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Dermal absorption

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dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Published in peer reviewed literature, non-guideline, animal experimental study, minor restrictions in design and/or reporting but otherwise adequate for assessment

Data source

Reference Type:
In vivo percutaneous absorption studies of volatile organic solvents in hairless mice II. Toluene, ethylbenzene and aniline
Susten AS, Niemeier RW and Simon SD
Bibliographic source:
J. Applied. Toxicol, Vol 10(3), 217-225

Materials and methods

Test guideline
no guideline followed
Principles of method if other than guideline:
Percutaneous absorption was assessed in hairless mice using a direct method.
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
- Name of test material (as cited in study report): [14C]-ethylbenzene
- Supplied by: Pathfinder Laboratories, St Louis, MO, USA
- Substance type: single-ring, radiolabelled aromatic solvent
- Radiochemical purity (if radiolabelling): >98%
- Specific activity (if radiolabelling): 33.47 mCi mmol^-1
- Locations of the label (if radiolabelling): 14C
- Reagent grade non-labelled ethylbenzene used for dilutions
- Amount of isotope: 2.48 µCi/nominal 5 µL dose (equivalent to approximately 100 µCi/kg bw)

Test animals

other: albino hairless (HRS/J)
Details on test animals or test system and environmental conditions:
- Source: Jackson Laboratories, Bar Harbor, ME, USA
- Age at study initiation: no data
- Weight at study initiation: 23-32 g
- Fasting period before study: no
- Housing: individually in shoe-box plastic cages with sawdust bedding (prior to dermal application)
- Individual metabolism cages: yes (within 5 seconds of dermal application for 4 hours)
- Diet: Purina Rodent Chow (Purina, St Louis, MO, USA) ad libitum (prior to dermal application)
- Water: ad libitum (prior to dermal application)
- Acclimation period: no data

- Temperature: 23±2.5°C
- Humidity: 55±15%
- Air changes (per hr): no data
- Photoperiod: 12hrs dark / 12hrs light

IN-LIFE DATES: no data

Administration / exposure

Type of coverage:
unchanged (no vehicle)
Duration of exposure:
4 hours after dermal application
- Amount applied (mean ± SD): 4.75 ± 0.22 ± / 4.10 ± 0.19 mg
- Amount applied (range): 4.39-4.89 µL / 3.79-4.30 mg
- Amount of isotope in nominal 5 µL doses: 2.48 µCi
- Nominal radioactive dose/mouse: 100 µCi/kg bw
No. of animals per group:
2 mice/experiment for a total of 6 experiments (data excluded from one mouse due to technical problems)
Control animals:
Details on study design:
- Equipment: Stainless steel skin depot device - skin contact area approximately 0.8 cm2. This comprised an outer stainless steel casing with inner stainless steel wire mesh basket containing 100-150 mg solid sorbent (for collection of evaporated vapour)
- Solid sorbent: coconut-derived activated charcoal (20/40 mesh)
- Desorbing agent (to desorb radioactivity from charcoal): non-labelled toluene
- Procedure: 5-10 mins before application, skin depot device glued to backs (mid thoracic region) of anaesthetised mice. Approx 5 µL of treatment solution placed in the skin depot device so it was just above the skin surface but below the solid sorbent using blunted needle of a 10 µL microsyringe and a 21-gauge "guide needle".
- Determination of radioactivity: 5 µL test solution injected into three 10 mL flasks containing suitable solvent. 0.1 mL aliquots (in triplicate) removed and analysed to determine average total 14C/flask and mean of 3 flasks considered to be nominal radioactive dose. Radioactivity (compound) remained in the guide needle and was subtracted from the nominal dose.

REMOVAL OF TEST SUBSTANCE: not applicable, mice killed at end of 4 hour application

- Expired air: at intervals of 0-15, 15-30, 30-60, 60-120, 120-180 and 180-240 mins after start of application

After 4 hours application, the mice were killed and the following collected:
- Skin depot (evaporated test substance)
- Wipe of treated skin site (unabsorbed test substance)
- Skin application site (bound test substance)
- Carcass minus treated skin site
- Faeces
- Urine
- Cage wash

SAMPLE PREPARATION: Treated skin and carcass digested in sodium hydroxide and aliquots of the digests oxidised.

- Method type(s) for identification: Liquid scintillation counting

Results and discussion

Signs and symptoms of toxicity:
not specified
Dermal irritation:
not specified
Absorption in different matrices:
- Expired air: 14.3 ± 6 % of absorbed dose
- Skin application site (bound test substance): 4.5 ± 1 % of absorbed dose
- Carcass minus treated skin site: 15.5 ± 2 % of absorbed dose
- Excreta (faeces and urine): 65.6 ± 5 % of absorbed dose
Total recovery:
- Total recovery:
- Recovery of applied dose acceptable: Yes (>90%)
- Distribution (% nominal dose recovered): 3.4 ± 1.0, 86.7 ± 1, 5.0 ± 1 and 95.2 ± 1 % for absorbed, skin depot, guide needle and total recovered, respectively
Percutaneous absorption
3.61 %
Remarks on result:
other: 294±14 sec
absorption rate = 37±31 µg/cm2/min

Any other information on results incl. tables

Average amount applied to skin: 4.10 mg of which 148 µg (3.61%) absorbed. The % of absorbed dose collected in expired air was related to the vapour pressure of the compound. The cumulative % of absorbed dose found in expired air was 9.3% for 0-15 min. For most mice, breath excretion rate was highest during 0 -15 mins but for 5 mice was higher during 15 -30 or 30 -60 mins. A breath decay curve showed decreasing trend with time showing that absorption of ethylbenzene was complete 15 minutes after application. There was initial rapid decay followed by a more gradual decay indicative of a two-compartment model. Estimated contact time during which absorption could occur was 5 min and the percutaneous absorption rate was calculated as 37 µg/cm2/min.

Applicant's summary and conclusion

In an in vivo percutaneous absorption study using hairless mice and a direct method for volatile chemicals, total absorption of ethylbenzene was 3.61% of the achieved dose. A breath decay curve indicated absorption was complete 15 minutes after application. Evaporation rates were used to derive an estimated contact time of 5 min and the percutaneous absorption rate was calculated to be 37 µg/cm2/min.