The German Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) summarized and re-evaluated the data for methyldiethanolamine 105-59-9 to derive an occupational exposure limit value (maximum concentration at the workplace, MAK value) considering all toxicological end points. Relevant studies were identified from a literature search and also unpublished study reports were used. There are no studies investigating the carcinogenic effects of methyldiethanolamine. Methyldiethanolamine is a methylated metabolite of diethanolamine. Diethanolamine increased the incidence of liver and kidney tumours in a dermal carcinogenicity study in mice at the lowest dose tested of 40 mg/kg body weight and day. Mechanistic studies indicate that methyldiethanolamine, like diethanolamine, may disrupt choline homoeostasis, which is thought to have caused the liver tumours. The same mechanism has been suggested for kidney tumours, but has not been experimentally proven. Human relevance for this mechanism cannot be ruled out and methyldiethanolamine, like diethanolamine, has therefore been classified in Carcinogen Category 3. Methyldiethanolamine is neither mutagenic nor clastogenic. For this reason, despite its classification in Carcinogen Category 3, a MAK value can be derived. Studies with repeated inhalation exposure to methyldiethanolamine are not available. In a comparison of structurally related ethanolamines, methyldiethanolamine was found to lie between diethanolamine and triethanolamine in terms of irritation and basicity. Diethanolamine, which is a much stronger irritant than methyldiethanolamine, has a MAK value of 1 mg/m3. On this basis, a MAK value of 2 mg/m3 has been established for methyldiethanolamine. Aerosol impaction is not expected to occur because this concentration is below vapour saturation. The margin between the MAK value of 2 mg/m3 and the concentration at which a carcinogenic effect may occur is sufficiently large. Peak Limitation Category I with an excursion factor of 1 has been derived in analogy to the other ethanolamines. The only available study investigating developmental toxicity of methyldiethanolamine was carried out according to OECD Test Guideline 421. As this study does not include a full investigation of teratogenicity, methyldiethanolamine has been assigned to Pregnancy Risk Group D. Based on studies in rats, percutaneous absorption is expected to contribute significantly to systemic toxicity. Therefore, methyldiethanolamine has been designated with “H”. The limited results from animal studies do not suggest a skin-sensitizing potential. Furthermore, in spite of widespread use, only two cases involving occupational exposure have been reported. Data for respiratory sensitization are not available.
Hartwig et al. (Thu,) studied this question.