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.

National highway induced selected chemical properties of soils across tea bowl of India: scale and assessment

“…Exploring the Mn in the soil is essential as it provides Mn status and its availability towards plant uptake. Furthermore, Mn biogeochemical cycle is also associated with the biogeochemical cycle of other micronutrients (Queiroz et al 2021). Total Mn in experimental soil is figured out in Fig.…”

Iron geochemistry in tropical estuarine soils affected by anthropic and natural disasters

“…The more reduced physicochemical environment in the estuary is related to organic matter inputs due to the growth of estuarine plants at Doce River (i.e., Eleocharis acutangula and Typha domingensis (Queiroz et al 2021b). In fact, after the deposition in the estuary plants colonized the tailings, promoting the organic matter inputs (e.g., litterfall and dead roots).…”

“…These complexes are strongly stable, virtually irreversible , and guarantee the low bioavailability of metals . However under transitory/cyclic anoxic conditions Fe oxyhydroxides experience a reductive dissolution which leads to a decrease in their stability and in their capacity to retain metals Queiroz et al 2021b).…”

“…These characteristics are accountable for an intense dissolution rate . In response to these characteristics, the associated metals and phosphorus are made bioavailable Queiroz et al 2021b) posing severe environmental risks to the Doce River estuary. In fact, previous studies reported a high concentrations of metals (Queiroz et al , 2021a and phosphorus (Queiroz et al 2021b) associated with the estuary Fe oxyhydroxides.…”

“…In response to these characteristics, the associated metals and phosphorus are made bioavailable Queiroz et al 2021b) posing severe environmental risks to the Doce River estuary. In fact, previous studies reported a high concentrations of metals (Queiroz et al , 2021a and phosphorus (Queiroz et al 2021b) associated with the estuary Fe oxyhydroxides. Thus, the mineralogical changes caused by the active redox environment such as smaller particles size observed in SEM micrographs (Fig.…”