Naphthalene: MAK Value Documentation, addendum - Translation of the German version from 2022

The German Senate Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) has summarized and re-evaluated the data for naphthalene [91-20-3] considering all toxicological end points. Relevant studies were identified from a literature search. The critical effects are the carcinogenic effects in rodents. No data in humans are available for these effects. In carcinogenicity studies, inhalation of naphthalene was found to cause neuroblastomas and adenomas in the noses of rats as well as bronchioloalveolar adenomas and carcinomas in mice. Naphthalene is not mutagenic in vitro, but robust data in vivo are not available. In general, DNA damage is induced in vitro and in vivo mostly at toxic doses. Mechanistic studies suggest that the carcinogenic potential arises from a non-genotoxic mechanism of action. This mechanism is initiated only at high concentrations by severe local inflammation leading to increased cell proliferation. However, a number of uncertainties remain. Thus, at present, a primary genotoxic mechanism of action cannot be ruled out completely for naphthalene. There are no studies from which an effect threshold in humans can be derived. Naphthalene thus remains classified in Carcinogen Category 2. As data for the accessibility of the germ cells are not available, naphthalene remains classified in Germ Cell Mutagen Category 3 B. No sensitizing potential can be derived from the available data. Naphthalene can be absorbed via the skin in toxicologically relevant amounts and remains designated with an "H".