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Abstract Title: Assessment of Artisanal and Small-Scale Gold Mining Mercury Pollution in French Guiana Watersheds Using Hg Stable Isotopes
Presenter Name: Naomi Nitschke
Company/Institution: IPREM/ISTerre
Session: Mercury in Artisanal Gold Mining
Co-Authors: Naomi Nitschke

Abstract Information :

Artisanal and small-scale gold mining (ASGM) has a major impact on mercury contamination to the environment in the Amazon basin. In this study, we analyzed total mercury (Hg) concentration and its stable isotope composition in sediments sampled in the 2000s across the main watersheds of French Guiana including the Maroni, the Oyapock and the Comt‚ rivers. The sampled sites include pristine locations and areas subject to historical and present ASGM activities to different degrees. Total Hg values ranged between 0.021 and 4.32 æg.g-1 with no significant difference between watersheds. The total concentration of Hg in sediments is already an indicator of the contamination of a site, with high concentrations observed in the vicinity of illegal mining areas. Isotopic data provides additional information concerning this contamination. Hg mass dependent fractionation (even-MDF) was always negative and exhibited a large range of values (ë202Hg : -2.82 to -0.43 ?), while mass independent fractionation (odd-MIF) displayed a lower variability (?199Hg : -0.70 to 0.01?). Using these two isotopic dimensions, all sites are distributed along a linear gradient which indicates a mixing between two Hg sources end-members; i) the isotopic composition of liquid Hg used in ASGM for the amalgamation of gold, and ii) the one of geogenic Hg present in pristine soils from French Guiana. These results suggest that Hg isotopic composition in river sediments can be used as an assessment tool to evaluate the proportion of Hg coming from soils weathering versus elemental Hg used for gold amalgamation in ASGM activities in tropical environments.

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