HEAVY METALS (Hg, Cu, Mn, Cr e Ni) CONTENTS IN THE RIO DAS PEDRAS LAGOON, MOJI-GUAÇU RIVER BASIN (SÃO PAULO STATE, BRAZIL)

Abstract

The presence of heavy metals in a sediment profile from the Rio das Pedras lagoon, located at the Moji-Guaçu river floodplain, São Paulo, was investigated. Samples were stratified at each 1 cm, sieved in 63 m m and digested in a strong acid solution (HNO3 + HF + HClO4) in PTFE bomb. The extracts were analyzed by emission plasma spectrometry (ICP-AES) for Al, Cu, Mn, Cr and Ni contents. For Hg, the direct pyrolysis of samples and atomic fluorescence spectrometry detector AFS were employed. By using Al as a normalizer agent, an enrichment of metals concentration, with exception for Mn was observed. Average concentration for Cu (0.12 mg g-1) and Mn (1.12 mg g-1) were considered high in comparison to those concentrations in an unpolluted environment. Probably, these data are related to the agricultural activity (sugarcane plantation) around the lagoon, or to the Moji-Guaçu river transport in the flood season. Hg, Cr and Ni concentrations were similar the those verified in unpolluted areas. The chronology inventigation, determined by the 210Pb technique, indicated that the 25 cm long sediment profile shows a 135 years of deposition history of the suspended material in this lagoon.