Abstract-The acute toxicity of metal-polynuclear aromatic hydrocarbon (PAH) mixtures (i.e., Cd, Hg, Pb, fluoranthene, and phenanthrene) associated with sediments was assessed in two benthic copepods. Schizopera knabeni was exposed to sediment amended with single contaminants and mixtures. Adult S. knabeni were highly tolerant of single-contaminant exposures to phenanthrene, Cd, Hg, and Pb as well as a mixture of Cd, Hg, and Pb. Binary experiments revealed that although phenanthrene was synergistic with Cd and Hg, the phenanthrene-Cd synergism was much stronger (2.8 times more lethal than predicted). When a mixture of Cd, Hg, and Pb was combined with phenanthrene, a synergistic response was observed, eliciting 1.5 times greater lethality than predicted. A Cd-phenanthrene synergism in S. knabeni was also observed in aqueous exposures, suggesting that the interaction was related to a pharmacological insult rather than a sediment-related exposure effect. An antagonism between Cd, Hg, and Pb was indicated, and this antagonism may have moderated the Cd-phenanthrene synergism in mixtures containing Cd, Hg, Pb, and phenanthrene. Experiments with Amphiascoides atopus revealed that phenanthrene and fluoranthene were each synergistic with Cd in aqueous exposures. Our studies suggest that interactive toxicity among metal-PAH mixtures may be common among benthic copepods and that strong synergistic effects observed in binary mixtures may be moderated in more diverse contaminant mixtures. However, the strength of the observed synergisms raises concerns that established sediment quality criteria may not be protective for organisms jointly exposed to PAH and metals, especially Cd-PAH mixtures.
The effects of sediments contaminated with sublethal concentrations of phenanthrene (PAH) and metals (Cd, Hg, Pb) were evaluated in relation to their influence on the feeding activity of a harpacticoid copepod, Schizopera knabeni. A metal mixture (at the ratio of 5Pb:3Cd:2Hg) and Cd alone reduced grazing rates of S. knabeni feeding on (14)C-labeled microalgae. Cadmium alone and Cd combined with phenanthrene significantly decreased grazing rates of S. knabeni at Cd concentrations above 49 mg kg(-1) dry sediment. No grazing was observed in 98, 106, or 157 mg kg(-1) dry sediment Cd alone or in sediment contaminated with phenanthrene (98 mg kg(-1) dry sediment) combined with Cd at these concentrations. Phenanthrene alone also caused a significant decrease (55%) in S. knabeni grazing rates. Feeding ceased above 344 mg kg(-1) dry sediment of the metal mixture alone and combined with phenanthrene. Results were consistent with an independent effect on feeding when Cd and phenanthrene were combined. When other metals were added (Pb and Hg) to the mixture, results were consistent with an additive influence on feeding rate. Because the underlying mechanisms of toxicity for metals and PAH are probably different, our observations suggest that reductions in grazing probably did not directly contribute to the lethal effects of phenanthrene or metals. The absence of interactive effects on feeding suggests that metal-PAH interactive effects on lethality have a different underlying mechanism and that reductions in grazing probably did not directly contribute to the lethality effects of phenanthrene or metals in S. knabeni.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.