Stability of Dimethyl Mercury in Seawater and Its Conversion to Monomethyl Mercury

Black, Frank J.; Conaway, Christopher H.; Flegal, A. Russell

doi:10.1021/es9001218

Cited by 65 publications

(60 citation statements)

References 43 publications

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“…Once in the fog droplet, MMHg could undergo photo-demethylation to inorganic Hg as has been observed in sea water (Monperrus et al, 2007;Black et al, 2009), rain water and simulated fog water (Bittrich et al, 2011). We wondered if this could account for the coastal-inland MMHg concentration gradient that was observed (Figure 4).…”

Section: Investigating the Marine Source Of Hg Species In Fogmentioning

confidence: 91%

Total- and monomethyl-mercury and major ions in coastal California fog water: Results from two years of sampling on land and at sea

Weiss-Penzias

Coale

Heim

et al. 2016

Elementa: Science of the Anthropocene

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Marine fog water samples were collected over two summers (2014)(2015) with active strand collectors (CASCC) at eight coastal sites from Humboldt to Monterey counties in California, USA, and on four ocean cruises along the California coastline in order to investigate mercury (Hg) cycling at the ocean-atmosphere-land interface. The mean concentration of monomethylmercury (MMHg) in fog water across terrestrial sites for both years was 1.6 ± 1.9 ng L -1 (<0.01-10.4 ng L -1 , N = 149), which corresponds to 5.7% (2.0-10.8%) of total Hg (HgT) in fog. Rain water samples from three sites had mean MMHg concentrations of 0.20 ± 0.12 ng L -1 (N = 5) corresponding to 1.4% of HgT. Fog water samples collected at sea had MMHg concentrations of 0.08 ± 0.15 ng L -1 (N = 14) corresponding to 0.4% of HgT. Significantly higher MMHg concentrations in fog were observed at terrestrial sites next to the ocean relative to a site 40 kilometers inland, and the mean difference was 1.6 ng L -1 . Using a rate constant for photo-demethylation of MMHg of -0.022 h -1 based on previous demethylation experiments and a coastal-inland fog transport time of 12 hours, a mean difference of only 0.5 ng L -1 of MMHg was predicted between coastal and inland sites, indicating other unknown source and/or sink pathways are important for MMHg in fog. Fog water deposition to a standard passive 1.00 m 2 fog collector at six terrestrial sites averaged 0.10 ± 0.07 L m -2 d -1, which was ∼2% of typical rainwater deposition in this area. Mean air-surface fog water fluxes of MMHg and HgT were then calculated to be 34 ± 40 ng m -2 y -1 and 546 ± 581 ng m -2 y -1 , respectively. These correspond to 33% and 13% of the rain fluxes, respectively.

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Section: Investigating the Marine Source Of Hg Species In Fogmentioning

confidence: 91%

Total- and monomethyl-mercury and major ions in coastal California fog water: Results from two years of sampling on land and at sea

Weiss-Penzias

Coale

Heim

et al. 2016

Elementa: Science of the Anthropocene

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“…After incubation, bottles for all time points were fixed with H 2 SO 4 and stored at -4°C or -40°C for methylcobalamin as noted above. Because DMHg decomposes to MMHg in acidic conditions [Black et al, 2009] Hg isotopes were measured individually and were integrated using MATLAB scripts to quantify relative isotopic ratios in the MMHg (as methylethylHg) and Hg(II) (as diethylHg)…”

Section: Methodsmentioning

confidence: 99%

Transformations of mercury in the marine water column

Munson¹

2014

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Methylation of mercury (Hg) in the marine water column has been hypothesized to serve as the primary source of the bioaccumulating chemical species monomethylmercury (MMHg) to marine food webs. Despite decades of research describing mercury methylation in anoxic sediments by anaerobic bacteria, mechanistic studies of water column methylation are severely limited. These essential studies have faced analytical challenges associated with quantifying femtomolar concentrations of the methylated Hg species dimethylmercury (DMHg) and MMHg in marine systems. In addition, the complex biogeochemical cycling of Hg in natural systems require consideration of gaseous, dissolved, and particulate species of Hg in order to probe potential controls on its ultimate transfer into marine food webs.The presented work provides a comprehensive study of Hg chemical speciation and transformations in Tropical Pacific waters. We developed an analytical method for MMHg determination from seawater that has the potential to ease measurements of MMHg distributions, as well as mechanistic studies of Hg species transformations.We used this method, in addition to previously established methods, to measure dissolved and particulate Hg species distributions and fluxes along a transect of the Pacific Ocean. Over significant gradients in oxygen utilization and primary productivity, we observed a region of methylated Hg species focused in the Equatorial Pacific that appeared spatially separated from higher concentrations in North Pacific Intermediate Waters. From the first full water column depth profiles of this region, we also observed the intrusion of elevated Hg into deep waters of the Equatorial and South Pacific Ocean.In addition we observed substantial potential rates of mercury methylation in subsurface and low oxygen waters along the Pacific transect as well as the Sargasso Sea using Hg isotope tracers. We observed dynamic production and decomposition of methylated Hg in low productivity waters, despite low ambient methylated Hg concentrations. From the addition of bulk organic matter as well as individual compounds important for methylation in anaerobic bacteria, we observe no simple limitation of Hg methylation in marine waters but highly dynamic conversion of Hg between methylated and inorganic species. List of Tables 13 Chapter 1: Introduction 15Chapter 2: Determination of monomethylmercury from seawater with ascorbic acidassisted direct ethylation Despite these guidelines, it is estimated that 0.6-11% of US women ages 16-49 have blood mercury (Hg) levels above the recommended limit for safe exposure [Mahaffey et al, 2004].Estimates of fish sources suggest that up to 90% of fish consumed in the US are from marine and estuarine environments [Sunderland, 2007]. As a result, understanding the factors that controlMMHg sources and transfer in marine environments is crucial for minimizing potential health threats to humans and marine life. Mercury from Marine Waters to BiotaThe need to quantify MMHg sources in natural waters is r...

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“…Bryan and Langston (1992) estimated that only 3 % of organic mercury in the natural environment occurs as dimethylmercury. However, it was shown that concentrations of dimethylmercury (subpicomolar) can be higher than concentrations of monomethylmercury (less than 0.05 pM) in intermediate and deep waters (Black et al, 2009). The production of dimethylmercury by microorganisms and its liberation to the environment are supposed to be a detoxification mechanism (Leermakers et al, 1993;Hobman et al, 2000).…”

Section: Methylationmentioning

confidence: 99%

“…Mason and Sullivan (1999) have found that dimethylmercury could relatively rapidly degrade to monomethylmercury in the presence of light (2 × 10 −4 to 2 × 10 −5 s −1 ). However, more recent experiments by Black et al (2009) showed that dimethylmercury is stable in natural seawater and the rate of its photodegradation is about 1.3 × 10 −7 s −1 . Dimethylmercury can be decomposed to methyl radicals and elemental mercury by photolysis, or oxidized by hydroxyl radical (Stein et al, 1996).…”

Section: Demethylationmentioning

confidence: 99%

Chemical and physical transformations of mercury in the ocean: a review

Batrakova¹,

Travnikov²,

Rozovskaya³

2014

Ocean Sci.

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Abstract.Mercury is well known as a dangerous neurotoxin enriched in the environment by human activities. It disperses over the globe, cycling between different environmental media. The ocean plays an important role in the global mercury cycle, acting both as a dispersion medium and as an exposure pathway. In this paper, we review the current knowledge on the major physical and chemical transformations of mercury in the ocean. This review describes the mechanisms and provides a compilation of available rate constants for the major processes in seawater, including oxidation and reduction reactions under light and dark conditions, biotic and abiotic methylation/demethylation, and adsorption by particles. These data could be useful for the development of transport models describing processes undergone by mercury in the ocean.

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Stability of Dimethyl Mercury in Seawater and Its Conversion to Monomethyl Mercury

Cited by 65 publications

References 43 publications

Total- and monomethyl-mercury and major ions in coastal California fog water: Results from two years of sampling on land and at sea

Total- and monomethyl-mercury and major ions in coastal California fog water: Results from two years of sampling on land and at sea

Transformations of mercury in the marine water column

Chemical and physical transformations of mercury in the ocean: a review

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