PARENT SESSION
41 - Physiological and Molecular Mechanisms of Toxicity
8:00 AM to 6:30 PM, Tuesday, 14 May 2002
Exhibition Area

(41-20) Mechansims of photoinduced toxicity of PAHs.

Huang, Xiao-Dong^*,1, El-Alawi, Y.¹, Lampi, M¹, Diener, L.¹, Dixon, G¹, Greenberg, B¹, ¹ Department of Biology, University of Waterloo, Waterloo ON Canada, Waterloo, ON

ABSTRACT- Mechanisms of Photoinduced Toxicity of Polycyclic Aromatic Hydrocarbons Huang X.-D., M. Lampi, Y. El-Alawi, L. Diener, D. G. Dixon and B. M. Greenberg Department of Biology, University of Waterloo, Waterloo, ON Canada Polycyclic aromatic hydrocarbons (PAHs) are found in most industrial environments. They are priority contaminants because of their acute toxicity, mutagenicity and carcinogenicity. Sunlight exposure of these compounds increases their toxicity and carcinogenicity. There are two mechanisms involved in photoinduced toxicity of PAHs. They are photosensitization and photomodification (mainly photo-oxidation). Through photosensitization process, PAHs generate reactive oxygen species that are hazardous to living organisms. By photomdification process (photooxidation), PAHs generate photomodified products, usually oxyPAHs. These oxyPAHs have shown to be more toxic and carcinogenic than the parent compounds. In particular, if the oxy PAHs are present in a mixture, the toxicity is greatly enhanced. In the past several years we have investigated presence and toxicity of these oxyPAHs in aquatic environments. We have found that oxyPAHs are widely present in the environment. In many cases, the concentrations of oxyPAHs are comparable with that of intact PAHs. More importantly, we have found that mechanisms of toxicity of these oxyPAHs are different from the parent compounds. They are concentrated in mitochondria or chloroplast and interfere with electron transport reactions in mitochondria or chloroplast. Some of them are enzyme inhibitors, while others intercept electrons from electron transport reactions and pass them on to oxygen generating reactive, toxic oxygen species. These mechanisms of oxyPAH toxicity are particularly damaging to living organisms. Synergetic effects of mixtures of PAHs and oxyPAHs are often observed in toxicity testing. This may partially explain why toxicity and/or risks of PAH mixtures in the environment are often underestimated.

Key words: PAHs, oxyPAHs, toxicity, mechanisms