dose-h/mL): naphthalene (0.0199 +/- 0.0020)> dodecane (0.0107 +/- 0.0009) > hexadecane (0.0017 +/- 0.0003). In contrast, deposition within dosed skin showed the reverse pattern.

Endpoint:
dermal absorption, other
Remarks:
Mathematical description
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
supporting study
Study period:
2008
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles: non-GLP. Source of data is from secondary literature.
Qualifier:
no guideline available
Principles of method if other than guideline:
A mathematical description of uptake of aromatic and aliphatic hydrocarbons into the stratum corneum of human skin in vivo was developed. A simple description based on Fick’s laws of diffusion was used to predict the spatiotemporal variation of undecane and dodecane in the stratum corneum of human volunteers. The estimated values of the diffusion coefficients for each chemical were comparable to values predicted using in vitro skin systems and biomonitoring studies.
GLP compliance:
no
Species:
other: model
Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined
Conclusions:
Estimated diffusion coefficients (Dsc, cm2/min×10E−8 +/- S.D.). Undecane: 4.2 +/- 1.2; Dodecane: 5.0 +/- 0.7
Executive summary:

Estimated diffusion coefficients (Dsc, cm2/min×10E−8 +/- S.D.). Undecane: 4.2 +/- 1.2; Dodecane: 5.0 +/- 0.7

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2004
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Acceptable well-documented study report which meets basic scientific principles.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
Principles of method if other than guideline:
The penetration and skin retention of nonane, dodecane and tetradecane was assessed in vitro using hairless rats' skin.
GLP compliance:
not specified
Radiolabelling:
yes
Remarks:
Radiolabelled (3H) nonane (specific activity 2.4 mCi/g), dodecane and tetradecane (specific activity 2.6 mCi/g)
Species:
mouse
Strain:
CD-1
Sex:
male
Details on test animals or test system and environmental conditions:
Hairless rats (CD, male, 50-56 days, Charles River Laboratories, Hartford, CT) were acclimatized to laboratory conditions for three days prior to experiments and were on standard animal chow and water ad libitum. The temperature and humidity of the room were maintained at 22+/-1°C and 35-45% RH, respectively.
Type of coverage:
open
Duration of exposure:
15 uL every 2 h for 8 h a day for four days
Doses:
15 uL every 2 h for 8 h a day for four days
Control animals:
yes
Details on study design:
Skin barrier function and irritation in hairless rats: The control and treatment sites were marked as circular areas (3 cm2) on the dorsal surface of the rats (two treatment sites and a control site). The chemicals were applied unocclusively at the treatment sites at 15 uL every 2 h for 8 h a day for four days. The animals were anaesthetized during the measurement of TEWL and erythema. The measurements were performed before application of the chemicals and at 8, 24, 32, 48, 56, 72, 80, 96 and 104 h during the exposure period. The TEWL were measured using Tewameter TM 210. The probe of Tewameter was placed perpendicular to the surface of the skin and a stable reading of TEWL was reached in about 60 s. The skin irritation (erythema) was evaluated by visual scoring by the method of Draize.

Assessment of biomarkers in skin and blood after dermal exposures
Hairless rats were exposed to different chemicals by the same procedure as described in skin irritation studies. The rats were divided into four groups of four animals in each group. Three groups served as treatment groups for nonane, dodecane and tetradecane and the fourth group served as a control. After dermal exposures (104 h), the rats were anaesthetized with halothane, blood was collected into heparinized centrifuge tubes by cardiac puncture and the animals were sacrificed by an overdose of halothane anaesthesia. The skin of the exposed sites was collected and the adhering fat and subcutaneous tissue were removed and samples were wrapped in aluminium foil and then immediately snap frozen in liquid nitrogen and stored at -80°C until analyzed. The blood samples were centrifuged at 6000 g and plasma was separated and stored at -80°C until analyzed. Frozen skin samples (1.0 g) were pulverized using a tissue pulverizer in 2.5 mL homogenization buffer (14 mM Tris-Ci, 120 mM NaCl, 3 mM KC1; pH 7.4). The homogenate was centrifuged at 13000 g for 30 min and the supernatant was collected and stored at -80°C until analyzed. Protein levels were determined in the supernatant of each skin sample using the BCA Protein Assay Kit. Plasma and skin samples were subjected to quantitative analysis using EIA kits for IL-1a and TNF-a according to the manufacturer’s protocol. Each sandwich EIA kit used a polyclonal antibody to the specific protein to bind the target protein in the sample. After a short incubation, the excess sample was washed out and a monoclonal antibody labelled with the enzyme horseradish peroxidase was added. The labelled antibody was attached to the specific protein of interest and captured on the plate. Next, the excess-labelled antibody was washed out, and the substrate was added. The substrate reacted with the labelled antibody bound to the sample protein and the colour was read at 490 or 405 nm in a plate reader. The detection limits of ETA kits were: IL-1a, 195 pg/mL; TNF-a, 420.7 pg/mL.
Details on in vitro test system (if applicable):
In vitro skin penetration studies: The dorsal skin was excised from hairless rats (CD, male, 50-56 days, Charles River Laboratories, Hartford, CT) after sacrifice with an overdose of halothane anaesthesia. The adhering fat and subcutaneous tissue were removed and the fresh skin was mounted between the donor and receptor compartments of Franz diffusion cells with the SC facing the donor compartment. Each Franz cell had a diffusional surface area of 0.636 cm2 and the maximum capacity of donor and receptor compartments was 1.0 and 5.0 mL, respectively. The temperature of the receptor compartment was maintained at 37+/- 0.1°C with an external, constant-temperature circulator water bath. The receptor compartment was filled with 6% Brij 98 in normal saline, which was stirred continuously with a magnetic bar at 600 rpm. Nonane, dodecane or tetradecane (0.5 mL) spiked with the respective radiolabeled chemicals (2.5 uCi in each cell) were placed in the donor compartment and covered with Parafilm, aluminium foil and a plastic cap that fit snugly to the neck of the donor compartment to prevent evaporation of the chemicals. At predetermined time intervals (0.25, 0.5, 1, 2, 3, 4, 6 and 8 h), samples (0.5 mL) were taken from the receptor compartment, and the cell was refilled with the same volume of fresh Brij solution. Brij 98 (6%) is a good solubilizing receiver solution, and does not damage the skin and cause increased permeability due to its property to maintain sink conditions of the receptor cell. The samples were mixed with 3 mL of scintillation cocktail and the 3H samples were counted on a liquid scintillation counter. Each experiment was repeated at least nine times using skin from different rats.

In vitro skin retention studies: For skin absorption studies, the hairless rat skin was exposed to test chemicals as described under skin penetration studies. After each exposure period (0.25, 0.5, 1, 2, 3, 4, 6 and 8 h), the receptor chamber was sampled for determination of the total amount of the chemical permeated at that time interval. The amount of test chemical in the skin (SC, epidermis and dermis) was determined by horizontal skin sectioning techniques. The skin was collected from the diffusion cell and its surface was gently wiped. The active diffusion area of the skin (0.636 cm2) was then cut with a biopsy punch and the SC was stripped six times with an adhesive tape. Under usual conditions, 10 tape strips are adequate to remove the entire SC in hairless rat skin. In the preliminary experiments, it was found that for the skin treated with the above chemicals, six strips were adequate for removal of SC and a further attempt at stripping resulted in detachment of epidermis layer from dermis. The amount of SC removed was determined by weighing the tapes before and after stripping. The weight and thickness of skin (epidermis and dermis) was determined after stripping of SC. The tissue was then sandwiched between two cover slips and frozen on the cryobar stage of a cryotome at -60°C. The frozen skin was placed on the chuck and covered with an excess of cryomatrix. The spatula and cover slips exposed to epidermal and dermal surfaces were gently rinsed with a few drops of methanol and collected into designated scintillation vials for SC tapes, epidermal and dermal sections, respectively. Four sections of 25 um each were sectioned and collected as epidermis. The remaining portion of skin was sectioned into 25-um slices and collected as dermis. As the sections were associated with the cryomatrix, the weight of epidermis could not be directly determined. From the knowledge of the thickness and weight of the stripped skin and the thickness of epidermis sections, the weight of epidermis was calculated, assuming the density of epidermis and dermis were the same. The tape strips and skin slices were digested separately in Soluene for about 1 h; 3 mL of scintillation cocktail was added and the 3H samples were counted on a scintillation counter as described in the skin penetration experiments. The amount of chemical in the SC, epidermis and dermis were normalized and represented as milligrams of the chemical per gram of the tissue.
Signs and symptoms of toxicity:
not examined
Dermal irritation:
yes
Remarks:
unoccluded, nonane and dodecane (erythema scores 1.6 and 2.0, respectively), tetradecane (erythema score 3.5)

In vitro skin penetration and absorption studies: All the chemicals showed a lag time of about 1 h. The flux of dodecane was about 3- and 77-fold higher than nonane and tetradecane, respectively. From the data, it is clear that retention of all three chemicals in SC is much higher than epidermis and dermis at all time points. Under infinite dose conditions, the chemicals diffused rapidly into SC and reached plateau levels within 1 h. The absorption of chemicals in SC at all time points were in the following order: tetradecane > dodecane > nonane. This shows a linear relationship between the carbon chain length and the absorption of the chemicals in the SC. The extent of retention of the chemicals to SC can be directly correlated to the log Kp (r2 = 0.9900) and molecular weight (r2 = 0.8782) of these chemicals. The absorption pattern of chemicals in epidermis and dermis, in contrast to SC, demonstrated a parabolic relationship between the molecular weight of the hydrocarbon and their skin retention. Dodecane showed the highest skin retention in the epidermis and dermis followed by nonane and tetradecane.

 

Skin barrier changes and irritation studies: The skin barrier function was assessed by measuring the TEWL in rats during unocclusive chemical exposures. The control sites did not show any increase in the TEWL throughout the study (in comparison to values at 0 h). All the chemicals demonstrated a significant increase in the TEWL during the dermal exposure period (P< 0.001). Nonane showed steady levels of TEWL throughout the study. The TEWL of tetradecane and dodecane showed a steep rise in the TEWL after 48 and 72 h, respectively and also these chemicals produced extremely high levels of TEWL towards the end of 104 h of the study (3- and 7-fold high TEWL by dodecane and tetradecane, respectively, in comparison to control). Overall the increase in the TEWL was in the following descending order: tetradecane > dodecane> nonane. Erythema values of all the chemicals steadily increased during the period of the study. As demonstrated by TEWL experiments, the erythema scores increased with increase in the molecular weight of the hydrocarbon. While nonane and dodecane produced moderate erythema (erythema scores 1.6 and 2.0, respectively for nonane and dodecane, respectively), tetradecane produced severe erythema (erythema score 3.5).

 

IL-1a was undetectable in the skin due to dermal exposures of these chemicals whereas in the blood high levels of IL-la were detected, indicating rapid clearance of the cytokine from the skin into the blood. While the IL-1a level in the blood by nonane was similar to control, dodecane and tetradecane increased the blood levels of IL- 1a 3-fold in comparison to the control (P<0.05). TNF-a was detected in the skin whereas its levels were not detectable in blood, indicating its local accumulation in the skin layers and induction of irritation and inflammation. All the chemicals increased TNF-a levels in the skin at least 6-fold higher than the control. Tetradecane induced maximum expression of TNF-a (10-fold) followed by nonane and dodecane, which induced 6.9- and 6.2-fold higher TNF-a levels, respectively, in comparison to control (P<0.05).

Executive summary:

The penetration and skin retention of nonane, dodecane and tetradecane was assessed in vitro using hairless rats' skin. The effects of unocclusive dermal exposures of these chemicals (15 uL every 2 h for 8 h a day for four days) on the transepidermal water loss (TEWL) and erythema were measured in CD hairless rats. The expression of interleukin 1alpha (IL-1a) and TNF-alpha in the skin and blood were measured at the end of dermal exposures. The flux of dodecane was 3- and 77-fold higher than nonane and tetradecane. The retention of chemicals in stratum corneum (SC) was in the order of tetradecane > dodecane > nonane, and directly correlated to the log Kp (r2 = 0.9900) and molecular weight of the chemicals (r2 = 0.8782). The TEWL and erythema data indicate that irritation was in the following order: tetradecane > dodecane > nonane. Likewise, the expression of IL-la in the blood and TNF-alpha in the skin after dermal exposures was higher for tetradecane followed by dodecane and nonane compared to control. In conclusion, the aliphatic hydrocarbon chemicals of the present study induced cumulative irritation upon low-level repeat exposures for a four-day period. The affinity of the chemicals to SC and their gradual accumulation in the skin in the present study is the probable cause for the differences in the skin irritation profiles of different aliphatic chemicals.

Description of key information

Short description of key information on bioaccumulation potential result:

If C9-C14 aliphatic, <2% aromatic hydrocarbon fluids are absorbed, they are typically metabolized by side chain oxidation to alcohol and carboxylic acid derivatives.  These metabolites can be glucuronidated and excreted in the urine or further metabolized before being excreted.  The majority of the metabolites are excreted in the urine and to a lower extent, in the feces.  Excretion is rapid with the majority of the elimination occurring within the first 24 hours of exposure.  As a result of the lack of systemic toxicity and the ability of the parent material to undergo metabolism and rapid excretion, bioaccumulation of the test substance in the tissues is not likely to occur.

Short description of key information on absorption rate:

C9-C14 aliphatic, <2% aromatic hydrocarbon fluids are poorly absorbed dermally with an estimated overall percutaneous absorption rate of approximately 2ug/cm2/hr or 1% of the total applied fluid. Regardless of exposure route, C9-C14 aliphatic, <2% aromatic hydrocarbon fluids are rapidly metabolized and eliminated.

Key value for chemical safety assessment

Additional information

C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids are readily absorbed when inhaled or ingested.  C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids are poorly absorbed dermally with an estimated overall percutaneous absorption rate of approximately 2ug/cm2/hr or 1% of the total applied fluid.  Regardless of exposure route, C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids are rapidly metabolized and eliminated. Bioaccumulation of C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids is not expected.

Discussion on bioaccumulation potential result:

C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids are apparently well absorbed if ingested or inhaled. C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids undergo metabolism and rapid excretion; bioaccumulation of the test substance in the tissues is not likely to occur. 

 

C9 to C14 isoalkanes are taken up into the blood and distributed to the internal organs including brain, liver, kidney and fat.  Twelve hours after the exposure, levels in blood, brain, liver and kidney were below detection levels; levels in fat were about half those found at the end of the exposure period.  These data demonstrate that isoalkanes are rapidly eliminated and do not accumulate. The concentration of isoalkanes in blood, brain, liver and fat increased with increasing number of carbon atoms. The C9 and C10 isoalkanes showed increasing concentrations in fat during the exposure period and high concentrations 12 hr after cessation of exposure.

 

Inhaled n-alkanes, nC9-nC13, are taken up into the blood and distributed to the internal organs including the brain.  There is also a corresponding reduction in the blood/air and brain/air ratios with increasing carbon numbers up to C10.  At high carbon numbers the ratios decrease suggesting blood/brain barrier effects for high molecular weight hydrocabons (Nilsen et. al 1988). Thus the efficiency of uptake into both blood and brain also decreases with increasing carbon number. A brain/blood ratio of 11.4 and a fat/blood ratio of 113 were determined for n-nonane. n-Decane was found to have a half-life of 2 hours. The percentage retention of n-alkanes showed an inverse linear relationship to chain length that was describable by the regression line: (percentage retained) = 115.9 – 3.94 * (number of carbon atoms). This line had a correlation coefficient of -0.995, standard error of estimate Sy * x= 3.30, t = 30.85 and P < 0.001. Paraffin having more than 29 carbon atoms thus would not be absorbed to a significant extent under these conditions.

 

Based on a study of jet propellant 8 (JP-8) jet fuel components, the in vitro (rat liver microsomal oxidation) nonlinear kinetic constants for n-nonane and n-decane were V(max) (nmol/mg protein/min) = 7.26 +/- 0.20 and 2.80 +/- 0.35, respectively, and K(M) (micro M) = 294.83 +/- 68.67 and 398.70 +/- 42.70, respectively. Metabolic capacity as assessed by intrinsic clearance, V(max)/K(M), was approximately four-fold higher for nonane (0.03 +/- 0.005) than for decane (0.007 +/- 0.001).

 

The blood/brain ratio and the fat/blood ratios for trimethylcyclohexane were determined to be 11.4 and 135, respectively. A marked decrease in biological concentrations of trimethylcyclohexane during the initial phase of exposure indicates that this hydrocarbon is capable of inducing its own metabolic conversion resulting in lower steady state levels.

 

The tissue disposition after 3 weeks of exposure to dearomatised white spirit, mixed aliphatic, and cycloaliphatic constituents was determined. After 3 weeks of exposure the concentration of total white spirit was 1.5 and 5.6 mg/kg in blood; 7.1 and 17.1 mg/kg in brain; 432 and 1452 mg/kg in fat tissue at the exposure levels of 400 and 800 ppm, respectively. The concentrations of n-nonane, n-decane, n-undecane, and total white spirit in blood and brain were not affected by the duration of exposure. Two hours after the end of exposure the n-decane concentration decreased to about 25% in blood and 50% in brain. A similar pattern of elimination was also observed for n-nonane, n-undecane and total white spirit in blood and brain. In fat tissue the concentrations of n-nonane, n-decane, n-undecane, and total white spirit increased during the 3 weeks of exposure. The time to reach steady-state concentrations is longer than 3 weeks. Post-exposure decay in blood could be separated into two phases with half-lives of approximately 1 and 8 hr for n-nonane, n-decane, and n-undecane. In brain tissue two slopes with half-lives of 2 and 15 hr were identified. In fat tissue, only one slope with half-life of about 30 hr was identified. In conclusion, after 3 weeks of exposure the fat:brain:blood concentration coefficients for total white spirit were approximately 250:3:1.

 

Nilsen, O., Haugen, O., Zahlsen, K. Halgunset, J., Helseth, A., Aarset, H., and Eide,1988. Toxicity of n-C9 to n-C13 alkanes in the rat on short term inhalation. Pharmacology and Toxicology 62:259-266.

 

Discussion on absorption rate:

There have not been any in vivo dermal absorption studies of C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids, but there have been in vitro studies of some constituents, particularly dodecane.  Due to the structural similarity of these molecules to other constituents of the C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids, it seems reasonable to assume that the solvents would have toxicokinetic properties similar to those of these constituents.  

 

IN VIVO

 

Ten healthy adult volunteers (five males and five nonpregnant females) with no occupational exposure to jet fuel were recruited for participation. One of the volunteer’s forearms was placed palm up inside the exposure chamber, and two aluminum application wells (10 cm2 per well) were pressed against the skin to prevent JP-8 from spreading during the experiment. Neat JP-8 (1.0 mL) was applied to the volar forearm. The exposure chamber was sealed for the duration of the experiment (0.5 h). At the end of the exposure period, the two exposed skin sites were wiped with a gauze pad and tape-stripped as many as 10 times. Blood samples were drawn from the unexposed arm at baseline, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, and 3.5 h.

 

The permeability coefficients (cm/h) of the aliphatic hydrocarbons were determined to be: Decane 6.5E-06, Undecane 4.5E-07, and Dodecane 1.6E-06.

 

A simple mathematical model based on Fick’s laws of diffusion was used to predict the spatiotemporal variation of undecane and dodecane in the stratum corneum of human volunteers using the same data as above. The estimated values of the diffusion coefficients (Dsc, cm2/min×10E−8 +/- S.D.) were determined to be: undecane, 4.2 +/- 1.2 and Dodecane, 5.0 +/- 0.7.

 

IN VITRO

Several in vitro studies used porcine skin flaps to determine the absorption and disposition of several aliphatic compounds. There are some general conclusions of the absorption and disposition of C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids. All of the tested chemicals showed a lag time of about 1 h. The retention of aliphatic chemicals in stratum corneum is much higher than epidermis and dermis at all time points. Under infinite dose conditions, the chemicals diffused rapidly into stratum corneum and reached plateau levels within 1 h. The absorption of chemicals in stratum corneum at all time points were in the following order: tetradecane > dodecane > nonane. This shows a linear relationship between the carbon chain length and the absorption of the chemicals in the stratum corneum. The absorption pattern of chemicals in epidermis and dermis, in contrast to stratum corneum, demonstrated a parabolic relationship between the molecular weight of the hydrocarbon and their skin retention.

 

Dermal absorption values for several of the C9-C14 aliphatic, < 2% aromatic hydrocarbon fluids have been experimentally determined. The permeability coefficients (cm/h) for decane, undecane, and dodecane were determined to be 6.5*10E-6, 4.5*10E-07, and 1.6*10E-06, respectively. In a second experiment, the diffusion coefficient values (cm2/h) of for dodecane (DOD), tridecane (TRI), and tetradecane (TET) were determined to be (0.21 +/-0.02)*10E-6, (6.849 +/- 0.57)*10E-6, (0.209 +/- 0.04)*10E-6, respectively.

 

Binding to the stratum corneum can be determined by calculating the Log PC (octanol/water) values. There is an increase in binding of the aliphatic JP-8 components to with increasing Log PC value. Log PC values are 8.76 +/- 0.74, 13.15 +/- 1.05, 15.85 +/- 1.36 for dodecane (DOD), tridecane (TRI), and tetradecane (TET), respectively.

 

The flux, JSS (nmol/cm2 per h)*10E-2, values were determined to be 1.94 +/- 0.39, 13.80 +/- 0.82, and 1.40 +/- 0.20 for DOD, TRI, and TET, respectively. The permeability coefficients, Kp (cm/h)*10E-4, were 0.37 +/- 0.13, 18.46 +/- 1.50, 0.64 +/- 0.20 for DOD, TRI, and TET, respectively. The diffusion coefficient values, D (cm/h)*10E-6, were determined to be 0.21 +/- 0.02, 6.84 +/- 0.57, and 0.20 +/- 0.04 for DOD, TRI, TET, respectively. The lag time (hours) was determined to be 1.33 +/- 0.07, 0.89 +/- 0.17, and 1.62 +/- 0.34 hours for DOD, TRI, and TET, respectively. FTIR results suggest that all of the test chemicals significantly (P<0.05) extracted SC lipid and protein in comparison to control. TRI exhibited greater extraction of the SC lipid and protein as well as greater transport through the skin than other chemicals.

OVERVIEW OF PERCUTANEOUS ABSORPTION OF HYDROCARBON SOLVENTS

There are no studies of repeated dose toxicity of hydrocarbon solvents using the dermal route of administration. Accordingly, where it is necessary to calculate dermal DNELs, systemic data from studies utilizing other routes of administration, normally inhalation but also oral data, can be used in some situations.  In accordance with ECHA guidance, read across from oral or inhalation data to dermal should account for differences in absorption where these exist (R8, example B.6). In fact, hydrocarbon solvents are poorly absorbed in most situations, in part because some are volatile and do not remain in contact with the skin for long periods of time and also because, due to their hydrophobic natures, do not partition well into aqueous environments and are poorly absorbed into the blood. 

 

           If these differences in relative absorption are introduced into the DNEL calculations to calculate external doses, the DNELs based on systemic effects are highly inflated. This seems potentially misleading as it implies that substances have different intrinsic hazards when encountered by different routes whereas in fact the differences are due ultimately to differences in absorbed dose. Accordingly, it is our opinion that it would be more transparent if the differences in absorption were taken into account in the exposure equations rather than in DNEL derivation. 

 

           Shown below is a compilation of percutaneous absorption information for a number of hydrocarbon solvent constituents covering carbon numbers ranging from C5 to C14 as well as examples of both aliphatic and aromatic constituents. The low molecular weight aliphatic hydrocarbons (n-pentane, 2-methylpentane, n-hexane, n-heptane, and n-octane) were tested by Tsuruta (1982) using rat skin in an in vitro model system. As shown (Table 1), the highest percutaneous absorption value was 2 ug/cm2/hr for pentane. Lower values (< ~ 1 ug/cm2/hr) were reported for aliphatic hydrocarbons ranging from hexane to octane. Several authors have assessed the percutaneous absorption of higher molecular weight aliphatic constituents including Baynes et al. (2000), Singh and Singh (2003), Muhammad et al. (2005), and Kim et al., (2006). The first three of these authors used porcine skin models and reported that, except for one anomalous result with tridecane, the percutaneous absorption values for aliphatic constituents ranging from nonane to tetradecane were well below 1 ug/cm2/hr. Rat and human skin are considered to be more permeable than human skin (Kim et al., 2006), so these numbers can be considered conservative. 

 

           Kim et al. (2006) reported results of percutaneous absorption studies with human skin under in vivo conditions. In this case, the assessment method was based on tape stripping. The authors reported percutaneous absorption values ranging from 1 – 2 ug/kg/day for decane, undecane and dodecane. These values are higher than those reported by other authors, most likely because this technique measures absorption into the skin but not through the skin as was done in the studies listed above. Accordingly, it seems likely that these numbers are conservative as well.

 

           With respect to aromatic hydrocarbons, most of the reported percutaneous absorption values [Baynes et al. (2000); Singh and Singh (2003); Mohammad et al. (2005); and Kim et al. (2006)] are less than 2 ug/cm2/day. The only exceptions are the values for naphthalene from Mohammad et al. (2005) which range from 4.2-6.6 ug/cm2/hr. 

 

           After considering all of the above, it seems reasonable to assume apparent that across the entire range of hydrocarbon solvent constituents, percutaneous absorption values are less than 2 ug/cm2/day. Accordingly, when systemic dermal DNELs are calculated using route to route extrapolations, the values will not be corrected for differences in absorption. Rather, 2 ug/cm2/hr will be used as a common percutaneous absorption rate for all hydrocarbon solvents for which dermal exposure estimates are provided. 

           

Table 1: Summarized information on percutaneous absorption of hydrocarbon solvent constituents (C5-C16). 

 

Constituent

Molecular Weight

nmol/min/cm2

nmol/hr/cm2

ug/cm2/hr

Reference

Aliphatic Constituents

 

 

 

 

 

Pentane

72

0.52

31.2

2.2

Tsuruta et al. 1982

 

 

 

 

 

 

2-methyl pentane

86

0.02

1.2

0.1

Tsuruta et al., 1982

 

 

 

 

 

 

n-hexane

86

0.02

0.6

0.5

Tsuruta et al., 1982

 

 

 

 

 

 

n-heptane

100

0.02

1.2

0.1

Tsuruta et al., 1982

 

 

 

 

 

 

n-octane

114

0.08 x 10-3

0.005

0.0005

Tsuruta et al., 1982

 

 

 

 

 

 

Nonane

128

 

 

0.03

Muhammad et al., 2005

Nonane

 

 

 

0.38

McDougal et al., 1999

 

 

 

 

 

 

Decane

142

 

 

2

Kim et al., 2006

Decane

 

 

 

1.65

McDougal et al., 1999

 

 

 

 

 

 

Undecane

156

 

 

0.06-0.07

Muhammad et al., 2005

Undecane

 

 

 

1.0

Kim et al., 2006

Undecane

 

 

 

1.22

McDougal et al., 1999

 

 

 

 

 

 

Dodecane

170

 

 

0.02-0.04

Muhammad et al., 2005

Dodecane

 

 

 

2

Kim et al., 2006

Dodecane

 

 

 

0.3

Singh and Singh, 2003

Dodecane

 

 

 

0.51

McDougal et al., 1999

Dodecane

 

 

 

0.1

Baynes et al. 2000

 

 

 

 

 

 

Tridecane

184

 

 

0.00-0.02

Muhammad et al., 2005

Tridecane

 

 

 

2.5

Singh and Singh, 2003

Tridecane

 

 

 

0.33

McDougal et al., 1999

Tetradecane

198

 

 

0.3

Singh and Singh, 2003

Hexadecane

 

 

7.02 x 10E-3

0.00004

Singh and Singh, 2002

 

 

 

 

 

 

Aromatic Constituents

 

 

 

 

 

Trimethyl benzene

120

 

 

0.49 - 1.01

Muhammad et al., 2005

Trimethyl benzene

 

 

 

1.25

McDougal et al., 1999

 

 

 

 

 

 

Naphthalene

128

 

 

6.6 - 4.2

Muhammad et al., 2005

Naphthalene

 

 

 

0.5

Kim et al., 2006

Naphthalene

 

 

 

1.4

Singh and Singh 2002

Naphthalene

 

 

 

1.8

Baynes et al. (2000)

Naphthalene

 

 

 

1.0

McDougal et al., 1999

 

 

 

 

 

 

1 methyl naphthalene

142

 

 

0.5

Kim et al., 2006

Methyl naphthalene

 

 

 

1.55

McDougal et al., 1999

 

 

 

 

 

 

2-methyl naphthalene

 

 

 

0.5

Kim et al., 2006

2-methyl naphthalene

 

 

 

1.1

Singh and Singh, 2002

 

 

 

 

 

 

 

 

 

 

 

 

Dimethyl naphthalene

156

 

 

0.62 – 0.67

Muhammad et al., 2005

Dimethyl naphthalene

 

 

 

0.59

McDougal et al. 1999

 

 

Table 2: Estimated percentages of various hydrocarbon solvent constituents absorbed

 

Based on the information provided below, an overall estimate of 1% for all hydrocarbon solvents seems reasonable. 

 

 

Representative Substance

Estimate of Percent absorption

Reference for percent value

 

 

 

Trimethyl benzene

0.2%

Based on data in Muhammad et al. (2005)

Naphthalene

1.2%

Riviere et al. 1999

Dodecane (75%)

0.63%

Riviere et al., 1999

TMB (25%)

0.2%

Muhammad et al., 2005

 

 

 

Hexadecane (70%)

0.18%

Riviere et al., 1999

Naphthalene (30%)

1.2%

Riviere et al., 1999

 

 

 

Pentane

-

 

 

 

 

Hexane

-

 

 

 

 

Heptane

0.14%

Singh et al. 2003

 

 

 

Dodecane

0.63%

Riviere et al. 1999

 

 

 

Hexadecane

0.18%

Riviere et al., 1999

 

 

 

 

References

 

Kim, D., Andersen, M., and Nylander-French (2006). Dermal absorption and penetration of jet fuel components in humans. Toxicology Letters 165:11-21.

 

McDougal, J., Pollard, D., Weisman, W., Garrett, C., and Miller, T. (2000). Assessment of skin absorption and penetration of JP-8 jet fuel and its components. Toxicological Sciences 25:247-255.

 

Muhammad, F., N. Monteiro-Riviere, R. Baynes, and J. Riviere (2005). Effect of in vivo jet fuel exposure on subsequent in vitro dermal absorption of individual aromatic and aliphatic hydrocarbon fuel constituents. Journal of Toxicology and Environmental Health Part A. 68:719-737.

 

Riviere, J., Brooks, J., Monteiro-Riviere, N., Budsaba, K., and Smith, C. (1999). Dermal absorption and distribution of topically dosed jet fuels jet A, JP-8 andJP-8(100). Toxicology and Applied Pharmacology 160:60-75.

 

Singh Somnath, Zhao Kaidi, Singh Jagdish. (2002). In vitro permeability and binding of hydrocarbons in pig ear and human abdominal skin. Drug and chemical toxicology, (2002 Feb) Vol. 25, No. 1, pp. 83-92.

 

Singh, S. and Singh, J. (2003). Percutaneous absorption, biophysical and macroscopic barrier properties of porcine skin exposed to major components of JP-8 jet fuel. Environmental Toxicology and Pharmacology 14:77-85.

 

Singh, S., Zhao, K., Singh, J. 2003. In vivo percutaneous absorption, skin barrier perturbation and irritation from JP-8 jet fuel components. Drug Chem. Toxicol 26:135-146.

 

Tsuruta, H. et al. (1982). Percutaneous absorption of organic solvents III. On the penetration rates of hydrophobic solvents through the excised rat skin. Industrial Health 20:335-345.