Predicting the toxicity of metals-contaminated field sediments using interstitial water metal and acid volatile sulfide normalizations

Several studies have investigated the utility of interstitial metals concentrations and simultaneously extracted metals/acid volatile sulfide ratios (SEM/AVS) in explaining the bioavailability of sediment-associated metals to benthic organisms in the laboratory and field. These studies have used both metal-spiked and field-contaminated freshwater and saltwater sediments, with acute, chronic, and colonization designs. Organism responses were generally predictable given known metals-sediment chemistry interactions. Sediment toxicity was not related to dry weight metals concentrations. Spiked sediments with SEM/AVS ratios { 1 or IWTU > 0.5 were generally toxic. Metals were available in the order of their sulfide solubility product constants. The presence of non-metal contaminants and other metal-binding phases in field sediments can confuse interpretation of organism response. However, SEM/AVS ratios and IWTUs can provide valuable insight into the role of metals in the toxicity of field sediments, relationship between the chemistry of anaerobic sediments and their toxicity to aerobic organisms, and importance of the seasonal cycle of metal sulfides. The difference (SEM-AVS) between the molar concentrations should be used over the previously recommended SEM/AVS ratios; toxicity predictions are identical and insight can be gained into the amount of additionalmore » available sulfide metal-binding capacity, or the extent to which it has been exceeded, and, along with organism response, the potential importance of other metal binding phases.« less