Estimation of the Natural and Anthropogenic Components of Heavy Metal Fluxes in Fresh Water Sinos River, Rio Grande Do Sul State, South Brazil

Abstract

The Sinos river receives the effluents released by one of the most important industrial centres in South Brazil. To evaluate the environmental impact of heavy metal contamination in the Sinos river is a difficult task, because the river basin is dominated by basaltic rocks that are naturally rich in metals. Therefore, a part of the metal concentrations in the river water originates from a natural source, i.e. rock weathering. The anthropogenic sources of heavy metals are also widespread along the river. The analysis of the heavy metal concentrations in the Sinos river water was not enough either to identify spatial gradients along the river, or to quantify the anthropogenic metal inputs partially responsible for these concentrations. To estimate the anthropogenic inputs, this study proposes an approach based on mass balance of heavy metal fluxes, including the estimate of the natural component using a natural tracer (Fe). The approach estimated the metal loads released by the anthropogenic activities into the river (Total ∼28.0 ton yr−1: Cu 1.8 ton yr−1; Zn 8.3 ton yr−1; Cr 11.4 ton yr−1; Cd 1.5 ton yr−1; and, Pb 5.0 ton yr−1), and identified the critical river segment contaminated by heavy metals (87% of the total estimated anthropogenic inputs occur in the lower basin). These results agree with contamination source data reported by the governmental environment agency for effluent emitted into the Sinos river.