Volume 6, Issue 6 (June 2009)
Chemical Speciation and Heavy Metal Mobility in Contaminated Marine Sediments
Management of sediments from coastal areas, contaminated with heavy metals and organic substances, is a very critical issue. Management decisions are usually based on total pollutant concentrations and various guidelines that are used by different countries. Heavy metals can be mobilized from polluted sediments if they are exposed to changing environmental conditions that occur during excavation, disposal at sea, or disposal in confined facilities. This paper examines the changes in heavy metals partitioning to binding phases in contaminated marine sediments and the release of metals to the environment. Environmental conditions are simulated by submitting sediments to a modified elutriation test with oxygenated and deoxygenated seawater. A sequential extraction procedure is used to determine the binding fractions of heavy metals in the sediments. Fractionation analysis of excavated marine sediments from the port of Piraeus, Greece showed that copper is primarily associated with organic matter, whereas lead and zinc are primarily associated with iron oxides. Under anoxic conditions, the metals bound to the various binding fractions remain practically stable. On the other hand, under oxic conditions, an increase in the concentration of metals associated with carbonates and a decrease in the concentration of metals associated with organic matter and iron oxides were observed. Both under oxic and anoxic conditions, actual metal mobility was very low and less than 0.5 % of total metal mass was found in the dissolved phase.