Mercaptoacetic acid

Skin irritation / corrosion

Administrative data

Endpoint:

skin corrosion: in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2002

Report date:

2002

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: Directive 2000/33/EC, B.27

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Mercaptoacetic acid

EC Number:

200-677-4

EC Name:

Mercaptoacetic acid

Cas Number:

68-11-1

Molecular formula:

C2H4O2S

IUPAC Name:

2-sulfanylacetic acid

Details on test material:

Test substance : thioglycolic acid
CAS no.: 68-11-1
Source: Bruno Bock Chemische Fabrik GmbH & Co KG
Batch: 1673
Purity: 99.0%
Description: clear colourless liquid

In vitro test system

Test system:

human skin model

Remarks:

EpiDerm Skin Model Kit Supplier: MatTek Corporation, Ashland, MA, USA. Batch 4006, Kit F, stored at approx. 4°C in the dark.

Source species:

human

Vehicle:

unchanged (no vehicle)

Details on test system:

The study was performed to assess the corrosivity potential of the test material using the EpiDerm Skin Model (MatTek, Ashland, MA, USA). The test is based on the assumption that corrosivity potential is related to toxicity to the EpiDerm tissue. The study was validated by the inclusion of a positive control material, 8.0 N Potassium Hydroxide and a negative control material, sterile distilled water. The study design complies with the requirements of method 27 ATP 2000/33/EC. The experimental design of the study consists of a test for Direct Reduction of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) by the test material, followed by the main study. For the main study, duplicate EpiDerm tissues were treated with 50 µl of test material and exposed for 3 minutes and 60 minutes. The tissues were incubated at 37°C in a humidified atmosphere of 5% C02 in air for the appropriate exposure times. Negative control-treated tissues (50 µl sterile, distilled water), and positive control-treated tissues (8.0 N Potassium Hydroxide), were also exposed for 3 minutes and 60 minutes. Duplicate EpiDerm tissues were used for the above. At the end of the exposure period each EpiDerm tissue was rinsed using Dulbecco's phosphate buffered saline (DPBS) and placed into a `holding plate', until all of the tissues had been treated and rinsed. They were then transferred to an MTT `loading plate', and incubated at 37°C for 3 hours in a humidified atmosphere of 5% CO2 in air. At the end of this time, each EpiDerm tissue was blotted dry and placed into an MTT `extraction plate' in order to extract all of the reduced MTT from the tissues. At the end of the extraction period, the extracted MTT solution was mixed for each EpiDerm tissue and 3 x 200 µl samples for each tissue were transferred to the appropriate wells of a 96 well plate. The absorbency at 540nm (OD540) of each well was measured with the Anthos 2001 microplate reader. Data are presented in the form of % viability (MTT conversion relative to negative controls) for each of the two exposure times.  The ability of the test material to directly reduce MTT in the direct MTT reduction test proved inconclusive. There was a possibility that if the test material could not be totally rinsed off the EpiDerm tissues, that any residual test material present on the tissue may directly reduce MTT and could have given rise to a false negative result. Therefore a corrective procedure using a "freeze killed" control EpiDerm tissue, also treated with the test material, was necessary to quantify this possibility.

Control samples:

yes, concurrent negative control

yes, concurrent positive control

yes, concurrent MTT non-specific colour control

Amount/concentration applied:

50 µl

Duration of treatment / exposure:

3 and 60 min

Number of replicates:

2

Test system

Amount / concentration applied:

undiluted

Results and discussion

In vitro

Results

Irritation / corrosion parameter:

% tissue viability

Remarks:

Time point: 3 min.

Value:

4.96

Vehicle controls validity:

not examined

Negative controls validity:

valid

Positive controls validity:

valid

Remarks on result:

other: Corrosive

Other effects / acceptance of results:

The relative mean viability was 4.96% after 3 minutes exposure, and 6.60% after 60 minutes exposure. The relative mean viability of the test material-treated tissues was < 10% after 3 minutes exposure. The quality criteria required for acceptance of results in the test were satisfied.

Applicant's summary and conclusion

Interpretation of results:

Category 1A (corrosive) based on GHS criteria

Conclusions:

Thioglycolic acid is considered to be corrosive in vivo.

Executive summary:

The corrosive potential of thioglycolic acid (99% pure) was assessed using a human skin model, the EpiDerm Skin Model (Directive 2000/33/EC, B.27). Duplicate EpiDerm tissues were treated with 50 µl of thioglycolic acid and exposed for 3 minutes and 60 minutes. The tissues were incubated at 37°C in a humidified atmosphere of 5% CO₂ in air for the appropriate exposure times. Toxicity was determined by the conversion of MTT to formazan by viable cells in the test material treated tissues relative to the negative/solvent control-treated tissues.The study was validated by the inclusion of a positive control material, 8.0 N Potassium hydroxide.The relative mean viability was 4.96% after 3 minutes exposure, and 6.60% after 60 minutes exposure. As the relative mean viability of the test material-treated tissues was <10% after 3 minutes exposure, thioglycolic acid is considered to be corrosive in vivo.