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

Abstract

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 Hg 2+ in aquatic systems and a long-term component, involving the re-emission of Hg deposited in soils particularly because of changes in soil use.

The impacts of land use changes in the mercury flux in the Madeira River, Western Amazon

“…This simple, cheap and reliable technique produced about 2,000 tons of gold from 1975 to 2002, leaving behind nearly 3,000 tons of Hg in the region's environment (Lacerda 2003). The Madeira River Basin was the second most important gold mining area in the Amazon.…”

A description of mercury in fishes from the Madeira River Basin, Amazon, Brazil

“…It has been estimated that between 2000 to 3000 tons of Hg's have been released in the middle of the Amazon environment and nowadays small gold extraction activities using Hg can still be found (Malm, 1998;Lacerda & Salomons, 1998;Lacerda, 2003). About 60% of this mercury is believed to be were lost to the atmosphere and 40% went directly to the watercourses (Pfeiffer & Lacerda, 1988).…”

“…Studies performed in distant areas and without gold mining activities registrations in the high Negro River reveal elevated Hg concentrations, what it carries to consider its natural source (Fadini & Jardim, 2001). Continually, deposited Hg in soils and sediments suffers continuous transformations and interactions with environmental compartments, which eventually transform and remobilize Hg to food chains, including the increase of its bioavailability through methylation (Malm et al, 1990;Roulet et al, 1998;Lacerda, 2003).…”

Emissões naturais e antrópicas de metais e nutrientes para a bacia inferior do rio de contas, Bahia

“…No caso dos solos ainda é levada em consideração a taxa de perda de solo. Os principais tipos de solos presentes na área estudada são podsólicos ( 37,47,73 A derivação das contribuições destes dois aportes naturais mostra que a contribuição dos solos domina o aporte natural de N, Cu e Pb e representa entre 10 a 80% do total para Cd, P, Zn e Hg, para as duas sub-bacias estudadas (Tabela 1). Este resultado é devido às baixas concentrações destes últimos nos perfis pedológicos litorâneos do que um enriquecimento na precipitação.…”