Environmental risk assessment of metal contamination by mining in the Amazon Basin

Abstract

Several anthropogenic pressures contribute to the modification of ecosystems and hydrological regimes in the Amazon basin. Among them, mining is of great concern due to the remobilization and emission of potentially toxic elements, such as metals, which have detrimental consequences for the ecosystem and human health. Our study aimed to establish the background metal concentrations for water and sediments and the increase of metal exposure caused by mining in four geochemical regions of the Amazon basin: 1) Western; 2) Central; 3) Northern and 4) Southern. Furthermore, we evaluated the environmental risk of mining activities to the aquatic ecosystem and the ecological risk assessment in fish populations. A total of 53 studies spanning mined and non-mined areas reporting metal concentrations for As, Hg, Mn, Fe, Cd, Cu, Cr, Pb, Ni, and Zn were reviewed. The mean background metal concentration values were compared with the environmental quality standards thresholds for the protection of aquatic life in sediment (CCME) and water (CCME and USEPA). Overall, for non-mined areas, all metals are below the established thresholds allowed for the protection of aquatic life in sediments and water, namely, our metal concentration data for reference sites are within international quality standards. The southern peripheral area has the highest levels of background metal concentration in the entire basin for Cd, Cu, Hg, Mn, and Zn. For mining areas, As, Cu, Fe, Hg, Mn, and Pb exceed the mean background metal concentration, and Cd exceeds the threshold TEL in sediment samples, and for water Cd, Cr, Fe, Hg, Mn and, Zn exceed the mean background value, and Fe and Hg exceed the short-term threshold and Zn exceeds the long-term threshold. Metals with the highest percentages of environmental risk for the basin in the sediment were Pb (67,12 %), As (76,36%), Mn (91,89%), and in water were Fe (83,33 %), Hg (86,26 %), Mn (100 %) and Zn (100 %), since these metals have an increase in the concentration of 10 to 100 times higher concerning the mean background values. Finally, according to the ecological assessment As, Cd, Cu, Hg and Pb show a high risk of metal concentration in Amazonian fish Populations.