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Manganese: The overlooked contaminant in the world largest mine tailings dam collapse.

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.

SUBMITTER: Queiroz HM

PROVIDER: S-EPMC8382573 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The collapse of the B1 Dam of VALE SA mining company in Brumadinho, Minas Gerais, Brazil was the largest humanitarian disaster and occupational accident in the country's history, and it posed challenges regarding the management and identification of multiple victims. We evaluated the impact of the iron ore tailings on the victims' bodies. We examined the scientific identification of the victims and the dynamics of the disaster over the 1st year after it occurred. We also determined the socio-demographic profiles of the victims. In this retrospective, cross-sectional study, we investigated the expert reports of the victims' biological remains from 25 January 2019 to 25 January 2020. We analysed the socio-demographic data, identification methods, identification status, identification time, and necroscopic information. During the study period, 259 of 270 victims were identified, and 603 biological materials were analysed; among them, 86.2% were body parts and 13.8% were whole bodies. Of the total cases registered that year, 476 (78.9%) were submitted during the first 10 weeks after the disaster. Friction ridge analysis accounted for 67.9% of primary identifications and DNA analysis did so for 91.6% of re-identification cases. Body dismemberment was 3.4 times greater among mine workers than among community victims. Adult males accounted for the greatest number of victims (P < 0.001). Polytraumatic injury was the prevalent single cause of death. Necropsy examination revealed the occurrence of asphyxia in 7% of cases. The higher number of fatalities and greater dismemberment among employees than with community residents underlines the occupational dangers in the mining industry and clarifies the dynamics of the disaster. In the initial weeks after the dam collapsed, friction ridge analysis was the most appropriate method for identification. Subsequently, DNA analysis became the most-used technique for identification and re-identification owing to the great volume of body parts and decomposed biological tissue. Autopsy allowed diagnosis of the causes of death to be clarified according to the Brazilian criminal legal system.

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Manganese: The overlooked contaminant in the world largest mine tailings dam collapse.

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