Fact Sheet - Mercury
Population at risk: 19 million people
Estimated DALYs: 1.5 million
Introduction
Mercury (Hg) is a heavy metal that occurs in several forms including elemental mercury, inorganic mercury and organic mercury. Each of these forms has a different toxicity and is associated with a different exposure pathway. Elemental mercury, also known as metallic mercury, is naturally occurring in the environment and is often extracted from cinnabar ore. This form of mercury may be refined into the liquid state after being heated to 1,000 degrees Fahrenheit. It is then used in products such as thermometers, electricity switches and dentals fillings, as well as for the production of caustic soda and chlorine gas. However, one of the most common uses of mercury in LMICs is for the extraction of gold from gold-containing ores.1
Inorganic mercury includes a series of mercury compounds such as mercuric chloride, mercuric acetate and mercuric sulfide.2 However, exposure to harmful levels of inorganic mercury is usually uncommon. Organic mercury is produced when elemental mercury is combined with carbon and is most commonly found in the environment as methylmercury, a compound that forms when microorganisms in water bodies metabolize elemental mercury.3 Due to the structure of the compound, this form of organic mercury accumulates in the fatty tissues of many organisms, including those consumed by humans.
Mercury can enter the environment naturally and from industrial sources resulting from industrial mining, chemical manufacturing, fertilizer manufacturing, solid waste disposal and metal smelting. However, the largest anthropogenic source of mercury release into the environment in LMICs results from artisanal small-scale gold mining (ASGM).4
Pure Earth estimates that 19 million people are at risk for exposure to mercury globally, with an estimated burden of disease of 1.5 million DALYs. As of 2015, the Toxic Sites Identification Program has identified over 450 sites around the world where exposure to mercury threatens the health of the population.
It is estimated that the livelihoods of at least 10 million people are dependent on artisanal small scale gold mining (ASGM), nearly all of whom use quicksilver (elemental mercury) to extract gold from ore. Many of these miners and their families are exposed to dangerously high levels of elemental mercury: in the workplace, in the home and in their communities. However a Disability Weight, necessary for the calculation of DALYs, has not been established for this type of exposure and therefore it is not possible to calculate DALYs from elemental mercury exposure for inclusion in the report. Pure Earth is currently in the process of setting up a research programme with German specialists to make progress in this area and it is hoped that it will be possible to include DALY estimates for mercury in future reports.
Because the scale of exposure is so significant and some estimates are needed, the approach used has been to capture this DALY burden through a surrogate value. In rough terms, the typical DALY value for a moderately contaminated lead site is taken as equivalent to that of a heavily contaminated mercury site. This is reasonable because both metals have similar adverse impacts on the developing brain of children. Because this neurological outcome (and in particular, IQ decrement) comprises the largest share of DALYs from lead, this is seen as the best analog for which data is presently available. It must be noted that this approach has not been subject to formal peer review and therefore can at best be considered indicative.
Pathways & Exposure Routes
Processes such as ASGM involve the heating of elemental mercury, resulting in the release of mercury vapors into the environment. These mercuric vapors can then settle as dust onto soil surfaces or surface water bodies through precipitation.5Waste piles with elemental mercury may lead to further contamination if they are not properly protected from natural forces such as wind and rainfall, and the mine waste leachates can persist in rivers, lakes and streams for years, posing serious health risks.6
Individuals may be exposed to mercury via inhalation, ingestion and dermal contact. The most direct pathway for mercury exposure is through inhalation of mercury vapors, which may reach the brain and cause permanent damage to the body. Exposure to methylmercury, a potent neurotoxin, often results from the consumption of contaminated food sources, such as fish and shellfish. Studies have also shown that livestock can develop high levels of mercury from grazing in contaminated areas, providing yet another possible route of mercury exposure for humans.7 Other common routes of exposure to mercury in LMICs may include absorption through skin and the consumption of breast milk from exposed women.
Associated Health Effects
Those exposed occupationally are most at risk from mercury poisoning due to their repeated direct contact with mercury. One study found that over half of ASGM workers in Indonesia experience chronic mercury intoxication, while those less exposed, such as mineral processors and nearby populations, also had high levels of mercury exposure.8 In general, infants are most at risk for developmental problems from mercury exposure, which may occur through breast-feeding.9
Health effects most commonly reported among ASGM workers and community members are neurological in nature and may include tremor, ataxia, memory problems and vision disorders. Additional symptoms reported by ASGM workers include headache, mood swings, muscle weakness, trouble sleeping, dizziness, irritation of the mouth, fatigue, difficulty walking, persistent cough, thoracic pain and rhinitis.10,11 A higher incidence of kidney and autoimmune dysfunction may also be found in such communities, resulting from the inhalation of elemental mercury vapour or the consumption of methyl mercury contaminated fish. Pregnant women consuming contaminated fish may also contribute to neurodevelopmental problems in developing fetuses, with symptoms including mental retardation, delayed development, language disorders, seizures and a loss of memory. Acrodynia, characterized by redness and severe discomfort in the extremities, may result in children chronically exposed to mercury.12;
Exposure to methylmercury, a potent neurotoxin, causes unique harmful effects on the body. Its introduction into the body may influence enzymes, as well as cell membrane and neuron functioning.13 The impacts of methylmercury became well known in the 1950s, after it was realized that 30 years of mercury-laden industrial wastewater dumped from the Minamata Plant in Minamata, Japan was the cause of over a thousand cases of mercury poisoning.14 While few symptoms were seen in mothers, children suffered from paralysis and intelligence disorders. Sensory disturbance, mental retardation, cerebellar ataxia, dysarthria, numbness, deformed or shaking limbs, visual problems, and auditory disorders are all symptoms common of what is now known as Minamata disease. Methylmercury exposure may also result in arthritis, miscarriage, respiratory failure, neurological damage and death.15
1 Kampalath RA, Jay JA. Sources of mercury exposure to children in low-and middle-income countries. Journal of Health Pollution. 2015;5(8):33-51
2 U.S. EPA (U.S. Environmental Protection Agency). Mercury compounds. Air Toxics Web site. http://www3.epa.gov/airtoxics/hlthef/mercury.html. Published 2000. Updated 2015. Accessed September 5, 2015
3 Braune B, Chélat J, Amyot M, et al. Mercury in the marine environment of the Canadian arctic: Review of recent findings. Sci Total Environ. 2015;509:67-90
4 Pacyna EG, Pacyna J, Sundseth K, et al. Global emission of mercury to the atmosphere from anthropogenic sources in 2005 and projections to 2020. Atmos Environ. 2010;44(20):2487-2499
5 Zheng N, Wang Q, Zheng D. Health risk of hg, pb, cd, zn, and cu to the inhabitants around huludao zinc plant in china via consumption of vegetables. Sci Total Environ. 2007;383(1):81-89
6 Gray JE, Theodorakos PM, Fey DL, Krabbenhoft DP. Mercury concentrations and distribution in soil, water, mine waste leachates, and air in and around mercury mines in the big bend region, texas, USA. Environ Geochem Health. 2015;37(1):35-48
7 Chibunda R, Janssen C. Mercury residues in free-grazing cattle and domestic fowl form the artisanal gold mining area of Geita district, Tanzania. Food Addit Contam. 2009;26(11):1482-1487
8 Bose-O'Reilly S, Drasch G, Beinhoff C, et al. Health assessment of artisanal gold miners in Indonesia. Sci Total Environ. 2010;408(4):713-725
9 Bose-O.Reilly S, Lettmeier B, Roider G, Siebert U, Drasch G. Mercury in breast milk.A health hazard for infants in gold mining areas? Int J Hyg Environ Health. 2008;211(5):615-623
10 Yard EE, Horton J, Schier JG, et al. Mercury exposure among artisanal gold miners in Madre de Dios, Peru: A cross-sectional study. Journal of Medical Toxicology. 2012;8(4):441-448
11 Tomicic C, Vernez D, Belem T, Berode M. Human mercury exposure associated with small-scale gold mining in Burkina Faso. Int Arch Occup Environ Health. 2011;84(5):539-546
12 Gibb H, O'Leary KG. Mercury exposure and health impacts among individuals in the artisanal and small-scale gold mining community: A comprehensive review. Environ Health Perspect. 2014;122(7):667-672
13 Hong Y, Kim Y, Lee K. Methylmercury exposure and health effects. Journal of Preventive Medicine and Public Health. 2012;45(6):353
14 Ministry of the Environment, Japan. Lessons from minamata disease and mercury management in japan. Ministry of the Environment, Japan Web site. http://www.env.go.jp/chemi/tmms/pr-m/mat01/en_full.pdf. Published 2013. Updated 2013. Accessed October 2, 2015
15 Rice KM, Walker Jr EM, Wu M, Gillette C, Blough ER. Environmental mercury and its toxic effects. Journal of Preventive Medicine and Public Health. 2014;47(2):74, Rice KM, Walker Jr EM, Wu M, Gillette C, Blough ER. Environmental mercury and its toxic effects. Journal of Preventive Medicine and Public Health. 2014;47(2):74
