RIVER flows have constant interaction between water and bed sediments; for this reason knowledge of the characteristics of the sediments is fundamental to understand water chemistry. This study determined the concentrations of heavy metals in water and sediments in the affluents and the effluents of the Mediterranean Chilean reservoirs Cogotí, Corrales, La Paloma, and Recoleta. We explore possible ecological risk and toxicity using the enrichment factor (EF), risk assessment code (RAC), threshold effect concentrations (TEC) and probable effect concentrations (PEC). The results showed that five metals: Al, Fe, Cu, Mn and Zn out of the ten measured metals were detected in both surface water and the sediments. The risk assessment code (RAC) suggested that Fe represents a medium risk in the affluent of Cogotí Reservoir: Cu, Zn and Mn represent a medium to high risk in all the dams and in both zones (affluents and effluents). The enrichment factor (EF) determined that the five metals were lithogenic. Fe, Cu, and Mn are the elements that present the greatest toxicity to microorganisms in these aquatic systems.

In order to determine the effect of a dam on metal concentrations in riverine fish species, we studied fish inhabiting the influent (Cachapoal River) and effluent (Rapel River) of the Rapel Reservoir in central Chile. Heavy metals were quantified in gills, liver and muscle of the catfish Trichomycterus areolatus and the silverside Basilichthys microlepidotus. Also, the bioaccumulation index (BAI) was estimated by considering heavy metal concentrations obtained from water and sediment. Results showed the presence of Al, Cu, Fe, Mn, Pb and Zn in the fish organs. The analysis showed high metal concentrations in catfish inhabiting the influent compared to those collected in the effluent. These results indicate a possible filter effect of the dam for most of the metals identified in the fish organs, because metal concentrations decreased in the effluent. Finally, catfish exhibited a larger BAI for most metals analyzed.