Mass balance estimation of natural and anthropogenic heavy metal fluxes in streams near the camaquã copper mines, Rio Grande do sul, Brazil

Abstract

The Camaquã Copper Mines were closed in 1996 after more than one century of active exploitation. The mines are located in the basin of João Dias creek in the upper course of the Camaquã River, Rio Grande do Sul State, Southern Brazil. The mine-generated effluents enriched in heavy metals were released into the João Dias creek. Both anthropogenic and natural inputs of heavy metals were mixed and added along the creek, and thus simple analysis of metal concentrations in the water is not sufficient to determine whether the inputs are from natural or anthropogenic sources. This study is an attempt to solve these questions based on mass balance studies of heavy metal fluxes between fluvial segments, and shows that this approach is appropriate to differentiate between natural sources and mining (anthropogenic) activities into the basin (total ∼ 410 t yr⁻¹, Fe ∼ 263 t yr⁻¹, Al ∼ 130 t yr⁻¹, Cu ∼ 16 t yr⁻¹, Zn ∼ 3 t yr⁻¹). It also identifies the critical fluvial segments contaminated by heavy metals — about 98% of the total anthropogenic input occurred in the creek segment under direct influence of mining activities without any effluent control. The study also shows the low dilution capability of the João Dias creek and the tendency to “export” heavy metals out of the basin, rather than incorporate them in bottom sediments.