Heavy metal distribution in recent sediments of the Tiete-Pinheiros river system in Sao Paulo state, Brazil

The concentrations and possible chemical associations of Al, Fe, Mn. Ca. Cu. Pb, Cd, Zn, Ni and Cr in sediments of the Tiete-Pinheiros river system in Sao Paulo state, Brazil, were studied using a 3-step sequential extraction protocol recommended by the Standards, Measurements and Testing Programme (SM&T, formerly BCR). A single extraction with 0.1 mol l(-1) HCl was applied in parallel to anoxic and air-dried samples. The river system crosses the metropolitan area of Sao Paulo (MASP), which houses a population of nearly 17 million people, and receives a large load of industrial and domestic wastes. Samples were collected from reservoirs in the surroundings of MASP, named Billings, Pirapora and Rasgao, and from the Barra Bonita reservoir, that is located in the Tiete river, 270 km downstream from Sao Paulo city. The distribution of metals indicates the recent pollution characteristics for samples from the Billings. Pirapora and Rasgao reservoirs. In these sediments the metals are associated to a large degree with reactive forms such as sulphides and carbonates, or adsorbed to amorphous oxyhydroxides of Fe and Mn. In samples from Barra Bonita, heavy metals are mainly associated with the residual fraction, suggesting that their concentrations are controlled significantly by transport processes with fine particles as carriers from diffuse pollution sources. (C) 2001 Elsevier Science Ltd. All rights reserved.