PARENT SESSION

PT10 Toxicity of Complex Mixtures
Exhibit Hall
8:00 AM - Tuesday, 11 November 2003

(PT164) Joint Toxicity of Sediment-Bound Cadmium & Phenanthrene in Hyalella azteca.

Gust, K¹, ¹ Dept. of Biological Sciences, Louisiana State University, Baton Rouge, LA, US

ABSTRACT- Mixtures of heavy metals and PAHs are becoming increasingly prevalent in benthic and wetland sediments as a result of urbanization and industrial contamination. The joint toxicity of combined metals and PAHs is poorly understood and may deviate from the summed concentration-responses of the individual pollutants. Hyalella azteca will be exposed to varying concentrations of sediment-amended Cd and phenanthrene to examine joint toxicity through the use of 10 day bioassays following US EPA standard methods. The LC50 for Cd spiked into fine-grain freshwater bayou sediment (TOC = 2.3-3.1%, AVS = 8.5-10.9 mol/g) is 444mg kg^-1 (95% C.I. 384-504mg kg^-1) and the IC50 for growth inhibition is 289 mg kg^-1 (95% C.I. 71-506mg kg^-1). Preliminary results suggest that phenanthrene bound to this sediment may elicit mortality and effect growth rate. The amphipods will be exposed to individual and combined doses of Cd and phenanthrene in a factorial treatment arrangement to produce individual and combined dose response curves (DRCs). The single contaminant DRCs will be used to generate theoretical concentration additive and response additive (independent) DRCs with which the empirically derived combined contaminant DRCs will be compared statistically. This analysis will allow precise determination of concentration additive, independent, synergistic or antagonistic joint toxicity as well as concentration dependent effects. The null hypothesis of this study states: The joint toxicity of sediment bound cadmium and phenanthrene for lethality and growth inhibition in Hyalella is concentration additive. The joint-toxicity of combined pollutants is influenced by the chemistries of the individual chemicals, the relative bioavailability of each in a given environment, uptake and depuration kinetics; and the toxicological modes of action, possible interactions, and detoxification mechanisms employed once accumulated by biota. This complexity may result in deviations from concentration additive joint toxicity (a major assumption of US EPA regulatory policy) and impact the predictive power of conventional risk assessment and sediment quality guidelines for complex mixtures of metals and PAHs.

Key words: PAH, metals, Hyalella azteca, contaminant mixtures