Sediment Nickel Bioavailability and Toxicity to Estuarine Crustaceans of Contrasting Bioturbative Behaviors – An Evaluation of the SEM-AVS Paradigm

Robust sediment quality criteria require chemistry and toxicity data predictive of concentrations where population/community response should occur under known geochemical conditions. Understanding kinetic and geochemical effects on toxicant bioavailability is key, and these are influenced by infaunal sediment bioturbation. This study used fine-scale sediment and porewater measurement of contrasting infaunal effects on carbon-normalized SEM-AVS to evaluate safe or potentially toxic nickel concentrations in a high-binding Spartina saltmarsh sediment (4%TOC; 35–45 μmol-S2–·g–1). Two crustaceans producing sharply contrasting bioturbation -- the copepod Amphiascus tenuiremis and amphipod Leptocheirus plumulosus -- were cultured in oxic to anoxic sediments with SEM[Ni]-AVS, TOC, porewater [Ni], and porewater DOC measured weekly. From 180 to 750 μg-Ni·g–1 sediment, amphipod bioturbation reduced [AVS] and enhanced porewater [Ni]. Significant amphipod uptake, mortality, and growth-depression occurred at the higher sediment [Ni] even when [SEM-AVS]/f oc suggested acceptable risk. Less bioturbative copepods produced higher AVS and porewater DOC but exhibited net population growth despite porewater [Ni] 1.3–1.7× their aqueous [Ni] LOEC. Copepod aqueous tests with/without dissolved organic matter showed significant aqueous DOC protection, which suggests porewater DOC attenuates sediment Ni toxicity. The SEM[Ni]-AVS relationship was predictive of acceptable risk for copepods at the important population-growth level.