WET DEPOSITION OF METHYL MERCURY IN NORTHWESTERN ONTARIO COMPARED TO OTHER GEOGRAPHIC LOCATIONS

Concentrations of methyl mercury (MeHg) and total mercury (THg) in pre cipitation were measured at the Experimental Lakes Area (ELA), a remot e field station in northwestern Ontario. We found that precipitation w as a source of both MeHg and THg to boreal ecosystems, but at lower ra tes than in industrialized regions of North America and Scandinavia. M eHg concentrations in precipitation ranged from 0.010 to 0.179 ng L(-1 ) and were highest when events originated west of the ELA. THg concent rations in precipitation ranged from 0.95 to 9.31 ng L(-1) and were hi ghest when the events came from the southeast. There was no relationsh ip between THg and MeHg over time in precipitation. Inputs of both MeH g and THg to ecosystems were highest during summer months.