Potential for photoenhanced toxicity of spilled oil in Prince William Sound and Gulf of Alaska waters

Photoenhanced toxicity is the increase in the toxicity of a chemical in the presence of ultraviolet light (UV) compared to a standard laboratory test conducted with fluorescent lighting (minimal UV). Oil products, weathered o il, and specific polycyclic aromatic compounds present in oil are 2 to grea ter than 1000 times more toxic in the presence of UV. The photoenhanced tox icity of oil to fish and aquatic invertebrates appears to occur through a p rocess of photosensitization, rather than photomodification of the aqueous phase oil. In photosensitization, the bioaccumulated chemical transfers lig ht energy to other molecules causing toxicity through tissue damage rather than a narcosis mechanism. The available evidence indicates that phototoxic components of oil are specific 3-5 ring polycyclic aromatic hydrocarbons ( PAHs) and heterocycles. Determinants of photoenhanced toxicity include the extent of oil bioaccumulation in aquatic organisms and the spectra and inte nsity of UV exposure. No studies have specifically investigated the photoen hanced toxicity of spilled oil in Alaska waters. Although there are substan tial uncertainties, the results of this evaluation indicate there is potent ial for photoenhanced toxicity of spilled oil in Prince William Sound and t he Gulf of Alaska. The potential hazard of photoenhanced toxicity may be gr eatest for embryo and larval stages of aquatic organisms that are relativel y translucent to UV and inhabit the photic zone of the water column and int ertidal areas. Photoenhanced toxicity should be considered in oil spill res ponse because the spatial and temporal extent of injury to aquatic organism s may be underestimated if based on standard laboratory bioassays and exist ing toxicity databases. Additionally, the choice of counter measures and oi l removal operations may influence the degree of photoenhanced toxicity. (C ) 2001 Elsevier Science Ltd. All rights reserved.