Mercury Pollution at Gold Mining Sites in the Amazon Environment

Mercury Pollution at Gold Mining Sites in the Amazon Environment

Elmer Diaz

University of Idaho

Principles of Environmental Toxicology

November 2000

Abstract

Mercury is being released into the Amazon environment in large quantities

from gold mining operations. Hg is lost to the atmosphere, waters, and soils. In this

case study, the fate of Hg released into the environment by gold mining operations,

sources, pathways, receptors and controls is reviewed. One of the major sources of

Hg into the environment is the burning of the gold-mercury amalgam, which releases

from 30 to 170 tons of Hg every year into the Amazon atmosphere. Mercury

emissions to the atmosphere represent 45 to 87% of the total Hg emitted from gold

mining and may account for a global input of 200 to 420 tons/year. At gold dealer

shops or in amalgam burning sites, Hg emissions range from 5.50 to 292 µg/m3

respectively. Degassing emissions from contaminated soils, waters, and tailings of

Hg vapor to the atmosphere can reach up to 5000 µg/g. Discharging metallic Hg into

rivers during the amalgamation process also represents the second largest source of

contamination. Hg is being exported from tailings to adjacent aquatic ecosystems.

Although Hg leaching from tailings seems a slow process, the migration of tailings

themselves over the years may be the most important Hg dispersal mechanism. Hg

concentrations in sediments close to operating dredges can reach values of up to

157 µg/g decreasing to background levels of less than 0.04 µg/g a few kilometers

downstream.

Great physicochemical and limnological characteristics of Amazonian

environments allow for rapid turnover of Hg into Methyl mercury (MeHg). Fish are the

main transfer pathway of Hg from a contaminated environment to humans. Therefore,

it is the major source of methyl-mercury to humans. Hg concentrations in fish from

contaminated sites can range from 0.9 to 2.89 µg/g. People in the Amazons are

being exposed to Hg from...