Abstract :
WHAM, incorporating Humic Ion Binding Model VI, was used to analyse published data describing the binding of Hg(II) and methylmercury (CH3Hg) by isolated humic substances. For Hg(II), the data covered wide ranges of pH and levels of metal binding, whereas for CH3Hg the range of metal binding was relatively narrow. Data were fitted by adjustment of a single model parameter, log KMA, the intrinsic equilibrium constant characterising, in the standard version of the model, the binding of metal ions and their first hydrolysis products to humic carboxylic acid groups. Other model parameters, including those characterising the tendency of metal ions to interact with “softer” ligand atoms (N and S), were held at their default values. The importance of the first hydrolysis products in binding was considered, and also the possible influence of competition by residual Fe(III), bound to the humic matter.
