2-ethylhexyl nitrate

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vivo

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

not indicated

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Unknown GLP status. 8-fold excess of application rate: may limit absorption percent due to saturation but enables to maximize absorption rate, furthermore this excess may be balanced by the tendency to volatilize. No analysis of amounts in stratum corneum, skin, blood, organs, carcass: this was however taken into account to revise the original conclusions on dermal absorption percent and rate.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 427 (Skin Absorption: In Vivo Method)

Version / remarks:

not referenced in publication

Deviations:

yes

Remarks:

excessive amount applied (79 µL/cm2 vs 10 µL/cm2 recommended); no analysis of stratum corneum, skin, blood, organs, carcass.

GLP compliance:

not specified

Test material

Radiolabelling:

yes

Remarks:

14C

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Kingston, NY, USA
- Age at study initiation: Adult (9-1 1 weeks)
- Weight at study initiation: approximate weight range of 125-150g
- Housing: suspended, stainless-steel mesh cages prior to study
- Glass metabolic cages: immediately after dosing
- Diet: certified rodent diet (Agway Prolab RMH 3000 or 3200) ad libitum except for 4h immediately after dosing
- Water: domestic tap water ad libitum
- Acclimation period: at least 5 days (incl. 1 day in actual study room)

ENVIRONMENTAL CONDITIONS,
IN-LIFE DATES:
All other details not indicated

Administration / exposure

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Duration of exposure:

6h

Doses:

- Nominal doses: 1 g/kg bw
- No other details given

No. of animals per group:

four rats (for ADME studies)

Control animals:

no

Details on study design:

DOSE PREPARATION, VEHICLE: applied as such undiluted

APPLICATION OF DOSE:
The dose was applied inside Pyrex glass containment cells (area 2.27 cm2) adhered to the clipped backs of the rats with cyanoacrylate. The cell was covered to prevent evaporation.

TEST SITE
- Preparation of test site: 24h before the dermal administration, hair was clipped from 25cm2 of dorsal skin
- Area of exposure: 2.27 cm2 (area of Pyrex glass cell)
- Covering amount (calculated by RSS/CSR author) = 1000 mg/kg dose x 0.150 kg mean weight / 2.27 cm2 / [0.8344 mg/µL density] = 79 µL/cm2
- Type of cover / wrap if used: see above
- Time intervals for shavings or clippings: once before application

SITE PROTECTION / USE OF RESTRAINERS FOR PREVENTING INGESTION: yes: (describe)/no

REMOVAL OF TEST SUBSTANCE
- Removal of protecting device: after 6 h, the Pyrex cells were opened
- Washing procedures and type of cleansing agent: the dose remaining was recovered by aspiration, exposure site was washed repeatedly with a soap solution and dried
- Time after start of exposure: 6h

SAMPLE COLLECTION/preparation/storage
- Collection of urine: Urine was collected at up to 96h from each rat into frozen containers
- Collection of feces: at up to 96h from each rat into frozen containers and homogenized with water. Portions were combusted prior to assay for radioactivity.
- Collection of expired air: drawn through silica gel to adsorb volatile organic materials (removed with methanol extraction), followed by 2.5 M sodium hydroxide to collect expired CO2.
- Collection also of aspirated solution and washings (non-absorbed dose)
- Terminal procedure: 96h sacrifice
- Analysis of blood/organs/carcass: no
- Collection time-points: 0-8h, 8-24h, 24-48h, 48-96h

ANALYSIS
- Method type(s) for identification: liquid scintillation spectrometry for urine, feces, methanol and sodium hydroxide solutions (expired air)

- no other details indicated

Results and discussion

Signs and symptoms of toxicity:

not examined

Remarks:

mention that "Single dermal exposures to 2-EH cause only slight dermal irritation and no evidence of toxicity"

Dermal irritation:

not examined

Remarks:

idem above

Absorption in different matrices:

See table

Total recovery:

See table

Percutaneous absorption

Dose:

1 g/kg

Parameter:

percentage

Absorption:

>= 5.7 - <= 14.6 %

Remarks on result:

other: 96h

Remarks:

revised by RSS/CSR author

Conversion factor human vs. animal skin:

see Endpoint summary under 7.1.2

Any other information on results incl. tables

Cumulated recovery data (% applied dose) after application of 1 g/kg [14C] 2-EH in female rats for 6h

Sample	Total at 96h
Urine	3.32
Feces	0.57
Expired air: silica gel trap	1.41
Expired air: NaOH trap	0.43
Total absorbed*	5.73
Dose on exposed site at 6h	34.99
Exposed site wash at 6h	38.95
Dose on cell cover at 6h	11.43
Total non-absorbed*	85.37
Cage wash	0.87
Total recovered*,**	91.97
Min and max dermal absorption***	5.7 to 14.6

*: lowest limit, due to non-sampled skin/organs/blood/carcass (absorbed) and stratum corneum (non-absorbed)

**: total of all lines above (absorbed, non-absorbed, cage wash=unknown)

***: min: total absorbed; max: 100 - total non absorbed

Applicant's summary and conclusion

Executive summary:

Based on a study in female rats treated dermally at 1 g/kg with adequate occlusion and limitation of evaporation, 2EH was characterized by:

- a dermal absorption of 5.7 to 14.6% of the applied dose; however this may be underestimated due to 8-fold higher applied amount vs. guideline recommendation;

- an indicative dermal absorption rate (assuming a constant rate over exposure period) of 0.63 to 1.61 mg/cm2/h.

Ranges depend whether non-recovered radioactivity and cage wash were considered as absorbed or not.