Alkylated mercury species (monomethylmercury, MeHg, and dimethylmercury, DMeHg) exhibit significant bioaccumulation, and pose significant risks to ecosystems and human health. Although decades of research have been devoted to understanding MeHg formation and degradation, little is known about the DMeHg formation in aquatic systems. Here, we combine complementary experimental and computational approaches to examine MeHg speciation and DMeHg formation in sulfidic aqueous solutions, with an emphasis on the formation and decomposition of the binuclear bis(methylmercuric(II)) sulfide complex (CH3Hg)2S. Experimental data indicate that the reaction 2CH3Hg+ + HS- = (CH3Hg)2S has a log K = 26.0. Thus, the binuclear (CH3Hg)2S complex is likely to be the dominant MeHg species under high MeHg concentrations typically used in experimental investigations of MeHg degradation by sulfate-reducing bacteria (SRB). Our finding of a significant abiotic removal mechanism for MeHg in sulfidic solutions through the formation of relatively insoluble (CH3Hg)2S suggests careful reexamination of reported “oxidative demethylation” of MeHg by SRB and perhaps other obligate anaerobes. We provide evidence for slow decomposition of (CH3Hg)2S to DMeHg and HgS, with a first-order rate constant k = 1.5 0.4 x 10-6 h-1. Quantum chemical calculations suggest that the reaction proceeds by a novel mechanism involving rearrangement of the (CH3Hg)2S complex facilitated by strong Hg-Hg interactions that activate a methyl group for intramolecular transfer. Predictions of DMeHg formation rates under a variety of field and laboratory conditions indicate that this pathway for DMeHg formation will be significant in laboratory experiments utilizing high MeHg concentrations, favoring (CH3Hg)2S formation. In natural systems with relatively high MeHg/[H2S]T ratios (the oxic/anoxic interface, for example), DMeHg production may be observed, and warrants further investigation.
Experimental and computational evidence show that dimethylmercury is produced from decomposition of bis(methylmercury(ii)) sulfide.
Kanzler, Charlotte R., et al. "Emerging investigator series: methylmercury speciation and dimethylmercury production in sulfidic solutions." Environmental Science: Processes & Impacts, vol. 20, no. 4, Jan. 2018. https://doi.org/10.1039/C7EM00533D
Kanzler, Charlotte R., Lian, Peng, Trainer, Emma Leverich, Yang, Xiaoxuan, Govind, Niranjan, Parks, Jerry M., & Graham, Andrew M. (2018). Emerging investigator series: methylmercury speciation and dimethylmercury production in sulfidic solutions. Environmental Science: Processes & Impacts, 20(4). https://doi.org/10.1039/C7EM00533D
Kanzler, Charlotte R., Lian, Peng, Trainer, Emma Leverich, et al., "Emerging investigator series: methylmercury speciation and dimethylmercury production in sulfidic solutions," Environmental Science: Processes & Impacts 20, no. 4 (2018), https://doi.org/10.1039/C7EM00533D
@article{osti_1439665,
author = {Kanzler, Charlotte R. and Lian, Peng and Trainer, Emma Leverich and Yang, Xiaoxuan and Govind, Niranjan and Parks, Jerry M. and Graham, Andrew M.},
title = {Emerging investigator series: methylmercury speciation and dimethylmercury production in sulfidic solutions},
annote = {Alkylated mercury species (monomethylmercury, MeHg, and dimethylmercury, DMeHg) exhibit significant bioaccumulation, and pose significant risks to ecosystems and human health. Although decades of research have been devoted to understanding MeHg formation and degradation, little is known about the DMeHg formation in aquatic systems. Here, we combine complementary experimental and computational approaches to examine MeHg speciation and DMeHg formation in sulfidic aqueous solutions, with an emphasis on the formation and decomposition of the binuclear bis(methylmercuric(II)) sulfide complex (CH3Hg)2S. Experimental data indicate that the reaction 2CH3Hg+ + HS- = (CH3Hg)2S has a log K = 26.0. Thus, the binuclear (CH3Hg)2S complex is likely to be the dominant MeHg species under high MeHg concentrations typically used in experimental investigations of MeHg degradation by sulfate-reducing bacteria (SRB). Our finding of a significant abiotic removal mechanism for MeHg in sulfidic solutions through the formation of relatively insoluble (CH3Hg)2S suggests careful reexamination of reported “oxidative demethylation” of MeHg by SRB and perhaps other obligate anaerobes. We provide evidence for slow decomposition of (CH3Hg)2S to DMeHg and HgS, with a first-order rate constant k = 1.5 0.4 x 10-6 h-1. Quantum chemical calculations suggest that the reaction proceeds by a novel mechanism involving rearrangement of the (CH3Hg)2S complex facilitated by strong Hg-Hg interactions that activate a methyl group for intramolecular transfer. Predictions of DMeHg formation rates under a variety of field and laboratory conditions indicate that this pathway for DMeHg formation will be significant in laboratory experiments utilizing high MeHg concentrations, favoring (CH3Hg)2S formation. In natural systems with relatively high MeHg/[H2S]T ratios (the oxic/anoxic interface, for example), DMeHg production may be observed, and warrants further investigation.Experimental and computational evidence show that dimethylmercury is produced from decomposition of bis(methylmercury(ii)) sulfide.},
doi = {10.1039/C7EM00533D},
url = {https://www.osti.gov/biblio/1439665},
journal = {Environmental Science: Processes & Impacts},
issn = {ISSN ESPICZ},
number = {4},
volume = {20},
place = {United States},
publisher = {Royal Society of Chemistry},
year = {2018},
month = {01}}
Journal Article
·
Thu Jun 10 20:00:00 EDT 2021
· Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
·OSTI ID:1809955