Use of sequential extraction procedures for the analysis of cadmium and lead in sediment samples from a constructed wetland

There is a need to establish a reliable and inexpensive sequential extraction technique, suitable for routine analysis and could assess the toxic potential of sediment samples. The method described in this paper was designed for the determination of the mobile and bioavailable proportion of cadmium (Cd) and lead (Pb) in sediments. Three fractions were determined: the exchangeable fraction, the fraction bound to the organic matter and the residual fraction, The exchangeable fraction represents the fraction of adsorbed metals that are easily affected by changes in ionic composition of water; the fraction bound to the organic matter represents the fraction that under oxidising conditions in natural waters may be released as soluble metals. The residual phase represents the remaining metal in the mineral structure of the sediments. For the present study the fractions bound to carbonates, or bound to iron and manganese oxides, were not analysed because the pH values of the sediment samples were shown to be very stable throughout the study period and the samples used were not subjected to anoxic conditions. In this paper the accuracy and usefulness of the three-step extraction method was evaluated using contaminated sediment samples from a constructed wetland
receiving urban runoff.