Heteroatomic molecular complexes between Hg and DOM are identified in water.
For the first time, we positively identify major Hg-DOM complexes such as C10H21N2S4Hg+ and C8H17N2S4Hg+ based on both the exact molecular mass and patterns of Hg stable isotope distributions. Heteroatomic molecules, especially those containing multiple sulfur and nitrogen atoms in DOM, are among the most important in forming strong complexes with Hg.
The study represents the first step to unambiguously identify specific DOM molecules in Hg binding, which are critically important in affecting Hg biological uptake and conversion to neurotoxic MeHg in the environment.
The chemical speciation and bioavailability of Hg is markedly influenced by its complexation with naturally DOM in aquatic environments. However, to date, analytical methodologies capable of identifying such complexes are scarce. For the first time, we utilize ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) coupled with electrospray ionization to identify individual Hg-DOM complexes. The measurements were performed by direct infusion of DOM in 1:1 methanol:water solution at a Hg-to-dissolved-organic-carbon (DOC) molar ratio of 3×10-4. Heteroatomic molecules, especially those containing multiple S and N atoms, were found to be among the most important in forming strong complexes with Hg. Major Hg-DOM complexes of C10H21N2S4Hg+ and C8H17N2S4Hg+ were identified based on both the exact molecular mass and patterns of Hg stable isotope distributions detected by FTICR-MS. Density functional theory was used to predict the solution-phase structures of candidate molecules. These findings represent the first step to unambiguously identify specific DOM molecules in Hg binding, so as to fully understand environmental factors affecting Hg biological uptake and conversion to neurotoxic MeHg in the natural environment.
Chen, H., R.C. Johnston, B.F. Mann, R.K. Chu, N. Tolic, J.M. Parks, and B. Gu. 2017. "Identification of Mercury and Dissolved Organic Matter Complexes Using Ultrahigh Resolution Mass Spectrometry." Environmental Science and Technology Letters 4(2):59–65. DOI:10.1021/acs.estlett.6b00460.
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