Mercury poisoning is caused by exposure to mercury and damages the nervous system * . Mercury is a metal in the form of a silvery liquid at room temperature, but it can also turn into a vapor. It forms chemical compounds known as salts that are used in industry and can form compounds in the ocean, which can enter the human body through the consumption of saltwater fish.
In the early 1950s, people living in the town of Minamata in southern Japan began to notice that the local cats were acting strangely. They would stand on their hind legs, run around aimlessly, go into convulsions * , and die. The townspeople called this mysterious illness the “dancing cat disease.” They also noticed that there were dead fish floating on the sea and dead crows along the edge of the ocean. In April 1956, the illness spread to humans; 11 people in the town were treated by doctors for convulsions and difficulty in walking and talking. The doctors thought at first that the patients were suffering from a contagious disease that affected the central nervous system * . By October 1956, 40 people in Minamata had been diagnosed with the illness and 14 had died.
Researchers from a nearby university were called in to solve the puzzle. They found that the patients all came from fishermen's families living along the bay, and that all ate fish and shellfish on a daily basis. Their cats were fed the leftover fish. The researchers then suspected a kind of food poisoning caused by a heavy metal. In 1959, mercury was identified as the metal in question, and its source was identified as a chemical factory in Minamata that had been releasing mercury into the bay in its wastewater. The fish and shellfish absorbed the mercury and concentrated it in their bodies. Larger and larger amounts of mercury built up in the local food chain * . When the mercury in the fish and shellfish increased to a high level, humans and their pets began to suffer from mercury poisoning.
By 2001, 2,265 patients had been identified as suffering from Minamata disease; 1,784 had already died. The chemical factory was forced to give the victims financial compensation as well as change its manufacturing methods.
Mercury poisoning is a potentially fatal disorder of the nervous system, lungs, kidneys, and other organs caused by exposure to liquid mercury, mercury vapor, mercury salts, or organic mercury (mercury combined with carbon). Some mercury enters the environment naturally from volcanoes and the breakdown of certain rocks in the earth's crust; coalburning power plants, explosives, and other human industrial processes release mercury into the air. The mercury in the atmosphere enters the food chain when it falls back to earth and is absorbed by tiny organisms in the ocean that provide food for fish and shellfish.
People can be exposed to mercury by touching liquid mercury from a broken thermometer or fluorescent light bulb; breathing the vapors that liquid mercury releases at room temperature; accidentally swallowing small disk batteries or other substances that contain mercury compounds; or eating large amounts of fish with organic mercury in their tissues. Mercury affects the fetus * of a pregnant woman who ingests it; the fetus can die before birth, or the baby can be born with serious birth defects.
Mercury poisoning was more common several centuries ago than it is now because it was used in making felt and other textile industries. The phrase “mad as a hatter” came about because the people who made felt hats were exposed to mercury during the manufacturing process and eventually suffered brain damage. Mercury was added to cosmetics and was used to treat syphilis * , a sexually transmitted disease. It was even used in laxatives. After mercury was found to cause brain damage and even death, people began to find replacements for it in manufacturing, cosmetics, and medical treatments.
Mercury poisoning was relatively uncommon in the United States as of 2016. The American Association of Poison Control Centers reported 1,300 cases of exposure to mercury in 2013; 109 were in children younger than six years of age. Of these patients, 19 had moderate effects and 5 had severe effects, but no one died. Fatal cases of mercury poisoning in the 1990s were accidents. In 1997 a professor of chemistry at Dartmouth College died seven months after spilling a mercury compound on her latex * glove. At that time it was not known that this particular form of mercury could seep through latex to reach the skin. In March 2008, a man in Oklahoma died of mercury poisoning after trying to use mercury to extract gold from computer parts. There have been three fatal cases of mercury poisoning reported in Europe since 2010, two of them intentional, but none in the United States.
Mercury poisoning can be transmitted from a pregnant woman to her fetus because organic mercury from eating fish can cross the placenta * and affect fetal growth. In many cases, the woman has a miscarriage * or the baby is born with intellectual disability * .
As the case of the Minamata tragedy indicates, mercury poisoning can affect groups of people as well as individuals, and it can be mistaken at first for an outbreak of a contagious disease. Mercury poisoning is not spread from person to person in the way that bacterial or viral diseases are.
The symptoms of mercury poisoning vary somewhat depending on the form of mercury to which the person was exposed. Liquid mercury is not easily absorbed through the skin but can damage the lungs and travel to the central nervous system when a person breathes its vapors. The compounds of mercury that are found in batteries can be taken into the body through the skin or through accidental eating. They accumulate in and eventually damage the kidneys. Organic mercury is absorbed through the digestive tract and builds up in the brain, kidney, liver, hair, and skin. Some forms of organic mercury, such as the compound that killed the chemistry professor, can be absorbed directly through the skin.
The most noticeable symptoms of mercury poisoning are:
People who have swallowed batteries containing mercury may have vomiting and other severe digestive problems caused by the mercury damaging the tissues of the intestines.
Long-term exposure to mercury vapor can cause loss of teeth, inflammation of the gums, a metallic taste in the mouth, chest pain, difficulty breathing, and heavy sweating.
The doctor can also take samples of the patient's blood and urine * to see how much mercury is in the body. These tests do not always help in confirming the diagnosis. Urine tests are useful in evaluating whether the patient was exposed to liquid mercury or mercury salts.
Individuals who have breathed in large amounts of mercury vapor or have swallowed certain mercury compounds need emergency treatment in a hospital to keep their airway open. Contaminated clothing is removed, and exposed skin is washed down with generous amounts of water. If patients show signs of kidney failure, they are treated with hemodialysis * . Doctors use chelation therapy * for patients with severe mercury poisoning. Chelation therapy involves the use of medications that combine with the mercury to prevent the body from absorbing it and make it easier for the body to excrete the mercury.
Most adults with mild exposure to mercury recover completely. Children are more vulnerable to long-term damage from mercury poisoning than adults; babies born to mothers who have eaten fish containing high levels of mercury are at risk of lifelong muscle disorders, learning disorders, and problems with vision or hearing. There are six factors that influence the person's chances of recovery:
Mercury poisoning is preventable with proper precautions. In terms of mercury in the food chain, the Food and Drug Administration (FDA) recommends eating 8 to 12 ounces of fish each week, even pregnant women and children, because fish is rich in essential nutrients for growth and development. The FDA also recommends that people choose fish and shellfish with the lowest possible mercury levels.
In the home or workplace, people can lower their risk of mercury poisoning by using wood preservatives, insecticides, explosives, and other products containing mercury only in well-ventilated areas. People who work in chemistry laboratories should follow safety guidelines for working with mercury very precisely, remembering that mercury can penetrate latex gloves. Fluorescent bulbs or thermometers containing mercury should be handled very carefully if broken because of the danger of inhaling mercury vapor. The mercury from a broken thermometer or light bulb should be sponged up, sealed inside a plastic bag, and taken to a hazardous waste facility rather than removed with a vacuum cleaner, because vacuuming will spread mercury vapor.
See also Environmental Diseases: Overview • Lead Poisoning
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Landrigan, Philip J., and Ruth A. Etzel, editors. Textbook of Children's Environmental Health. New York: Oxford University Press, 2014.
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MedlinePlus. “Mercury.” U.S. National Library of Medicine, National Institutes of Health. https://www.nlm.nih.gov/medlineplus/mercury.html (accessed March 7, 2016).
American Association of Poison Control Centers. 515 King St., Suite 510, Alexandria, VA 22314. Telephone: 703-894-1858. Website: http://www.aapcc.org (accessed March 7, 2016).
Environmental Protection Agency. 1200 Pennsylvania Ave. NW, Washington, DC 20460. Telephone: 202-272-0167. Website: http://www.epa.gov (accessed March 7, 2016).
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* nervous system is a network of specialized tissue made of nerve cells, or neurons, that processes messages to and from different parts of the human body.
* convulsions (kon-VUL-shuns), also called seizures, are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.
* central nervous system (SEN-trul NER-vus SIS-tem) is the part of the nervous system that includes the brain and spinal cord.
* food chain refers to the eating relationships between different organisms in a specific environment.
* fetus (FEE-tus) is the term for an unborn human after it is an embryo, from nine weeks after fertilization until childbirth.
* syphilis (SIH-fih-lis) is a sexually transmitted disease that, if left untreated, can lead to serious life long problems throughout the body, including blindness and paralysis.
* latex (LAY-tex) is a substance made from a rubber tree and is used in such items as medical equipment (especially gloves), toys, and other household products.
* placenta (pluh-SEN-ta) is an organ that provides nutrients and oxygen to a developing baby; it is located within the womb during pregnancy.
* miscarriage (MIS-kare-ij) is the end of a pregnancy through the death of the embryo or fetus before birth.
* intellectual disability is a condition in which people have belowaverage intelligence that limits their ability to function normally.
* Parkinson's disease is a disorder of the nervous system that causes shaking, rigid muscles, slow movements, and poor balance.
* urine is the liquid waste material secreted by the kidneys and removed from the body through the urinary tract.
* hemodialysis (HEE-mo-dye-ALis-is) is a method for removing waste products from the blood in patients with kidney failure.
* chelation therapy (chee-LAYshun) is a technique used to treat patients with lead or mercury poisoning by administering medications that combine with the metal to keep the body from absorbing it.