Studies concerning the contamination and pollution sources of polycyclic aromatic hydrocarbons (PAHs) in the Yodo River System, Japan, are summarized in this review. Mutagenicity and genotoxicity have been frequently detected in the tributary rivers of Yodo River, and novel contaminants such as phenylbenzotriazole type mutagens, nitrated PAHs, and heterocyclic amines have been suggested to be the causative agents. The contribution of nonsubstituted PAHs to the toxicity is considered to be low since only few ng/l of phenanthrene, fluoranthene, and pyrene have been found in the river waters. The application of an aryl hydrocarbon receptor (AhR) dependent bioassay in evaluating the combined toxicity caused by various pollutants in environmental samples is also introduced. Point and non-point sources of pollution discharging into the Lake Biwa-Yodo River System, including treated sewage effluents and deposited road particles, have been investigated using the AhR-dependent reporter gene assay. The results suggested the presence of newly identified AhR ligands such as anthraquinone dyes or unidentified AhR ligands in the treated sewage effluents and the road particles, respectively. Finally, toxic effects of PAHs that are mediated via AhR binding are also summarized.

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