Predicting toxicity of sediments spiked with silver

Previous experiments conducted with freshwater sediments spiked with silver have shown that, when expressed on a dry weight basis, the toxicity of sil ver is sediment-specific and dependent on the form of silver added (e.g., A gNO3, Ag2S). This study was conducted to assess the usefulness of silver in terstitial water toxic units (IWTU) and acid volatile sulfide (AVS) concent rations in predicting the biological effects of silver species across sedim ents, regardless of the species of silver present. Two saltwater sediments were spiked with a series of concentrations of silver. The amphipod, Ampeli sca abdita, was then exposed to the sediments in ten-day toxicity tests. Am phipod mortality was sediment-specific when expressed on a dry weight basis , but not when based on IWTU or simultaneously extracted metal (SEM)-AVS. S ediments with an excess of AVS relative to SEM had IWTU <0.5, and were gene rally not toxic. Sediments with an excess of SEM relative to AVS had silver IWTU >0.5, but no measurable AVS, and were generally toxic. Sediments with measurable AVS were not toxic. Reanalysis of the previously published data from the freshwater sediments spiked with silver showed mortality to be co rrelated with nominal SEM-AVS and with silver IWTU. Taken together, these r esults support the use of AVS and silver IWTUs in predicting the toxicity o f silver in sediments.