Mercury cycle
Encyclopedia
The mercury cycle is a biogeochemical cycle
involving mercury
. Mercury is notable for being the only heavy metal which is liquid at room temperature. It is a volatile metal and evaporates easily, going into the atmosphere.
, Hg
S
. Here mercury (Hg2+) is bound very tightly to sulfur, but weathering releases the mercury to the environment slowly. There are also trace amounts of mercury in coal
. Mining mercury or burning coal results in releasing mercury. Volcanoes and forest fires are also sources of mercury.
Chlorine
factories, among other sources, release mercury into the atmosphere. This mercury is deposited back onto land and water. Inorganic mercury can be converted by bacteria into the organometallic cation known as methylmercury
, MeHg+. This accumulates in fish. Over long periods of time, some mercury recombines with sulfur and is buried in sediments. Then, the cycle repeats itself all over again.
Preindustrial deposition rates of mercury from the atmosphere may be about 4 ng /(1 L of ice deposit). Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times.
Natural sources, such as volcano
es, are responsible for approximately half of atmospheric mercury emissions. The human-generated half can be divided into the following estimated percentages:
The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomass burning, an important source in some regions.
Current atmospheric mercury contamination in outdoor urban air is (0.01–0.02 µg/m3) indoor concentrations are significantly elevated over outdoor concentrations, in the range 0.0065–0.523 µg/m3 (average 0.069 µg/m3).
Mercury also enters into the environment through the improper disposal (e.g., land filling, incineration) of certain products. Products containing mercury include: auto parts, batteries
, fluorescent bulbs, medical products, thermometers, and thermostats. Due to health concerns (see below), toxics use reduction
efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol
instead of mercury. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are being replaced by electronic thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.
The United States Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest possible extent. Thus, industries that release high concentrations of mercury into the environment agreed to install maximum achievable control technologies (MACT). In March 2005 EPA rule added power plants to the list of sources that should be controlled and a national cap and trade
rule was issued. States were given until November 2006 to impose stricter controls, and several States are doing so. The rule was being subjected to legal challenges from several States in 2005 and decision was made in 2008. The Clean Air Mercury Rule was struck down by a Federal Appeals Court on February 8, 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants. The court opinion cited the negative impact on human health from coal fired power plants' mercury emissions documented in the EPA Study Report to Congress of 1998.
Historically, one of the largest releases was from the Colex plant, a lithium-isotope separation plant at Oak Ridge. The plant operated in the 1950s and 1960s. Records are incomplete and unclear, but government commissions have estimated that some two million pounds of mercury are unaccounted for.
One of the worst industrial disasters
in history was caused by the dumping of mercury compounds into Minamata Bay, Japan. The Chisso Corporation, a fertilizer
and later petrochemical company, was found responsible for polluting the bay from 1932–1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease
.
Mercury and most of its compounds are extremely toxic and are generally handled with care; in cases of spills involving mercury (such as from certain thermometers
or fluorescent light bulbs) specific cleaning procedures are used to avoid toxic exposure. Essentially, it is recommended to physically merge smaller droplets on hard surfaces, combining them into a single larger pool for easier removal by using an eyedropper, or by pushing it into a disposable container which must then be dealt with according to local regulations. Vacuum cleaners and brooms should not be used because they cause greater dispersal of the mercury. Afterwards, sulfur
powder, zinc
powder, or some other element that readily forms an amalgam (alloy) with mercury (e.g. finely-divided Cu
or Bi
) at ordinary temperatures is sprinkled over the area and subsequently collected and properly disposed of. Cleaning porous surfaces and clothing is not effective at removing all traces of mercury and it is therefore advised to discard these kinds of items should they be exposed to a mercury spill.
Mercury can be inhaled and absorbed through the skin and mucous membranes, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or compounds of mercury that may decompose when heated, is always carried out with adequate ventilation in order to avoid exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as dimethylmercury
and methylmercury
. However, inorganic compounds, such as cinnabar are also highly toxic by ingestion or inhalation of the dust. Mercury can cause both chronic and acute poisoning.
, OSHA
, and NIOSH all treat mercury as an occupational hazard, and have established specific occupational exposure limits. Environmental releases and disposal of mercury are regulated in the U.S. primarily by the United States Environmental Protection Agency
.
Case control studies have shown effects such as tremors, impaired cognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapor even at low concentrations in the range 0.7–42 μg/m3. A study has shown that acute exposure (4 – 8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3 resulted in chest pain, dyspnea
, cough, hemoptysis
, impairment of pulmonary function, and evidence of interstitial pneumonitis
. Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism
, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams, and depression.
(NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid
(DMPS), and dimercaptosuccinic acid
(DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP. Chelation therapy
with both drugs resulted in the mobilization of a small fraction of the total estimated body mercury. DMSA was able to increase the excretion of mercury to a greater extent than NAP.
and shellfish
have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury
, a highly toxic organic compound of mercury. Species of fish that are high on the food chain
, such as shark
, swordfish
, king mackerel
, albacore tuna, and tilefish
contain higher concentrations of mercury than others. As mercury and methylmercury are fat soluble, they primarily accumulate in the viscera, although they are also found throughout the muscle tissue. When this fish is consumed by a predator, the mercury level is accumulated. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain
amass body burdens of mercury that can be ten times higher than the species they consume. This process is called biomagnification
. Mercury poisoning
happened this way in Minamata
, Japan
, now called Minamata disease
.
Biogeochemical cycle
In ecology and Earth science, a biogeochemical cycle or substance turnover or cycling of substances is a pathway by which a chemical element or molecule moves through both biotic and abiotic compartments of Earth. A cycle is a series of change which comes back to the starting point and which can...
involving mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. Mercury is notable for being the only heavy metal which is liquid at room temperature. It is a volatile metal and evaporates easily, going into the atmosphere.
Processes
Most natural mercury occurs as cinnabarCinnabar
Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...
, Hg
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
S
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
. Here mercury (Hg2+) is bound very tightly to sulfur, but weathering releases the mercury to the environment slowly. There are also trace amounts of mercury in coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
. Mining mercury or burning coal results in releasing mercury. Volcanoes and forest fires are also sources of mercury.
Chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
factories, among other sources, release mercury into the atmosphere. This mercury is deposited back onto land and water. Inorganic mercury can be converted by bacteria into the organometallic cation known as methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
, MeHg+. This accumulates in fish. Over long periods of time, some mercury recombines with sulfur and is buried in sediments. Then, the cycle repeats itself all over again.
Releases of mercury in the environment
Natural sources, such as volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es, are responsible for approximately half of atmospheric mercury emissions. The human-generated half can be divided into the following estimated percentages:
- 65% from stationary combustion, of which coal-fired power plants are the largest aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants fueled with gas where the mercury has not been removed. Emissions from coal combustion are between one and two orders of magnitude higher than emissions from oil combustion, depending on the country.
- 11% from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines. Hydrogeochemical release of mercury from gold-mine tailings has been accounted as a significant source of atmospheric mercury in eastern Canada.
- 6.8% from non-ferrous metalNon-ferrous metalIn metallurgy, a non-ferrous metal is a metal that is not ferrous, that is, any metal, including alloys, that does not contain iron in appreciable amounts...
production, typically smelters. - 6.4% from cementCementIn the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
production. - 3.0% from waste disposal, including municipal and hazardous wasteHazardous wasteA hazardous waste is waste that poses substantial or potential threats to public health or the environment. According to the U.S. environmental laws hazardous wastes fall into two major categories: characteristic wastes and listed wastes.Characteristic hazardous wastes are materials that are known...
, crematoria, and sewage sludge incineration. This is a significant underestimate due to limited information, and is likely to be off by a factor of two to five. - 3.0% from caustic soda production.
- 1.4% from pig ironPig ironPig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...
and steelSteelSteel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
production. - 1.1% from mercury production, mainly for batteries.
- 2.0% from other sources.
The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomass burning, an important source in some regions.
Current atmospheric mercury contamination in outdoor urban air is (0.01–0.02 µg/m3) indoor concentrations are significantly elevated over outdoor concentrations, in the range 0.0065–0.523 µg/m3 (average 0.069 µg/m3).
Mercury also enters into the environment through the improper disposal (e.g., land filling, incineration) of certain products. Products containing mercury include: auto parts, batteries
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...
, fluorescent bulbs, medical products, thermometers, and thermostats. Due to health concerns (see below), toxics use reduction
Waste management
Waste management is the collection, transport, processing or disposal,managing and monitoring of waste materials. The term usually relates to materials produced by human activity, and the process is generally undertaken to reduce their effect on health, the environment or aesthetics...
efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
instead of mercury. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are being replaced by electronic thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.
The United States Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest possible extent. Thus, industries that release high concentrations of mercury into the environment agreed to install maximum achievable control technologies (MACT). In March 2005 EPA rule added power plants to the list of sources that should be controlled and a national cap and trade
Emissions trading
Emissions trading is a market-based approach used to control pollution by providing economic incentives for achieving reductions in the emissions of pollutants....
rule was issued. States were given until November 2006 to impose stricter controls, and several States are doing so. The rule was being subjected to legal challenges from several States in 2005 and decision was made in 2008. The Clean Air Mercury Rule was struck down by a Federal Appeals Court on February 8, 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants. The court opinion cited the negative impact on human health from coal fired power plants' mercury emissions documented in the EPA Study Report to Congress of 1998.
Historically, one of the largest releases was from the Colex plant, a lithium-isotope separation plant at Oak Ridge. The plant operated in the 1950s and 1960s. Records are incomplete and unclear, but government commissions have estimated that some two million pounds of mercury are unaccounted for.
One of the worst industrial disasters
Industrial disasters
This article lists notable industrial disasters, which are disasters caused by industrial companies, either by accident, negligence or incompetence. They are a form of industrial accident where great damage, injury or loss of life are caused....
in history was caused by the dumping of mercury compounds into Minamata Bay, Japan. The Chisso Corporation, a fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
and later petrochemical company, was found responsible for polluting the bay from 1932–1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease
Minamata disease
', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...
.
Toxicity of mercury
Mercury-in-glass thermometer
A mercury-in-glass thermometer, also known as a mercury thermometer, was invented by German physicist Daniel Gabriel Fahrenheit in 1724 and is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube allow the temperature to be read by the length of the mercury within the...
or fluorescent light bulbs) specific cleaning procedures are used to avoid toxic exposure. Essentially, it is recommended to physically merge smaller droplets on hard surfaces, combining them into a single larger pool for easier removal by using an eyedropper, or by pushing it into a disposable container which must then be dealt with according to local regulations. Vacuum cleaners and brooms should not be used because they cause greater dispersal of the mercury. Afterwards, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
powder, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
powder, or some other element that readily forms an amalgam (alloy) with mercury (e.g. finely-divided Cu
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
or Bi
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
) at ordinary temperatures is sprinkled over the area and subsequently collected and properly disposed of. Cleaning porous surfaces and clothing is not effective at removing all traces of mercury and it is therefore advised to discard these kinds of items should they be exposed to a mercury spill.
Mercury can be inhaled and absorbed through the skin and mucous membranes, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or compounds of mercury that may decompose when heated, is always carried out with adequate ventilation in order to avoid exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as dimethylmercury
Dimethylmercury
Dimethylmercury is an organomercury compound. This colorless liquid is one of the strongest known neurotoxins. It is described as having a slightly sweet smell, although inhaling enough vapor to detect its odor would be hazardous....
and methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
. However, inorganic compounds, such as cinnabar are also highly toxic by ingestion or inhalation of the dust. Mercury can cause both chronic and acute poisoning.
Occupational exposure
Due to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. The World Health OrganizationWorld Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
, OSHA
Occupational Safety and Health Administration
The United States Occupational Safety and Health Administration is an agency of the United States Department of Labor. It was created by Congress of the United States under the Occupational Safety and Health Act, signed by President Richard M. Nixon, on December 29, 1970...
, and NIOSH all treat mercury as an occupational hazard, and have established specific occupational exposure limits. Environmental releases and disposal of mercury are regulated in the U.S. primarily by the United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
.
Case control studies have shown effects such as tremors, impaired cognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapor even at low concentrations in the range 0.7–42 μg/m3. A study has shown that acute exposure (4 – 8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3 resulted in chest pain, dyspnea
Dyspnea
Dyspnea , shortness of breath , or air hunger, is the subjective symptom of breathlessness.It is a normal symptom of heavy exertion but becomes pathological if it occurs in unexpected situations...
, cough, hemoptysis
Hemoptysis
Hemoptysis or haemoptysis is the expectoration of blood or of blood-stained sputum from the bronchi, larynx, trachea, or lungs Hemoptysis or haemoptysis is the expectoration (coughing up) of blood or of blood-stained sputum from the bronchi, larynx, trachea, or lungs Hemoptysis or haemoptysis ...
, impairment of pulmonary function, and evidence of interstitial pneumonitis
Pneumonitis
Pneumonitis or pulmonitis is a general term that refers to inflammation of lung tissue.Pneumonia is pneumonitis combined with consolidation and exudation...
. Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism
Erethism
Erethism or erethism mercurialis is a symptom complex of mercury poisoning, presenting with excessive shyness, timidity and social phobia. This was common among hat makers of old England who used mercury to stabilize the wool in a process called felting...
, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams, and depression.
Treatment
Research on the treatment of mercury poisoning is limited. Currently available drugs for acute mercurial poisoning include chelators N-acetyl-D, L-penicillaminePenicillamine
Penicillamine is a pharmaceutical of the chelator class. It is sold under the trade names of Cuprimine and Depen. The pharmaceutical form is D-penicillamine, as L-penicillamine is toxic...
(NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid
2,3-Dimercapto-1-propanesulfonic acid
2,3-Dimercapto-1-propanesulfonic acid and its sodium salt are chelating agents that form complexes with various heavy metals. They are related to dimercaprol, which is another chelating agent....
(DMPS), and dimercaptosuccinic acid
Dimercaptosuccinic acid
Dimercaptosuccinic acid , is the organosulfur compound with the formula HO2CCHCHCO2H. This colorless solid contains two carboxylic acid and two thiol groups, the latter being responsible for its mildly unpleasant odour. It occurs in two diastereomers, meso and the chiral dl forms...
(DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP. Chelation therapy
Chelation therapy
Chelation therapy is the administration of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication—those involving lead, arsenic or mercury—the standard of care in the United States dictates the use of dimercaptosuccinic acid...
with both drugs resulted in the mobilization of a small fraction of the total estimated body mercury. DMSA was able to increase the excretion of mercury to a greater extent than NAP.
Fish
FishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and shellfish
Shellfish
Shellfish is a culinary and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater environments, some kinds are found only in freshwater...
have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
, a highly toxic organic compound of mercury. Species of fish that are high on the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
, such as shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
, swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...
, king mackerel
King mackerel
The king mackerel is a migratory species of mackerel of the western Atlantic Ocean and Gulf of Mexico. It is an important species to both the commercial and recreational fishing industries.-Description:...
, albacore tuna, and tilefish
Tilefish
Tilefishes, also known as blanquillo, are mostly small perciform marine fish comprising the family Malacanthidae.They are usually found in sandy areas, especially near coral reefs....
contain higher concentrations of mercury than others. As mercury and methylmercury are fat soluble, they primarily accumulate in the viscera, although they are also found throughout the muscle tissue. When this fish is consumed by a predator, the mercury level is accumulated. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
amass body burdens of mercury that can be ten times higher than the species they consume. This process is called biomagnification
Biomagnification
Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance that occurs in a food chain as a consequence of:* Persistence...
. Mercury poisoning
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...
happened this way in Minamata
Minamata, Kumamoto
is a city located in Kumamoto prefecture, Japan. It is on the west coast of Kyūshū. The city was founded on April 1, 1949.As of 2008, the city has an estimated population of 27,856 and the density of 171 persons per km²...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, now called Minamata disease
Minamata disease
', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...
.