Critical evaluation and application of sequential extraction for sediment analysis

M.Sc.Sediment analysis, especially for trace metals, is important since aquatic sediments act as sinks for metals in the environment. Total element analysis yields insufficient information on the bioavailability and the geochemical fate of these metals. Sequential extraction procedures were developed to determine the partitioning of metals in sediment phases. The need for comparability of data produced world-wide led to the development of a sequential extraction procedure, which was proposed by the Community Bureau of Reference as a standard procedure (refered to as the BCR protocol). We contributed to the validation of the BCR procedure by using well-defined in-house model sediments. The results obtained for the model sediments showed that the BCR procedure could distinguish effectively between anthropogenically introduced metals and metals that form part of the mineral structure of the sediment components. The BCR procedure was applied to the sediments of the Vaal Dam and its contributing rivers. The amount of metals extracted in the first three steps of the sequential extraction procedure were low, indicating a very small contribution of anthropogenically introduced metals. It was therefore concluded that these sediments were relatively unpolluted compared to water systems in, for example, Europe