Factors controlling the abiotic photo-degradation of monomethylmercury in surface waters

Black, Frank J.; Poulin, Brett A.; Flegal, A. Russell

doi:10.1016/j.gca.2012.01.019

Cited by 129 publications

(232 citation statements)

References 67 publications

(110 reference statements)

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“…Interestingly, the photodegradation of CH 3 Hg + depends on the wavelength-specific incident photon flux, on DOM contents and salinity, but does not depend on nitrate photolysis [3]. It has been shown that rates of CH 3 Hg + photodegradation are decreased with increasing salinity and DOM contents [3]. Increasing DOM contents with the CH 3 Hg + aqueous media can act as a barrier to reach the incident light intensity toward the CH 3 Hg + component which could presumably decline the rates of CH 3 Hg + photodegradation.…”

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confidence: 98%

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confidence: 99%

“…Studies show that the photo-Fenton reaction or the reactive oxygen species, including hydroxyl radical (HO • ), 1 O 2 , triplet excited state of DOM (3DOM*), and hydrated electron (e aq -), play a minor role in CH 3 Hg + photodegradation in aqueous media [3,4,6]. Interestingly, the photodegradation of CH 3 Hg + depends on the wavelength-specific incident photon flux, on DOM contents and salinity, but does not depend on nitrate photolysis [3]. It has been shown that rates of CH 3 Hg + photodegradation are decreased with increasing salinity and DOM contents [3].…”

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confidence: 99%

“…Methyl mercury (CH 3 Hg + ), a neurotoxin, is the most toxic form of mercury that occurs in natural waters [1][2][3][4]. It is a cause of concern because of increasing worldwide pollution by mercury in both water and atmosphere [3,5].…”

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confidence: 99%

“…It is a cause of concern because of increasing worldwide pollution by mercury in both water and atmosphere [3,5]. Photodegradation of CH 3 Hg + is one of the main removal pathways from surface waters, and it has been shown to occur in the presence of dissolved organic matter (DOM) but not in ultra-pure water [2,4]. Several mechanisms for the photodegradation of CH 3 Hg + have been proposed, including: (1) direct photodegradation of CH 3 Hg-DOM complexes via intramolecular electron transfer [4] and (2) indirect photodegradation of CH 3 Hg-DOM by free radicals/ reactive oxygen species such as singlet oxygen (1O2) and the hydroxyl radical (HO•) [1,2,6].…”

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The mechanism behind the DOM effects on methylmercury photodegradation

et al. 2015

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Methyl mercury (CH 3 Hg + ), a neurotoxin, is the most toxic form of mercury that occurs in natural waters [1][2][3][4]. It is a cause of concern because of increasing worldwide pollution by mercury in both water and atmosphere [3,5]. Photodegradation of CH 3 Hg + is one of the main removal pathways from surface waters, and it has been shown to occur in the presence of dissolved organic matter (DOM) but not in ultra-pure water [2,4]. Several mechanisms for the photodegradation of CH 3 Hg + have been proposed, including: (1) direct photodegradation of CH 3 Hg-DOM complexes via intramolecular electron transfer [4] and (2) indirect photodegradation of CH 3 Hg-DOM by free radicals/ reactive oxygen species such as singlet oxygen (1O2) and the hydroxyl radical (HO•) [1,2,6]. Studies show that the photo-Fenton reaction or the reactive oxygen species, including hydroxyl radical (HO • ), 1 O 2 , triplet excited state of DOM (3DOM*), and hydrated electron (e aq -), play a minor role in CH 3 Hg + photodegradation in aqueous media [3,4,6]. Interestingly, the photodegradation of CH 3 Hg + depends on the wavelength-specific incident photon flux, on DOM contents and salinity, but does not depend on nitrate photolysis [3]. It has been shown that rates of CH 3 Hg + photodegradation are decreased with increasing salinity and DOM contents [3]. Increasing DOM contents with the CH 3 Hg + aqueous media can act as a barrier to reach the incident light intensity toward the CH 3 Hg + component which could presumably decline the rates of CH 3 Hg + photodegradation. Several gaps still exist concerning the proposed photodegradation pathways, including two unresolved key questions: (1) how does DOM form bonds with CH 3 Hg + ? and (2) How is the newly formed complex excited upon irradiation? A couple of considerations may help in shedding some light over this issue and could provide scope for further research in the field. The first issue is the formation of p-electron bonding systems between CH 3 Hg + [Hg 1+ = 1s22s22p63s23p64s23d104p65s24d105p66s14f145d10] and DOM (CH 3 Hg-DOM), through electron donation from the functional groups of high molecular weight DOM to an empty sorbital of CH 3 Hg + (ligand-to-metal charge transfer) [7]. Note that the p-electron bonding system is not formed with low-molecular-weight DOM, because the formed complex would not be stable enough. The overall conditional complexation constants (K 0 DOM) between Hg(II) and DOM (extracted humic acids, fulvic acids and hydrophobic acids) show very strong interactions (K 0 DOM = 1023.2±1.0 L/kg) at Hg/DOM ratios below approximately 1 lg Hg/mg DOM, which are indicative of mercury-thiol bonds [8].

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confidence: 99%

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confidence: 99%

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The mechanism behind the DOM effects on methylmercury photodegradation

et al. 2015

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Mercury in Water

Xia

Johs

et al. 2019

Encyclopedia of Water

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Mercury (Hg) is a global pollutant threatening our water resources and human health. Every one of us contains some levels of Hg or methylmercury (MeHg) in our body from consumption of contaminated food such as fish and rice in some countries. Our understanding of the behavior of Hg in natural aquatic environments is limited because the key factors controlling microbial uptake and conversion of inorganic Hg to neurotoxic MeHg remain obscure. MeHg concentrations in water can bioaccumulate up to eight orders of magnitude in the food chain. Metallic or elemental Hg can evaporate and be transported around the globe, plus it readily undergoes chemical, photochemical, and biological transformations (i.e. oxidation, reduction, methylation, and demethylation) in water and sediments. Natural dissolved organic matter (DOM) plays a critical role in mediating these transformations because of its exceptionally strong binding affinity for Hg and its dual functional roles in reducing and oxidizing Hg. Recent discovery of Hg‐methylation genes has significantly advanced our understanding of MeHg biosynthesis, although the simultaneous degradation of MeHg at low concentrations (i.e. picomolar to nanomolar) by anaerobic and methanotrophic bacteria is also recognized now as a potentially important process for controlling net MeHg production, a key factor that determines Hg concentrations and bioaccumulation in biota. Treatment technologies for Hg removal from water are available, but they are mostly applicable to industrial waste streams and at contamination sites with high Hg concentrations (i.e. micromolar to millimolar). Reductions in Hg human exposure might be achievable by decreasing anthropogenic releases, such as coal combustion, over the long‐term since Hg methylation responds to Hg inputs, particularly to freshly deposited Hg in natural aquatic systems.

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Geochemistry of Great Salt Lake

Wurtsbaugh

Belovsky

Baxter

et al. 2019

Encyclopedia of Water

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The Great Salt Lake is terminal, lacking outflow, and is descended from vast Lake Bonneville through evaporation. It is akin to a puddle on the tarmac with a similar surface area to volume ratio. It is an avian wildlife habitat of hemispheric importance, and lies adjacent to a metropolitan population of 2.5 million, with correspondingly increasing water demands and anthropogenic effluents. Engineered partitions spanning the lake generate density‐driven flow among the layered concentrated brines, which show dramatic vertical redox transitions and corresponding contrasts in trace element behaviors, some of which show elevated burdens in the ecosystem. We describe this system in four parts, starting with the geographic and hydrologic framework (Section 1) that determines its limnologic and hydrodynamic characteristics (Section 2) that shape its ecosystem (Section 3), which interacts dynamically with its geochemical characteristics (Section 4).

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Factors controlling the abiotic photo-degradation of monomethylmercury in surface waters

Cited by 129 publications

References 67 publications

The mechanism behind the DOM effects on methylmercury photodegradation

The mechanism behind the DOM effects on methylmercury photodegradation

Mercury in Water

Geochemistry of Great Salt Lake

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