CADMIUM DISTRIBUTION BY URBAN SEDIMENTS ON IMPERMEABLE AREAS OF PORTO ALEGRE (BRAZIL)

Abstract

Urban environments may be considered as sources of pollution and, consequently, important agents in degradation of bodies of water due to the input of a large quantity of substances, which are transported from the drainage basin through surface run-off. Heavy metals, as cadmium (Cd), are subproducts of industrial activities; however, in recent years, studies have shown that even in residential areas results have indicated high concentrations of this element. This study measured the Cd concentrations in 20 composed samples of urban sediments samples collected from an urban basin of 5 km² with three kinds of soil occupation (residential, commercial and industrial) located in the city of Porto Alegre – RS. Concentrations of metal were determined by acid digestion (EPA 3050) in 209, 150, 63 e 45 μm grain size fractions followed by atomic emission spectrophotometry with inductively coupled plasma. Mean values of 0.5 (± 0.5); 0.62 (± 0.75); 0.87 (± 1.17); 1.12 (± 1.5) e 1.69 (± 2.37) μg.g-1 were obtained for 209, 150, 90, 63 and 45 μm grain size fraction, respectively. Cd concentrations were interpolated (Inverse Distance Weight) and represented geographically using Idrisi© Andes software. The results of the interpolations have permitted to observe high concentrations in the commercial and residential areas, characterized by high fluxes of vehicles most part of the day, so considered a potential source of cadmium. This study is important because it allows the establishment of control objectives within sustainable management of water resources, concerning future cenarios of local water resources.

Key words: Cadmium, diffuse pollution, GIS, urban sediment.