Measurement of Complexation of Methylmercury(II) Compounds by Freshwater Humic Substances Using Equilibrium Dialysis

Abstract

Humic and fulvic acids from lakes in Ontario, Canada, have been isolated and been examined for their ability to bind methylmercury(II). Equilibrium dialysis has been applied to differentiate between bound and unbound fractions of MeHg(II). Losses of methylmercury(II) from solutions containing 0.5-100 ng/L MeHg(II) and 10 mg/L humic substances (HS) are negligible over a 24-h time interval when using acid-cleaned glass beakers, membrane closures, and cellulose ester membranes having a molecular weight cutoff of 500. Dialysis equilibrium for MeHg(II) is reached within this period of time. For each humic material, two classes of binding sites could be detected. Log K values of conditional stability constants for the strong and the weaker binding sites were in the range of 13.02-14.48 and 12.15-13.07, respectively. Binding capacities have been calculated as 0.2-13 of ng MeHg(II)/mg of HS for the strong sites and 1.2-72 ng of MeHg(II)/mg of HS for the weaker sites. Calculation of equilibrium distribution shows that methylmercury(II)-HS complexes predominate in oxidized freshwaters with low sulfide concentrations. In anoxic waters, CH 3 HgSH should prevail. The CH 3 HgCl complex is too weak to compete with either of the latter complexes.

Effects of ano×ia and sulfide on concentrations of total and methyl mercury in sediment and water in two Hg-polluted lakes

“…In the hypolimnion of the lower lake, in which sulfide could not be detected during the study period, [IHg] (Regnell et al 1997). This is likely the case because virtually all filter-passing Hg(II) and MeHg in nonsulfidic water is bound to dissolved or colloidal organic matter (Stordal et al 1996;Hintelmann et al 1997) and because oxides are efficient scavengers of dissolved and colloidal organic compounds (Tipping and Woof 1983). However, as discussed by Tipping and Woof (1983), organic matter can accumulate in hypolimnia not only as a result of dissolution of oxides but also as a result of anaerobic decomposition of particulate organic matter resulting in dissolved and colloidal forms.…”

“…4). Yet another explanation for hypolimnetic Hg enrichment is that Hg(II) and MeHg form soluble complexes with bisulfide and (or) polysulfide or that Hg(II) forms colloidal HgS (Wang and Driscoll 1995;Hintelmann et al 1997;Paquette and Helz 1997). However, precipitation of Hg(II) as HgS(s) or its coprecipitation with FeS may also occur, depending on several factors such as the free sulfide concentration, pH, Fe(II) concentration, and the level and quality of dissolved organic matter (Dyrssen and Wedborg 1991;Ravichandran et al 1999).…”

“…The sulfide levels that we measured in the hypolimnion of the upper lake fell within the range that Benoit et al (1999) stated would lead to sulfide complexation of Hg(II) and to negligible amounts of Hg(II)-DOC complexes. Also, using the equilibrium calculations provided by Hintelmann et al (1997), sulfide would outcompete DOC in the complexation of MeHg.…”

Removal of Hg2+ and methylmercury in waters by functionalized multi-walled carbon nanotubes: adsorption behavior and the impacts of some environmentally relevant factors

“…The strong sorption of Hg 2+ to MWCNTs make it requires low dose of MWCNTs to remove Hg 2+ , and high (>90%) and almost equal removal efficiencies were obtained in the studied range of MWCNTs concentration (0.5−2.0 g/L) for all the four MWCNTs. Due to the relatively weak sorption of MeHg to MWCNTs, the removal efficiency four adsorbing processes in the solution: (i) NOM could combine with Hg 2+ and MeHg [25,43]; (ii) MWCNTs could adsorb Hg 2+ and MeHg [17,21,29,37,[44][45][46]; (iii) MWCNTs could adsorb NOM and form MWCNTs-NOM complexes [47]; and (iv) NOM could stabilize the dispersion of MWCNTs [26,27]. Depending on the characteristics of MWCNTs and NOM, as well as the aqueous chemistry parameters, these four processes showed different strength and therefore resulted in varied removal efficiency of Hg 2+ and MeHg.…”

pH Dependence of CH3Hg+-binding Sites in Humic Acid: An X-ray Absorption Study

“…)과 메틸수은은 부식물질과 강하게 결합 하는데, 보고된 유기물의 무기수은과 메틸수은의 결합반 응 log K 값은 각각 > 30 과 > 10 (Hintelmann et al, 1995(Hintelmann et al, & 1997으로 무기수은이 메틸 수은보다 더 강한 결합을 이루는 것으로 보인다 (Tipping, 2007). 또는 2개의 황 원자와 결합된다 (Xia et al, 1999;Hesterberg et al, 2001;Skyllberg et al, 2000;Nagy et al, 2011).…”