Linkage between speciation of Cd in mangrove sediment and its bioaccumulation in total soft tissue of oyster from the west coast of India

• Bioaccumulation of Cd does not depend on total Cd loading in bottom sediment
• Consumption of edible oyster may become a major source for Cd
• Water soluble, exchangeable, carbonate/bicarbonate forms of Cd are bioavailable.
• Fe/Mn oxyhydroxide phase may control Cd bioavailability in sediment.
• Bioaccumulation of Cd in oyster depends on Cd-speciation in the system.

This study established a mechanistic linkage between Cd speciation and bioavailability in mangrove system from the west coast of India. High bioaccumulation of Cd was found in the oyster (Crassostrea sp.) even at low Cd loading in the bottom sediment. Bioaccumulation of Cd in the oyster gradually increased with the increasing concentrations of water soluble, exchangeable and carbonate/bicarbonate forms of Cd in the sediments. Fe/Mn oxyhydroxide phase was found to control Cd bioavailability in the sediment system. Cd-associated with sedimentary organic matter was bioavailable and organic ligands in the sediments were poor chelating agents for Cd. This study suggests that bioaccumulation of Cd in oyster (Crassostrea sp.) depends not on the total Cd concentration but on the speciation of Cd in the system.

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