Photolysis, oxidation and subsequent toxicity of a mixture of polycyclic aromatic hydrocarbons in natural waters

Photodegradation of a mixture of three polycyclic aromatic hydrocarbons fluorene (FLU), dibenzofuran (DBF), and dibenzothiophene (DBT) using UV and UV/H2O2 processes was studied. Treating a mixture of the PAHs stimulated a more realistic contamination composition present in polluted water. Effects of pH, PAH concentration, and water matrix composition on removal rates and efficiencies of these compounds are discussed. Batch experiments were conducted using both monochromatic low pressure (LP, 253.7 nm) and polychromatic medium pressure (MP, 200–400 nm) UV sources, in a quasi-collimated beam setup. A synergistic effect was observed during direct photolysis and LP-UV/H2O2 of the mixture as compared to photodegradation as a single component in an aqueous solution. Similar results were obtained for FLU using MP-UV/H2O2 whereas, degradation of DBF and DBT was inhibited in a mixture. Natural water enhanced the direct photolysis compared to laboratory buffered water, whereas, degradation of the PAHs in the natural water was inhibited using the UV/H2O2 process. Toxicity testing using a luminescent inhibition bioassay was correlated to intermediates generated during UV-based oxidation reactions.