Mercury in fish
Encyclopedia
Fish
and shellfish
concentrate mercury in their bodies, often in the form of methylmercury
, a highly toxic organic compound of mercury. Fish products have been shown to contain varying amounts of heavy metals, particularly mercury
and fat-soluble pollutants from water pollution
. Species of fish that are long-lived
and high on the food chain
, such as marlin
, tuna
, shark
, swordfish
, king mackerel
, tilefish
, northern pike
, and lake trout
contain higher concentrations of mercury than others.
The presence of mercury in fish can be a health issue, particularly for women who are or may become pregnant, nursing mothers, and young children.
and methylmercury
is present in only small concentrations in seawater
. However, it is absorbed, usually as methylmercury
, by algae
at the start of the food chain
. This algae is then eaten by fish and other organisms higher in the food chain. Fish efficiently absorb methylmercury, but only very slowly excrete it. Methylmercury is not soluble and therefore is not apt to be excreted. Instead, it accumulates, primarily in the viscera although also in the muscle tissue. This results in the bioaccumulation
of mercury, in a buildup in the adipose tissue of successive trophic level
s: zooplankton
, small nekton
, larger fish etc. Anything which eats these fish within the food chain
also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as swordfish
and shark
s or birds like osprey
and eagle
s have higher concentrations of mercury in their tissue than could be accounted for by direct exposure alone. Species on the food chain can amass body concentrations of mercury up to ten times higher than the species they consume. This process is called biomagnification
. For example, herring contains mercury levels at about 0.01 ppm while shark contains mercury levels greater than 1 ppm.
The table in provides a list of fishes and shellfishes and their mercury content.
-burning power plants and chlorine production
plants. The largest source of mercury contamination in the United States is coal-fueled power plant emissions. Chlorine chemical plants use mercury to extract chlorine from salt, which in many parts of the world is discharged as mercury compounds in waste water, though this process has been replaced for the most part by the more economically viable membrane cell process, which does not use mercury. Coal contains mercury as a natural contaminant. When it is fired for electricity generation, the mercury is released as smoke into the atmosphere. Most of this mercury pollution can be eliminated if pollution-control devices are installed.
and FDA recommend that women who are pregnant or plan to become pregnant within the next one or two years, as well as young children avoid eating more than 6 ounces (one average meal) of fish
per week.
In the United States, the FDA has an action level for methylmercury in commercial marine and freshwater fish that is 1.0 parts per million (ppm). In Canada, the limit for the total of mercury content is 0.5 ppm. The Got Mercury?
website includes a calculator for determining mercury levels in fish.
Species with characteristically low levels of mercury include shrimp
, tilapia
, salmon
, pollock
, and catfish
(FDA March 2004). The FDA characterizes shrimp, catfish, pollock, salmon, sardines, and canned light tuna as low-mercury seafood, although recent tests have indicated that up to 6 percent of canned light tuna may contain high levels. A study published in 2008 found that mercury distribution in tuna meat is inversely related to the lipid content, suggesting that the lipid concentration within edible tuna tissues has a diluting effect on mercury content. These findings suggest that choosing to consume a type of tuna that has a higher natural fat content may help reduce the amount of mercury intake, compared to consuming tuna with a low fat content. Also, many of the fish chosen for sushi
contain high levels of mercury.
According to the US Food and Drug Administration (FDA), the risk from mercury by eating fish and shellfish shall not be a health concern for most people. However, certain seafood might contain levels of mercury that may cause harm to an unborn baby (and especially its brain development and nervous system). In a young child, high levels of mercury can interfere with the development of the nervous system. The FDA provides three recommendations for young children, pregnant women, and women of child-bearing age:
, on Kyushu
island in Japan, noticed strange behavior in animals. Cats would exhibit nervous tremors, dance and scream. Within a few years this was observed in other animals; birds would drop out of the sky. Symptoms were also observed in fish, an important component of the diet, especially for the poor. When human symptoms started to be noticed around 1956 an investigation began.
Fishing was officially banned in 1957. It was found that the Chisso Corporation, a petrochemical company and maker of plastics such as vinyl chloride, had been discharging heavy metal waste into the sea. They used mercury compounds as catalysts in their syntheses. It is believed that about 5,000 people were killed and perhaps 50,000 have been to some extent poisoned by mercury.
Mercury poisoning
in Minamata, Japan, is now known as Minamata disease
.
A book by Jane Hightower, Diagnosis Mercury: Money, Politics and Poison
, published in 2008, discusses human exposure to mercury through eating large predatory fish
such as swordfish, shark, king mackerel, large tuna, etc.
Fish
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...
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. Fish products have been shown to contain varying amounts of heavy metals, particularly mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
and fat-soluble pollutants from water pollution
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
. Species of fish that are long-lived
Longevity
The word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected ....
and 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 marlin
Marlin
Marlin, family Istiophoridae, are fish with an elongated body, a spear-like snout or bill, and a long rigid dorsal fin, which extends forward to form a crest. Its common name is thought to derive from its resemblance to a sailor's marlinspike...
, tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
, 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:...
, 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....
, northern pike
Northern Pike
The northern pike , is a species of carnivorous fish of the genus Esox...
, and lake trout
Lake trout
Lake trout is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char , touladi, togue, and grey trout. In Lake Superior, they can also be variously known as siscowet, paperbellies and leans...
contain higher concentrations of mercury than others.
The presence of mercury in fish can be a health issue, particularly for women who are or may become pregnant, nursing mothers, and young children.
Biomagnification
MercuryMercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
and methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
is present in only small concentrations in seawater
Seawater
Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...
. However, it is absorbed, usually as methylmercury
Methylmercury
Methylmercury is an organometallic cation with the formula . It is a bioaccumulative environmental toxicant.-Structure:...
, by algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
at the start of 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...
. This algae is then eaten by fish and other organisms higher in the food chain. Fish efficiently absorb methylmercury, but only very slowly excrete it. Methylmercury is not soluble and therefore is not apt to be excreted. Instead, it accumulates, primarily in the viscera although also in the muscle tissue. This results in the bioaccumulation
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
of mercury, in a buildup in the adipose tissue of successive trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
s: zooplankton
Zooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
, small nekton
Nekton
Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water able to move independently of water currents....
, larger fish etc. Anything which eats these fish within 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...
also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as 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...
and 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....
s or birds like osprey
Osprey
The Osprey , sometimes known as the sea hawk or fish eagle, is a diurnal, fish-eating bird of prey. It is a large raptor, reaching more than in length and across the wings...
and eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...
s have higher concentrations of mercury in their tissue than could be accounted for by direct exposure alone. Species on the food chain can amass body concentrations of mercury up to 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...
. For example, herring contains mercury levels at about 0.01 ppm while shark contains mercury levels greater than 1 ppm.
Range of contamination
U.S. government scientists tested fish in 291 streams around the country for mercury contamination. They found mercury in every fish tested, according to the study by the U.S. Department of the Interior. They found mercury even in fish of isolated rural waterways. Twenty five percent of the fish tested had mercury levels above the safety levels determined by the U.S. Environmental Protection Agency for people who eat the fish regularly.The table in provides a list of fishes and shellfishes and their mercury content.
Sources
Much (an estimated 40%) of the mercury that eventually finds its way into fish originates with coalCoal
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...
-burning power plants and chlorine production
Chlorine production
This article presents the industrial and laboratory methodologies to prepare elemental chlorine.- Gas extraction :Chlorine can be manufactured by electrolysis of a sodium chloride solution . The production of chlorine results in the co-products caustic soda and hydrogen gas . These two products,...
plants. The largest source of mercury contamination in the United States is coal-fueled power plant emissions. Chlorine chemical plants use mercury to extract chlorine from salt, which in many parts of the world is discharged as mercury compounds in waste water, though this process has been replaced for the most part by the more economically viable membrane cell process, which does not use mercury. Coal contains mercury as a natural contaminant. When it is fired for electricity generation, the mercury is released as smoke into the atmosphere. Most of this mercury pollution can be eliminated if pollution-control devices are installed.
Current advice
The complexities associated with mercury transport and environmental fate are described by USEPA in their 1997 Mercury Study Report to Congress. Because methylmercury and high levels of elemental mercury can be particularly toxic to a fetus or young children, organizations such as the U.S. EPAUnited 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...
and FDA recommend that women who are pregnant or plan to become pregnant within the next one or two years, as well as young children avoid eating more than 6 ounces (one average meal) of fish
Fishing
Fishing is the activity of trying to catch wild fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping....
per week.
In the United States, the FDA has an action level for methylmercury in commercial marine and freshwater fish that is 1.0 parts per million (ppm). In Canada, the limit for the total of mercury content is 0.5 ppm. The Got Mercury?
Got Mercury?
Got Mercury? is a public awareness campaign about mercury levels in seafood. It is sponsored by the Sea Turtle Restoration Project and its parent organization, the Turtle Island Restoration Network...
website includes a calculator for determining mercury levels in fish.
Species with characteristically low levels of mercury include shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, tilapia
Tilapia
Tilapia , is the common name for nearly a hundred species of cichlid fish from the tilapiine cichlid tribe. Tilapia inhabit a variety of fresh water habitats, including shallow streams, ponds, rivers and lakes. Historically, they have been of major importance in artisan fishing in Africa and the...
, salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
, pollock
Pollock
Pollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...
, and catfish
Catfish
Catfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
(FDA March 2004). The FDA characterizes shrimp, catfish, pollock, salmon, sardines, and canned light tuna as low-mercury seafood, although recent tests have indicated that up to 6 percent of canned light tuna may contain high levels. A study published in 2008 found that mercury distribution in tuna meat is inversely related to the lipid content, suggesting that the lipid concentration within edible tuna tissues has a diluting effect on mercury content. These findings suggest that choosing to consume a type of tuna that has a higher natural fat content may help reduce the amount of mercury intake, compared to consuming tuna with a low fat content. Also, many of the fish chosen for sushi
Sushi
is a Japanese food consisting of cooked vinegared rice combined with other ingredients . Neta and forms of sushi presentation vary, but the ingredient which all sushi have in common is shari...
contain high levels of mercury.
According to the US Food and Drug Administration (FDA), the risk from mercury by eating fish and shellfish shall not be a health concern for most people. However, certain seafood might contain levels of mercury that may cause harm to an unborn baby (and especially its brain development and nervous system). In a young child, high levels of mercury can interfere with the development of the nervous system. The FDA provides three recommendations for young children, pregnant women, and women of child-bearing age:
- Do not eat sharkSharkSharks 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....
, swordfishSwordfishSwordfish , 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 mackerelKing mackerelThe 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:...
, or tilefishTilefishTilefishes, 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....
because they might contain high levels of mercury. - Eat up to 12 ounces (2 average meals) a week of a variety of fish and shellfishShellfishShellfish 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...
that are lower in mercury. Five of the most commonly eaten fish and shellfish that are low in mercury are: shrimpShrimpShrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, canned light tuna, salmonSalmonSalmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
, pollockPollockPollock is the common name used for either of the two species of marine fish in the Pollachius genus. Both P. pollachius and P. virens are commonly referred to as pollock. Other names for P...
, and catfishCatfishCatfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
. Another commonly eaten fish, albacoreAlbacoreThe albacore, Thunnus alalunga, is a type of tuna in the family Scombridae. This species is also called albacore fish, albacore tuna, albicore, longfin, albies, pigfish, tombo ahi, binnaga, Pacific albacore, German bonito , longfin tuna, longfin tunny, or even just tuna...
or big eye ("white") tuna depending on its origin might have more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, it is recommended that you should not eat more than up to 6 ounces (one average meal) of albacore tuna per week. - Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but consume no other fish during that week.
Background
In the 1950s, inhabitants of the seaside town of MinamataMinamata, 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...
, on Kyushu
Kyushu
is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....
island in Japan, noticed strange behavior in animals. Cats would exhibit nervous tremors, dance and scream. Within a few years this was observed in other animals; birds would drop out of the sky. Symptoms were also observed in fish, an important component of the diet, especially for the poor. When human symptoms started to be noticed around 1956 an investigation began.
Fishing was officially banned in 1957. It was found that the Chisso Corporation, a petrochemical company and maker of plastics such as vinyl chloride, had been discharging heavy metal waste into the sea. They used mercury compounds as catalysts in their syntheses. It is believed that about 5,000 people were killed and perhaps 50,000 have been to some extent poisoned by mercury.
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...
in Minamata, Japan, is now 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...
.
A book by Jane Hightower, Diagnosis Mercury: Money, Politics and Poison
Diagnosis Mercury: Money, Politics and Poison
Diagnosis Mercury: Money, Politics and Poison is a 2008 book by Jane Hightower. The book explains that mercury is a poison and that the majority of mercury in the environment comes from coal-fired power plants. But the book is mainly concerned with human exposure from the eating of large predatory...
, published in 2008, discusses human exposure to mercury through eating large predatory fish
Predatory fish
Predatory fish are fish that predate upon other fish or animals. Some predatory fish include perch, muskie , pike, walleye, salmon.Levels of large predatory fish in the global oceans are estimated to be about 10% of their pre-industrial levels...
such as swordfish, shark, king mackerel, large tuna, etc.
See also
- Friend of the SeaFriend of the SeaFriend of the Sea is a project for the certification and promotion of seafood from sustainable fisheries and sustainable aquaculture. It is the only certification scheme which, with the same logo, certifies both wild and farmed seafood. Friend of the Sea started as a project of the Earth Island...
- Got Mercury?Got Mercury?Got Mercury? is a public awareness campaign about mercury levels in seafood. It is sponsored by the Sea Turtle Restoration Project and its parent organization, the Turtle Island Restoration Network...
- Mercury cycleMercury cycleThe 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.-Processes:...
- Mercury in tuna
- Safe Harbor Certified SeafoodSafe Harbor Certified SeafoodSafe Harbor Certified Seafood is the first brand developed under San Rafael, California based Micro Analytical Systems, Inc. . Seafood bearing the Safe Harbor seal is tested for overall mercury content to be under the FDA's action level of 1ppm, histamine, Escherichia coli O157:H7 and salmonella...
- Seafood WatchSeafood WatchSeafood Watch is one of the best known sustainable seafood advisory lists, and has influenced similar programs around the world. It is a program designed to raise consumer awareness about the importance of buying seafood from sustainable sources...
, sustainable consumer guide (USA) - Sustainable seafoodSustainable seafoodSustainable seafood is seafood from either fished or farmed sources that can maintain or increase production in the future without jeopardizing the ecosystems from which it was acquired...
External links
- Health policy for pregnant women The NRDC created the chart below as a guideline to how much tuna can be eaten by children, pregnant women or women wanting to conceive, based on their weight.
- Recommendations for Fish Consumption in Alaska Bulletin No. 6 June 15, 2001 Mercury and National Fish Advisories Statement from Alaska Division of Public Health
- Methylmercury in Sport Fish: Information for Fish Consumers
- FDA Tests Show Mercury in White Tuna 3 Times Higher than Can Light, Says Mercury Policy Project
- FDA - Mercury Levels in Commercial Fish and Shellfish
- Federal Study Shows Mercury In Fish Widespread, Inescapable
- Healthy Sushi selector
- Find a healthy fish for consumption
- Smart and healthy choices when consuming seafood