Temporal biogeochemical dynamics for iron, manganese, and cooper in soils of the Rio Doce estuary subjected to reducing conditions

• Grant number: 21/14957-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: March 01, 2022
• End date: February 28, 2023
• Field of knowledge: Physical Sciences and Mathematics - Geosciences
• Principal Investigator: Diego Barcellos
• Grantee: Ramilly Érika Moreira de Souza
• Host Institution: Instituto de Ciências Ambientais, Químicas e Farmacêuticas (ICAQF). Universidade Federal de São Paulo (UNIFESP). Campus Diadema. Diadema , SP, Brazil

Abstract

Chronic metal contamination for time spans of months and years remains an environmental, economic, and ecological concern at the Rio Doce estuary, after the largest environmental disaster in Brazil, due to an upstream collapse of a mine tailings dam. The material that reached the estuary is composed mostly of iron (Fe) oxides, which are capable of absorbing and releasing metals of environmental concern and toxicological risks, such as copper (Cu) and manganese (Mn). Previous studies demonstrated the release of bound metals from the Fe oxides at the Rio Doce within 20 days and raised up question if the release of metals would persist for a longer time (months). Thus, our objective is to test the following hypothesis: within a period of several months (120 days), the Fe oxides from the mine tailings will maintain the release of bound metals (Cu and Mn), when exposed to anoxic (oxygen-free) conditions, when compared to oxic conditions. To test this hypothesis, we are proposing a redox incubation experiment, by exposing the Rio Doce soils to either anoxic or oxic conditions, and destructively harvesting triplicated reactors within the following days of the experiment: 0, 10, 20, 30, 40, 60, and 120. For each treatment and day sampled, extractions with 0.5 mol L-1 HCl will be performed to quantify FeII, as well as the Cu and Mn phases. From another batch of triplicated reactors along with the experiment, a geochemical fractionation of Fe, Cu, and Mn will be performed for six distinct fractions. Results from this project will be fundamental to comprehending biogeochemical mechanisms involving the release of metals from Fe oxides of the mine tailings over periods of months (120 days and beyond). With the annual arrival of more sediments from upstream sources (containing mine tailings), our results will help predict potential chronic metal contamination in impacted estuaries.(AU)