Mercury contamination in the Red river watershed: a review of the contaminated sites

This study is based on two sampling campaigns covering the whole Vietnamese Red River watershed in 40 sites at low and high water levels during 2009 in order to determine the seasonal and spatial variations of Hg concentrations in stream sediments. The results showed that the Hg concentrations during low water level were clearly higher than that during high water level, demonstrating an effect of particle (grain) size (i.e. significant contribution of less mercury-contaminated particles in high water level). In addition, in order to assess spatial distribution of the Hg contamination in the Red River watershed and localize geochemical anomalies, multidimensional statistical analyses combined with Hg maps generated by GIS tool were used. We observed that the high mercury anomalies are originated from the important pollutant sources (mining/smelting) located in the upstream and mid- Red River watershed, demonstrating an impact of anthropogenic activities on river Hg concentrations. 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