Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems

Point, David; Sonke, Jeroen E.; Day, Rusty D.; Roseneau, David G.; Hobson, Keith A.; Pol, Stacy S. Vander; Moors, Amanda J.; Pugh, Rebecca S.; Donard, Olivier F. X.; Becker, Paul R.

doi:10.1038/ngeo1049

Cited by 134 publications

(200 citation statements)

References 42 publications

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“…The second method extrapolates the fractionation factor to the approximate MMHg/DOC of surface ocean water using two published experiments and the assumption that there is no fractionation of the 199 Hg value at DOC = 0 (ref. 22). Estimates of per cent photochemical degradation using the first method are about twice as high as estimates using the second method, but the proportional shift in photochemical degradation with depth is the same with both methods.…”

Section: Methodsmentioning

confidence: 62%

“…20 unmodified, and as modified by ref. 22, to obtain the range of values reported in the text. The first method uses the observed 199 Hg value and the fractionation factor determined experimentally 20 using 1 mg l −1 DOC and much higher MMHg/DOC than present in surface ocean water.…”

Section: Methodsmentioning

confidence: 99%

“…Mapping observed 199 Hg values to experimental data 20 and to a proposed extrapolation of these data to the MMHg/DOC ratio of North Pacific surface water 22 suggests that these fish preserve the isotopic composition of residual MMHg that has undergone between 46 and 80% photochemical degradation at a mean depth of 10 m and between 9 and 21% photochemical degradation at a depth of 590 m (Methods). Estimates of percentage photochemical degradation could be even higher for lower TP fish, which may have up to 20% inorganic Hg (ref.…”

Section: Mercury Isotope Variation In Pacific Ocean Fishmentioning

confidence: 99%

“…Mercury displays mass-dependent fractionation (MDF; δ 202 Hg) during all biotic and abiotic chemical reactions that have been investigated and large magnitude mass-independent fractionation (MIF; 199 Hg, 201 Hg) during photochemical radical pair reactions (see Methods for definition of δ 202 Hg, 199 Hg and 201 Hg). The combination of Hg MDF and MIF provides a probe into the reaction pathways and biogeochemical history of Hg and can also provide a fingerprint of sources of Hg to ecosystems [19][20][21][22] . Coupling estimates of TP with Hg concentrations can allow for an understanding of MMHg biomagnification in marine food webs 5,21 .…”

mentioning

confidence: 99%

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Methylmercury production below the mixed layer in the North Pacific Ocean

et al. 2013

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Mercury enters marine food webs in the form of microbially generated monomethylmercury. Microbial methylation of inorganic mercury, generating monomethylmercury, is widespread in low-oxygen coastal sediments. The degree to which microbes also methylate mercury in the open ocean has remained uncertain, however. Here, we present measurements of the stable isotopic composition of mercury in nine species of marine fish that feed at different depths in the central North Pacific Subtropical Gyre. We document a systematic decline in δ 202 Hg, 199 Hg and 201 Hg values with the depth at which fish feed. We show that these mercury isotope trends can be explained only if monomethylmercury is produced below the surface mixed layer, including in the underlying oxygen minimum zone, that is, between 50 and more than 400 m depth. Specifically, we estimate that about 20-40% of the monomethylmercury detected below the surface mixed layer originates from the surface and enters deeper waters either attached to sinking particles, or in zooplankton and micronekton that migrate to depth. We suggest that the remaining monomethylmercury found at depth is produced below the surface mixed layer by methylating microbes that live on sinking particles. We suggest that microbial production of monomethylmercury below the surface mixed later contributes significantly to anthropogenic mercury uptake into marine food webs.M ercury (Hg) is a globally distributed atmospheric pollutant that can form monomethyl-Hg (MMHg), which is neurotoxic and bioaccumulative in aquatic food webs. The main pathway for human exposure to MMHg is through consumption of piscivorous marine fish 1 . In the ocean Hg primarily exists as inorganic Hg(ii) or Hg (0) [5][6][7] . In agreement with these vertical profiles, total Hg (THg) levels in commercially important predatory pelagic fish and their prey increase with median depth of occurrence 8,9 , which is indicative of both foraging depth and habitat utilization. However, the biogeochemical factors controlling the distribution and speciation of Hg in the ocean and the bioaccumulation of MMHg in marine food webs are still not well understood 10 .Microbial activity and both dark and photochemical inorganic reactions ultimately control the chemical speciation and subsequent bioavailability of Hg (ref. 2), thus an understanding of the competing processes that produce and degrade MMHg at different depths in the ocean is critical to tracing its bioaccumulation in fish and biomagnification in marine food webs. MMHg typically comprises only a small fraction of THg in North Pacific sea water (<15%; ref. 4) but nearly all of the Hg (>95%) in large marine fish 2,11 and most of the Hg (>80%) in small fish with trophic position (TP) as low as 2.5 (ref. 12). DMHg concentrations are generally small relative to MMHg (refs 3,4,13), although at some (refs 13,14). As DMHg is not bioaccumulated and because its Hg isotopic composition has not been measured, it is not treated in detail here. MMHg production in the oxygen minimum zone (OMZ) of...

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Section: Methodsmentioning

confidence: 62%

Section: Methodsmentioning

confidence: 99%

Section: Mercury Isotope Variation In Pacific Ocean Fishmentioning

confidence: 99%

mentioning

confidence: 99%

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Methylmercury production below the mixed layer in the North Pacific Ocean

et al. 2013

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“…Species-specific Hg isotope fractionation of MeHg has recently been observed in biological samples [138,139] and in chemical transformation processes such as methylation [140] and demethylation [138,141,142]. The fingerprint of mass-dependent and -independent fractionation of MeHg in natural environmental samples was suggested to be a good indicator of important processes in the global cycle of MeHg and will be helpful to understand and quantify these processes [138].…”

Section: Chromatographic Separation Coupled With Mc-icp-ms To Measurementioning

confidence: 99%

Recent advances in speciation analysis of mercury, arsenic and selenium

2012

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Mercury (Hg), arsenic (As) and selenium (Se) are ubiquitous in the environment and exist in a variety of species, which have great influence on their transport, bioaccumulation and toxicity. This review presents the recent research progress in speciation analysis of Hg, As, and Se, with emphasis on enhanced cold vapor generation as interface for liquid chromatography and atomic spectrometry, speciation of volatile species in gas phase, and isotope dilution technique to improve the precision and accuracy of speciation. Hyphenated techniques to characterize the complexes of Hg and As with phytochelatins and chromatographic separation coupled with multi-collector-inductively coupled plasma mass spectrometry to measure species-specific isotopic ratios, are also briefly discussed. Mercury (Hg) and arsenic (As) are among the most highly toxic elements for humans and ecosystems and can cause serious environmental and human health problems even at low concentrations [1,2]. Selenium (Se) is an "essential toxin" for human health. It has been recognized as an important antioxidant and anti-cancer element. However, Se can also pose negative impact such as defective skin and hair loss [3]. The adsorption/uptake, transport, bioaccumulation, metabolism and toxicity of these elements strongly depend on their chemical species present in environmental and biological samples. In the environment, one species can transform to another through chemical or biological processes. For example, in anaerobic sediments, sulfur-reducing or iron-reducing bacteria can methylate inorganic mercury into highly toxic methylmercury (MeHg) [4,5]. Therefore, speciation analysis of Hg, As and Se is of great importance in order to elucidate the biogeochemcal cycle and toxicology of these elements. Speciation analysis mainly involves chromatographic separation (gas chromatography (GC) or high performance liquid chromatography (HPLC)) hyphenated with element-specific spectrometry or molecular mass spectrometry. This review presents the recent advances in speciation analysis of Hg, As, and Se based on chromatographic separation, with emphasis on enhanced cold vapor generation (CVG) as interface for LC and atomic spectrometry, speciation of volatile Hg, As and Se in gas phase, and isotope dilution technique to improve the precision and accuracy of speciation. Hyphenated techniques to characterize the complexes of Hg and As with phytochelatins and chromatographic separation coupled with multi-collector-inductively coupled plasma mass spectrometry (MC-ICP-MS) to measure species-specific isotopic ratios, are also briefly introduced.

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A decline in Arctic Ocean mercury suggested by differences in decadal trends of atmospheric mercury between the Arctic and northern midlatitudes

Chen

Jacob

Soerensen

et al. 2015

Geophysical Research Letters

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Atmospheric mercury (Hg) in the Arctic shows much weaker or insignificant annual declines relative to northern midlatitudes over the past decade (2000–2009) but with strong seasonality in trends. We use a global ocean‐atmosphere model of Hg (GEOS‐Chem) to simulate these observed trends and determine the driving environmental variables. The atmospheric decline at northern midlatitudes can largely be explained by decreasing North Atlantic oceanic evasion. The midlatitude atmospheric signal propagates to the Arctic but is countered by rapid Arctic warming and declining sea ice, which suppresses deposition and promotes oceanic evasion over the Arctic Ocean. The resulting simulation implies a decline of Hg in the Arctic surface ocean that we estimate to be −0.67% yr−1 over the study period. Rapid Arctic warming and declining sea ice are projected for future decades and would drive a sustained decline in Arctic Ocean Hg, potentially alleviating the methylmercury exposure risk for northern populations.

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Methylmercury photodegradation influenced by sea-ice cover in Arctic marine ecosystems

Cited by 134 publications

References 42 publications

Methylmercury production below the mixed layer in the North Pacific Ocean

Methylmercury production below the mixed layer in the North Pacific Ocean

Recent advances in speciation analysis of mercury, arsenic and selenium

A decline in Arctic Ocean mercury suggested by differences in decadal trends of atmospheric mercury between the Arctic and northern midlatitudes

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