Análise de metais biodisponíveis em sedimentos na bacia hidrográfica do Rio Tega - RS

Abstract

Human activities may cause significant impacts on water resources, especially due to the release of domestic and industrial effluents. Sediments are the main compartment for accumulating pollutants, particularly metals such as lead (Pb), cadmium (Cd), chromium (Cr), zinc (Zn) and copper (Cu). Environmental persistence, toxicity and the ability to bioaccumulate and biomagnify at food chains of these pollutants play an important role in environmental diagnostics and water resource management systems. This study aimed to evaluate the behavior of a water body through the analysis of bioavailable metals in sediments and in the water column of 5 sampling points of the Rio Tega watershed (RS), in order to contribute to the development of environmental diagnosis studies and the consolidation of academic knowledge in Brazil. Five sampling campaigns involving in situ and laboratorial analyzes of water quality were carried out using Standard Methods. The metal compounds in sediments were analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES) and in water samples by atomic absorption. The results showed higher concentrations for the sediment samples compared to the surface water samples, especially for Cu, Ni, Zn and Cr, which also showed concentrations above the Probable Effects Level – PEL, recommended in the Sediment Quality Guidelines. The highest concentrations of metals in sediment were observed at sampling points 1 and 2, located in the urban area, which also presented the worst index for water quality. At the sampling point 3, the mean concentrations of metals in sediment were the lowest, although this point drains the industrial zone of the city, which do not present good quality. At sampling point 4, located in a dam, it is also evident the accumulation of metallic species. The sampling point 5, located in the place where the watershed drains out, indicates its contribution to the Rio das Antas, from which it is tributary. Since Caxias do Sul city is the second metal mechanic pole in Brazil, with the development of galvanic activities, it is evident the contribution of this kind of industries to the increase of metal concentration in the water body. The results indicate the importance for monitoring sediment quality and promote efficient control of local sources of pollution. However, further development of new strategies and tools for environmental management related to water resources is still necessary.