| Polycyclic aromatic hydrocarbons (PAH) are a unique class of persistent, bioaccumulative compounds with two or more fused benzene rings and are formed through the incomplete combustion or decomposition of organic materials. When PAHs are exposed to ultraviolet radiation (285-400 nm), many compounds undergo photochemical reactions that increase the toxicity to aquatic organisms. Complex PAH mixtures in emissions from motorized watercraft engines have been shown to be a major source of phototoxic PAH in Sierra Nevada lakes. Environmental data were collected in Lake Tahoe, CA/NV over a three-year period, during low and high watercraft usage, resulting in observed concentrations that ranged from non-detect to 385 ng/L total phototoxic PAH in the water column.; The purpose of this study was to investigate the effects of comparable emissions from two-stroke and four-stroke marine engines and natural sunlight UV on the morbidity, fecundity and mortality of the cladoceran Ceriodaphnia dubia that is considered a sensitive indicator species for zooplankton in aquatic systems. Laboratory bioassays were designed to closely approximate natural systems and were based on the results of environmental sampling.; The major PAHs found in Lake Tahoe waters, as well as a series of marine engine experiments, were the lower molecular weight compounds with higher aqueous solubilities, and the phototoxic PAHs detected most often were: acenaphthylene, anthracene, fluoranthene and pyrene. Mortalities were observed in bioassay treatments containing 900 ng/L total phototoxic PAH with UV exposure, approximately one-half the concentration seen in UV filtered treatments. Behavioral changes were observed at lower concentrations than mortality concentrations, 300 ng/L for two-stroke and 900 ng/L for four-stroke emissions. In all cases, UV exposure resulted in behavioral changes and mortalities at lower concentrations than UV filtered treatments. Concentrations inhibiting fecundity were found at levels as low as 15 ng/L total phototoxic PAH, and the effects were significant at 150 ng/L. Thus, UV exposure and emission sources were significant indicators of daphnid survival and reproductive success. |
