Evaluating Copper Behavior in Urban Surface Waters Under Anthropic Influence. A Case Study from the Iguaçu River, Brazil

Abstract

The goal of this work was to investigate the changes in copper behavior in Iguacu River, a body of water strongly affected by urban inputs. This work was carried out in a subtropical Brazilian watershed suffering with high loads of raw sewage discharges from the Metropolitan Region of Curitiba. A comparison between sampling sites located upstream and downstream from the urban region revealed that human inputs are able to modify the water chemistry of the river in a short distance basis, that is, approximately nine miles. Probably, the most important alterations were the creation of an anaerobic environment as well as the enhancement of humic-coated suspended solids. These two aspects were determinant to explain the high concentrations observed for particulate copper (57% of total recoverable copper) and dissolved copper sulfide species (13%) in the water column. Copper in the sediment was also higher in the downstream site, probably due to the sedimentation of the Cu-enriched particles. However, copper sulfides at the bottom sediment may also be a potential source for the metal in the water column due to the creation of anaerobic conditions in both compartments. Labile copper concentration was not affected by the changes in water chemistry. Despite the fact that sewage discharges motivate the enhancement of organic matter, but not the increase in potential complexing agents, additional ligands such as chloride, carbonates, and anthropogenic dissolved organic ligands can be now computed as a part of the labile fraction.