Single and combined effects of sediment-associated PAHs on three species of freshwater macroinvertebrates

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous pollutants of sedime nts. Sediment quality criteria often use toxicity data for individual PAHs. However, PAHs always occur in field sediments as a complex mixture of comp ounds. In this study, the toxicity of phenanthrene (P), fluoranthene (FLA) and benzo(k)fluoranthene (B), alone or in combination, was assessed using m onospecific sediment tests of acute toxicity (between 24 h and 14 days). Th e test sediments were spiked formulated sediments. Toxicity of PAHs was det ermined on a freshwater pelagic organism, Daphnia magna, on an epibenthic o rganism, Hyalella azteca, and on a benthic organism, Chironomus riparius. T he phototoxicity of fluoranthene and phenanthrene was verified. Benzo(k)flu oranthene was not phototoxic and presented no toxicity for the three organi sms tested up to 300 mg/kg, concentration rarely found in the environment. For all PAHs, the toxicity towards Daphnia magna was two-fold higher in the sediment toxicity tests than in the water-only standard tests, probably du e to suspended contaminated particles and contact of daphnids with sediment . For phenanthrene, the LC50s found were 50, 15 and 20 mg/kg dry weight sed iment, respectively for Daphnia magna, Hyalella azteca and Chironomus ripar ius. The bioassays on fluoranthene yielded LC50s of 10, 5 and 15 mg/kg dw r espectively for Daphnia magna, Hyalella azteca and Chironomus riparius. LC5 0s of the PAHs mixture (1/3 of each compound by weight) were around 10 mg/k g dry weight sediment for Hyalella azteca and 20 mg/kg for Chironomus ripar ius. The effects of PAHs in the mixture seemed to be synergistic. This stud y gives new data about PAH toxicity and showed that the additivity of PAH e ffects could be inadequate to assess the environmental risk.