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Publication MIO : SylvaineGoix, Laurence Maurice, Laure Laffont, Raphaelle Rinaldo, Christelle Lagane, Jerome Chmeleff, Johanna Menges, Lars-Eric Heimbürger (MIO) ,RégineMaury-Brachet, Jeroen E.Sonke - Quantifying the impacts of artisanal gold mining on a tropical river system using mercury isotopes

Version imprimable de cet article

in Chemosphere
https://doi.org/10.1016/j.chemosphere.2018.12.036
Available online 8 December 2018

Highlights

• Hg isotope ratios measured in soils and river sediments from French Guiana.
• Hg isotope ratios coupled to multiple linear regression to quantify anthropogenic Hg.
•Active ASGM activities increase THg in sediments by 78%.
• Up to 70% of anthropogenic Hg originates from liquid Hg used in ASGM.

Abstract

In some locations, artisanal and small-scale gold-mining (ASGM) represents a significant source of anthropogenic Hg to freshwater environments. The Hg released from ASGM can contaminate aquatic fauna and pose health risks to downstream populations. Total Hg (THg) concentrations, speciation, and isotopic compositions were analyzed in water, suspended particulate matter, soil, and bottom sediment samples from pristine areas and in places of active and legacy gold mining along the Oyapock River (French Guiana) and its tributaries.

Mass-independent fractionation (MIF) of even Hg isotopes in top soils (Δ200Hg = −0.06 ± 0.02‰, n = 10) implied the uptake of gaseous Hg (0) by plants, rather than wet deposition, as the primary Hg source. Odd isotope MIF was lower in deep soils (Δ199Hg = −0.75 ± 0.03‰, n = 7) than in top soils (Δ199Hg = −0.55 ± 0.15‰, n = 3). This variation could be attributed to differences between the isotopic signatures of modern and pre-industrial atmospheric Hg.

Combining a Hg-isotope binary mixing model with a multiple linear regression based on physico-chemical parameters measured in the sediment samples, we determined that active mined creek sediments are contaminated by ASGM activities, with up to 78% of THg being anthropogenic. Of this anthropogenic Hg, more than half (66–74%) originates from liquid Hg (0) that is released during ASGM. The remaining anthropogenic Hg comes from the ASGM-driven erosion of Hg-rich soils into the river. The isotope signatures of anthropogenic Hg in bottom sediments were no longer traceable in formerly mined rivers and creeks.