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PT14 Toxicity of Mixtures
(PT226) Sediment May Mediate Synergistic Lethal Toxicity Between Cd and Phenanthrene in Hyalella azteca.
Gust, K1, 1 Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, US
ABSTRACT- Contaminants with dissimilar toxicology and dissimilar chemical properties (i.e. metals and PAHs) are hypothesized to elicit independent joint-toxic effects. We tested this hypothesis by exposing Hyalella azteca to natural sediments spiked with Cd and phenanthrene (Phen) in 10-d bioassays using US EPA standard methods. H. azteca exhibited synergistic lethal toxicity to combined Cd and Phen in sediment exposures. Sublethal concentrations of Phen reduced the 10-d LC50 of Cd in H. azteca by nearly 50% (95% C.I. 37-59%). In contrast, exposure to Cd-Phen mixtures in aqueous solution did not elicit synergistic lethal affects. LC50 values for H. azteca in 24, 48 and 72h aqueous exposures suggested predominantly independent lethal toxicity. Eight-day Cd uptake and elimination rate kinetics were unaffected by the presence of Phen in aqueous exposures. These results suggest the synergistic toxicity found in H. azteca is sediment mediated. Combined Cd and Phen may modify bioavailability and/or alter H. azteca's sediment processing activity enhancing bioaccumulation. Bioassays investigating uptake and elimination kinetics of Cd from sediment exposures are currently being conducted to determine if Phen increases Cd tissue concentrations. Additionally, bioassays investigating the effect of Phen on Cd porewater and overlying water concentrations are being conducted to determine if Phen increases the bioavailability of Cd in sediments. Though the lethal joint toxicity of Cd and Phen in sediment exposures was synergistic, their combined effect on H. azteca growth rate was independent. Benthic invertebrates' association with sediment may influence joint toxicity of Cd and Phen and therefore standard aqueous tests including WET tests and single compound bioassays may miss potentially hazardous mixture effects found in sediment environments. These results suggest Cd and Phen mixtures may cause synergistic or independent toxicity in H. azteca depending on the endpoints investigated and the experimental protocols employed. Therefore, risk assessment protocols for environments containing metal-PAH mixtures must include methods to detect interactive effects between contaminants to optimize environmental protection.
Key words: PAHs, Hyalella azteca, Metals, Sediment Toxicity
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