Registration Dossier

Administrative data

Key value for chemical safety assessment

Additional information

The Ames Test and V79/HPRT assay with 1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione was negative. The Ames test and CA assay with methyl-2-mercaptobenzimidazole, zinc salt - as a surrogate for methyl-2 -mercaptobenzimidazole

(1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione) was also negative.

Justification for selection of genetic toxicity endpoint
The results of the Ames tests, the chromosome aberration test and the HPRT test were considered

Short description of key information:
1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione was investigated in the Salmonella/microsome test (Ames test). Result: negative, no evidence of mutagenic activity of 1,3-Dihydro-4(or5)-methyl-2H-benzimidazole-2-thione was seen (with and without mutagenic activation). In a scond Ames test methyl-2-mercaptobenzimidazole, zinc salt was investigated in the Salmonella/microsome test with and without metabolic activation. This test was also negative
In an chromosome aberration test duplicate cultures of human lymphocytes were exposed to methyl-2-mercaptobenzimidazole, zinc salt at concentrations of 0, 31.25, 62.5, 125, 250, 375, and 500 µg/ml for 4 hours (with and without metabolic activation) and then examined for chromosomal aberrations. The test material was non-clastogenic to human lymphocytes in vitro in this assay.
An additional study according OECD 476 was performed to investigate the potential of 1,3-Dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione to induce gene mutations at the HPRT locus in V79 cells of the Chinese hamster. The assay was performed in two independent experiments. The cells were exposed to the test item for 4 hours in the first and second experiment with and without metabolic activation. Under the experimental conditions reported the test item did not induce gene mutations at the HPRT locus in V79 cells. Therefore, 1,3-Dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione was negative in this HPRT assay.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Reliable in-vitro assays were negative. Therefore, a classification is not justified.