Total metal concentrations and partitioning of Cd, Cr, Cu, Fe, Ni and Zn in sewage sludge

Application of the BCR three-step sequential extraction procedure to sewage sludge samples collected at an urban wastewater treatment plant Domˇzale, Slovenia. is reported. The total concentrations of Cd, Cr, Cu, Fe, Ni and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry FAAS, ETAAS. under optimised measurement conditions. Total acid digestion including hydrofluoric acid HF. treatment and aqua regia extraction were compared in order to estimate the efficiency of aqua regia extraction for determination of total metal concentrations in sewage sludge. It was found experimentally that aqua regia quantitatively leached these heavy metals from the sewage sludge and could therefore be applied in analysis of total heavy metal concentrations. The total concentrations of 856 mg kgy1 Cr, 621 mg kgy1 Ni and 2032 mg kgy1 Zn were higher than those set by Slovenian legislation for sludge to be used in agriculture. Total concentrations of 2.78 mg kgy1 Cd, 433 mg kgy1 Cu and 126 mg kgy1 Pb were below those permitted in the relevant legislation. CRM 146R reference material was used to follow the quality of the analytical process. The results of the BCR three-step sequential extraction procedure indicate high Ni and Zn mobility in the sludge analysed. The other heavy metals were primarily in sparingly soluble fractions and hence poorly mobile. Due to the high total Ni concentration and its high mobility the investigated sewage sludge could not be used in agriculture.