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Reference
Endpoint:
specific investigations: other studies
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1st February 2006 - 10th February 2006
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: OECD TG 428:Skin Absorption: In Vitro Method.
Qualifier:
according to guideline
Guideline:
other: OECD .Guideline Dokument No. 28: The Conduct of Skin Absorption Studies.
Qualifier:
according to guideline
Guideline:
other: European Commission Guidance Document on Dermal Absoprtion. Sanco/222/2000 rev. 7
Version / remarks:
19 March 2004
GLP compliance:
yes
Type of method:
in vitro
Endpoint addressed:
dermal absorption
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No. of test material: A H Marks & Co Ltd; SEL/ 1895
- Expiration date of the lot/batch: 13th January 2008

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: ambient temperature in the dark; for radioactive labeled substance in glass bottle < -15 °C

RADIOLABELLING INFORMATION
- Radiochemical purity: This material was shown to have a radiochemical purity of greater than 99.2 % by TLC and 98% by HPLC (certificate of analysis SEL/ 1895)
- Specific activity: 1849.3 MBq /mmol (5.63 MBq /mg)
- Locations of the label: 14C


Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Each dose preparation was analysed by LSC to determine homogeneity and the specific activity of the test material dosed ([14C]-radiolabelled test material plus unlabelled test material).
Dose / conc.:
806 other: g/kg
Remarks:
concentrate formulation (= 500 MCPP-P-2-EHE g/L)
Dose / conc.:
5.04 other: g/kg
Remarks:
aqueous spray strength solution (= 3.13 g MCPP-P 2-EHE /L)
Details on study design:
- Human skin samples obtained at surgery or post mortem
- Exposed membrane area: 2.54 cm2
- discs of approximately 3.3 cm diameter of prepared skin membrane were mounted, dermal side down, in diffusion cells held together and placed in a water bath maintained at 32 ± 1°C
- Membrane integrity determined by measurement of electrical resistance across the skin membrane
- receptor chambers of cells were filled with receptor fluid (50% ethanol in water) and placed in a water bath maintained at normal skin temperature of 32 ± 1ºC to ensure that the test substance can freely partition into the receptor fluid from the skin membrane and never reaches a concentration that would limit its diffusion
- Preparation of formulations: unlabeled MCPP-P 2-EHE was mixed with an appropriate volume of 14C-radiolabelled MCPP-P 2-EHE in ethanol; ethanol was removed and the blank materials anionic surfactant, non-ionic surfactant and aliphatic solvent were added; preparation was mixed until homogenous
- Application rate: 10 µL/cm2 (total applied: 25.4 µL) for 24 h, cells were unoccluded (donor chambers were covered with filters containing activated carbon, to capture any volatile materials)
- samples of receptor fluid were taken and analyzed by liquid scintillation counter (after 1, 2, 3, 4, 6, 8, 10, 16, 20 and 24 hours)
Details on results:
For the concentrate:
- Recovery of radiolabelled test material was 103%
- 100% of applied dose was removed by skin washing 24 h after application
- Proportion of applied dose present in receptor fluid following 24 h exposure was 0.56%
- A total of 0.53% of applied dose remained in membrane, while 0.17% of this was present in the stratum corneum
- MCPP-P acid absorption rate was 1.21 μg/cm2/h between 1-24 hour

For 1 /160 v/v aqueous dilution:
- Recovery of radiolabelled test material was 97.1% of the applied dose
- 93.1% of applied dose was removed by skin washing 24 h after application
- Proportion of applied dose present in receptor fluid following 24 h exposure was 1.30%
- Total of 0.95% of applied dose remained in epidermal membrane, while 0.44% of this was present in the outer layers
- Rate of MCPP-P acid absorption was 0.02 μg/cm2/h

Summary of absorption and penetration of the test formulation

 Time/Compartment  Concentrate formulation  1/160 v/v spray strength dilution
 6 hours  5.84 µg/cm2 (0.12%)  0.05 µg/cm2 (0.16%)
 8 hours  8.25 µg/cm2 (0.17%)  1.08 µg/cm2 (0.26%)
 10 hours  10.8 µg/cm2 (0.22%) 0.12 µg/cm2 (0.36%) 
 24 hours  27.8 µg/cm2 (0.56%)  0.42 µg/cm2 (1.30%)
 Membrane residue at 24 hours (after tape stripping)  18.1 µg/cm2 (0.36%)  0.16 µg/cm2 (0.50%)
 Amount in stratum corneum (removed by tape strips)  8.45 µg/cm2 (0.17%)  0.14 µg/cm2 (0.44%)

Since it is possible that penetrated MCPP-P 2-EHE may exist in the receptor fluid as both the ester and MCPP-P acid, the results of the study have been expressed in terms of MCPP-P acid.

Conclusions:
In vitro, a very slow absorption rate for MCPP-P-2 EHE was measured after 24 h exposure to human skin preparations.
Executive summary:

The in vitro absorption of MCPP-P 2-EHE through human epidermis was determined according to OECD TG 428. The concentrate formulation (500 g/L) and the 1/600 v/v aqueous spray strength dilution containing 3.13 g/L of the formulation in water were applied. The spray dilution used represented a typical in-use application rate equivalent to 2.5 liter 500 g/L concentrate in 400 L of water. The absorption process was followed using [14C]-labelled MCPP-P 2-EHE, which was added prior to application. Doses were applied at a rate of 10 µL/cm2 and the cells were unoccluded for an exposure period of 24 hours. The receptor fluid was sampled at frequent time intervals and the test material remaining in the upper layers of the skin was quantified by tape stripping.Since it is possible that penetrated MCPP-P 2-EHE may exist in the receptor fluid as both the ester and MCPP-P acid, the results of the study have been expressed in terms of MCPP-P acid.

MCPP-P acid absorption rate was 1.21 μg/cm2/h for the concentrate and 0.02 μg/cm2/h for the dilution. The results obtained in this study indicate that MCPP-P acid is absorbed through human epidermis, from the concentrate formulation and its 1 /160 v/v aqueous dilution, at a very slow rate.

Description of key information

In vitro, a very slow absorption rate for MCPP-P-2 EHE was measured after 24 h exposure to human skin preparations.

Additional information

The in vitro absorption of MCPP-P 2-EHE through human epidermis was determined according to OECD TG 428. The concentrate formulation (500 g/L) and the 1/600 v/v aqueous spray strength dilution containing 3.13 g/L of the formulation in water were applied. The spray dilution used represented a typical in-use application rate equivalent to 2.5 liter 500 g/L concentrate in 400 L of water. The absorption process was followed using [14C]-labelled MCPP-P 2-EHE, which was added prior to application. Doses were applied at a rate of 10 µL/cm2 and the cells were unoccluded for an exposure period of 24 hours. The receptor fluid was sampled at frequent time intervals and the test material remaining in the upper layers of the skin was quantified by tape stripping. Since it is possible that penetrated MCPP-P 2-EHE may exist in the receptor fluid as both the ester and MCPP-P acid, the results of the study have been expressed in terms of MCPP-P acid.

MCPP-P acid absorption rate was 1.21μg/cm2/h for the concentrate and 0.02μg/cm2/h for the dilution. The results obtained in this study indicate that MCPP-P acid is absorbed through human epidermis, from the concentrate formulation and its 1 /160 v/v aqueous dilution, at a very slow rate.