Abstract
In 2006 the use of mercury (Hg) was banned for gold mining in French Guiana. However, mining of old placers could mobilize Hg accumulated in soils and sediment. This study aimed to measure the current impact of a mining concession (Boulanger site) on the Hg load in the watershed. Turbidity, Total Mercury (THg), and Monomethylmercury (MMHg) were measured in water, suspended particulate matter (SPM), river sediment and sediments from old tailing ponds along a river section of 30 km up and downstream from a mining concession in French Guiana during a dry and a rainy season. Total dissolved Hg (THgD) concentrations varied little from up- to down-stream but were all higher (fourfold on average) during the rainy season (3.2 to 4.4 ng L−1), than during the dry season and consistent with previous data known for the Amazonian area. Dissolved MMHg (MMHgD) represented up to 30% of THgD during the dry season, which is higher than previous results (typically around 2%). Mercury concentrations in sediments were highest in the vicinity of areas affected by old (before 2006) rather than new gold mining practices. Even though Hg was banned in 2006, present gold mining practices still release natural Hg and Hg inherited from older mining practices into the watershed.
Highlights
Mercury (Hg) is a toxic metal and a global pollutant, historically used in alluvial gold-mining to amalgamate and recover gold
Except for point 4 (1020 ng g−1 ), the average Hg concentration in pond sediments was 190 ng g−1, which is very similar to values obtained in 2006 for the same ponds
The range of values found here are much lower than Hg contents reported in Venezuela [23], where Hg in pond sediments ranged from 160 ng g−1 to 542 μg g−1, but comparable to those found in abandoned ponds in Colombia [24]
Summary
Mercury (Hg) is a toxic metal and a global pollutant, historically used in alluvial gold-mining to amalgamate and recover gold. In 2005, small-scale gold mining was estimated to contribute to more than 10% of the annual global anthropic Hg load to the atmosphere [1]. Use of Hg for gold mining was officially banned in French Guiana in 2006. “inherited” Hg in old gold mined areas is still present and remains a potential source of Hg to the environment. In addition to Hg inputs from gold mining, Amazonian soils naturally contain high Hg concentrations due to the equatorial pedoclimatic situation (on average 10 times higher than temperate soils) [4]. During gold mining and generally during all deforesting operations [5,6,7,8], Hg adsorbed to colloids (clay, organic matter, and iron or aluminum oxides) is exported to the watershed, contaminating downstream ecosystems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
