The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re-evaluated the developmental toxicity of xylene [1330-20-7]. In 2019, the maximum concentration at the workplace (MAK value) of xylene was lowered to 50 ml/m3 after taking into account the increased respiratory volume at the workplace (see List of MAK and BAT Values, Section I b and I c). The critical effect of xylene is acute neurotoxicity. Due to mixed exposure and the limited validity of epidemiologic studies, no conclusions can be drawn with respect to developmental toxicity in humans. In animal studies, xylene did not demonstrate a teratogenic potential. Significant decreases in foetal body weights were observed in rats in prenatal toxicity studies after inhalation exposure to the o-isomer or the technical mixture at a concentration of 500 ml/m3 and above; the NOAEC was 100 ml/m3. This effect was observed with the m- and p-isomers only at higher concentrations. Maternal toxicity in the form of reduced maternal body weight gains was observed at 1000 ml/m3 and 2000 ml/m3 after exposure to all isomers and the mixture, respectively. The littermates of pregnant rats exposed to p-xylene at concentrations up to 1589 ml/m3 from days 7 to 16 of gestation did not show treatment-related effects on acoustic startle response or figure-8 maze activity. As the o-isomer proved to be more potent in lowering foetal body weights, but was not examined in the aforementioned study, and as comprehensive data are not available for the developmental toxicity of the isomers and the mixture, the classification of xylene in Pregnancy Risk Group D has been retained.
