Testing readsorption of trace elements during partial chemical extractions of bottom sediments

The importance of postextraction readsorption of As, Cd, Cu, Ni, Pb, and Zn has been evaluated for each step of a sequential extraction procedure by measuring the recovery of small amounts of trace elements added during the extraction of oxic lake sediments. For all the cases examined but one, the trace element spikes (<100% of the amount present in control samples) were recovered within the limits given by the experimental errors. These results contrast with the large percentages of postextraction readsorption observed for these trace elements in previous studies, a consequence of the use by previous investigators of either large spikes (greatly exceeding the amounts present in the control samples) during extractions of natural sediments or simple model sediments.