Photoactivation and toxicity of mixtures of polycyclic aromatic hydrocarbon compounds in marine sediment

Abstract The direct toxicity and photoinduced toxicity of sediment-associated acenaphthene, phenanthrene, fuoranthene, and pyrene were determined for the marine amphipod Rhepoxynius abronius. The four polycyclic aromatic hydrocarbons (PAHs) were spiked into sediment in a concentration series of either single compounds or as approximately equitoxic mixtures of all four compounds. Standard 10-d sediment toxicity tests were conducted under fluorescent lighting. After 10 d, survivors were exposed for 1 h to ultraviolet (UV) radiation in the absence of sediment and then tested for their ability to bury in uncontaminated sediment. The 10-d median lethal concentrations (LC50s) were 2.31 mg acenaphthene/g organic 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 sum of toxic units (ΣTU) of the four PAHs in the approximately equitoxic mixtures. The ΣTU LC50 was then calculated for the mixture treatments. If the toxicologic interaction of a mixture of contaminants is additive, ΣTU LC50 =1.0. The observed LC50 (1.55 ΣTU) was slightly, but significantly, greater than unity, indicating that the 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. Effects of UV radiation on the toxicity of the mixture of four PAHs could be explained by the photoactivation of fluoranthene and pyrene alone. These results are consistent with predictions based on photophysical properties of PAH compounds.