The kinetics of near ultraviolet light-mediated phototransformation of 2-aminofluorene (2-AF) was studied using high performance liquid chromatography (HPLC) and the Ames/Salmonella mutagenicity bioassay. Employing tester strains TA98, TA1538, and the nitroreductase-deficient TA98NR without the addition of exogenous metabolic enzymes, we were able to detect and discriminate between the UVA exposure-dependent formation of two stable photoproducts, 2-nitrosofluorene (2-NOF) and 2-nitrofluorene (2-NO2F). Mutagenicity of irradiated 2-AF solutions (using dimethyl sulfoxide as a solvent) in the various tester strains indicates the rapid formation of the photo-labile 2-NOF, after which 2-NO2F accounts for the preponderance of mutagenic activity. Continued UVA irradiation (greater than 72 h at 6.8 J/m2/s) of 2-AF results in the formation of greater than 30 photoproducts resolvable on HPLC, several of which, in addition to 2-NOF and 2-NO2F, are mutagenic on Salmonella but are chemically undefined to date. Prolonged irradiation ultimately destroys the photo-induced mutagenicity of 2-AF. However, UVA-induced 2-AF photoproducts are stable for several weeks when stored in sealed vials in the dark. Light potentiated oxidation of aromatic amines constitutes an alternative mechanism for the transformation of aromatic amines into proximate mutagens/carcinogens.
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