The element mercury (Hg), the planet Mercury, and the word mercurial all derive from the Latin word mercurlis. If one describes someone as mercurial, the meaning is that they frequently change their mind. This description applies to the element Hg in the ecosystem that is our Earth. Mercury, once released into the ecosystem, can exist as elemental Hg, oxidized Hg(II), oxidized Hg(I), or methylmercury. These forms are interchangeable and Hg moves from one to the other with ease depending on the environmental conditions it encounters. Mercury cannot be destroyed so it is on Earth in some form forever. The purpose of this article is to describe natural and anthropogenic sources of Hg; how Hg enters our environment; how Hg is transformed into dangerous species that have enormous and well documented negative effects on human health, especially that of pre-birth infants, neonatal infants and growing children; efforts and lack of efforts to control Hg emissions and to recover Hg from wastes; and the ability of Molecular Recognition Technology (MRT) products to selectively separate and recover Hg using green engineering and green chemistry processes from solutions where Hg is found as an impurity, especially at low concentrations. The case is made that global Hg pollution is extensive; and, in many cases, uncontrolled; health effects from Hg exposure can be devastating; and there is need for more effective technologies to separate and recover Hg to prevent its uncontrolled and pervasive dispersion in Earth’s environment.
Background. Mercury is one of the most toxic metals known and no essential role is known for it in either human or animal nutrition [1]. Toxic effects of Hg in localized geographical areas, such as the Almadan deposit in Spain, were well known millennia ago. Global industrial growth during the past two centuries has required mining large quantities of base metals, traditional and artisanal mining of large amounts of Au, and the combustion of large amounts of coal for energy purposes. Mercury is either found embedded in these sources in small quantities or is used in processing ores, as in the case of Au. Without proper control, large amounts of Hg are released to the environment in these processes posing a global threat to human, animal, and plant health [1-8]. Mercury has three forms: (1) elemental Hg, which is released to the atmosphere by industrial processes, (2) inorganic salts, one of which, calomel (mercurous chloride), was widely used as a common and effective laxative for humans in past centuries, and (3) organic compounds, such as methylmercury, which are the most toxic form of Hg. Methylmercury is a toxin formed through natural microbial processes in river, lake or ocean sediments that concentrates many fold as it moves up the food chain to fish or other species consumed by people with damaging results. Methylmercury can cross the brain-blood barrier and penetrate skin. It affects brain and muscle tissue, causing paralysis and brain damage. The most devastating effects are seen in pre-birth infants, neonatal infants, and growing children where brain and other organs are developing.
Mercury has high affinity for sulfur and is found as an impurity in sulfide ores of base metals. Mercury is also found as a primary constituent in minable ore deposits, e.g., cinnabar, HgS. Mercury has not been produced as a principal mineral commodity in the United States since 1992 [9]. It is recovered as a byproduct from Au-Ag mine operations in Nevada and from secondary products such as batteries, fluorescent lamps, dental amalgam, medical devices, and thermostats. Mine production of Hg is small and relatively constant globally, except in China where production has increased sharply from about 1,400 tons annually from 2008 through 2013 to 2,800 tons in 2015 and to 4,000 tons in 2016 [9]. Total mine production in 2016 was 4,500 tons so China’s share was nearly 90% of the total. Estimates of the total amount of Hg mined globally vary from about 4,500 to about 9,000 tons per year depending on the source of information, accounting for the different values given here. Qiu, Li, and Feng [3] have published a detailed account of Hg mining in China and its environmental and health impacts. China is rich in cinnabar ore resources and ranks third in total Hg resources in the world. It is also the only nation where mining of Hg is still practiced. Qui, et al. [3] point out that Three global mercuriferous belts have been discovered, circumPacific, Mediterraneancentral Asia, and MidAtlantic Ridge. These belts are mainly distributed along global plate tectonic boundaries. Most world largescale Hg mines are distributed in those three belts, such as Almaden Hg mine, Spain; Idrija Hg mine, Slovenia; Monte Amiata Hg mine, Italy; New Almaden Hg mine, United States; Palawan Hg mine, Philippines; and Wanshan Hg mine, China. Approximately one million tons of Hg have been produced in the past 500 years with more than 75% originating in Europe and North America. The Almaden mines in Spain, alone, contributed one-third of this amount [3]. These data plus the knowledge that Hg has been mined for millennia, has been produced and/or used extensively for about two hundred years in industrial processes, and is extremely toxic in the methylmercury form give cause to ponder how much Hg is in the global environment, is it increasing through human activity, and is there cause to be concerned about long term ecological and health effects from its presence.
Natural sources of Hg have created background levels that have been present on Earth since long before people arrived. These background levels are indicated in Figure 1, where ice core records of Hg deposition from Wyoming extending over three centuries are given [2,4]. Background levels from 1700 to about 1850 are assumed to extend to the present. Sharp increases of Hg concentrations in the environment began in the late 1800s. Of an estimated 5,500 to 8,900 tons of Hg emitted annually from all sources, ~10% is of natural origin and ~90% is either of anthropogenic origin (30%) or is re-emitted from deposited sources (60%). The large increase in anthropogenic Hg emitted since ~1850, to ~20 ng L-1 in ~1990, is consistent with the rise of industrialization, primarily in Western Europe and the United States. Spikes observed for eruption of three volcanoes (Tambora, Krakatoa, St. Helens) show Hg emissions from these natural sources, although large, to be short-lived and to not persist over decades as do anthropogenic emissions. Currently, the greatest proportion of anthropogenic emissions of Hg to the atmosphere originates in three global regions: east and southeast Asia (40%, with China accounting for three-quarters of this or about one-third of the global total), South America (13%), and Sub-Saharan Africa (16%) [2]. The remaining ~30% is divided evenly over remaining global regions with none over 10%. Emissions of Hg in China originate with smelting of non-ferrous metals such as Zn and Pb, coal combustion, roasting of cinnabar, and artisanal and small-scale Au mining (ASGM). On a global scale, ASGM is prevalent in South America and sub-Saharan Africa as well as China [5]. It has been estimated that Hg released into the atmosphere has an average residence time of 0.5–2 years, making it probable that atmospheric Hg contamination has worldwide implications, especially for human health, in the global commons [6].
Figure 1. Ice core record of mercury deposition from sources in Wyoming, USA. Elevated levels associated with the 1850–1884 gold rush probably reflect local/regional sources rather than a global signature. Increasing environmental levels of mercury associated with industrialization, however, are found in environmental archives like this ice core around the globe. Reproduced from ref. 2 with permission.
Health Effects of Mercury Pollution. The World Health Organization guideline for chronic exposure to inorganic Hg vapor is 1 µg/m3. The U.S. EPA has an even lower value, 0.3 µg/m3for chronic inhalational exposure to inorganic Hg [7]. These values are often exceeded in regions where Hg is used for ASGM and other activities. Mercury forms an amalgam with Au that is easily separated from gangue material. In northwest Columbia, miners bring their amalgam to be burned at a central location, recovering the Au while releasing Hg into the atmosphere. Tests at one location showed Hg levels as high as 999 µg/m3 [7]. An estimated 1,000 metric tons of Hg were used globally in ASGM in 2011, more than for any other use of Hg. One-third of this Hg is thought to go into the atmosphere, while the rest ends up in piles of soils, mining waste, and waterways that are subject to further dispersion by natural events. Children are frequently used in ASGM operations. Extensive damage can be done to the developing brains of these young children. Few, if any, of the children know that Hg is toxic. It is estimated that 10-15 million people in 70 countries work in the ASGM trade [7]. In Mali, children as young as 6 were seen digging mine shafts, carrying and crushing stone, and panning for Au alongside adults. One estimate put 20,000-40,000 children in Mali alone working in the ASTM trade. Very few precautions against the ever-present Hg fumes were observed among these workers. Pregnant women and women of childbearing age are routinely seen burning the Au-Hg amalgam, because many male miners see this as “women’s work.”
The chemistry of Hg gives reason for great concern about ecological and human health effects. A United Nations global assessment in 2013 provides information on sources, emissions, releases, and environmental transport of Hg [2]. Mercury is released to the environment from natural sources and processes as well as from human activities. Mercury cycles among air, land, and water sites until it is eventually removed from the system through burial in deep ocean sediments or lake sediments or through entrapment in stable mineral compounds. However, Hg can re-enter the environment from these or other sources either by disturbance of sediments, mining, combustion of coal, or formation of methylmercury in aquatic systems, especially if Hg is dumped as waste into lake or ocean environments [2,6]. The ability of the food chain to concentrate methylmercury in the environment is shown by an example from the Wisconsin Mercury Sourcebook [10] in which the statement is made that a 22-inch Northern Pike weighing two pounds can have a mercury concentration as much as 225,000 times as high as that of the surrounding water.
Mercury is much more widely dispersed than many other metals because it can enter the environment as neutral Hg in the gaseous state, making long range transport possible before it falls to Earth. Its long retention time in the atmosphere upon release during coal combustion or smelting of ores plus its ability to form methylmercury makes Hg a truly dangerous species to global human and animal health. Mercury is easily transformed from Hg(II) to Hg(0) or vice versa in the environment making its presence in either form very dangerous. Campbell and Gailer [8] have described health and environmental effects of Hg including mechanisms for the action of Hg in human and animal subjects. These authors summarize the Hg problem as follows: Mercury has been recognized as a global pollutant for over 40 years, in large measure because of its presence in fish and seafood and its effects on human consumers. Only quite recently has it been recognized that Hg can also have subtle but potentially important neurological effects on aquatic organisms themselves. In recognition of the pervasive presence of Hg and its neurotoxicity, the United Nations Environment Programme (UNEP) is currently spearheading a transition to a lowHg world and this initiative resulted in a global treaty to reduce mercury emissions that was signed by 141 countries in October 2013. Reducing Hg emissions is certainly a worthy initiative, but given the unique biogeochemical properties of Hg (e.g., its propensity to change oxidation state and to be methylated) and its consequent ability to escape from aquatic sediments and reenter the food web, it is destined to remain a major problem for the foreseeable future.
Minamata Bay Disaster. The Minamata Bay disaster resulted from poisoning that occurred in humans who ingested fish and shellfish contaminated by methylmercury formed from Hg discharged in waste water from a chemical plant into Minamata Bay, Japan in the mid-20th century. Stephen Juan described the disaster in 2006, 50 years after the disease was detected in patients in Minamata City, Japan, in these words [11]: It is now 50 years since the most horrific mercury poisoning disaster the world has ever seen took place in Minamata, Japan. In May 1956, four patients from the city of Minamata on the west coast of the southern Japanese island of Kyushu were admitted to hospital with the same severe and baffling symptoms. They suffered from very high fever, convulsions, psychosis, loss of consciousness, coma, and finally death. Soon afterwards, 13 other patients from fishing villages near Minamata suffered the same symptoms and also died. As time went on, more and more people became sick and many died. Doctors were puzzled by the strange symptoms and terribly alarmed. It was finally determined that the cause was mercury poisoning.
Mercury was in the waste product dumped into Minamata Bay on a massive scale by a chemical plant. The mercury contaminated fish living in Minamata Bay. People ate the fish, were themselves contaminated, and became ill. Local bird life as well as domesticated animals also perished. In all, 900 people died and 2,265 people were certified as having directly suffered from mercury poisoning – now known as Minamata disease. Beyond this, victims who recovered were often socially ostracised, as were members of their families. It was wrongly believed by many people in the community that the illness was contagious.
The chemical plant was suspected of being the culprit in the environmental disaster almost from the beginning of the illness outbreak, yet speaking out against the chemical plant was forbidden. The plant was a major employer and enjoyed considerable economic and political clout all the way to the national government. Defenders of the chemical plant argued that it must be innocent since the plant had been in operation since 1907 without previous problems. It manufactured fertilizer. A riot by local fishermen in 1959 finally moved the government to investigate the cause of the illnesses and deaths. Even so, it took officials 12 years from the first deaths to finally admit the cause of the contamination and order a halt to the mercury dumping into Minamata Bay.
Yet the Minamata disaster story is still not over. In 2006, in the Seishin Shinkeigaku Zasshi, Dr K Eto from the Japanese Ministry of the Environment and the National Institute for Minamata Disease, writes that: “Over the years, new facts have gradually surfaced, especially after 1995, with the resolution of the political problems surrounding Minamata disease”. For example, the mystery as to why the first 50 years of plant operation brought forth no disaster has been recently solved. It has been revealed that the plant modified its operations in August 1951 and started dumping large amounts of mercury directly into Minamata Bay only from that time.
The health of survivors and their children are being monitored. A permanent museum and annual community ceremonies commemorate the worst mercury poisoning environmental disaster ever. Today, 50 years on, the lessons of Minamata remain.
Juan [11] points out two oddities from history. Sir Isaac Newton, one of the greatest of all scientists, suffered two incidents of uncharacteristically erratic behavior. Some historians suspect that he had a mild case of Hg poisoning, since he was known to be conducting experiments with Hg at the time. The other example relates to the use of Hg in the haberdashery business well into the 20th century. Individuals in this business were noted for touching brushes with their tongues. Mental illnesses were common in this community. This is the basis for the name “Mad Hatter” in Lewis Carroll’s Alice in Wonderland.
Minamata Convention. On January 19, 2013, the Minamata Convention on Mercury at the fifth session of the Intergovernmental Negotiating Committee in Geneva, Switzerland came to an agreement on measures to be taken to protect human health and the environment from the adverse effects of Hg. Committee recommendations were adopted at a Diplomatic Conference on October 10, 2013 at Kumamoto, Japan. Major highlights of the Minamata Convention included a ban on new Hg mines, phase-out of existing mines, phase-out and phase-down of Hg use in several products and processes, control measures on emissions to air and on releases to land and water, and international regulation of the informal sector for artisanal and small-scale gold mining [6]. The Convention also addressed interim storage of Hg and its disposal once it becomes waste, sites contaminated by Hg and health issues related to Hg. A key factor in shaping obligations under the Convention is controlling anthropogenic releases of Hg throughout its lifecycle.
Natural and Anthropogenic Sources of Mercury. Natural sources of Hg emissions and releases include natural weathering of Hg-containing rocks, erupting volcanoes, and geothermal activity. It is estimated that such occurrences account for about 10% of the 5,500 to 8,900 tonnes of Hg being emitted and re-emitted annually to the atmosphere from all sources.
Anthropogenic sources of Hg emissions and releases account for about 30% of the total amount of Hg entering the atmosphere each year [2]. Main industrial sources of atmospheric Hg are coal combustion, mining, and industrial activities that process ores to produce various metals or process other raw materials to produce cement. In these activities, Hg is emitted because it is present as an impurity in fuels and raw materials. In these cases, Hg emissions and releases are sometimes referred to as ‘by-product’ or ‘unintentional’ emissions or releases. Unintentional Hg emissions can be reduced to very low values by application of pollution control measures at power plants and industrial plants. Emissions of Hg have been sharply reduced in countries where these measures have been applied, mainly Western Europe, Canada, and the United States. However, over half of global coal combustion and most global mining operations take place in nations where such control is spotty or non-existent.
Additional anthropogenic sources include sectors where Hg is used intentionally. ASGM activity is the largest of these. In ASGM operations, Hg emissions and releases result from the intentional use of Hg to extract gold from rocks, soils, and sediments [5,7]. Gold is recovered from the Au-Hg amalgam by burning the Hg off, usually with an open flame. No attempt is made to recover the Hg, which is released into the atmosphere for global dispersion. ASGM activities are responsible for major sources of Hg releases and human health problems worldwide, but especially in eastern Asia, Sub-Saharan Africa, and South America. ASGM operations are essentially unregulated and are the largest global Hg polluter, releasing more Hg into the environment than all the world’s coal fired power plants combined [5,6]. Other intentional-use release sectors include waste from consumer products, the chlor-alkali industry, and the production of vinyl-chloride monomer. Mercury present in lamp phosphors is an issue in recycling of rare earth metals from these spent products. Binnemans, et al. [12] point out the difficulties involved in use of traditional separation technologies for Hg separation from waste fluorescent lamps. Use of Hg in these lamps has decreased sharply in recent years, but disposal of spent lamps as waste products remains a significant source of Hg pollution. Disposal of spent lamps is usually as landfill or incineration followed by deposit in landfill. In both cases, opportunity exists for the Hg to be re-mobilized into the environment.
The third category consists of re-emissions and comprises about 60% of emissions to the atmosphere. Mercury previously deposited from air onto soils, surface waters, and vegetation from past emissions can be emitted back to the air [2]. Re-emission is a result of natural processes that convert inorganic and organic forms of mercury to elemental mercury, which is volatile and therefore readily returns to the air. Mercury deposited to plant surfaces can be re-emitted during forest fires or biomass burning. Mercury may be deposited and re-emitted many times as it cycles through the environment. Since Hg cannot be destroyed, a significant portion of Hg ever emitted continues to circulate. As the environmental burden of Hg increases (Figure 1), a greater amount of this toxic metal is available for circulation through ecosystems. A significant and increasing amount of Hg remains active depositing in soils or sediments, entering food chains as methylmercury, being re-mobilized by rains or floods, doing damage to human and animal tissue, in an eternal round. Mercury levels in air, water, and land become elevated and remain that way for a long time (Figure 1).
Control of Mercury Emissions. Control technology is available to remove Hg from coal combustion operations and medical and hazardous waste incinerators. Scrubbers of various types and adsorption of Hg onto activated carbon are common methods used. These methods are efficient in reducing the amount of Hg emitted to the atmosphere. However, they create an additional problem in that the Hg infused carbon must be disposed of. This is problematic because the waste is hazardous. Essentially, the current approach is to simply transfer the mercury from the gaseous phase to the solid phase. It is questionable whether the overall ecological burden is lessened by this approach. There are acidic cation exchange resins (ion exchange or IX) that bind mercury from sodium chloride and sodium hydroxide. However, the IX resin must be regenerated by large amounts of concentrated hydrochloric acid, creating a toxic, highly acidic, waste stream laced with mercury. The spent IX resin must then be either disposed of in landfill or by incineration with any residual Hg. The IX approach, although effective in removing Hg to low levels in the primary waste stream, comes at a high cost, as it creates large amounts of secondary hazardous waste that must be dealt with.
Recovery of Hg from other sources is even more problematic. Recycling rates for Hg from products, such as Hg-containing fluorescent light bulbs, is in the 1-10% range indicating that large amounts of Hg are discarded to landfill [13]. Recovery of Hg from ASGM sources is zero. Combustion of coal and incineration of medical and other wastes in countries where uses of Hg-control technologies are non-existent or spotty results in large emissions of Hg to the commons. Pollution of water bodies by heavy metals, including Hg, is of increasing concern [14]. Concentration of target metals by precipitation followed by treatment with IX resins is a common treatment method, but with generation of large amounts of waste that eventually goes to landfill, where the heavy metals have the possibility of re-entering the environment.
Much of the Hg emitted globally in industrial processes, discarded into landfills, and emitted in incineration processes is not recovered resulting in increased global burden of this metal. The portion of this Hg that eventually finds its way to waterways will nearly all be converted to methylmercury by microorganisms with resulting potential harm to human and animal health. Development of new, simplified technologies for separation and recovery of trace amounts of Hg from commercial products and waste streams of variable size are needed. Improved technologies capable of highly selective recovery of Hg in the presence of complex matrices would be valuable since such matrices are usually present and interfere with targeted separations. Recovery of Hg rather than dispersal to the commons is important because this allows reuse or disposal/storage of Hg in an environmentally safe manner. In short, it is of great importance that Hg be controlled in its use, movement, recovery, and storage. Uncontrolled mercury and treatment of mercury-containing streams by inefficient technologies, that simply transfer the problem from one phase to another and/or create entirely new secondary waste streams, pose significant hazards to ecology on planet Earth.
Molecular Recognition Technology. An MRT product, SuperLig® 88, is effective in separating and recovering Hg in the Hg2+ form from g L-1 to mg L-1 and lower Hg concentrations [15]. Many situations exist where Hg-selectivity by MRT SuperLig® products and simplicity of MRT systems are useful in recovery of Hg from streams where it is an impurity for reuse, storage, or disposal in an environmentally safe manner [16].
Green engineering [17] and green chemistry [18] aspects of MRT processes make this technology ideal for the challenging tasks of separating and recovering Hg from solutions of small or large volume in which it is an impurity. Commercial MRT processes are simple in design and operation, do not use solvents, normally operate in column mode, generate minimal waste, and are effective in separation and recovery of Hg from solutions where it is present at g L-1 to mg L-1 or lower concentrations [15]. Additionally, and perhaps most importantly, the SuperLig® resin concentrates the mercury isolating it in a small volume that can be safely disposed of or re-used. This contrasts with IX resins that require regeneration using a very corrosive acid (concentrated hydrochloric acid), thus creating a new secondary waste stream. In operation, a column is packed with SuperLig® 88 resin, which selectively removes Hg from a feed solution allowing the remainder to pass on to raffinate. Following washing of the column to remove residual feed solution, bound Hg is eluted from SuperLig® 88 with a small amount of eluent to obtain a solution concentrated many hundred-fold in Hg. The column is regenerable for multiple uses. No Hg remains on the column following elution. These features make capital and operating expenses lower when compared with costs associated with conventional separation systems, especially considering the costs associated with generation of secondary waste streams. MRT systems can be modular making them available at locations where they are needed.
The MRT process has been used commercially for removal and recovery of Hg from H2SO4solutions in which it is an impurity that must be removed to produce high purity H2SO4 [15]. Commercial H2SO4 is made from by-product SO2 derived from smelting and roasting ores containing Zn, Pb, and Cu. Mercury present in these ores volatilizes during ore treatment and appears in downstream products such as H2SO4. Without any treatment for Hg removal, approximately half of the Hg originally present in the ore will be found in the product acid. Partial removal of Hg upstream in commercial processes is desirable and normally achieved, but significant amounts, especially in the absence of adequate controls, report to the product acid. The present standard for commercial H2SO4 is <1 mg Hg L-1 while a content of <0.5 mg L-1 is required if the H2SO4 is used in products such as fertilizer that may be linked to the food chain.
Removal of Hg to these levels is challenging to current commercial separation methods. Conventional processes for Hg removal involve gas absorption [19]. Gas absorption processes require high capital investment costs, and are not flexible enough to deal with changes in Hg input levels. In the process, Hg is transferred from the gas phase to a solid phase absorbent. This absorbent is treated as a hazardous waste with the possibility of Hg leakage into the environment through the process of discharge to landfill or incineration.
The MRT process is used for bulk Hg removal and as a ‘polisher’ for Hg in these solutions. A lead-trail column MRT pilot test program was conducted at a base metal smelting location [15,20] to remove Hg from a plant H2SO4 stream of general composition 93% H2SO4. Mercury concentrations in the feed were in the range of 100 to 200 mg L-1. Used in bulk removal mode, the MRT system maximizes removal of Hg from the feed stream, reducing the Hg concentration to the mg L-1 concentration level, and, in some cases, to concentrations as low as 1.0 mg L-1. Use of the MRT system in polishing mode, with up to five MRT columns in series, allowed the Hg concentration to be further reduced to <0.1 mg L-1. The MRT green chemistry procedure provides a simple and effective means for Hg removal and recovery from H2SO4 solutions. Main benefits to the industrial company of the process include: (1) treatment of the liquid phase acid product using a simple green engineering system, eliminating need for large, high capital cost gas handling equipment; (2) achievement of sustainable levels of Hg at the <0.1 mg L-1 concentration level in H2SO4solutions, a level which cannot be assured by other processes; (3) recovery of a pure, concentrated Hg product that can be handled in an environmentally safe manner avoiding undesirable discharge of Hg to the commons, and (4) minimal generation of waste. A key difference between MRT and other separation processes is that in MRT processes recovered Hg is concentrated many hundred-fold in the final volume enabling recovery of pure Hg. Other processes recover toxic metals, such as Hg, on a material that becomes, in effect, a hazardous waste and is disposed of in landfill or incinerated. In these cases, the toxic metal may be subject to natural processes that re-introduce it into the environment. MRT is a promising candidate for use in separation and recovery of Hg from products where it is an undesirable impurity, such as H2SO4, or from end-of-life products where it is a component, such as fluorescent lamps.
Summary. Mercury presents a global challenge. For global health and environmental reasons Hg pathways need to be controlled and, if possible, Hg needs to be recovered rather than dispersed into the environment at concentrations so small that it becomes unrecoverable. Mercury control is a daunting task and present anthropogenic activities make the likelihood for widespread control of this metal in the future doubtful. Mercury is concentrated over its crustal abundance [4] in ores, such as cinnabar, and in natural products, such as coal. Prior to the industrial age, about 1850, Hg levels in the environment were low, but constant. Commencing about 1850, these levels increased markedly with use of Hg to form Au-Hg amalgams in Au mining, increased coal combustion, and increased use in chemical and industrial processes. Generally, mercury used or released from these activities went into the commons, became widely dispersed, and unrecoverable. Mercury at any level is toxic to humans, particularly pre-natal and young children where vital organs are developing rapidly. This toxicity is markedly increased by Hg deposited in lakes, oceans, and other water bodies where it is converted nearly 100% by microbial action in sediments to methylmercury. Methylmercury is concentrated many fold as it moves up the food chain to fish and other sea or fresh water animals that are eaten by humans. Effort is needed to find ways to better control Hg movement and, where possible, prevent its dispersal into the commons where control becomes impossible. Reduced use of Hg in chemical and industrial applications has been achieved in many cases by finding substitutes, and clean energy technologies, such as MRT, are effective in separating and recovering Hg from commercial products, such as H2SO4. Mercury emissions from artisanal Au mining pose a significant global threat to human health with no solution in sight. Government input through legislative action and enforcement of regulations, such as those suggested in the Minamata Convention, is much needed in these cases. Unfortunately, artisanal mining occurs in areas where government action is minimal. Development and use of green chemistry separation and recovery processes, such as MRT, are recommended wherever possible to reduce the environmental burden of Hg.
References
1. Pan, J., Chon, H.-S., Cave, M.R., Oates, C.J., Plant, J.A., 2012. Toxic trace elements, in Pollutants, Human Health and the Environment: a Risk Based Approach, J.A. Plant, N. Voulvoulis, and K.V. Ragnarsdottir (Eds.), Wiley-Blackwell, Oxford, pp. 87– 114.
2. UNEP, 2013. Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport. UNEP Chemicals Branch, Geneva, Switzerland, Accessed April 15, 2017.
3. Qiu, G., Li, P., Feng, X., 2016. Mercury Mining in China and Its Environmental and Health Impacts. In R.M. Izatt (Ed.), Metal Sustainability: Global Challenges, Consequences, and Prospects. Oxford: Wiley., pp. 200-220.
4. Izatt, R.M., Izatt, S.R., Bruening, R.L., Izatt, N.E., Moyer, B.A., 2014. Challenges to Achievement of Metal Sustainability in Our High-Tech Society, Chemical Society Reviews, 43, 2451-2475.
5. Wade, L., 2013. Gold’s Dark Side, Science, 341, 1448-1449.
6. Krabbenhoft, D.P., Sunderland, E.M., 2013. Global Change and Mercury, Science 341, 1457-1458.
7. Schmidt, C.W., 2013. Quicksilver and Gold: Mercury Pollution from Artisanal and Small-Scale Gold Mining, Environmental Health Perspectives, Accessed May 3, 2017.
8. Campbell, P.G.C., Gailer, J., 2016. Effects of non-essential metal releases on the environment and human health. In R.M. Izatt (Ed.), Metal Sustainability: Global Challenges, Consequences, and Prospects. Oxford: Wiley, pp. 221-252.
9. George, M.W., Mercury, Accessed April 10, 2017.
10. Huber, K., 1997. Wisconsin Mercury Sourcebook: A Guide to Help Your Community Identify and Reduce Releases of Elemental Mercury, Accessed April 15, 2017.
11. Juan, S., 2006. The Minamata Disaster-50 Years on: Lessons learned, Accessed April 15, 2017.
12. Binnemans, K., Jones, P.T., Blanpain, B., Van Gerven, T., Yang, Y., Walton, A., Buchert, M., 2013. Recycling of Rare Earths: A Critical Review, Journal of Cleaner Production, 51, 1-22.
13 Reck, B.K., Graedel, T.E., 2012. Challenges in Metal Recycling, Science, 337, 690-695.
14. Wang, L.K., Chen, J.P., Hung, Y-T. Shammas (Eds.), 2009. Heavy Metals in the Environment, CRC Press, New York, N.Y.
15. Izatt, R.M., Izatt, S.R., Izatt, N.E., Krakowiak, K.E., Bruening, R L., Navarro, L., 2015. Industrial applications of Molecular Recognition Technology to green chemistry separations of platinum group metals and selective removal of metal impurities from process streams. Green Chemistry, 17, 2236-2245.
16. Izatt, R.M., Bradshaw, J.S., Bruening, R.L., Bruening, M.L., 1994. Solid phase extraction of ions of analytical interest using Molecular Recognition Technology, American Laboratory, pp 28C-28M.
17. O’Connor, M.P., Zimmerman, J.B., Anastas, P.T., Plata, D.L., 2016. A strategy for material supply chain sustainability: enabling a circular economy in the electronics industry through green engineering. ACS Sustainable Chemistry & Engineering, 4, 5879-5888.
18. Anastas, P., Eghbali, N., 2010. Green Chemistry: Principles and Practice. Chemical Society Reviews, 39, 301-312.
19. Louie, D. K., 2005. Handbook of Sulphuric Acid Manufacturing, DKL Engineering. Inc. Thornhill, Ontario, Canada, 2005.
20. Izatt, S.R., Bruening, R.L., Izatt, N.E., Dale, J.B., 2003. 132nd Annual Meeting, TMS (The Minerals, Metals & Materials Society), San Diego, CA, 2003, March 2–6. EPD Congress 2003, M. E. Schlesinger (Ed.), TMS, Warrendale, PA, pp. 135–145.