| Abstract: | Mercury is a global contaminant of concern due to its transformation by microorganisms to form methylmercury, a toxic species that accumulates in biological tissues. The effect of dissolved organic matter (DOM) isolated from natural waters on reactions between mercury(II) (Hg) and sulfide (S(-II)) to form HgS(s) nanoparticles across a range of Hg and S(-II) concentrations was investigated. Hg was equilibrated with DOM, after which S(-II) was added. Dissolved Hg (Hgaq) was periodically quantified using ultracentrifugation and chemical analysis following the addition of S(-II). Particle size and identity were determined using dynamic light scattering and X-ray absorption spectroscopy. S(-II) reacts with Hg to form 20 to 200nm aggregates consisting of 1-2 nm HgS(s) subunits that are more structurally disordered than metacinnabar in the presence of 2 x 10-9 to 8 x 10-6M Hg and 10 (mg C)L-1 DOM. Some of the HgS(s) nanoparticle aggregates are subsequently dissolved by DOM and (re)precipitated by S(-II) over periods of hours to days. At least three fractions of Hg-DOM species were observed with respect to reactivity toward S(-II): 0.3 μmol reactive Hg per mmol C (60 percent), 0.1 μmol per mmol C (20 percent) that are kinetically hindered, and another 0.1 μmol Hg per mmol C (20 percent) that are inert to reaction with S(-II). Following an initial S(-II)-driven precipitation of HgS(s), HgS(s) was dissolved by DOM or organic sulfur compounds. HgS(s) formation during this second phase was counterintuitively favored by lower S(-II) concentrations, suggesting surface association of DOM moieties that are less capable of dissolving HgS(s). DOM partially inhibits HgS(s) formation and mediates reactions between Hg and S(-II) such that HgS(s) is susceptible to dissolution. These findings indicate that Hg accessibility to microorganisms could be controlled by kinetic (intermediate) species in the presence of S(-II) and DOM, undermining the premise that equilibrium Hg species distributions should correlate to the extent or rate of Hg methylation in soils and sediments. |
| Genre: | Article |
| ProdID: | 70037230 |
| Citation Author: | Slowey, Aaron J. |
| Citation Contributing Office: | Branch of Regional Research WR |
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| Citation End Page: | 4708 |
| Citation Issue: | 16 |
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| Citation Language: | English |
| Citation Larger Work Title: | Geochimica et Cosmochimica Acta |
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| Citation Number Of Pages: | 16 |
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| Citation Publisher: | Elsevier |
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| Citation Search Results Text: | Rate of formation and dissolution of mercury sulfide nanoparticles: The dual role of natural organic matter; 2010; Article; Journal; Geochimica et Cosmochimica Acta; Slowey, Aaron J. |
| Citation Start Page: | 4693 |
| Citation Volume: | 74 |
| Citation Year: | 2010 |
| Type: | citation/reference |
| Text: | Rate of formation and dissolution of mercury sulfide nanoparticles: The dual role of natural organic matter; 2010; Article; Journal; Geochimica et Cosmochimica Acta; Slowey, Aaron J. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1016/j.gca.2010.05.012 |
| Date Other: | Fri, 1 Jan 2010 00:00 -0600 |
| Publisher: | Elsevier |
