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Dermal absorption

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dermal absorption in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: comparable to guideline study with acceptable restrictions

Data source

Reference Type:
A Comparative Study of the Rates of in Vitro Percutaneous Absorption of Eight Chemicals Using Rat and Human Skin.
Barber ED, Teetsel NM, Kolberg KF and Guest D
Bibliographic source:
Fundamental and Applied Toxicology 19: 493-497

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 428 (Skin Absorption: In Vitro Method)
not specified
GLP compliance:
not specified

Test material

Constituent 1
Chemical structure
Reference substance name:
Bis(2-ethylhexyl) phthalate
EC Number:
EC Name:
Bis(2-ethylhexyl) phthalate
Cas Number:
Molecular formula:
1,2-bis(2-ethylhexyl) benzene-1,2-dicarboxylate
Details on test material:
-Purity >97%
-Specific activity: 500µCi/g
-Source: Sigma Chemical Co

Test animals

other: stratum corneum of human skin (autopsy sample) or full thickness rat F-344 skin
not specified

Administration / exposure

Type of coverage:
unchanged (no vehicle)
Duration of exposure:
32 hours
0.3ml undiluted 14C-DEHP applied to 1.02-0.636 (288-576mg/cm²)
Details on in vitro test system (if applicable):
- Source of skin: stratum corneum human skin (autopsy sample) or full thickness rat F-344 skin

- Diffusion cell: Franz-type diffusion cell
- Receptor fluid: based on Dulbecco's phosphate buffer (pH 7.1) isotonic saline
- Test temperature: 30 or 37°C

Experimental design.
Each study consisted of a 3-phase experiment as follows.
In Phase I a determination of the permeability to 3H2O was made for each skin specimen. The permeability to 14C test chemical was determined in Phase 2 and then, in Phase 3, the permeability to 3H20 was determined a second time.
For most of the compounds, duplicate studies were performed.

Skin samples from multiple human donors or rats were used. Each sample of human stratum corneum or full thickness rat skin was placed, with the external surface uppermost, over the opening of the receptor chamber of a diffusion cell (1.02 or 0.636 cm2 contact area). An O-ring was used to make a seal between the skin preparation and the donor cham ber and the apparat us was clamped in place to secure the tissue.

On each day, the receptor chambers were filled with "receptor solution" which consisted of Dulbecco's phosphate-buffered (pH 7.1) isotonic saline containing penicillin, 100 Units/ml, streptomycin 100 µg/ml. amphotericin B (as Fungizone) 0.25 µg/ml. Volpo-20, 60 mg/ml, was included in the receptor fluid for the studies on DEHP, 2-EH, EEP. and EP.

Duplicate background (0 hr) samples were taken from the receptor chamber of each cell and then 300 µl of 3H20 or 14C-test chemical was applied in the donor chamber. The diffusion cells were incubated at a constant temperature of 37 or 30°C for 8 hr (the studies on DEHP and 2-EH were 32 hr). In all cases the rat and human data were generated at the same temperature. Duplicate samples were taken hourly and assayed for radioactivity by liquid scintillation spectrometry. The receptor chambers were refilled after each sampling with fresh receptor fluid to maintain constant volume.
After Phases I and 2, the donor and receptor chambers were rinsed with saline or 50% ethanol:water, depending on the solubility of the test substance. The donor chambers were then filled with saline and the receptor chamber was filled with receptor solution. The cells were allowed to stir overnight, alter which they were emptied, rinsed, and refilled with the appropriate solution for the vent day experiment.

The rate of increase in the concentration of radioactivity n the receptor chamber of each tell was used to calculate a permeability constant (cm/hr) and an absorption rate (mg/cm2/hr) for each test chemical or 3H2O.
Each of the chemicals in these studies was tested as an undiluted liquid except for urea which was tested as a dilute (53 µg/ml) aqueous solution. The duration of exposure in Phase 2 of each study was 8 hr except for the studios with DEHP and 2-EH in which permeation was measured for 32 hr.

Results and discussion

Signs and symptoms of toxicity:
not examined
Dermal irritation:
not examined

Any other information on results incl. tables

The permeability constants for 3H2O in human stratum corneum varied from 0.74 to 2.96 x10e-3 cm/hr with an overall mean and standard deviation (10 studies) of 1.56 ± 0.83 x10e-3 cm/hr. The corresponding values for full thickness rat skin varied from 1.09 to 5.13 x10-3 cm/hr with an overall mean and standard deviation (12 studies) of 2.97 ± 1.26 x 10e-3 cm/hr. Thus, the ratio of the rates (rat/human) for absorption of 3H20 was 1.90.

The ratio of the permeability constants (rat/human) is presented and it can be seen that the ratio is greater than 1.0 in each case, indicating that these compounds penetrate full thickness rat skin more rapidly than they penetrate human stratum corneum.

The range of permeability constants for bath species vary over approximately four orders of magnitude with 3H2O as the most rapid penetrant and DEHP as the slowest.

EEA, DEHP, and EEP gave slight to moderate damage for rat skin but showed no such effect for human stratum corneum. EP and 2-EH showed more pronounced damage for rat skin; however, human stratum corneum also seemed refractory to these chemicals.

Absorption rate data of DEHP Human * Rat **
Permeability constant (Kp: 10-5cm/hr) 0,0105 0,0431
Percutaneous permeability rate (J:µg/cm²/hr) 0,1 0,42
* Stratum corneum
**Full thickness skin

Applicant's summary and conclusion

Executive summary:

Absorption, permeability constant and percutaneous absorption rate of (14C) DEHP was determined in the stratum corneum of human skin (autopsy sample) and full thickness rat skin Fischer-334 with a Franz-types diffusion cell.

0.3 ml (14C)-labeled undiluted DEHP was applied to 1.02 or 0.636 cm2of skin (288-576 mg/cm2). The receptor solution was based on Dulbecco’s phosphate-buffered (pH 7.1) isotonic saline. Diffusion cells were maintained at 37 or 30ºC.

The percutaneous permeability rates were 0.1 µg/cm²/h and 0.42µg/cm²/h and the permeability constant (Kp) were 0.0105 and 0.0431 10e-5 cm/hr in human strateum corneum and rat skin, respectively.