Regional distribution of mercury in sediments of the main rivers of French Guiana (Amazonian basin).

Valérie Laperche,Pierre Laporte,Jennifer Hellal,Régine Maury-Brachet,François Blanchard,Bernard Joseph,Dominique Breeze

doi:10.1186/2193-1801-3-322

Abstract

Use of mercury (Hg) for gold-mining in French Guiana (up until 2006) as well as the presence of naturally high background levels in soils, has led to locally high concentrations in soils and sediments. The present study maps the levels of Hg concentrations in river sediments from five main rivers of French Guiana (Approuague River, Comté River, Mana River, Maroni River and Oyapock River) and their tributaries, covering more than 5 450 km of river with 1 211 sampling points. The maximum geological background Hg concentration, estimated from 241 non-gold-mined streams across French Guiana was 150 ng g-1. Significant differences were measured between the five main rivers as well as between all gold-mining and pristine areas, giving representative data of the Hg increase due to past gold-mining activities.These results give a unique large scale vision of Hg contamination in river sediments of French Guiana and provide fundamental data on Hg distribution in pristine and gold-mined areas.

Highlights

A clear link has been established between mercury (Hg) contamination in the Amazon region and gold mining activities due to the use of metallic Hg in the mining process (Veiga et al 1999), in some cases, the link between Hg contamination and gold mining is not always clear
This study presents results of total Hg in sediments and compares them with values measured in other Amazonian regions to distinguish the anthropogenic impact from the natural background level
The background Hg level in river sediments of the whole of French Guiana was estimated to be 108 ± 42 ng g−1, depending on the mud/sand ratio

Summary

Introduction

A clear link has been established between mercury (Hg) contamination in the Amazon region and gold mining activities due to the use of metallic Hg in the mining process (Veiga et al 1999), in some cases, the link between Hg contamination (soil, sediment, fish or human) and gold mining is not always clear. Quenel et al (2007) found high levels of Hg in the hair of the Amerindian population of Trois Sauts in the upper Oyapock River (French Guiana); yet there is no gold mining in this area. The background level was evaluated from 51 samples collected on the Upper Oyapock (south of the Oscar’s village, Figure 1) This part of the river and its tributaries are known to be free of alluvial gold mining activity. The mean Hg concentration in the muddy sediment of the Upper Oyapock is 100 ± 30 ng g−1 This value is close to the one calculated from the 241 sediments collected in the un-gold-minedstreams (NGWS in Table 2) of the whole of French Guiana (108 ± 42 ng g−1). The background levels vary between 70 ± 33 ng g−1 and 122 ± 32 ng g−1 depending on geology and locality of the sector

Methods

Results

Conclusion