It was in the mid-20th century that a series of public health incidents in Minamata, Japan was caused by industrial dumping. Industrial waste containing methylmercury bioaccumulated in the aquatic ecosystem as it was taken in by small organisms. The methylmercury then underwent biomagnification as fish ate these organisms, raising the amount of mercury to toxic levels. When the local humans and animals ate these fish, they were exposed to the toxic effects of mercury, culminating in what is now known as Minamata disease. Symptoms of this disease include numbness in limbs and ataxia, responsible for the “dancing cat fever” phenomenon. Extreme cases resulted in insanity, paralysis, coma, and death.
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Mercury has an expansive history going back as far as ancient times and has been a known toxin for nearly as long. Exposure to mercury can occur in many different forms. The mechanism of toxicity involves changing the structure of proteins that are necessary to regulate bodily functions. Control of mercury exposure is best done through prevention and phasing out products that use mercury. Mercury is a neurotoxin that can cause permanent damage to the brain, kidneys, and lungs, while high-level exposure can lead to mercury poisoning and eventually death.
Background and History
Mercury was believed to have mystical probabilities. For centuries, mercury has been used in medicinal treatments. It was used to treat syphilis and was used in antiseptics, skin ointments, laxatives, diuretics, bowel washouts for the treatment of colorectal cancer, and scabicides (Langford 1999). The usage of and exposure to mercury compounds were known in many industries. Mercury gilding was an ancient technique used in metalworking. According to the EPA, mercury can be mixed with materials containing gold. When heated, the mercury vaporizes and leaves gold. This method is used to extract pure gold from mining. In the 18th century, mercury was also used to cure the felt used to manufacture felt hats. The subsequent prolonged exposure led to mercury poisoning in hat makers, coining the phrase “mad hatter.” Certain mercury compounds were used to make dye colors, such as mercury (II) sulfide which was an ore known as cinnabar from which the bright red vermillion dye was obtained. In paints, mercury was previously used as a preservative but has long since been phased out. Today, it is used as a solvent for the silver-tin amalgams used in dental ﬁlling.
Though there have been many cases of mercury poisoning in history, one of the most prominent is that in Minamata, Japan. This particular case arose from the dumping of chemical waste by the Chisso Corporation. In 1956, the first patient affected by Minamata disease was admitted to the Chisso factory hospital (Mosa 2017). Doctors established a relationship between methylmercury contamination in fish and the neurologic symptoms manifesting in humans.
Another case emerged in Canada in the mid-1960s. The Dryden Chemical Company had a pulp and paper mill which made paper with mercury waste as a byproduct from bleaching. Mercury entered the river system and elevated mercury levels, affecting local fish. Scientific reports estimated 50 to 70 years were needed until levels returned to normal and the environment fully recovered. On behalf of indigenous people and himself, Lamm sued the Dryden Chemical Company for $3.75 million in 1971 for the social and economic ramifications (Mosa 2017).
An incident in 1972 in Iraq involved the use of methylmercury fungicide and resulted in thousands of people suffering from mercury poisoning (Trasande 2005). Mercury-coated seed grain had been imported for the next growing season, but it had not been meant for consumption. Iraqi people in rural areas consumed the grain as food, due in part by the foreign warning labels and the lack of understanding of the health risks.
Mercury is poisonous in all forms. It can exist as an inorganic compound such as a metal, vapor, or salt. They can also exist as organic compounds, an example being methylmercury. According to the World Health Organization, human exposure to mercury is mainly from contaminated fish and shellfish, dental fillings, or occupational exposure.
The most common form of organic mercury exposure is through the consumption of marine fish. Approximately 77% of methylmercury exposure is from offshore fisheries (Sunderland et al.). Some mercury in fish occurs naturally from underwater volcanic eruptions. However, the way a significant amount of mercury enters aquatic food chains is through anthropogenic emissions. This can occur through the release of mercury from coal combustion as it washes into rivers and eventually the ocean. The combustion of coal is used to generate electricity, but the process releases mercury vapors that eventually precipitate into bodies of water.
People can also be exposed to mercury through products that contain mercuric compounds. Davidson (2004) estimates that 50% of dental amalgams contain mercury, making it the most common way for humans to be exposed to inorganic mercury. Exposure occurs through preparation or replacement of these dental fillings, during which mercury vapor may be inhaled.
Occupations that are at the greatest risk of mercury exposure are those that use mercury in processing materials or handle products containing mercury, such as “amalgam makers, barometer makers, battery makers, chemical laboratory workers, chlor-alkali petrochemical workers, dentists, fluorescent lamp makers, gold and silver extractors, insecticide makers, Hg miner workers and thermometer makers” (Shirkhanloo 2014).
Mechanism of Toxicity
The toxic effects of mercury are induced by protein precipitation, enzyme inhibition, and generalized corrosive action. Which human organs are affected by mercury often depends on the form, dosage, and rate of exposure (Broussard 2002). Mercury handicaps cell function by changing the tertiary and quaternary structures of protein (Bernhoft 2012).
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Mercury alters the structure of proteins through its ability to bind to sulfhydryl, phosphoryl, carboxyl, amide, and amine groups (Broussard 2002). As mercury easily binds to proteins that contain these groups, which includes enzymes, the change in structure that follows prevents the protein from performing its function.
Inorganic mercury includes metallic mercury vapor, mercurous mercury, and mercuric mercury. Mercury vapor is highly lipid soluble, allowing it to easily cross cell membranes. Due to this property, it has the potential to negatively affect any organ or subcellular structure. Even though mercurous mercury is less readily absorbed by organs, it has the capacity to be converted to mercuric mercury and induce toxicity. Methylmercury, an organic mercury compound, typically reacts to sulfhydryl groups within a body. This property also allows it to interfere with the function of any cellular or subcellular structure. It disrupts many subcellular elements in the central nervous system and other organs and in mitochondria; other adverse eﬀects have resulted in damage to parts of the brain and the peripheral nervous system” (Bernhoft 2012).
Acute exposure to mercury is associated with bronchitis that could lead to respiratory failure, which may be paired with central nervous system symptoms such as tremor or erethism. Chronic exposure usually results in neurological dysfunction (Bernhoft 2012).
As mercury can have negative side effects even with small levels of exposure, it is advised to pursue a strategy of prevention and mitigation. According to the World Health Organization, ways to reduce human exposure to mercury include promoting clean energy sources, eliminating the use of mercury in certain industrial processes, and phasing out the use of products that contain non-essential mercury.
The burning of coal for energy is an example of point source mercury pollution. By placing limits on factory emissions or moving away from coal as a source of energy, the amount of mercury that enters the environment may be lessened. Clean energy alternatives include natural gas, solar, wind, water, geothermal, bioenergy, and nuclear energy.
Using mercury in artisanal and small-scale gold mining is hazardous and puts those populations at risk. Safer gold extraction techniques should be implemented in place of methods that use mercury. In industrial processes where mercury use is unavoidable, safer work practices are necessary to mitigate exposure. Regulations on factories are needed to restrict chemical dumping into bodies of water to prevent cases similar to mercury poisoning in Minamata, Japan.
Of the products that contain mercury, dental amalgams are cited as the highest risk of exposing people to mercury. Some products that previously contained mercury are now being phased out, such as mercury thermometers and fluorescent light bulbs. In the case of dental amalgams, it is impossible to completely stop their usage, as a 2009 WHO expert consultation concluded that it would be problematic for the public health and dental health sector. However, they could be phased down by researching and developing alternatives.
Mercury has long been used for its properties in medical and industrial fields. Through their usage in these fields, people have been exposed to the toxic effects of mercury directly and indirectly. Notable examples are dental amalgams and mercury in fish as a byproduct of burning coal. Since it readily binds to certain functional groups in proteins, it can easily affect neurological processes and human organs. Due to how easily it permeates the cell membrane, even small amounts of mercury can be very toxic. As a neurotoxin, mercury is capable of causing irreversible damage to the central nervous system and peripheral nervous system. In the worst cases, it can lead to mercury poisoning and death.
It poses a significant danger to human health and necessitates a decrease in use whenever possible. If a safer alternative is available, it should be substituted in the place of products containing mercury. To prevent incidents like Minamata disease, regulations on mercury handling and disposal should be put in place.
- Artisanal and Small-Scale Gold Mining Without Mercury. (2018, November 21). Retrieved from https://www.epa.gov/international-cooperation/artisanal-and-small-scale-gold-mining-without-mercury
- Davidson, P., Myers, G., & Weiss, B. (2004). Mercury Exposure and Child Development Outcomes. Pediatrics, 113(4), 1023-9.
- Langford, N., & Ferner, R. (1999). Toxicity of mercury. Journal of Human Hypertension, 13(10), 651-6.
- Mercury: Element of the Ancients. (2016). Retrieved November 29, 2018, from http://www.dartmouth.edu/~toxmetal/mercury/history.html
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- Mosa, A., & Duffin, J. (2017). The interwoven history of mercury poisoning in Ontario and Japan. CMAJ : Canadian Medical Association Journal = Journal De L’Association Medicale Canadienne, 189(5), E213-E215.
- Robin A. Bernhoft, “Mercury Toxicity and Treatment: A Review of the Literature,” Journal of Environmental and Public Health, vol. 2012, Article ID 460508, 10 pages, 2012. https://doi.org/10.1155/2012/460508.
- Shirkhanloo, H., Golbabaei, F., Hassani, H., Eftekhar, F., & Kian, M. J. (2014). Occupational Exposure to Mercury: Air Exposure Assessment and Biological Monitoring based on Dispersive Ionic Liquid-Liquid Microextraction. Iranian journal of public health, 43(6), 793-9.
- Sunderland, E., & Selin, N. (2013). Future trends in environmental mercury concentrations: Implications for prevention strategies. Environmental Health, 12(1), 2.
- Trasande, L., Landrigan, P., & Schechter, C. (2005). Public health and economic consequences of methyl mercury toxicity to the developing brain. Environmental Health Perspectives, 113(5), 590-6.
- World Health Organization, “Inorganic mercury: environmental health criteria 118,” in International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland, 1991.
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