Partitioning of Metals Between Dissolved and Particulate Phases in the Salt Marshes of Essex and North Norfolk (UK)

Abstract

Partitioning of metals between dissolved and particulate sedimentary phases provides useful information which can be used to assess their mobility and sources. Bioavailability and toxicity has also been found in many cases to be related to metal partitioning. Sediment cores were taken from salt marsh areas in the Thames Estuary and along the Essex and North Norfolk coasts, and porewaters were separated by centrifugation and filtration. Concentrations of Cd, Cu, Fe, Mn, Ni and Pb in the porewaters, and in HCl/HNO3 digests of the total sediment, were determined by AAS. The order of metal mobility showed inter-site differences, indicating that the partitioning characteristics were influenced by physico-chemical and hydrodynamic controls. These inter-site differences were reflected in the partitioning distribution of Mn and the sediment redox potentials. Cadmium showed the strongest tendency to partition towards dissolved phases, and porewater concentrations decreased in the Essex salt marshes with increasing distance from the Thames. Lead was found to partition primarily towards sedimentary phases, indicating minimal mobility. The dissolved concentrations of Pb and Cu are not thought to represent an immediate threat to the salt marsh biota.