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

Fabiola Guzmán-Uria,Marc Pouilly,Isabel Morales-Belpaire,Dario Achá

doi:10.3390/app10238407

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.

Highlights

Mercury (Hg) is a significant environmental and health issue in the Amazon basin
We report additional data to those that were presented by Pouilly et al [11] about suspended particulate matter, total particulate mercury, particulate organic carbon, and the C/N ratio
Our results suggest that particulate mercury binds to organic carbon

Summary

Introduction

Mercury (Hg) is a significant environmental and health issue in the Amazon basin. Mercury’s toxicity is elevated due to the property of its organic form, methylmercury, to penetrate biological organisms and to generate accumulation during the individual’s life and magnification along the trophic chain. In tropical forests, typical vegetation with broad leaves facilitates the capture of mercury from atmospheric deposition. High contents of this metal have been reported for forest litter and topsoil [1]. Mercury content can be related to atmospheric deposition, but most originates from the runoff or lixiviation of superficial and subterraneous water from mercury-laden soils [2]. The influx of mercury to water bodies from runoff can be exacerbated by natural erosion and anthropic activities such as deforestation, agriculture, mining, or urbanization. In rivers that drain deforested watersheds, an increase in total mercury in the water column and surface sediments has been observed and attributed to the erosion of fine particles from soils [3,4].

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