Carbon dioxide-enriched soil contained almost 30 percent more mercury than regular soil, evidently because the soil had a greater capacity to trap and hold onto mercury, botany postdoctoral associate Sue Natali of the University of Florida said in the journal Oecologia.

Carbon dioxide, the main greenhouse gas, has increased nearly 40 percent since the industrial revolution and is widely expected to continue climbing unless power plant and other emissions are restricted or curtailed.

The soil's increased capacity to hold mercury could slow the element's release into water, so it might not hurt the fish people consume, Natali said.

But it also means the metal will remain a source of pollution for a long time, even if policymakers ban or restrict mercury emissions, she said.