Acetic anhydride

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated the maximum concentration at the workplace (MAK value) and the Pregnancy Risk Group of acetic anhydride [108‐24‐7]. Furthermore genotoxicity and skin absorption have been evaluated. Critical effects are irritation of mucous membranes in humans and inflammation reactions as well as hyper‐ and metaplasia in the upper respiration tract with a NOAEC of 1 ml/m3 in a 13‐week‐inhalation study with rats. Since 2014 the Commission uses an empirical approach to set MAK values for such substances. According to this, the MAK value for acetic anhydride has been lowered to 0.1 ml/m3. As local effects are critical, the assignment to Peak Limitation Category I is confirmed. As the LOAEC is fivefold as high as the NOAEC in the 13‐week‐inhalation study with rats, the true NAEC might be higher and the excursion factor of 2 is set. Taking into consideration the low systemic bioavailability and the data for the metabolite acetic acid, damage to the embryo and foetus is unlikely when the MAK value for acetic anhydride is not exceeded. Therefore, acetic anhydride is classified in Pregnancy Risk Group C. Absorption of acetic anhydride via the skin is unlikely, due to the rapid hydrolysis to acetic acid in aqueous solution. In addition, the irritation of undiluted acetic anhydride precludes a skin contact over a longer period. The substance is not genotoxic.