One of the uses of liquid metallic mercury that has escalated during the last fewdecades is
artisanal gold mining. Alluvial deposits of fine gold particles are often extracted using
mercury. The gold particles are dissolved in the mercury as an amalgam, and the mercury is
subsequently removed by heating with a gas torch. This use therefore exposes the gold miner
to a substantial amount of mercury vapor, and also leads to extensive release of mercury into
confined and sometimes ecologically sensitive areas. The annual consumption of mercury in
such mining operations is about 650 tons, mainly in Asia, Central Africa, and Latin America.
Another consequence of this practice is the contamination of soil, which can remain polluted
for many decades. Some previous gold mining sites in the United States (e.g., Carson River,
Nevada) are now recognized as being heavily contaminated with mercury, with estimated
amounts of mercury residues exceeding 6000 tons. Deposition of sewage sludge and
contamination from other industrial activities often involve mercuric salts with low
solubility (i.e., sulfides). Ecological and human health implications inorganic mercury in
the environment depend on the entent of mercury methylation. Recent studies using stable
mercury isotopes (Harris et al., 2007) have documented that sedimentation of airborne
mercury onto freshwater ecosystems within several months gets accumulated in fish in the
form of methylmercury.