Distribution and speciation of heavy metals in surficial sediments from the Tees Estuary, north-east England

Surface sediments from the Tees Estuary were analysed for grain size, organic carbon content and metal concentrations. Metal speciation was determined by sequential extraction. The sediments are largely organic-rich clayey-silts in which metal concentrations exceed background levels, and which attain peak values in the upper and middle reaches of the estuary. Cu, Pb and Zn concentrations appear to have declined since the 1970s. Cr, Pb and Zn are associated with the reducible, residual, and oxidizable fractions. Cd is similar, with the exchangeable fraction also significant. Cu is associated with the oxidizable and residual fractions, and Co and Ni, which are not highly enriched, are hosted mainly by the residual phase. Potential exists for the mobilization of Cr, Pb and Zn during diagenesis, as iron and manganese oxides are reduced, and for Cu, Cr and Zn mobilization as organic matter is mineralized within the sediment