Particulate Mercury and Particulate Organic Matter in the Itenez Basin (Bolivia)

Abstract

In rivers and other freshwater bodies, the presence of mercury can be due to direct contamination by anthropic activities such as gold mining. However, it can also be attributed to atmospheric deposition and erosion, runoff, or lixiviation from surrounding soils. In the case of the Amazon rainforest, high mercury contents have been reported for litter and topsoil, which could affect the mercury concentrations in water bodies. Samples of suspended particulate matter were obtained from a transect of the Itenez River, associated lakes, and some of its tributaries. The aim was to obtain information on particulate mercury’s origin in the study area and determine the relationship between particulate mercury and particulate organic carbon. The concentration of mercury, organic matter, and the C:N ratio of the suspended matter was determined. The concentration of particulate mercury by water volume depended on changes in suspended matter loads, which in turn were mostly affected by the nature of the watershed or sediment resuspension. The observed values for the percentage of organic matter and the C:N ratio suggest that most of the mercury content in rivers and lakes originated from soils. A positive correlation was found between mercury concentration by weight of particulate matter and organic carbon content in particles. This correlation might be due to the direct binding of mercury to organic matter through functional groups like thiols or to an indirect effect of oxyhydroxides that can adsorb mercury and are associated with organic matter.

Trace element accumulation in different edible fish species from the Bolivian Amazon and the risk for human consumption

“…Furthermore, by overlaying the results of mercury concentrations in this research to other local studies that examined the levels of this metal in the abiotic compartments of the ecosystem (water, suspended particles and sediment) ( Maurice-Bourgoin et al., 1999 , 2000 ; Guzmán-Uria et al., 2020 ) and/or other links in the food web (invertebrates) ( Molina et al., 2010 ), it seems that mercury pollution has an important presence, especially in certain areas of the Beni River related to gold mining ( Maurice-Bourgoin et al., 1999 ).…”

“…However, the degradation of aquatic ecosystems and the disruption of fish migration routes in Bolivia are threatening the contribution of fish to food security for these communities ( Camburn 2011 ; Van Damme et al., 2019 ). In this framework, one of the most significant threats to aquatic ecosystems in Bolivia is the pollution by trace elements, caused by the country's long mining history and the erosion of natural metal-bearing soils ( Maurice-Bourgoin and Quiroga 2002 ; Guzmán-Uria et al., 2020 ).…”

“…Although there is still much uncertainty in this regard ( Arrifano et al., 2018 ; Guzmán-Uria et al., 2020 ; Vasconcellos et al., 2021 ; Serra et al., 2021 ), it is probable that a significant part of the mercury in Amazonian ecosystems is the result of artisanal and small-scale gold mining (ASGM) ( Gerson et al., 2022 ; Mestanza-Ramón et al., 2022 ). Mercury is a trace metal used to extract gold from rocks through an amalgamation process and it has been banned worldwide since the Minamata convention, due to the negative effects it causes on human health and aquatic ecosystems ( Maurice-Bourgoin and Quiroga 2002 ).…”

“…Some efforts have been made to quantify and analyze the environmental situation related to trace contaminants in the Bolivian territory resulting in valuable information ( Van Damme et al., 2008 ; Benefice et al., 2010 ; Pouilly and Pérez 2014 ; Guzmán-Uria et al., 2020 ). Nevertheless, characterizing trace element pollution in Bolivian aquatic ecosystems deserves continuing efforts to obtain environmental data that can show objectively the whole impact of these pollutants.…”

Mercury and Methylmercury Contamination of Terrestrial and Aquatic Ecosystems

“…Samaniego et al [5] show evidence of the persistent contamination of abandoned and inactive mines in the Philippines, even 50 to 70 years later, releasing high amounts of Hg into riverine and marine environments. In current alluvial gold mines of the Amazon region, Guzmán-Uria et al [6] highlight the impact of soil degradation on the Hg release into downstream hydrosystems. Hellal et al [7] demonstrate that particulate Hg and MeHg transport rises downstream from gold mine sites, with the highest emissions during high water regimes (rainy season).…”