Metais pesados em sedimentos de fundo de igarapés (Manaus-AM)

Abstract

The objective of this study was to know the distribution of heavy metals cadmium, copper, cobalt, chromium, nickel, iron, manganese and zinc in the bottom sediments and the physicochemical composition of the waters of streams in the Amazon region. Samples were collected from the Quarenta and São Raimundo streams, which receive industrial effluents and domestic sewage, both located in the urban area of Manaus, and the Barro Branco stream (natural) located in the Adolfo Ducke Forest Reserve, in the rural area, 26 km from Manaus. For the determination of heavy metals in bottom sediments, sequential extractions were used, giving importance to the mobility of metals, in the different ways in which they may be associated. In the physical and chemical characteristics of the waters, the Barro Branco stream showed low acidity with a pH of 3.5 to 5.5, conductivity of 7.7 to 38.5 µS/cm and low levels of dissolved salts, typical of natural streams of dry land. The waters of the Quarenta and São Raimundo streams showed alterations in all the parameters of coming from domestic sewage and industrial effluents. The geochemistry of metals from the natural stream (Barro Branco) showed a different behavior from the streams that have been suffering impacts (São Raimundo and Quarenta). Chromium, iron and manganese predominated in more than 60% in the residual form in the bottom sediments of the igarapés. Zinc and copper are more than 70% available in the bottom sediments of the Quarenta and São Raimundo streams. The high concentrations of copper make it possible to identify it as the main pollutant in the Quarenta stream. The sediments of this stream, when compared to those of the other streams, showed an enrichment of the metals copper, chromium, nickel and zinc, which was attributed to leaching of solid waste enriched with metals from industrial activities and industrial effluent inputs.