Recent Developments in Mercury Science

ISOLDE reveals why mercury isotopes shape-shift from spheres to rugby balls
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As seafood is an important component of a healthy diet for many individuals, short-term solutions to elevated MeHg exposures will require changes in seafood consumption considering both risks and benefits [ 39 ]. While concentrations of MeHg in marine fish are likely to continue to exceed threshold levels, emissions reductions will have long-term benefits. Though full ecosystem recovery is only possible in the very distant future, policy action will benefit vulnerable species that accumulate MeHg and prevent further increases in MeHg in consumed species.

Environ Health. Air Pollution Studies No. Edited by: Pirrone N, Keating T. Sunderland EM: Mercury exposure from domestic and imported estuarine and marine fish in the U. Environ Health Perspect. Valera B, Dewailly E, Poirier P: Association between methylmercury and cardiovascular risk factors in a native population of Quebec Canada : A retrospective evaluation. Environ Res. Int J Circumpolar Health. Neurotoxicol Teratol. Environ Sci Technol.

Global Biogeochem Cycles. Environ Toxicol Chem. Limnol Oceanogr. Geochim Cosmochim Acta. Nat Geosci. Sci Total Environ. Patterns of global seafood mercury concentrations and their relationship with human health, version 3. Atmos Environ. Sippl K, Selin H: Global policy for local livelihoods: Phasing out mercury in artisanal and small-scale gold mining.

Selin N, Jacob D: Seasonal and spatial patterns of mercury wet deposition in the United States: Constraints on the contribution from North American anthropogenic sources. Selin NE: Science and strategies to reduce mercury risks: a critical review.

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J Environ Monit. Selin NE: Global biogeochemical cycling of mercury: A review. Annu Rev Environ Resour. Nutr Rev. Download references. EMS also acknowledges financial support from the U.

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Recent Developments in Mercury Science. Editors. David A. Front Matter. PDF · Mercury Speciation in the Environment Using X-ray Absorption Spectroscopy. Recent Developments in Mercury Science. Mercury Speciation in the Environment Using X-ray Absorption Spectroscopy. Pages Cooke Andrews, Joy.

Correspondence to Elsie M Sunderland. EMS initiated the manuscript. This article is published under license to BioMed Central Ltd. Reprints and Permissions. By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. Please note that comments may be removed without notice if they are flagged by another user or do not comply with our community guidelines.

Search all BMC articles Search. Abstract In their new paper, Bellanger and coauthors show substantial economic impacts to the EU from neurocognitive impairment associated with methylmercury MeHg exposures. Background In their recent article, Bellanger et al. Pathways of exposure A dominant fraction of human exposure to MeHg is from consuming marine fish. Sources of environmental mercury Anthropogenic mercury emissions result both from intentional uses of mercury and from releases as a byproduct of other activities [ 27 ]. Figure 1.

Full size image. It was estimated that Gg mercury was released from anthropogenic sources to the environment between the years and , of which Gg were emitted directly to the atmosphere 9. A significant part of this affects water ecosystems Constant efforts have, and are being carried out to mitigate emissions, e. Despite these efforts, heavy metal pollution remains a serious problem worldwide 7. Mercury has an overall high mobility, which facilitates its environmental cycling and uptake by living organisms 5 , 8.

The mobility and spread of mercury are closely connected to water and movement of natural waters As water is essential for life, and has significant contribution to the cycling of mercury in the environment, its contamination is a key issue. Current solutions to reduce mercury levels in aqueous streams include precipitation, flocculation, absorption, ion exchange, and solvent extraction Precipitation, e. This method poses limitations for large volumes containing trace amounts of mercury.

In addition, since metal sulphates tend to have low solubility in general, undesired co-precipitation of other metal ions can be problematic for solutions with complex chemical composition.

Recent Developments in Mercury Science | David A. Atwood | Springer

The selectivity of absorption and ion exchange techniques is also limited by chemical complexity. Very low or very high metal concentrations, and small or large feed volumes are other factors that limit use. Furthermore, it can be both difficult and costly to dispose of, or regenerate resulting contaminated absorption materials.

For these reasons, the development of improved technologies to remove toxic heavy metals from aqueous streams is of high importance, specifically chemical-free processes that do not generate secondary wastes, and are also highly effective at very low metal concentrations. In recent years, other approaches to remove mercury from aqueous streams have been suggested and evaluated 14 — Among them is the incorporation of mercury ions in a solid and stable metallic alloy, which is afterwards removed from solution.

Several such systems have been described 19 — One example is the use of gold nanoparticles coated with sodium citrate, where the latter acts as electron donor to facilitate reduction of mercury and formation of Au 3 Hg Brass shavings have shown potential for decontamination through a process where zinc oxidizes and donates its electrons to reduce mercury ions, which subsequently form an alloy with copper Sole copper or tin have also been used, and here the metals act as both electron donors and alloying components 19 , However, these methods have prominent drawbacks, notably stability, as the oxidized component will, under most conditions leach from the material and contaminate the water stream.

This was reported in the aforementioned studies. The chemical stability of, e. Moreover, additional physical separation, e. In another study, the use of metallic mossy filters eventually caused blocking of the filters with sludge mainly tin hydroxide , and a collapse of the system Electrochemistry is another technique that has potential for retrieval of metal ions. Mercury is noble enough to have its reduction potential inside the water stability window, making it possible to electroplate metallic mercury from aqueous solutions However, direct electroplating is not practical for decontamination, as metallic mercury is a liquid at ambient conditions, and its vapour pressure and concentration in air increases significantly with increasing temperature, making the system less stable Nonetheless, it is clear that alloy formation amalgamation and electrochemistry are interesting routes to develop improved methods for removal of mercury.

Amalgamation requires an interaction between metals, which means that mercury ions in solution need to be reduced to Hg 0. By doing this electrochemically, under controlled potential the use of chemical reducing agents is avoided, a clear advantage. A particularly promising way to carry out this can be to use the platinum—mercury system. The advantages include high stability in solution and high theoretical saturation capacity. A platinum atom can bind up to four mercury atoms, as PtHg 4 , while a gold one binds twelve times less mercury in its most stable form, Au 3 Hg 22 , The solubility of liquid mercury in platinum, and of platinum in liquid mercury are low at ambient conditions, e.

However, by applying a negative potential to the platinum, it is possible to increase the saturation solubility immensely. In fact, it is well known that electrochemistry can be used to form thin layers of platinum—mercury alloys The PtHg 4 amalgam exhibits sufficient adhesion to the platinum substrate, enabling cleaning of reacted platinum surfaces with cold nitric acid, alcohol, and freon jet without any amalgam losses Electrochemical formation of platinum—mercury alloys has been documented 28 , 29 , 31 but these efforts focused on studying the solid-state interactions occurring at the metallic interface.

While electrochemical alloy formation between platinum and mercury ions in solution appears plausible for decontamination purposes, this prospect has not been explored. The influence of parameters important for decontamination pH, uptake time, mercury concentration in solution, presence of other ionic species, electrochemical regeneration and re-use of the platinum substrate, uptake from solutions containing trace levels of mercury, and complete saturation of the substrate has not been reported.

Stability is a key issue for using this type of system for mercury retrieval, especially at low pH and long exposure times. Given these, the method of using platinum to form electrochemical alloys with mercury ions from solution for decontamination purposes appears plausible. However, to function as a practical method for decontamination, it must be possible to form relatively thick and uniform layers of PtHg 4 , preferably tens or hundreds of nm. In this study, we address the above-mentioned aspects. We analyse the alloying process in detail, in order to evaluate the limitations, and the prospects for large scale decontamination applications.

The alloying process is not affected by pH, and it is possible to remove mercury well below the limits allowed in drinking water. The system is efficient also in the presence of other cations and anions in solution, and reversible. By increasing the surface area using platinum nanoparticles, the time required for retrieval decreases significantly; a decontamination efficiency above This opens up new possibilities for cleaner and more efficient methods to remove mercury in a large number of applications, from treatment of highly acidic industrial streams to treatment of natural waters.

Deposition masks were used in the preparation of the electrodes, to obtain the pattern schematized in Fig. This design allowed us to control and estimate with precision the number of platinum atoms in contact with the solution active during retrieval. The contaminated feeds contained divalent mercury nitrate dissolved in nitric acid solutions. In both cases, there were no decreases or increases of the aqueous platinum or mercury concentrations.

This showed that the platinum and the platinum—mercury alloy layers are stable at low pH in the absence of applied electrical potential. Electrochemical alloy formation between divalent mercury in solution and metallic platinum. Counter electrode: platinum wire. Divalent mercury ions in solution light purple colour are first reduced on the platinum surface silver colour to elemental mercury. Elemental mercury darker purple forms thermodynamically stable PtHg 4 with the platinum atoms.

Upon formation of the first layers of PtHg 4 , mercury atoms penetrate the metallic alloy film to grow the alloy. Mercury concentration in solution plays an important role in practical decontamination applications; retrieval needs to be effective at low and high levels of mercury. The data was normalized to the initial mercury concentration in solution, to allow easier comparison. Retrieval is faster in the beginning, and it slows down with passing time. We interpret this by looking at the alloy formation mechanism as a multi-step process. The formation of PtHg 4 from metallic platinum and ionic mercury proceeds via a sequential route of electrochemical reduction of mercury, followed by formation of the alloy.

First, divalent mercury in solution is reduced on the platinum surface Eq. Mercury atoms will then move to subsurface positions by a place exchange mechanism with platinum atoms, followed by penetration into bulk platinum. The latter involves the inward shift of mercury atoms to attain the maximum coordination number with platinum This creates holes in bulk platinum, which allows further diffusion of mercury atoms. Diffusion is facilitated by the chemical potential gradient of mercury built up between the mercury deposit and the bulk platinum.

According to the aforementioned study 33 , the stoichiometry of the subsurface PtHg alloy changes from PtHg 2 , when a second monolayer of mercury is deposited Eq. Thus, PtHg 4 species are preferably formed over PtHg and PtHg 2 if sufficient bulk mercury is present, and if the reaction time is appropriate. The overall process is described by Eq. PtHg 4 is stable thermodynamically, having a negative enthalpy of formation, and this will stabilise mercury and prevent its dissolution This negative formation energy, together with the applied potential, provides the driving force to maximize coordination of mercury and platinum.

After the first layers of alloy is formed, additional mercury atoms need to penetrate into the metallic alloy film to grow the alloy Fig. It was reported that mercury is more abundant in the first layers after deposition 34 , which indicates that the diffusion of mercury is a slower process, and most likely the rate determining step in the decontamination. The reduction of available active platinum atoms on the surface slows down the absorption of more mercury.

These observations seem to correlate with those made by Wang et al. Past research states that amalgamation is unlikely to occur by migration of platinum atoms through the reaction product following dissociation of the atoms from the platinum lattice, and rather by transport of mercury atoms through the amalgam layer We have performed tests at higher temperature, and found out that retrieval is significantly faster upon increasing the temperature.

The fact that the intermetallic compounds formed at the mercury—platinum interface still allow for further reactions between the surface mercury and the bulk platinum is of high importance. We believe this property is vital for the decontamination of concentrated streams, as formation of relatively thick alloy layers at the interface will not completely stop further platinum—mercury interactions but rather slow them down. In this study, we focused on small platinum surfaces flat 2.

For practical applications, the slow diffusion of mercury in the alloy can be mitigated by using electrodes with sufficiently large surface area in relation to the amount of mercury in solution.

Control of mercury emissions: policies, technologies, and future trends

This hypothesis has been validated here by using larger surface area electrodes, and will be presented below. For industrial use, the electrodes can be designed to have large active surface by employing, e.

At significantly lower mercury concentrations of 0. This corresponds to 0. We correlate this with the aforementioned slower inward metal inter-diffusion of mercury once several layers of alloy are formed. These effects should be less preeminent at low concentrations due to increased number of interactions per available platinum active surface area. The predominant phase formed was PtHg 4 , as expected from the thermodynamics While it is possible to form other alloy phases under electrochemical conditions, e. PtHg 2 , we did not see any clear signs of phases other than PtHg 4.

This is likely to be explained by the fact that the experiments were carried out for long times. And if you for example decide to store your model objects in Google Cloud Storage, you would need to do this again. Example via providers. The providers in Mercury-ML aim to abstract most of this away and take care of the nitty-gritty while exposing a simple but also highly configurable API. Using the providers API instead of the containers of tasks APIs makes the most sense if you want to hardcode the providers you want to use.

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If you want to save the model in a different format, or copy it to a different store you must change your code to do so. Example via containers. Using the containers API makes the most sense when you want to steer your workflow via a configuration file. The containers are just light-weight classes that allow you to access various similar providers from a single location.

Want instead to save the model as a tensorflow graph? And want to store it in Google Cloud Storage instead? Simply change the config:. Example via tasks in conjunction with containers. Using the tasks API makes sense when you want to use a single function that defines a small workflow that involves more than one provider and requires multiple steps. The tasks API offers convenience more than anything else, but can be quite useful for small blocks of workflows that frequently occur together.

Find out more. The above is just a small example. Fully-fledged example workflows can be found here. A key component of how Mercury-ML is able to faciliate workflows also has to do with how it deals with data as it moves through the various phases of a machine learning pipeline.