The conventional Tessier and BCR sequential extraction methods were applied to metal partitioning in sewage sludge samples collected from a waste water treatment plant. The results obtained by sequential extraction methods for Cu, Cr, Ni, Pb and Zn were compared with those estimated from single extractions using identical operating conditions applied in each individual Tessier and BCR fraction. The metal content in the extracts was measured by flame atomic absorption spectrometry. In all fractions of the BCR method, and in the three first fractions of the Tessier method, the results obtained from single extractions were in good agreement with those obtained using the sequential procedures. The oxidizable fraction of the Tessier method should be leached from the solid residue of the reducible extraction, since a very low extraction efficiency was obtained for this fraction when it was directly extracted. The total extractable metal contents obtained by both single and sequential extractions were similar for all metals in the BCR method and for Cr, Ni and Pb in the Tessier method. The recoveries obtained ranged from 93.52 to 105.8% in the two studied samples. For Cu and Zn the overall extraction efficiency of the proposed method was slightly lower than that obtained with the sequential procedure (recoveries around 90%). The precision of the proposed Tessier and BCR single extraction methods (expressed as RSD) was lower than 8% for all metals.

Two sequential extraction schemes were employed for speciation of Cu, Cr, Pb, Ni and Zn in sewage sludges: the conventional Tessier scheme and the sequential extraction scheme proposed by the European Communities Bureau of Reference (BCR). Both sequential extraction schemes were compared in terms of operation time, matrix effects and extraction efficiency. Two sludge samples collected from an urban wastewater processing plant at different seasons were analysed by FAAS for total contents and for extractable metals present in each fraction. Partitioning patterns were obtained for each metal so that metal mobility could be predicted. Both sequential extraction schemes yielded similar performance when extraction efficiencies were compared but matrix effects caused by concomitants were less pronounced in the BCR scheme in comparison with the Tessier scheme.