Bioavailability and chronic toxicity of cadmium in sediment to the estuarine amphipod Leptocheirus plumulosus

Numerous studies have demonstrated the efficacy of interstitial water metal concentrations and simultaneously extracted metals/acid-volatile sulfide (SEM/AVS) ratios in explaining the acute toxicity of sediment-associated metals to benthic organisms. However, no full life-cycle chronic marine or estuarine tests have been conducted for this purpose. In this study, cohorts of newborn amphipods, Leptocheirus plumulosus, were exposed to cadmium-spiked estuarine sediment for 28 d to determine effects on mortality, growth, and reproduction relative to interstitial water and SEM/AVS normalization. Seven treatments of cadmium were tested: 0 (control), 0.34, 0.74, 1.31, 1.55, 2.23, and 4.82 M SEM(Cd)/AVS ratios (measured concentrations). Interstitial water cadmium (IWCd) and sediment concentrations of SEM(Cd) and AVS were monitored periodically and by depth during the exposure. When sediment SEM(Cd)/AVS ratios were less than or equal to 1.55, mean IWCd concentrations were less than the 96-h water-only cadmium LC50 for juvenile and subadult L. plumulosus, and mortality, growth, and reproduction were not affected. When SEM(Cd)/AVS ratios were greater than or equal to 2.23, IWCd concentrations were more than 100 times greater than the 96-h water-only cadmium LC50, and all amphipods died. These results are consistent with predictions of metal bioavailability from acute tests with metal-spiked sediments, i.e., that sediments with SEM(Cd)/AVS ratios <1 are not toxic, while sediments with SEM(Cd)/AVS ratios >1 may be toxic.