Interaction of Hg(II) with soil-derived humic substances

The complexation of Hg(II) with soil-derived humic substances was investigated using an iodide selective electrode. Humic substances were titrated with Hg(II) at fixed pH values, 4, 5, and 6. The binding behavior was successfully described with a continuous multiligand distribution model, which incorporated proton competitive binding and ionic strength effects. The parameters obtained from the three titration curves at different pH values were very similar with a Hg binding constant, 4.69 ± 0.19. Less Hg(II) was bound by humic substances at lower pH values due to competitive binding of protons.