BINDING OF METHYLMERCURY COMPOUNDS BY HUMIC AND FULVIC-ACIDS

Humic and fulvic acids were isolated from Fawn Lake in Ontario and inv estigated by membrane dialysis for their ability to bind CH3Hg+. By me asuring the distribution of methylmercury compounds in and outside of the dialysis membrane, for the first time, binding capacities and cond itional stability constants for CH3Hg+ and humic acids could be calcul ated. Equilibrium between inner and outer dialysis solution was reache d within 24 hours without losses of CH3Hg+ in humic solution. The rati o of bound to unbound CH3Hg+ increased with decreasing total CH3Hg+ le vels in the system. The percentage of free methylmercury compounds inc reased with decreasing pH. Fawn Lake humic acid showed two different b inding 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 CH3H g+ per mg of humic acid.