Comparison of dynamic mobilization of Co, Cd and Pb in sediments using DGT and metal mobility assessed by sequential extraction

Management of metal-contaminated sediments requires an accurate knowledge of metal distribution and metal exchanges between the solid and solution phase. The DGT technique (diffusive gradients in thin films) provides information about the characteristics of metal release from the particles to the porewaters. However, the species of metals that participate in the exchange are not well documented. The aim of this paper was to explore the DGT response of Co, Cd and Pb, to a range of reservoir sediments exhibiting gradients of physico-chemical parameters. We also characterized the chemical partitioning of the three metals by sequential extraction to determine the nature of the sediment-bound metals species that could participate to the metal resupply to the porewaters. Results from DGT experiments and sequential extraction show that specific geochemical phases are key factors for the mobilization of individual metals towards DGT: dissolved organic matter and manganese oxides for Co, acid-volatile sulfides for Cd and particulate organic matter for Pb. Moreover, the masses of metals trapped in DGT are mainly correlated with the concentrations of metals that are easily exchangeable, specifically sorbed or weakly bound to labile organic matter.