Carbon-rich soil could increase mercury levels

Terra Daily: Mercury pollution has already spurred public health officials to advise eating less fish, but it could become a more pressing concern in a warmer world. So suggests a paper that appears in a recent issue of the journal Oecologia. Sue Natali, a postdoctoral associate in botany at the University of Florida and the paper's lead author, compared mercury levels in soils under trees growing in air enriched with carbon dioxide to soil beneath trees in ambient air. Carbon dioxide, the main greenhouse gas, has increased nearly 40 percent since the industrial revolution and is expected to continue climbing unless power plant and other emissions are restricted or curtailed.

Natali's main finding: Soil samples from the carbon dioxide-enriched soil contained almost 30 percent more mercury - apparently because the soil had greater capacity than soil in today's atmosphere to trap and hold on to mercury. On the one hand, Natali said, that increased capacity could slow the mercury's release into water - its main conduit to aquatic wildlife and the fish that pose a hazard to people. On the other, it means that even if policy makers manage to ban or severely restrict mercury emissions, the metal will remain a source of pollution for a long time.

"From the time you cut off mercury emission to the time it positively affects fish, you might have this lag, because the soils hold on to the mercury better," Natali said.

Global mercury emissions today range from 4,400 to 7,500 tons per year, according to the Environmental Protection Agency. Natural sources such as volcanoes account for about half, with coal-fired power plants, smelters and incinerators contributing the remainder….

Mercury ore, US Geological Survey