G. R. Aiken J. N. Ryan M. Haitzer 2002 <div class="article_abstract"><div class="container container_scaled-down"><div class="row"><div class="col-xs-12"><div id="abstractBox" class="article_abstract-content hlFld-Abstract"><p class="articleBody_abstractText">The binding of Hg(II) to dissolved organic matter (DOM; hydrophobic acids isolated from the Florida Everglades by XAD-8 resin) was measured at a wide range of Hg-to-DOM concentration ratios using an equilibrium dialysis ligand exchange method. Conditional distribution coefficients (<i>K</i>_DOM‘) determined by this method were strongly affected by the Hg/DOM concentration ratio. At Hg/DOM ratios below approximately 1 μg of Hg/mg of DOM, we observed very strong interactions (<i>K</i>_DOM‘ = 10^23.2^±^1.0<span>&nbsp;</span>L kg^-¹<span>&nbsp;</span>at pH = 7.0 and<span>&nbsp;</span><i>I</i><span>&nbsp;</span>= 0.1), indicative of mercury−thiol bonds. Hg/DOM ratios above approximately 10 μg of Hg/mg of DOM, as used in most studies that have determined Hg−DOM binding constants, gave much lower<span>&nbsp;</span><i>K</i>_DOM‘ values (10^10.7^±^1.0<span>&nbsp;</span>L kg^-¹<span>&nbsp;</span>at pH = 4.9−5.6 and<span>&nbsp;</span><i>I</i><span>&nbsp;</span>= 0.1), consistent with Hg binding mainly to oxygen functional groups. These results suggest that the binding of Hg to DOM under natural conditions (very low Hg/DOM ratios) is controlled by a small fraction of DOM molecules containing a reactive thiol functional group. Therefore, Hg/DOM distribution coefficients used for modeling the biogeochemical behavior of Hg in natural systems need to be determined at low Hg/DOM ratios.</p></div></div></div></div></div> application/pdf 10.1021/es025699i en ACS Binding of mercury(II) to dissolved organic matter: The role of the mercury-to-DOM concentration ratio article