Bhoopesh Mishra*, Maxim I. Boyanov, Kenneth M. Kemner and Edward J. O’Loughlin,
{"title":"Reduction of HgII by MnII","authors":"Bhoopesh Mishra*, Maxim I. Boyanov, Kenneth M. Kemner and Edward J. O’Loughlin, ","doi":"10.1021/acsearthspacechem.3c00304","DOIUrl":null,"url":null,"abstract":"<p >The reduction of Hg<sup>II</sup> to Hg<sup>I</sup> or Hg<sup>0</sup> can lead to significant changes in Hg toxicity and mobility in the environment. Photochemical reduction is the primary process for the reduction of Hg<sup>II</sup> to Hg<sup>0</sup> in sunlit environments; however, dark reduction of Hg<sup>II</sup> can occur via microbial metabolic processes and/or reduction by reduced natural organic matter, Fe<sup>II</sup> mineral phases, Fe<sup>II</sup> sorbed to minerals, or aqueous Fe<sup>II</sup>. Here, we demonstrate a novel Hg<sup>II</sup> reduction pathway involving another environmentally relevant reductant, Mn<sup>II</sup>. Abiotic reduction of Hg<sup>II</sup>O by Mn<sup>II</sup> was studied as a function of pH and anion environment (perchlorate, sulfate, chloride) using X-ray absorption spectroscopy to characterize the solid-phase Hg and Mn species. At circumneutral pH of 7.5, about 70% of Hg<sup>II</sup> was reduced to elemental Hg<sup>0</sup> within 2 h. In contrast, 12 h were needed to achieve the same extent of reduction at pH 6.9. In the presence of sulfate and chloride, Hg<sup>I</sup> species were formed. Hg<sup>II</sup> reduction was initially rapid and coupled with the oxidation of soluble Mn<sup>II</sup>-oxides to insoluble Mn<sup>IV</sup>-oxides, followed by a significantly slower reduction of Hg<sup>II</sup> during the Mn<sup>II</sup>-catalyzed transformation of the Mn<sup>IV</sup>-oxides to hydroxide and oxyhydroxide minerals. The observed reduction of Hg<sup>II</sup> by Mn<sup>II</sup> at circumneutral pH could be an important transformation pathway for environmental Hg, affecting its bioavailability and mobility under mildly reducing conditions.</p>","PeriodicalId":15,"journal":{"name":"ACS Earth and Space Chemistry","volume":null,"pages":null},"PeriodicalIF":2.9000,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Earth and Space Chemistry","FirstCategoryId":"92","ListUrlMain":"https://pubs.acs.org/doi/10.1021/acsearthspacechem.3c00304","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
The reduction of HgII to HgI or Hg0 can lead to significant changes in Hg toxicity and mobility in the environment. Photochemical reduction is the primary process for the reduction of HgII to Hg0 in sunlit environments; however, dark reduction of HgII can occur via microbial metabolic processes and/or reduction by reduced natural organic matter, FeII mineral phases, FeII sorbed to minerals, or aqueous FeII. Here, we demonstrate a novel HgII reduction pathway involving another environmentally relevant reductant, MnII. Abiotic reduction of HgIIO by MnII was studied as a function of pH and anion environment (perchlorate, sulfate, chloride) using X-ray absorption spectroscopy to characterize the solid-phase Hg and Mn species. At circumneutral pH of 7.5, about 70% of HgII was reduced to elemental Hg0 within 2 h. In contrast, 12 h were needed to achieve the same extent of reduction at pH 6.9. In the presence of sulfate and chloride, HgI species were formed. HgII reduction was initially rapid and coupled with the oxidation of soluble MnII-oxides to insoluble MnIV-oxides, followed by a significantly slower reduction of HgII during the MnII-catalyzed transformation of the MnIV-oxides to hydroxide and oxyhydroxide minerals. The observed reduction of HgII by MnII at circumneutral pH could be an important transformation pathway for environmental Hg, affecting its bioavailability and mobility under mildly reducing conditions.
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.