MEASUREMENT OF METHYLMERCURY AND MERCURY IN RUN-OFF, LAKE AND RAIN WATERS

During one year, samples from eight drainage lakes, seven run-off stations and three deposition sites from various geographical areas in Sweden were collected and analyzed for methyl Hg (MeHg) and total Hg (Hg-tot). The MeHg concentrations ranged from 0.04 to 0.64 ng L-1, 0.04 to 0.8 ng L-1, and < 0.05 to 0.6 ng L-1 in run-off, lake water and rain water, respectively. The corresponding Hg-tot concentrations were found in the range 2 to 12 ng L-1, 1.35 to 15 ng L-1, and 7 to 90 ng L-1, respectively. A Hg-tot level of about 60 ng Hg L-1 was found in throughfall water. The MeHg and Hg-tot concentrations are positively correlated in both run-off and lake water, but not in rain and throughfall water. A strong positive correlation between the MeHg, as well as the Hg-tot concentration, and the water color is observed in both run-off and lake waters, which suggests that the transport of MeHg and other Hg fractions from soil via run-off water to the lake is closely related to the transport of organic substances; and is a consequence of the biogeochemical processes and the water flow pathway. The ratio between the mean values of MeHg and Hg-tot seems to be an important parameter, with an indicated negative coupling to the mean value of pH for run-off water, but a strong positive correlation to Hg-content in fish, the ratio between the area of the catchment and the lake, as well as to the retention time of lake.