2-Mercaptobenzothiazole: MAK Value Documentation, addendum - Translation of the German version from 2022

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) has summarized and re-evaluated the data for 2-mercaptobenzothiazole [149-30-4] considering all toxicological end points. Relevant studies were identified from a literature search and also unpublished study reports were used. The critical effect in humans and animals is sensitization. Data for chronic inhalation exposure are not available. The most sensitive systemic end point observed in a 13-week gavage study in rats was an increase in relative liver weights. The female rat was found to be the most sensitive species. A LOAEL of 188 mg/kg body weight and day was derived, which corresponds to a concentration in the air of 27.5 mg/m³. No conclusions can be drawn for systemic toxicity from a 2-year gavage study in rats because of the high spontaneous incidence of different pathological effects observed in the control group. As there are no data for inhalation exposure to the poorly soluble substance, a particle effect in the lungs cannot be excluded. Additionally, epidemiological and animal data suggest a carcinogenic potential. As a result, the present maximum concentration at the workplace (MAK value) has been suspended. 2-Mercaptobenzothiazole is not mutagenic in bacteria. Mutagenic and clastogenic effects in mammalian cells are observed only at high, mostly cytotoxic concentrations. In vivo data do not provide evidence of genotoxic effects in soma cells or male germ cells, even at concentrations that cause systemic toxicity. Overall, the data from epidemiological studies are not sufficient to draw definite conclusions about whether 2-mercaptobenzothiazole is a human carcinogen. A carcinogenicity study with gavage administration in rats observed adenomas of the pancreas, preputial glands and pituitary gland as well as fibromas and phaeochromocytomas. However, the increased incidence of tumours is neither clear evidence for nor against a carcinogenic potential because of a number of uncertainties inherent in the study. Thus, 2-mercaptobenzothiazole remains classified in Carcinogen Category 3 for suspected carcinogens. Dermal absorption is not expected to contribute significantly to systemic toxicity. 2-Mercaptobenzothiaziole is a known contact allergen. Therefore, the "Sh" designation has been retained. There are no data for respiratory sensitization.