Toluene: MAK Value Documentation, addendum - Translation of the German version from 2021

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) has re-evaluated the occupational exposure limit value (maximum concentration at the workplace, MAK value), the Pregnancy Risk Group, sensitization, absorption through the skin and germ cell mutagenicity of toluene [108-88-3]. Relevant studies were identified from a literature search. The critical effects of toluene are neurotoxicity in humans, especially on the central nervous system, behavioural toxicity and ototoxicity as well as effects on colour vision. No indication of chronic effects in the range of 50 ml toluene/m³ were observed in an epidemiological longitudinal study in rotogravure printing, even taking into account individual estimates of lifetime exposure to toluene. Extensive, well-controlled experimental studies demonstrate no short-term toxic effects on behaviour at exposures lower than 50 ml toluene/m³ (in some cases even higher), which would show up as a significant reduction in performance in neuropsychological tests. Therefore, on the basis of numerous human studies, the MAK value of 50 ml/m³ has been confirmed. As the critical effect of toluene is systemic, the classification in Peak Limitation Category II has been retained. Since exposure peaks of 200 ml/m³ and simultaneous physical work had an effect on neurophysiological parameters, but not on the performance tests, the excursion factor is reduced to 2. The most sensitive end point regarding developmental toxicity and developmental neurotoxicity is the decrease in perinatal body weight. The toxicokinetic data for the inhalation of toluene and the resulting blood concentrations do not indicate significant differences between humans and animals. The margin between the LOAEC of 1000 ml/m³ for minor and reversible effects on the body weight of the offspring on the first postnatal day in the rat and the MAK value is sufficient. Toluene therefore remains in Pregnancy Risk Group C despite the relatively narrow, 6-fold, margin between the NOAEC for developmental toxicity and the MAK value of 50 ml/m³. Toluene is not genotoxic in a large number of genotoxicity tests, including dominant lethal tests. Toluene can be absorbed via the skin in toxicologically relevant amounts. The designation with "H" is therefore retained. Data in animals and in vitro show no sensitizing potential of toluene.