Modification of metal partitioning by supplementing acid volatile sulfide in freshwater sediments

Acid volatile sulfide (AVS) is a component of sediments that complexes some cationic metals and thereby influences the toxicity of these metals to benthic organisms. Experimental manipulation of AVS in metal-contaminated sediments may provide a means to neutralize toxicity due to metals and thereby help assess the cause of sediment toxicity. This study evaluated the effect of spiking FeS, Na₂S, and Na₂S/FeSO₄ combined on the concentration of AVS, simultaneously extracted metals (SEM), and pore-water metals in uncontaminated and metal-enriched sediments. Experiments with solid FeS showed comparatively low effectiveness in increasing AVS. Spiking with either Na₂S or Na₂S/FeSO₄ combined increased AVS and/or reduced SEM metal in Cd-, Zn-, and Ni-spiked sediments and in a Cu-contaminated sediment collected from the field. Spiking with Na₂S/FeSO₄ caused marked reductions in dissolved metal concentrations in the pore waters of these sediments; spiking with Na₂S alone caused an apparent elevation in pore-water (Cu) metal that we believe is an artifact of metal sulfide formation in the filtered pore water. When the Na₂S/FeSO₄ treatment was evaluated under conditions simulating those in sediment toxicity tests, alterations of AVS/SEM were nearly quantitative, except for Ni-spiked sediment, which showed lower efficiency than the Cd, Zn, or Cu sediments. It appears that AVS spiking holds promise for the experimental manipulation of metal toxicity in sediments.