Impact of gold mining on mercury contamination and soil degradation in Amazonian ecosystems of French Guiana

2015

Partie d'ouvrage

Grimaldi Michel, Guédron Stéphane, Grimaldi C.

Brearley F.Q. (ed.), Thomas A.D. (ed.), Land-use change impacts on soil processes : tropical and savannah ecosystems

Wallingford : CABI, 2015, p. 95-107 ISBN 978-1-78064-210-9

This chapter focuses on the impact of artisanal small-scale gold mining (ASGM) on the Hg contamination of tropical soils, with special attention on how the change in land use (i.e., gold extraction practices) alters the soil processes that affect Hg fate and behaviour. The chapter explains the soil formation and transformation processes that determine the accumulation or mobilization of Hg, reflecting the dual role of soils as both 'sink' and 'source' of Hg. First, it compares the fate and behaviour of Hg from ASGM with that from the natural geochemical background, considering the nature and abundance of carrier phases and soil functioning. Then, it describes how former and current ASGM activities intensify the soil processes that favour Hg mobilization by surface and near-surface runoff to watercourses, Hg emission to the atmosphere and production of monomethyl-Hg. Further, this chapter combines research carried out in French Guiana, a territory located in northern South America with studies from Brazilian Amazonia. French Guiana, like much of Amazonia, is greatly impacted by ancient and current, legal and illegal ASGM activities. The impact on tropical soils, as well as on ecosystems as a whole, has been well studied in these areas. Furthermore, as the environmental legislation in force since 2006 in French Guiana prohibits the use of Hg at gold mining sites, it is relevant to compare ASGM with or without the amalgamation practice. For a better understanding of the soil processes involved, the main research issue is to promote mining practices that can reduce health and environmental risks. The chapter established that although the use of Hg has been officially prohibited in French Guiana since 2006, being replaced by techniques combining concentration by gravity and centrifugation, its use is common in other parts of the developing world. However, even when Hg amalgamation is not used, gold mining without any precautions creates conditions that favour the transport of Hg already present in the soils to river systems and its transformation into monomethyl-Hg. The risk of Hg contamination for humans thus tends to eclipse the other problems arising from ASGM operations. In fact, ASGM also causes complete deforestation of the areas exploited and consequently a loss of biodiversity and ecosystem functions, landscape modifications and soil degradation.

Pollution [038] ; Pédologie [068] ; Etudes, transformation, conservation du milieu naturel [082]

Fonds IRD [F B010065808]

fdi:010065808