Sediment\nBallet:\nUnveiling the Dynamics of Metal Bioavailability\nin Sediments Following Resuspension and Reequilibration

Assessing the risk of metal-contaminated\nsediments under\ndisturbed\nconditions is challenging due to the lack of methods that capture\ninstant changes in metal bioavailability. Existing approaches provide\ninadequate understandings of the processes regulating metal bioavailability\nunder nonequilibrium conditions. Experiments were conducted to improve\nour understanding of the metal bioavailability dynamics induced by\nsediment resuspension and subsequent redeposition (reequilibration).\nAn isotopically modified bioassay, a novel stable isotope tracing\ntechnique, was used to measure metal bioavailability (assimilation\nrates) to clams within short time windows. Changes in metal partitioning\nwere characterized by porewater analysis using in situ extraction\nand the diffusive gradients in thin-films technique. Results showed\nthat sediment resuspension released metals into porewater, while reequilibration\nscavenged metals from the porewater. The assimilation rates of Ni,\nCu, and Pb increased with the resuspension time, aligning with increasing\nporewater concentrations. Unexpectedly, during reequilibration, the\nmetal assimilation rates did not decrease. The discrepancies between\nbioavailability to the clam and porewater extrapolations may be due\nto differing sustained conditions of metals in sediments. Overall,\nthis study unveils the metal bioavailability dynamics in nonequilibrium\nsediments, which could not be accurately predicted relying solely\non porewater analysis. Incorporating rapid bioassays to determine\nbioavailability offers a valuable tool for robust ecological risk\nassessment.