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Sources

Mercury release occurs through both natural and anthropogenic processes. Natural processes are mainly geogenic such as volcanic activities and land emissions through the soil. Volcanoes release mercury from the underground reservoirs upon eruption. Land emissions are usually observed in regions closer to plate-tectonic boundaries where soils are enriched with minerals such as cinnabar (insoluble mercury sulfide, HgS). This mercury is released, usually as a salt, either by natural weathering of the rocks or by geothermal reactions. While natural phenomena account for a certain percentage of present-day emissions, anthropogenic emissions alone have increased mercury concentration in the environment by threefold. Global Mercury Assessment 2013 states main anthropogenic sources of mercury emission are artisanal and small-scale gold mining, fossil fuel burning, and primary production of non-ferrous metals. Other sources such as cement production, consumer product waste, crematoria, contaminated sites, and the chloralkali industry also contribute in relatively small percentages.