Registration Dossier

Administrative data

Endpoint:
dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant guideline study, acceptable for assessment

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2004
Report Date:
2004

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 428 (Skin Absorption: In Vitro Method)
GLP compliance:
yes (incl. certificate)
Remarks:
Inspectorate for Health Protection and Veterinary Public Health; Food and Consumer Product Safety Authority; 10 December 2003

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
UNLABELED MATERIAL
- Aqueous solution containing ca. 70wt% TBHP
- Technical grade TBHP-70, lot/batch no.: RB TBHP 1993

LABELED MATERIAL
- [14C]TBHP
- Supplier: TNO Prins Maurits Laboratory (the Netherlands)
- Position of radiolabel: the molecule was uniformly labelled
- Lot no: 01BLY121
- Specific activity: 4.25 mCi/mmol
- Molecular weight: 90.5 (at this specific activity)
- Radiochemical purity: >95%
Radiolabelling:
yes
Remarks:
Uniformly labelled TBHP, 4.25 mCi/mmol

Test animals

Species:
other: the rat was used as the donor species
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
Not applicable

Administration / exposure

Type of coverage:
other: semi-occlusive and occlusive
Vehicle:
water
Duration of exposure:
1, 2, 4 or 8 hr
Doses:
Concentrations used (based on 68.5% TBHP):
- nominal: 1%, 10%, 60%
- actual: 0.99%, 10.02%, 59.55%
Volume applied: 6.4 ul
Surface area exposed: 0.64 cm2

Equivalent nominal dose/surface area: 0.1, 1.0, 6.0 mg/cm2
No. of animals per group:
There were 4 replicates per concentration / timepoint
Details on in vitro test system (if applicable):
Rat skin exposed 1%, 10% or 60% aq. TBHP for time periods of 1-8 hr. The donor compartment was covered either with a charcoal filter (to trap TBHP evaporating from the skin surface; non-occlusive conditions) or a glass cover (to mimic occlusive conditions).

Results and discussion

Signs and symptoms of toxicity:
not specified
Remarks:
comment: not applicable, in vitro study
Dermal irritation:
yes
Remarks:
comment: skin damage in vitro at 60%
Absorption in different matrices:
Uptake increased with applied concentration, with maxima as follows:
- non-occluded: up to 12.4% absorbed (4 hr contact, 60% TBHP)
- occluded : up to 49.0% absorbed (8 hr contact, 10% TBHP)
COMMENT: only results for non-occluded exposure (considererd representative of uptake under normal occupational conditions) are reported in detail below.

60% TBHP caused visible damage to the skin membrane, with the surface becoming detatched from the basal layers. The report concluded that 60% TBHP was corrosive to rat skin whereas 10% and 1% were well tolerated.

Comparable uptake with 1% and 10% TBHP.
Total recovery:
Mean total recoveries (in a range 80-88%) were considered valid given the high volatility of the TBHP.
Percutaneous absorptionopen allclose all
Dose:
1%
Parameter:
percentage
Absorption:
2.8 %
Remarks on result:
other: 1 hr
Remarks:
charcoal cover
Dose:
1%
Parameter:
percentage
Absorption:
6 %
Remarks on result:
other: 4 hr
Remarks:
charcoal cover
Dose:
1%
Parameter:
percentage
Absorption:
7.4 %
Remarks on result:
other: 8 hr
Remarks:
charcoal cover
Dose:
10%
Parameter:
percentage
Absorption:
6 %
Remarks on result:
other: 1 hr
Remarks:
charcoal cover
Dose:
10%
Parameter:
percentage
Absorption:
3.8 %
Remarks on result:
other: 4 hr
Remarks:
charcoal cover
Dose:
10%
Parameter:
percentage
Absorption:
2.1 %
Remarks on result:
other: 8 hr
Remarks:
charcoal cover
Dose:
60%
Parameter:
percentage
Absorption:
7.4 %
Remarks on result:
other: 1 hr
Remarks:
charcoal cover
Dose:
60%
Parameter:
percentage
Absorption:
9.4 %
Remarks on result:
other: 2 hr
Remarks:
charcoal cover
Dose:
60%
Parameter:
percentage
Absorption:
12.4 %
Remarks on result:
other: 4 hr
Remarks:
charcoal cover
Conversion factor human vs. animal skin:
Total absorption by non-occluded rat skin of non-corrosive concentrations of TBHP in a range 3.1-3.5% over 8 hr.
EU Risk Assessment Report concludes that 3.5% dermal uptake is appropriate for 1-10% aq. TBHP.

Any other information on results incl. tables

At the higher concentration with charcoal and all concentrations with glass slides, a short lag time of less than 1 hour was seen with maximal penetration between 1 and 3 hours.

Absorption:

The relative amount of TBHP that reached the receptor fluid as well as total penetration (defined as the amount in the receptor fluid, the cell wash and the skin membranes) increased with the applied concentration. Using the charcoal filter, a maximum of approx. 12% of the applied dose reached the receptor fluid (high dose, 4 hr exposure) with a maximum total recovery of approx. 14% of the applied material. Under occlusion (glass cover) the maximum absorption recorded was in a range 30 -48% the applied dose, with a total recovery of 37 -51% .

Recovery:

The mean total recovery using the charcoal filter was 88.3 +/- 3.06%. When using a glass slide to occlude the donor compartment, the mean total recovery was 80.8 +/- 8.6%. Taking into account the high volatility of the test compound, these values were considered valid.

in vitro penetration of TBHP through rat skin using a charcoal cover:

1% TBHP over 8 hr

Applied dose (mg/cm2): 0.1

Penetration into receptor fluid

- % of dose: 2.1

- ug/cm2: 2.06

Flux constant (ug/cm2/hr): 0.788

Kp value x 10^3 (cm/hr): 0.079

Lag time (hr): 0.0

Total absorption (% dose): 3.5

10% TBHP over 8 hr

Applied dose (mg/cm2): 1.0

Penetration into receptor fluid

- % of dose: 2.08

- ug/cm2: 20.49

Flux constant (ug/cm2/hr): 8.215

Kp value x 10^3 (cm/hr): 0.082

Lag time (hr): 0.0

Total absorption (% dose): 3.1

60% TBHP over 4 hr

Applied dose (mg/cm2): 6.0

Penetration into receptor fluid

- % of dose: 11.98

- ug/cm2: 626.74

Flux constant (ug/cm2/hr): 280.84

Kp value x 10^3 (cm/hr): 0.472

Lag time (hr): 0.3

Total absorption (% dose): 14.1

in vitro penetration of TBHP through rat skin using a glass cover:

1% TBHP over 8 hr

Applied dose (mg/cm2): 0.1

Penetration into receptor fluid

- % of dose: 30.37

- ug/cm2: 29.78

Flux constant (ug/cm2/hr): 6.884

Kp value x 10^3 (cm/hr): 0.695

Lag time (hr): 0.8

Total absorption (% dose): 36.9

10% TBHP over 8 hr

Applied dose (mg/cm2): 1.0

Penetration into receptor fluid

- % of dose: 47.91

- ug/cm2: 471.85

Flux constant (ug/cm2/hr): 128.15

Kp value x 10^3 (cm/hr): 1.279

Lag time (hr): 0.5

Total absorption (% dose): 51.2

60% TBHP over 4 hr

Applied dose (mg/cm2): 6.0

Penetration into receptor fluid

- % of dose: 30.23

- ug/cm2: 1628.00

Flux constant (ug/cm2/hr): 800.82

Kp value x 10^3 (cm/hr): 1.345

Lag time (hr): 0.6

Total absorption (% dose): 36.9

COMMENTS:

- results for 8 hr duration considererd representative of full shift exposure to diluted TBHP;

- results for 4 hr duration considererd representative of half-shift exposure to non-diluted TBHP;

Applicant's summary and conclusion

Conclusions:
Dermal absorption of TBHP from products containing <10% TBHP is around 3.5% of the applied dose over 8 hr. Higher exposure concentrations are corrosive to skin.
Executive summary:

The dermal absorption of TBHP (1%, 10%, 60%, with mean nominal applied doses of 0.01, 1 and 6 mg/cm2) by rat skin in vitro was examined in a GLP-compliant guideline study. The absorption cell was covered with a charcoal filter (to trap TBHP evaporating from skin) or a glass cover (to mimic occlusive conditions). Exposure times between 1-8 hr were used to mimic part, half and full-shift exposures. The relative amount of TBHP that reached the receptor fluid as well as total penetration increased with the applied concentration. Mean total recoveries of 81-88% were obtained and considered valid (taking into account the high volatility of the test substance). Skin damage was observed with 60% TBHP (surface of membrane detached from basal layers) whereas 10% and 1% were well tolerated with comparable absorption (around 3.5% of the applied dose) recorded for treatments of 0.1 mg/cm2 (1% TBHP) and 1.0 mg/cm2 (10% TBHP) over 8 hr. It is concluded  that dermal absorption from products containing 10% TBHP or less is around 3.5% of the applied dose over 8 hr; higher doses are corrosive to skin.