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Gerbig, Chase A. ¹ ; Mayer, Marilyn ² ; Grimberg, Stefan J. ³

¹ Deptartment of Civil, Environmental, and Architectural Engineering, University of babyÖ±²¥app, Boulder, CO
² Deptartment of Civil and Environmental Engineering, Clarkson University, Potsdam, NY
³ Deptartment of Civil and Environmental Engineering, Clarkson University, Potsdam, NY

Conditional distribution coefficients (K_DOM') were measured for Hg(II) binding with two different types of organic matter at three redox potentials intended to simulate aerobic, nitrate reducing, and sulfate reducing soil regions. Complexation at aerobic and nitrate reducing conditions (210mV and 187mV, respectively) were measured using an equilibrium dialysis ligand exchange (EDLE) method. The K_DOM' values ranged from ~10²⁰ to ~10²³ for both isolates, were very similar for both conditions, and agree well with other studies. Complexation under sulfate reducing conditions (-400mV) was measured with the EDLE method using Ti(III) as a reducing agent, and yielded a K_DOM' of ~10²⁷. A similar dialysis method was used to determine the "apparent" K_DOM' under sulfate reducing conditions (-220 mV) in the presence of sulfide and cinnabar (HgS_(s)). While sequestering cinnabar within a dialysis membrane, DOM outside of the membrane was allowed to equilibrate with free Hg(II). The linear variation of total Hg outside of the membrane with DOM yielded an "apparent" K_DOM' of ~10³⁹. The large magnitude of this distribution coefficient is likely due to mixed sulfide-mercury-organic matter complexes. All experiments were carried out at pH 6.8. Binding strengths were consistent in Hg to DOM ratios ranging from 800ng per mg down to environmentally relevant ratios less than 20ng per mg.