RESUMO
A compost sample from a solid waste treatment plant of a Brasilian city, Araraquara, SP, was submitted to a sequential extraction procedure to evaluate the contamination and to asses the bioavailability of some heavy metals. The metal concentrations obtained by acid digestion (HNO3/HF/HCIO4) in the compost were (in mug.g-1): Cd=2.8; Cu=295; Pb=244 and Zn=1,481. The fraction of available metals, as extracted by magnesium chloride, was approximately 1 per cent for each of the metals Cu, Pb and Zn, and 16 per cent for Cd. The remaining amounts were sequentially leached off with increasingly stronger extractans, namely, sodium acetate, hydroxylamine hydrocloride and hydrogen peroxide. The bulk amounts found by this sequence were: Cd=46 per cent; Cu=74 per cent; Pb=21 per cent and Zn=79 per cent. Finally, the residual matrix was digested by a HF/HCIO4 treatment.