Emission and stability of mercury in the Amazon

Mercury pollution in the Amazon represents one of the most serious environmental issues faced by mankind today. From 70 to 170 t of Hg are discharged annually into the Amazon environment from informal gold mining operations. Vegetation fires are also a major source of Hg emissions with the form being more reactive than that from mining activities. The extent of biota contamination is also more widespread. Mercury must be rendered soluble and then converted into methylmercury in order to accumulate in the food-chain. Generally, it is regarded that oxidation of Hg must occur to produce significant dissolution. In this work, we examine the stability of metallic HE in aquatic environments. In contact with organic acids, evidence of Hg-organic complex formation has been found from both thermodynamic analysis and electrochemical experiments. Although methylation of these soluble species is not fully understood, formation of such complexes in dark-water rivers must contribute to increased bioavailability. (C) 1997 Canadian Institute of Mining and Metallurgy. Published by Elsevier Science Ltd. All rights reserved.