Mercury: The Toxic Pollutant That Keeps Coming Back

In fact, half of the mercury in the upper part of the ocean—where it accumulates in fish that humans eat—was emitted by people prior to 1950, according to a study published in May in the journal Global Biogeochemical Models. In total, 83 percent of the surface ocean's mercury ended up there from human activities. The finding has led researchers to suggest that mercury emissions be dramatically cut....

Most of the mercury emitted into the atmosphere rains down on the world's oceans, and the rest ends up on land. But its is a volatile element, and much of it evaporates and returns to the air after being deposited on land and into the ocean. In fact, a majority of the mercury (60 percent) that rains out from the air has been re-emitted from soil or water, returning like an undead pollutant that cannot be snuffed out.

The primary source of mercury emissions is small-scale (or "artisanal") gold mining, for example in Southeast Asia and South America, according to the study; a close second is emissions of mercury from burning coal. Together, the two account for about two-thirds of current mercury pollution, Amos said.

http://www.takepart.com/article/2013/07/10/mercury-toxic-pollutant-keeps-coming-back