Abstract
In 2015, the Rio Doce (in southeaster Brazil) received approximately 60 million tons of mine residues from the failure of the Fundão mine tailing Dam (in Mariana, MG, Brasil) reaching the Rio Doce's estuary, in Linhares, ES, Brasil, one of the greatest environmental disasters worldwide. The mine tailings contain mostly iron oxides, which may change the oxidation state at the fluctuating redox conditions in the estuary of the Rio Doce. Heavy metals are bound to the surface and within the structure of these iron minerals and may become bioavailable because of reduction and re-precipitation of iron oxides, increasing the environmental and health risks at the estuary. We sought the hypothesis that larger amounts of heavy metals will be released during the reduction of iron minerals during sequential redox fluctuations, when compared to steady oxic (aerobic) or anoxic (anaerobic) conditions. To test this hypothesis, we will incubate soils over three redox treatments over 32 days, as follows: redox fluctuations (alternating sequentially over oxic and anoxic conditions every 4 days), constantly oxic for 32 days, and constantly anoxic for 32 days. We will monitor iron species (FeII e FeIII), iron mineralogy, the metals Cu, Cr, Co, Mn, Ni, Pb e Zn, the emissions of the gases CO2, CH4, and N2O, and total and dissolved organic carbon, at the distinct redox treatments over the experiment. Thus, we will characterize and monitor the major actor for the release of heavy metals in that environment, the iron oxides, providing important mechanist understanding for the fate of the mine tailings at the Rio Doce estuary. Given the lack of information regarding metal's bioavailability and environmental risks, the results of this project will be fundamental for biogeochemical modeling of iron, metals and carbon, and to provide information for decision makers for mitigation and remediation assessments at the Rio Doce over short and long time spans. (AU)
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