Methanthiol

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated the maximum concentration at the work place (MAK value) of methyl mercaptan [74‐93‐1]. Available publications and unpublished study reports are described in detail. No new data are available that would be relevant for the derivation of a MAK value for methyl mercaptan. Therefore, the MAK value of 0.5 ml/m3 is retained based on slight behavioural changes at 2 ml/m3 in a 90‐day inhalation study in rats. The MAK value of 0.5 ml/m3 for methyl mercaptan is supported by a limited inhalation study with 3 volunteers exposed to ethanethiol, showing irritation and other symptoms after repeated exposure to ethanethiol in a concentration of 3.9 ml/m3, but not after 0.39 ml/m3. The behavioural changes in rats exposed to methyl mercaptan are interpreted as a result of the odour nuisance or the local irritation. Therefore, methyl mercaptan is classified in Peak Limitation Category I with an excursion factor of 1 as no studies in humans are available. In a screening study for repeated exposure and reproductive toxicity with sodium methanethiolate no foetotoxic effects were observed up to the highest dose tested of 45 mg/kg body weight, however, the teratogenicity was not examined. Methyl mercaptan remains assigned to Pregnancy Risk Group D. Skin contact is not expected to contribute significantly to systemic toxicity. There are no data on sensitization. Methyl mercaptan and sodium methanethiolate are neither mutagenic nor clastogenic.