Effects of Acid Volatile Sulfides (AVS) from Na2S-Amended Sediment on Hyalella azteca

Abstract

Ratios of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) have been used extensively for predicting bioavailability of divalent metals (i.e., Cd, Cu, Pb, Ni, Zn) in sediments of aquatic environments. However, the role of sulfides (as AVS) as a toxicant has been largely ignored. The aim of this research was to measure relationships of AVS (as sodium sulfide [Na2S]-amended sediment) and toxicity to a sensitive benthic amphipod Hyalella azteca to evaluate the exposure-response relationships among a series of sulfide exposures. The specific objectives were to (1) measure SEM/AVS ratios in a series of sodium sulfide (Na2S·9H2O)-amended sediments producing a range of sulfide concentrations and (2) measure responses of H. azteca (as mortality) in 96-h static sediment toxicity tests to exposures of Na2S-amended sediments. Amended sediments had a predictable increase in AVS concentrations and a concomitant decrease in ∑SEM/AVS ratios. Increasing concentrations of AVS resulted in a range of ∑SEM/AVS ratios that varied over more than an order of magnitude from 0.185 to 0.006. H. azteca survival decreased with increasing concentrations of “excess” AVS, with 96-h no observable effect concentration (NOEC) and LC50 of 0.041 and 0.019 ∑SEM/AVS, respectively. Clearly, the SEM/AVS model provides a useful tool for evaluating potential bioavailability of divalent metals and predicting ecological risk; however, this study demonstrates the need to consider sulfide (as AVS) as a potential source of toxicity in situations with low [<<1] ∑SEM/AVS ratios.