BINDING OF METHYLMERCURY COMPOUNDS BY HUMIC AND FULVIC-ACIDS

Humic and fulvic acids were isolated from Fawn Lake in Ontario and investigated by membrane dialysis for their ability to bind CH3Hg+. By measuring the distribution of methylmercury compounds in and outside of the dialysis membrane, for the first time, binding capacities and conditional stability constants for CH3Hg+ and humic acids could be calculated. Equilibrium between inner and outer dialysis solution was reached within 24 hours without losses of CH3Hg+ in humic solution. The ratio of bound to unbound CH3Hg+ increased with decreasing total CH3Hg+ levels in the system. The percentage of free methylmercury compounds increased with decreasing pH. Fawn Lake humic acid showed two different binding sites. The conditional stability constant of the stronger site was calculated as 1.3 x 10(12). This site was able to bind 0.2 ng CH3Hg+ per mg of humic acid.