Gold Mining and Mercury Pollution in The Ghanaian Pra River Basin, West Africa

摘要

In this work, levels, speciation and the spatial/temporal distribution of Hg in the Pra River basin in southwestern Ghana were investigated, to assess the environmental impact of Hg introduced into waterways by artisanal gold mining operations. Surface water, sediment, soil and human hair samples were collected along longitudinal transects from locations upstream of known point sources down to the river delta, using ultra-clean techniques and analyzed by CV-AFS. Our results show that total-Hg (THg) concentrations are very high in river waters (28 to 1961 ng/L), as well as in soil samples collected near sites of amalgam roasting (up to 185 mg/Kg or ppm). THg concentrations in reverine sediments ranged from very low values of about 0.011ppm to concentrations as high as 19ppm in the vicinity of mining sites. Overall, most sediment samples had rather very low THg as compared to published values from Hg-contaminated sites. Reported THg levels in human tissues were quite low as compared to proposed safe limits. MeHg was also detected in all samples, and in contrast to well-studied Hg contaminated systems in America and Europe, its levels in analyzed Ghanaian sediment samples were 2 to 3 times higher than most published values. Finally, laboratory experiments using riverine sediments were conducted to assess the potential rates of Hg methylation and MeHg demethylation in these tropical settings, and obtained data are presented.