Mercury contamination from gold mining

Many substances that might be considered toxic are in fact essential to life, for example the heavy metals Co, Cu, Fe, Se, Zn. Thus, there is a relationship between concentration of the substance and the health response it invokes. An element is essential to life when a deficient intake of the element consistently results in impairment of a life function from optimal to suboptimal (Fig. 1a). Moreover, when physiological levels of this element, but not of others, are supplemented or restored, the impairment is cured and optimal health is restored (Fig. 1a). By contrast, non-essential elements do not produce a positive health response. An organism may tolerate low concentrations of some non-essential elements (Fig. 1b). Even dangerous poisons such as arsenic oxide (As203) can be tolerated 

This ionic mercury (Hgll) adheres to aerosols and thus has a short (days to weeks) residence time in the atmosphere rainfall delivers it to the local soils and rivers. Ionic mercury is readily methylated (eqn. 5.24) by both abiotic and biotic pathways. However, most scientists now agree that methylation by anaerobic sulphate reducing bacteria (SRB) is most important. 

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Alpers CN, Hunerlach MP, May JT, Hothem RL (2005) Mercury contamination from historical gold mining in California. United States Geological Survey Fact Sheet 2005-3014, Sacramento, California. 

Comparatively high mercury concentrations of 5.7 mg/kg FW in crayfish abdominal muscle from Lahontan Reservoir, Nevada, an area heavily contaminated with mercury from gold mining operations some decades earlier, and... 

In Nome, Alaska, gold mining is responsible, in part, for the elevated mercury levels (max. 0.45 mg/kg DW) measured in modern beach sediments. However, higher concentrations (max. 0.6 mg/kg) routinely occur in buried Pleistocene sediments immediately offshore and in modem nearby unpolluted beach sediments (1.3 mg Hg/kg). This suggests that the effects of mercury contamination from mining are less than natural concentration processes in the Seward Peninsula region of Alaska. 

M.H.D. Pestana and M.L.L. Formoso, Mercury Contamination in Lavras do Sul, South Brazil a Legacy from Past and Recent Gold Mining, Set. Total Environ. 307(1-3), 125-140, May 20 (2003). 

The most mercury-contaminated site in North America is the Lahontan Reservoir and environs in Nevada. Millions of kilograms of liquid mercury used to process gold and silver ore mined from Virginia City, Nevada, and vicinity between 1859 and 1890, along with waste rock, were released into the Carson River watershed. The inorganic elemental mercury was readily methylated to water-soluble methylmercury. Over time, much of this mercury was transported downstream into the lower reaches of the Carson River, especially... 

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