Monomethylhydrazine: MAK Value Documentation, addendum - Translation of the German version from 2021

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) has re-evaluated the occupational exposure limit value (maximum concentration at the workplace, MAK value) of monomethylhydrazine [60-34-4] considering all toxicological end points. Relevant studies were identified from a literature search. The acute toxicity of monomethylhydrazine is caused by depletion of gamma-aminobutyric acid leading to the effects on the central nervous system. Chronic and subchronic exposure induces haemolytic effects and adverse effects on the liver. In carcinogenicity studies, inhaled monomethylhydrazine caused tumours of the lungs, liver, blood vessels and olfactory epithelium in female mice and tumours of the nose and adrenal glands in male hamsters. Orally applied, it induced tumours of the lungs and liver in mice and tumours of the colon and small intestine in hamsters. Monomethylhydrazine therefore remains classified in Carcinogen Category 2 and no MAK value can be derived. Monomethylhydrazine is genotoxic in vitro and in vivo and demonstrates a mutagenic potential in vitro. The substance forms methyl DNA adducts in vivo. On the basis of these effects and its structural similarity to 1,1-dimethylhydrazine and 1,2-dimethylhydrazine, which are genotoxic in germ cells, monomethylhydrazine has been classified in Germ Cell Mutagenicity Category 3 B. Monomethylhydrazine is irritating to the skin of dogs, guinea pigs and rabbits and to the eyes of rabbits. Although no valid studies considering dermal absorption are available, the "H" designation (for substances which can be taken up via the skin in toxicologically relevant amounts) has been retained because of the low dermal LD₅₀ values in animals. Although no studies considering its sensitizing potential are available, the "Sh" designation (for substances which cause sensitization of the skin) has been retained because of its structural similarity to the known contact allergen hydrazine.