PHOTOACTIVATION AND TOXICITY OF MIXTURES OF POLYCYCLIC AROMATIC HYDROCARBON COMPOUNDS IN MARINE SEDIMENT

The direct toxicity and photoinduced toxicity of sediment-associated a cenaphthene, phenanthrene, fluoranthene, and pyrene were determined fo r the marine amphipod Rhepoxynius abronius. The four polycyclic aromat ic hydrocarbons (PAHs) were spiked into sediment in a concentration se ries of either single compounds or as approximately equitoxic mixtures of all four compounds. Standard 10-d sediment toxicity tests were con ducted under fluorescent lighting. After 10 d, survivors were exposed for 1 h to ultraviolet (UV) radiation in the absence of sediment and t hen tested for their ability to bury in uncontaminated sediment. The 1 0-d median lethal concentrations (LC50s) were 2.31 mg acenaphthene/g o rganic carbon (OC), 2.22 mg phenanthrene/g OC, 3.31 mg fluoranthene/g OC, and 2.81 mg pyrene/g OC. These LC50s were used to calculate the su m of toxic units (Sigma TU) of the four PAHs in the approximately equi toxic mixtures. The Sigma TU LC50 was then calculated for the mixture treatments. If the toxicologic interaction of a mixture of contaminant s is additive, Sigma TU LC50 = 1.0. The observed LC50 (1.55 Sigma TU) was slightly, but significantly, greater than unity, indicating that t he interaction of PAHs in the mixture was less than additive. Exposure to UV radiation enhanced the toxic effects of fluoranthene and pyrene , but did not affect the toxicity of acenaphthene and phenanthrene. Ef fects of UV radiation on the toxicity of the mixture of four PAHs coul d be explained by the photoactivation of fluoranthene and pyrene alone . These results are consistent with predictions based on photophysical properties of PAH compounds.