PREDICTING THE TOXICITY OF METAL-SPIKED LABORATORY SEDIMENTS USING ACID-VOLATILE SULFIDE AND INTERSTITIAL WATER NORMALIZATIONS

Numerous studies have shown that dry weight concentrations of metals i n sediments cannot be used to predict toxicity across sediments. Howev er, several studies using sediments from both freshwater and saltwater have shown that interstitial water concentration or normalizations in volving acid-volatile sulfide (AVS) can be used to predict toxicity in sediments contaminated with cadmium, copper, nickel, lead, or zinc ac ross a wide range of sediment types. Six separate experiments were con ducted in which two or three sediments of varying AVS concentration we re spiked with a series of concentrations of cadmium, copper, lead, ni ckel, or zinc or a mixture of four of these metals. The amphipod Ampel isca abdita was then exposed to the sediments in 10-d toxicity tests. Amphipod mortality was sediment dependent when plotted against dry wei ght metals concentration but was not sediment dependent when plotted a gainst simultaneously extracted metal (SEM)/AVS or interstitial water toxic units (IWTUs). Sediments with SEM/AVS ratios <1.0 were seldom (2 .3%) toxic (i.e., caused >24% mortality), while sediments with SEM/AVS ratios >1.0 were frequently (80%) toxic. Similarly, sediments with <0 .5 IWTU were seldom toxic (3.0%), while sediments with >0.5 IWTU were toxic 94.4% of the time. These results, coupled with results from rela ted studies, demonstrate that an understanding of the fundamental chem ical reactions which control the availability of cadmium, copper, lead , nickel, and zinc in sediments can be used to explain observed biolog ical responses. We believe that using SEM/AVS ratios and IWTUs allows for more accurate predictions of acute mortality, with better causal l inkage to metal concentration, than is possible with sediment evaluati on tools which rely on dry weight metal concentrations.