Dimethyl sulfoxide (DMSO) [MAK Value Documentation, 2016]

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 dimethyl sulfoxide [67‐68‐5] of 50 ml/m3, considering the endpoints local and systemic toxicity as well as developmental toxicity. In a 13‐week inhalation study the olfactory and respiratory epithelia and the pharynx of rats are the target tissues, and a reduction of body weight gain, possibly secondary to the irritation, is seen. The NOAEC for these effects is 964 mg/m3 (297 ml/m3, vapour). 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, a MAK value of 50 ml/m3 can be calculated from this study, taking into account that a lower NOAEC has to be expected with chronic exposure. Therefore, the previous MAK value is confirmed. As local effects are critical, the assignment to Peak Limitation Category I and the excursion factor of 2 are confirmed. In a screening study with rats according to OECD test guideline 421, the borderline increase in incidences of pups with dilated renal pelvis seen in a developmental toxicity study, are not confirmed. However, in rabbits, dimethyl sulfoxide causes kidney malformations with a NOAEL of 300 mg/kg body weight. Therefore, damage to the embryo or foetus cannot be excluded even when the MAK value is observed and dimethyl sulfoxide is assigned to Pregnancy Risk Group B