Influence of contact time and sediment composition on the bioavailability of Cd in sediments

Stable isotope 111Cd was spiked into sediments of different organic content levels for 3 days to 2 months. Bioavailability of spiked Cd to deposit-feeders, assessed by in vitro Cd solubilization, generally decreased with contact time but became comparable with that of background Cd after 2 months. This could be explained by the gradual transfer of Cd from the more mobile geochemical phase (carbonate associated phase) to more refractory phases (Fe–Mn oxide associated phase, and organic associated phase) within 2 months. The sedimentary organic content had a weak effect on Cd solubilization, while the distribution of Cd in carbonate or Fe–Mn oxide associated phase could have a larger influence on the solubilization of sedimentary Cd and its change with contact time. The observations in this study emphasize the need to consider Cd sequestration over time in sediments of various compositions, which would be useful in risk assessment of contaminated sediments.

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► Cd may reach equilibrium in sediments after 2 months of aging.
► Sediment composition could affect change of Cd bioavailability with contact time.
► Sedimentary organic content has a weak effect on Cd bioavailability.
► Cd associated with carbonates is more bioavailable than Cd with Fe/Mn oxides.
► Change in Cd solid speciation explains decrease of Cd bioavailability over time.