Methylmercury in the ocean is transferred back into the atmosphere via volatilization and sea-spray aerosolization
the verdict
INSUFFICIENT LEANING
refutedsupported
the weight of evidence
3 sources for · 0 against
Available literature partially discusses mercury evasion and volatile methylated species air-sea exchange, but lacks comprehensive evidence establishing both volatilization and sea-spray aerosolization specifically for methylmercury.
environmental pool of methylated Hg (MeHg = MMHg + DMHg). There is evidence that DMHg can be formed both directly from inorganic Hg and from MMHg ( 14 ); however, the mechanisms are still unclear. Some studies have suggested that DMHg transforms into MMHg in the ocean ( 15 – 17 ); however, the pathways of conversion are still not unequivocally demonstrated. In addition, a recent study found that DMHg could undergo photochemical demethylation to form MMHg ( 18 ). Nevertheless, the volatility of DMHg opens the possibility of a previously underexamined pathway for MeHg transport through the atmosphere ( 19 )—i.e., DMHg, emitted from the surface ocean, is transformed to MMHg in the atmosphere, incorporated into precipitation and aerosols, potentially transported long distances through atmospheric circulation, and ultimately deposited into oceans and to the terrestrial landscape. Thus, if such pathways exist in many locations, then the MeHg exposure risk for wildlife and humans in some regions is not only from its in situ production but also from atmospheric deposition. This pathway needs more attention, given the potential for enhanced MMHg exposure ( 19 , 20 ). However, there has been little quantification of DMHg evasion from the global oceans or its atmospheric fate, and our understanding of this pathway is insufficient.
Globally, anthropogenic Hg emissions to the atmosphere have increased current atmospheric Hg concentrations by about 450% above natural levels ( 21 ). These emissions have spread Hg worldwide through atmospheric transport, ocean circulation, and river runoff, leading to an increase in total Hg (THg) concentrations in the oceans ( 3 ). A recent global Hg budget suggests that atmospheric Hg deposition, as Hg 0 and Hg II , supplies total fluxes to the open ocean and snow/ice of 7220 and 410 Mg year −1 , respectively ( 22 ). However, owing to a lack of the MeHg data in rain and aerosols, there are few compilations of the global atmospheric MeHg flux ( 2
Sources, Sinks and Biogeochemical Cycling of Mercury in the Ocean | Springer Nature Link
# Sources, Sinks and Biogeochemical Cycling of Mercury in the Ocean
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Global and Regional Mercury Cycles: Sources, Fluxes and Mass Balances
## Abstract
A review of the available information on the sources and sinks for oceanic mercury (Hg) illustrates the importance of the ocean in the global Hg cycle. The principal source of oceanic Hg is atmospheric deposition with riverine sources contributing about 10% of the total inputs. The primary loss term is gas evasion at the sea surface. Burial of Hg in ocean sediments is a minor sink (10% or less of the total flux). Mass balance estimates suggest that hydrothermal sources do not contribute significantly to the oceanic Hg pool. Overall, about 11 Mmol/yr is currently being added to (and lost from) the ocean reservoir. Much of this Hg is of anthropogenic origin. Mercury deposited to the ocean is effectively reduced, principally by biologically-mediated processes, to elemental Hg and this leads to a rapid recycling to the atmosphere of much of the deposited Hg. Reactive Hg is converted in deeper ocean wate
teria that process sulfate (SO4=) in the environment take up mercury in its inorganic form, and through metabolic processes convert it to methylmercury. The conversion of inorganic mercury to methylmercury is important for two reasons: (1) methylmercury is much more toxic than inorganic mercury, and (2) organisms require considerably longer to eliminate methylmercury. At this point, the methylmercury-containing bacteria may be consumed by the next higher level in the food chain, or the bacteria may release the methylmercury to the water where it can quickly adsorb to plankton, which are also consumed by the next level in the food chain.
Where does atmospheric mercury come from?
There are many sources of mercury to the environment, both natural and man related. Natural sources include volcanoes, natural mercury deposits, and volatilization from the ocean. The primary human-related sources include: coal combustion, chlorine alkali processing, waste incineration, and metal processing. Best estimates to date suggest that human activities have about doubled or tripled the amount of mercury in the atmosphere, and the atmospheric burden is increasing by about 1.5 percent per year.
Has there always been mercury contamination, or is this a recent problem?
This is a difficult question to answer, in part because of a lack of adequately preserved fish specimens of preindustrial age to compare against contemporary samples. However, several lines of evidence from recent studies on Wisconsin lakes suggest that increase pemissions to the atmosphere, and subsequent higher deposition rates to lakes, likely translate into higher mercury levels in fish. Although the total amount of mercury delivered to one of these lakes annually is very small it is strongly absorbed by organic material floating in the water such as plankton or bacteria. These microorganisms are consumed by organisms higher in the food chain, or after dying, settle to the bottom of the lake and are incorporated into bo
Everything we examined (3)
This check searched the claim as stated. It did not run a separate search for evidence against it.