MAK Value Documentation for Methyl acetate
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 acetate of 100 ml/m3 considering the critical endpoint respiratory tract irritation. A 28‐day study with rats shows a NOAEC for degeneration and necrosis of the olfactory epithelium of 350 ml/m3. A chronic NAEC of 125 to 167 ml/m3 can be extrapolated. Since 2014, the Commission uses an empirical approach to set MAK values for substances with critical effects on the upper respiratory tract or the eyes. According to this approach, the NAEC would correspond to a concentration of 63 to 84 ml/m3 for work place air. However, acetic acid resulting from the local enzymatic cleavage of methyl acetate by carboxylesterases is responsible for the effects to the olfactory epithelium, and not the substance itself. Thus, the activity of rat and human carboxylesterases is decisive in the respiratory tract irritation of methyl acetate. Based on a comparative analysis on vinyl acetate, in which rat olfactory enzyme activity was shown to be almost equivalent to that in humans, the same is assumed for methyl acetate and the interspecies extrapolation step is deemed unnecessary. The MAK value is retained at 100 ml/m3. As local effects are critical, the assignment to Peak Limitation Category I and the excursion factor of 4 are also retained.