Updating global Hg emissions from small-scale gold mining and assessing its environmental impacts

Small-scale gold mining is a significant source of Hg to the environment and may reach an annual input of about 450 t of Hg, mostly in South America, Russia and Asia. Countries of the Amazon Basin and Russia are the major contributors. On a regional scale, this source can contribute to more than 50% of the total Hg anthropogenic emission. Because of amalgam burning and bullion smelting under generally uncontrolled conditions, the majority of the emission is to the atmosphere. Therefore, on a global scale small-scale gold mining contributes about 20% of the total Hg atmospheric emissions from human activities. Most emissions occur in tropical developing countries. Preliminary results from research in the Amazon region suggest the Hg cycling in tropical rainforest environments is probably more dynamic and critical than in previously studied temperate environments, being strongly influenced by the existing ecological cycles and affected by land-use changes. At least two components of the Hg cycle can be identified. A short-term component, involving methylation of deposited Hg2+ in aquatic systems and a long-term component, involving the re-emission of Hg deposited in soils particularly because of changes in soil use.