Mercury occurs naturally in the earth’s crust, but human activities, such as the burning of coal, oil, and wood, mining and fuel combustion, have led to widespread global mercury pollution. Mercury release occurs both naturally such as volcanic eruption and land emission through the soil, and anthropogenic processes (human activities) such as artisanal and small–scale gold mining, fossil fuel burning, and primary production of non-ferrous metals. Although it is relatively small percentages of emission, the other sources of mercury emission are cement production, consumer products waste, contaminated sites, and the Chlor-alkali industry.

In the regions closer to plate tectonic boundaries, where soils are enriched with minerals such as cinnabar containing Mercury sulfide (HgS) released by either natural weathering of the rocks or by geothermal reactions. Mercury is precipitated into the oceans predominantly from the air in three main forms; in the state of gas (Hg0) by the process of air-water exchange, wet and dry precipitation of inorganic mercury (Hg2+ or HgII), and particle-bound mercury (Hg(P)). The other natural water channels also deliver mercury into the ocean. Organic mercury compounds called methyl mercury can also be discharged from these which will undergo chemical transformations such as oxidation-reduction, adsorption processes, and methylation-demethylation.