Updated 19.05.2020
A study conducted in the French Guiana basin where artisanal gold mining in occurs has shown there is mercury in the environment from these activities. It is even found in the piscivorous fish and indigenous communities that eat food from the rivers affected. These are important and innovative results for leading targeted preventative actions for at-risk populations and calling for the adoption of gold-mining techniques that do not use mercury.
Mercury is a toxic metal that can be released into the atmosphere through natural processes such as volcanic activity and soil erosion, but it is also released by human activities such as panning for gold. Artisanal and small-scale gold mining (ASGM) is the activity that leads to the greatest release of mercury into the environment: 775 tons were released into the atmosphere in 2015(1) and 800 tons end up in fresh water reserves(2) every year. A multidisciplinary team directed by Laurence Maurice, an environmental geochemist at the IRD, was interested in exactly what impact this type of gold mining had on the Oyapock River Basin in French Guiana. It is located along the Brazilian border and fed by the Camopi River(3). These watercourses drain an area of 24,630 km2.
Previous studies conducted in Bolivia by the same team did not detect any increase in mercury directly linked to panning for gold in rivers because the hydrographic basins are too large there and the hydrologic and sedimentary dynamics are too powerful. The smaller size of the Oyapock River Basin and the hydro-sedimentary dynamic of small creeks made it possible to overcome these obstacles. “The Oyapock River Basin is interesting because it has areas where gold is mined and areas where it is not. That was an essential characteristic for assessing the differences in mercury levels in the aquatic environment in mined and unmined areas”, stated Laurence Maurice.
Isotope signatures
Laurence Maurice prélève des cheveux dans une communauté Wayãpi, à Trois Sauts, pour analyser les niveaux d'imprégnation au mercure des populations locales.
© C.Furger
For their study, scientists relied on the fact that mercury has several naturally stable isotopes?Atoms that have the same number of electrons, but a different number of neutrons. Isotopes of a single element have identical chemical properties, but different physical properties.. Depending on its provenance, mercury in a given environment does not have the same signature, or isotopic fractionation, meaning the same proportions of the different stable isotopes. Therefore, in sediments, natural mercury can be traced by certain fractionation values and liquid mercury (used by gold miners to hold together gold flakes) by different fractionations. Between March 2010 and October 2013, scientists collected 46 samples of sediments, soils, and surface water. They also sampled 317 fish and 111 human hairs from the Wayãpis and Teko peoples, indigenous communities established in different sites in the Oyapock River Basin.
The results showed an apparent paradox in the environmental distribution of mercury and the health impacts: the areas where gold is mined and where the fish have the highest mercury concentrations are not the areas with the highest concentrations in humans. “There is, however, an explanation. In Trois Sauts, a village far from the gold mining sites, native populations were contaminated through their diets. Since they are isolated, they have a very traditional lifestyle based around hunting, growing cassava, and fishing. Their community therefore regularly ate fish, including fish with high levels of mercury. Around Camopi, a village downstream from gold mining sites, the situation is different. There is a grocery store and you can just cross the river to reach the Brazilian bank where there are a number of small businesses. The inhabitants here therefore have access to other foods, including processed foods, which reduces their consumption of fish”, explained Laurence Maurice.
Fishes harvested in Oyapock river by Wayãpis people for mercure analysis and tracing of its origins by isotopy.
© IRD/Laurence Maurice
Supporting prevention
The implications of this study are significant. On the one hand, it is significant because researchers succeeded in quantifying the effects of gold-mining on mercury contamination of the aquatic environment (up to 70% in the sediments of mined creeks) and on the other hand, it is significant because it helps support prevention aimed at local indigenous populations. During the restitution meetings, fliers were distributed in coordination with the ARS?The French Guiana regional health agency and the Guiana Amazonian Park explaining which species of fish were the most contaminated with mercury--namely, fish at the top of the food river's food chain, the piscivorous fish,--that people should avoid eating, especially during pregnancy. “The effects of in utero exposure to mercury are irreversible and range from mental and motor developmental delays to serious deformations and include vision problems as well as immune system effects”, stated the specialist. Starting this year, the research will be extended through a study on sustainable gold mining, this time at a multi-national level (including French Guiana, Guyana, and Suriname).
Notes :
1. Streets et al., 2018.Atmospheric Environment.
2. Obrist, D., Kirk, J.L., Zhang, L., Sunderland, E.M., Jiskra, M., Selin, N.E., A review of global environmental mercury processes in response to human and natural perturbations: changes of emissions, climate, and land use. Ambio , mars 2018, 47, 116e140.
3. Sylvaine Goix, Laurence Maurice, Laure Laffont, Raphaelle Rinaldo, Christelle Lagane, Jerome Chmeleff, Johanna Menges, Lars-Eric Heimbürger, Regine Maury-Brachet, Jeroen E. Sonke, Quantifying the impacts of artisanal gold mining on a tropical river system using mercury isotopes. Chemosphere 219 (2019) 684e694
Contact : Laurence Maurice
