Photoinduced toxicity of PAHs and alkylated PAHs to a marine infaunal amphipod

The marine infaunal amphipod Rhepoxynius abronius was exposed in standard 10-day toxicity tests to sediments contaminated with parent or alkylated PAHs. After exposures, mortalities (LC50 values) and the ability to rebury in control sediment (EC50 values) were determined. Survivors of these initial toxicity tests were then exposed to UV radiation in an environmental growth chamber for 1 h. The differences between EC50 values before and after UV exposure were used to assess the phototoxicity of the bioaccumulated contaminants. Contaminants with HOMO-LUMO gap energies between 7.2 and 7.7 eV produced up to an order-of-magnitude increase in toxicity with UV exposure. The strength of phototoxic responses within this HOMO-LUMO gap range varied with contaminants such that compounds with the lowest water solubilities appeared to be relatively less phototoxic. This suggests that these compounds were not taken up in sufficient quantities to produce a strong phototoxic response and points out the need to measure tissue residues in phototoxicity experiments. In general, these results support the HOMO-LUMO gap model of photoinduced toxicity.