THE EFFECT OF PH AND DISSOLVED-OXYGEN LEVELS ON METHYLATION AND PARTITIONING OF MERCURY IN FRESH-WATER MODEL SYSTEMS

Radio-labelled mercury, (HgCl2)-Hg-203, was added to water over lying sediment in freshwater model systems. The partitioning of Hg-203 between water, sediment and air and the concentration of methyl Hg-203 in the water did not differ significantly between systems with a water pH of 5.8 +/- 0.07 and 6.6 +/- 0.05. When the systems were made anaerobic and microbial activity was stimulated by the addition of tryptic soybroth (TSB), the level of methyl Hg-203 in the water increased by two orders of magnitude. There was also an increase in the concentration of total Hg-203 in the water, which was greater than the increase in methyl Hg-203, indicating release of both methyl Hg-203 and other Hg-203 species from sediment to water. In the systems that were kept aerobic, there was no increase in either total or methyl Hg-203 in the water after stimulating the microbial activity with TSB. However, volatilization of Hg-203 increased which was not the case in the anaerobic systems.