Metal readsorption and redistribution during the analytical fractionation of trace elements in oxic estuarine sediments

The present study considers a trace metal sequential extraction scheme based on the classical Tessier procedure in order to determine whether readsorption and redistribution processes occur during the metal extraction from oxic sediments of the Odiel Marshes Natural Park (Southwest Spain). The metals studied included As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. The trace metal standard addition approach was used to assess these phenomena, it being concluded that both readsorption and redistribution occur and their extent depends on the characteristics of the sediment. This may lead to serious misinterpretation of extraction data because the metal concentration determined in the extract may not be representative of the metal levels in the sediment fractions. Readsorption was mainly observed for Cu, Hg and As, when both 1 M MgCl2 and 1 M NaOAc (HOAc, pH 5) were used as extractants. This artefact was not observed when either 0.4 M NH2OH.HCl (25% (v/v) HOAc) or H2O2 were used to extract Cd, Cr, Cu, Ni, Pb and Zn from sediments with a organic matter content lower than 7%. (C) 1999 Elsevier Science B.V. All rights reserved.