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Effects of Sulfide Concentration and Dissolved Organic Matter Characteristics on the Structure of Nanocolloidal Metacinnabar

Author:
Poulin, Brett A., Gerbig, Chase A., Kim, Christopher S., Stegemeier, John P., Ryan, Joseph N., Aiken, George R.
Source:
Environmental Science & Technology 2017 v.51 no.22 pp. 13133-13142
ISSN:
1520-5851
Subject:
X-ray absorption spectroscopy, absorbance, bioavailability, environmental science, mercury, methylmercury compounds, organic matter, solubility, sulfides
Abstract:
Understanding the speciation of divalent mercury (Hg(II)) in aquatic systems containing dissolved organic matter (DOM) and sulfide is necessary to predict the conversion of Hg(II) to bioavailable methylmercury. We used X-ray absorption spectroscopy to characterize the structural order of mercury in Hg(II)–DOM–sulfide systems for a range of sulfide concentration (1–100 μM), DOM aromaticity (specific ultraviolet absorbance (SUVA₂₅₄)), and Hg(II)–DOM and Hg(II)–DOM–sulfide equilibration times (4–142 h). In all systems, Hg(II) was present as structurally disordered nanocolloidal metacinnabar (β-HgS). β-HgS nanocolloids were significantly smaller or less ordered at lower sulfide concentration, as indicated by under-coordination of Hg(II) in β-HgS. The size or structural order of β-HgS nanocolloids increased with increasing sulfide abundance and decreased with increasing SUVA₂₅₄ of the DOM. The Hg(II)–DOM or Hg(II)–DOM–sulfide equilibration times did not significantly influence the extent of structural order in nanocolloidal β-HgS. Geochemical factors that control the structural order of nanocolloidal β-HgS, which are expected to influence nanocolloid surface reactivity and solubility, should be considered in the context of mercury bioavailability.
Agid:
5864123