Toxicity and phototoxicity of mixtures of highly lipophilic PAH compounds in marine sediment: Can the Sigma PAH model be extrapolated?

The additivity of toxic units was tested using sediments contaminated with mixtures of highly Lipophilic (log K-OW > 4.5) parent and alkylated PAHs. T he direct toxicity and photoinduced toxicity of these mixtures were examine d in standard 10-day sediment toxicity tests using the infaunal amphipod Rh epoxinius abronius, with mortality and the survivors' ability to rebury as endpoints. Survivors of the initial 10-day tests were then exposed for 1 h to ultraviolet (UV) radiation and the results compared to initial (10-day) endpoints. Tissue residues and lipids were measured and biota-sediment accu mulation factor (BSAF) values determined. The results indicated that the bi oaccumulated contaminants were not initially toxic, however, they were high ly phototoxic. Although the summed toxic units of these contaminants appear ed to be nonadditive, additivity was not disproved as inaccuracies in extra polating the K-OW-LC50 QSAR or insufficient exposure duration might also ha ve accounted for the observed results. Critical body residue (CBR) estimate s for R. abronius were similar while BSAF values were much larger(10X) in c omparison to other studies, which used amphipods and PAHs. The phototoxicit y of mixtures of contaminants were similar to the phototoxicity of single c ontaminants when expressed on a molar basis, which suggests that phototoxic ities may be roughly additive.