Manganese: The overlooked contaminant in the world largest mine tailings dam collapse. (January 2021)

• Record Type: Journal Article
• Authors: Queiroz, Hermano M.; Ying, Samantha C.; Abernathy, Macon; Barcellos, Diego; Gabriel, Fabricio A.; Otero, Xosé L.; Nóbrega, Gabriel N.; Bernardino, Angelo F.; Ferreira, Tiago O.
• Is Part Of: Environment international. Volume 146(2021)
• Publication Date: 2021-01
• Subjects: Estuarine soils -- Manganese contamination -- Iron oxides -- Redox processes -- Toxicity; Environmental protection -- Periodicals; Environmental health -- Periodicals; Environmental monitoring -- Periodicals; Environmental Monitoring -- Periodicals; Environnement -- Protection -- Périodiques; Hygiène du milieu -- Périodiques; Environnement -- Surveillance -- Périodiques; Environmental health; Environmental monitoring; Environmental protection; Periodicals; 333.705
• DOI: 10.1016/j.envint.2020.106284
• Languages: English
• ISSNs: 0160-4120

Abstract

Highlights: The Fe-rich tailings adsorbed high Mn contents in its way to the estuary. Redox fluctuations led to precipitation of Mn oxides and poorly crystalline Fe oxides. Both Mn and Fe reduction in estuarine soils increased Mn contents in water. Dissolved Mn increased in 880% posing a risk to environmental and human health. Abstract: Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world's largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of Mn II arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when Fe III oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to Fe III, Mn III, and Mn IV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: −47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 µg L -1 ; 2017: 582 ± 626 µg L -1 ) in water and a decrease (~75%, 2015: 547 ± 498 mg kg −1 ; 2017: 135 ± 80 mg kg −1 ) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.