Trimethylbenzol (alle Isomere)
MAK-Begründung, Nachtrag
Andrea Hartwig1 (Vorsitz der Ständigen Senatskommission zur Prüfung gesundheitsschädlicher Arbeitsstoffe, Deutsche Forschungsgemeinschaft)MAK Commission2
1 Institut für Angewandte Biowissenschaften, Abteilung Lebensmittelchemie und Toxikologie, Karlsruher Institut für Technologie (KIT), Adenauerring 20a, Geb. 50.41, 76131 Karlsruhe, Deutschland
2 Ständige Senatskommission zur Prüfung gesundheitsschädlicher Arbeitsstoffe, Deutsche Forschungsgemeinschaft, Kennedyallee 40, 53175 Bonn, Deutschland
Abstract
The German Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) summarized and re-evaluated the data for trimethylbenzene, all isomers [95-63-8; 108-67-8; 526-73-8; 25551-13-7] to derive an occupational exposure limit value (maximum concentration at the workplace, MAK value) considering all toxicological end points. Relevant studies were identified from a literature search. The critical effect is preclinical neurotoxicity. A NOAEC of 25 ml/m3 was established in rats after inhalation exposure to 1,2,4-trimethylbenzene and 1,2,3-trimethylbenzene based on reduced performance in the rotarod test for motor coordination and prolonged latency times in the hot plate test. A MAK value of 5 ml/m3 was derived for trimethylbenzene on this basis. The assignment to Peak Limitation Category II with an excursion factor of 2 has been retained. The tumour incidence was not increased in male and female Sprague Dawley rats after 2-year gavage administration (4 days/week) of 1,2,4-trimethylbenzene doses of 800 mg/kg body weight per day. Trimethylbenzene was not mutagenic or clastogenic in vitro and did not induce micronuclei in vivo. Data for germ cells are not available. Therefore, trimethylbenzene (all isomers) has not been classified in a category for germ cell mutagens. No teratogenic potential can be inferred from the available studies that investigated developmental toxicity in rats and mice and trimethylbenzene has been assigned to Pregnancy Group D. Additionally, there are no experimental data showing that juvenile animals are more sensitive to trimethylbenzene-induced neurotoxic effects than adults. Therefore, there is no evidence that would require re-categorization of the substance from Pregnancy Group D to Pregnancy Group B (suspected). Skin contact is not expected to contribute significantly to systemic toxicity and there are no indications of sensitizing effects.
