The German Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) summarised and re-evaluated the data for the biological tolerance value (BAT value) for xylene 1330-20-7 after the occu- pational exposure limit value (maximum concentration at the workplace, MAK value) for this substance had been lowered from 100 to 50 ml/m3 taking into account the increased respiratory volume in the workplace. Since the last evaluation, new publications have been identified from a literature search and relevant studies are described in detail. For the derivation of the BAT value, both occupational field studies and experimental studies showed a good correlation between the xylene concentration in the air and the methylhippuric acid concentration in the urine. Considering the available studies and an increased respiratory volume for experimental studies without physical excercise, an average of 1800 mg methylhippuric acid/g creatinine can be expected after eight-hour exposure to xylene (all isomers) at the level of the MAK value and was therefore estab- lished as the BAT value. Sampling should take place at the end of exposure or the end of a shift. In 2021, the MAK value for xylene was re-evaluated with regard to develop- mental toxicity. No comprehensive studies on developmental neurotoxicity were avail- able, therefore, the assignment of xylene to Pregnancy Risk Group D was confirmed. As the BAT value was derived in correlation to the MAK value, Pregnancy Risk Group D applies to the BAT value as well.
Jäger et al. (2025) studied this question.