Registration Dossier

Administrative data

Endpoint:
dermal absorption, other
Remarks:
in vivo and in vitro
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference
Reference Type:
publication
Title:
Estimation of human percutaneous bioavailability for two novel brominated flame retardants, 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (EH-TBB) and bis(2-ethylhexyl) tetrabromophthalate (BEH-TEBP)
Author:
Knudsen GA, Hughes MF, Sanders JM, Hall SM, Birnbaum LS
Year:
2016
Bibliographic source:
Toxicology and Applied Pharmacology 311 (2016) 117–127

Materials and methods

Principles of method if other than guideline:
A parallelogram approach was used to predict human dermal absorption and flux for BEH-TEBP. [14C]-BEH-TEBP (BEH-TEBP = bis(2-ethylhexyl) tetrabromophthalate) was applied to human or rat skin at 100 nmol/cm² using a flow-through system. Intact rats received analogous dermal doses. Treated skin was washed and tape-stripped to remove “unabsorbed” [14C]-radioactivity after continuous exposure (24 h). “Absorbed” was quantified using dermally retained [14C]-radioactivity; “penetrated” was calculated based on [14C]-radioactivity in media (in vitro) or excreta + tissues (in vivo).
GLP compliance:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Bis(2-ethylhexyl) tetrabromophthalate
EC Number:
247-426-5
EC Name:
Bis(2-ethylhexyl) tetrabromophthalate
Cas Number:
26040-51-7
Molecular formula:
C24H34Br4O4
IUPAC Name:
bis(2-ethylhexyl) tetrabromophthalate
Specific details on test material used for the study:
BEH-TEBP (Lot # 256-061-0605-A-20130419-DJI) had a radiochemical purity of 99.9% (specific activity=60.5 mCi/mmol).
Radiolabelling:
yes

Test animals

Species:
other: rat
Strain:
other: SD rats
Sex:
female

Administration / exposure

Type of coverage:
other: non-occlusive steel mesh cap attached with polyacrylate glue to prevent ingestion of the test article.
Vehicle:
other: toluene
Duration of exposure:
24 hours
Doses:
100 nmol/cm² = ca. 0.07 mg/cm²
No. of animals per group:
4 rats
Control animals:
no
Details on study design:
In order to link data characterizing the fate of orally-administered BEH-TEBP in the female rat and the in vitro skin studies described above, 100 nmol/cm2 was applied to the dorsal surface of female SD rats (N = 4 rats/chemical, 11 weeks old, approximately 200 g, Harlan Laboratories. One day prior to dosing, animals were lightly anesthetized by isoflurane inhalation and an electric clipper was used to remove hair from the dorsal scapular region. Clipped areas were visually inspected for any nicks or cuts; animals were not used if nicks or cuts were found. Animals were returned to polycarbonate shoebox cages for recovery from anesthesia. Immediately prior to dosing, animals were again lightly anesthetized by isoflurane inhalation, the dosing area visually inspected for nicks and a 1 cm² area marked. Dosing solution (as described for in vitro samples) was applied inside the marked area using a 25 μL negative displacement pipette with a flexible tip. The vehicle was dried with gentle fanning and the dosing site was then covered with a non-occlusive steelmesh cap attachedwith polyacrylate glue to prevent ingestion of the test article. After dosing, animals were placed in plastic
Nalgene metabolism cages for collection of feces & urine. Animals were provided rat feed and tapwater for ad libitum consumption.
Feces, urine, and cage rinses were collected and analyzed at 4, 8, 12, and 24 h. Animals were euthanized by CO2 inhalation after 24 h. Following euthanasia, blood was collected by cardiac puncture, treated skin was excised, and complete necropsies were performed. Skin from the application area was treated in accordance with the OECD 427 method for in vivo testing of chemicals.
Details on in vitro test system (if applicable):
Full-thickness human skin was obtained from the National Disease Research Interchange (Philadelphia, PA, USA) from 4 Caucasian individuals aged 78–87 years old (2male and 2 female, dorsal/scapular skin, excised ≤12 h post-mortem, shipped at −80 °C).
Full-thickness female SD rat skin (N = 4/chemical, 10–11 weeks old) was obtained from Harlan Bioproducts for Science (Indianapolis, IN, USA). Twenty-four hours prior to excision, hair on the dorsal surface was clipped; the day of shipment,
the rats were humanely euthanized by CO2 inhalation and skin excised. The skin was shipped on dry ice and stored at −80 °C until use. In vitro dermal absorption tests were conducted according to the OECD Test Guideline 428 OECD, 2004a.
A flow-through diffusion cell system (0.64 cm² diffusional area) employed. Experiments for each species/chemical combination were run on separate days. On the day of the experiment, human or rat skin was thawed, direction of hair
growth assessed and dermatomed to approximately 300 μm thicknesses before placement in receptor fluid.
[14C]-BEH-TEBP in toluene (100 nmol/cm², ~1 μCi, 5 uL dose volume) were applied using a blunt tip Hamilton syringe (Franklin, MA, USA) to human and rat skin discs. The specific activity precluded testing at lower doses. Toluene was used as a vehicle due to limited solubility of the test chemical BEH-TEBP. The small dose volume combined with the rapid volatilization of the solvent (the flow-through cells were open to the air and the whole system was placed a fume hood) minimized
physiological effects (e.g., skin delipidation by toluene). After 24 h, the epidermal surface was washed. Washed and stripped skin was then chemically solubilized in 1 mL of Soluene 350 (Perkin Elmer) overnight in a water bath set at 37 °C. Hionic Fluor (Perkin Elmer) was added to the dissolved skin solution, and “absorbed” [14C]-radioactivity was quantified.

Results and discussion

Signs and symptoms of toxicity:
not specified
Dermal irritation:
not specified
Percutaneous absorption
Key result
Remarks on result:
other:
Remarks:
Based on the parallelogram methodology, conservative estimates predict approximately 7.8 ± 7.6% of BEH-TEBP may be absorbed into human skin in vivo; about 0.8±0.4% of the parent chemical is expected to reach systemic circulation after 24 h of continuous exposure.

Applicant's summary and conclusion

Conclusions:
BEH-TEBP in vitro penetrance was minimal (< 0.01%) for rat or human skin. BEH-TEBP absorption was 12± 11% for human skin and 41± 3% for rat skin. In vivo, total absorption was 27±9%; 1.2% reached systemic circulation. In vitro maximal BEH-TEBP flux was 0.3±0.2 and 1±0.3 pmol-eq/cm²/h for human and rat skin; in vivo maximum flux for rat skin was 16±7 pmol-eq/cm2/h. BEH-TEBP-derived [14C]-radioactivity in the perfusion media could not be characterized. <1% of the dose of BEH-TEHP is estimated to reach the systemic circulation following human dermal exposure under the conditions tested.
Executive summary:

A parallelogram approach was used to predict human dermal absorption and flux for BEH-TEBP. [14C]-BEH-TEBP (BEH-TEBP = bis(2-ethylhexyl) tetrabromophthalate) was applied to human or rat skin at 100 nmol/cm² using a flow-through system. Intact rats received analogous dermal doses. Treated skin was washed and tape-stripped to remove “unabsorbed” [14C]-radioactivity after continuous exposure (24 h). “Absorbed” was quantified using dermally retained [14C]-radioactivity; “penetrated” was calculated based on [14C]-radioactivity in media (in vitro) or excreta + tissues (in vivo).

BEH-TEBP in vitro penetrance was minimal (< 0.01%) for rat or human skin. BEH-TEBP absorption was 12± 11% for human skin and 41± 3% for rat skin. In vivo, total absorption was 27±9%; 1.2% reached systemic circulation. In vitro maximal BEH-TEBP flux was 0.3±0.2 and 1±0.3 pmol-eq/cm²/h for human and rat skin; in vivo maximum flux for rat skin was 16±7 pmol-eq/cm2/h. BEH-TEBP-derived [14C]-radioactivity in the perfusion media could not be characterized. <1% of the dose of  BEH-TEHP is estimated to reach the systemic circulation following human dermal exposure under the conditions tested.