Table of Contents
Definition of Heavy-Metal Poisoning
Heavy-Metal Poisoning – toxicity due to metals such as lead, mercury, copper, and iron can have serious and even lethal health consequences, especially among children.
Heavy metals occur naturally in the environment. They are present in soil and in plants that grow underground, and in water. Heavy metals are also the by-products of manufacturing processes. They can quickly accumulate to hazardous levels when they leach into drinking water supplies or enter the food chain when farmers irrigate crops using contaminated water. Some metal pollutants are also present in the air.
Numerous environmental laws enacted over the past 30 years have significantly reduced the presence of heavy metals as pollutants; and various standards, such as those for drinking water, require monitoring of metal and mineral levels. The US Environmental Protection Agency (EPA) monitors and enforces these laws.
Federal regulations have banned lead in paints, inks, and gasoline for several decades. Nonetheless lead poisoning continues to be a problem, particularly among children, who are vulnerable to damage at much lower levels of ingestion. Houses built before 1977 may still have leaded paint on the walls and especially wood trim, which young children may peel off and eat. Lead also can enter water supplies when the pipes that carry it are made of lead.
As the pipes deteriorate they release lead into the water they carry. Though many larger municipalities have replaced old lead pipes, many smaller ones have not. The smaller body size of children makes them especially vulnerable to toxic accumulations of lead. When the body stops receiving fresh supplies of lead, it can slowly process the lead that has accumulated, and eventually most body systems return to normal.
The natural forms of mercury are liquid or gas. It forms different chemicals when it combines with other substances. Manufacturing processes combine mercury with oxygen or chlorine to form inorganic combinations, called salts, used in industrial applications such as caustic soda and batteries. Dentists use inorganic mercury compounds in fillings for teeth. In nature mercury combines with carbon (methylmercury), usually in water, to form organic compounds. These organic mercury compounds accumulate in fish and shellfish.
The liquid nature of mercury has given rise to perceptions that it has mystical or supernatural abilities. Some spiritual and ritualistic practices use mercury, also called quicksilver or azogue, in baths, burned in candles, and sprinkled on surfaces. Like any other form of mercury, however, quicksilver is toxic. Many people who handle, breathe, or ingest quicksilver suffer mercury poisoning.
Excessive amounts of mercury in the body can result in permanent damage to the BRAIN and kidneys. Studies link two forms of mercury—mercury chloride and methylmercury—with an increased risk for developing cancer. Many people are concerned about the health risks possibly associated with mercury dental fillings (also called dental amalgam). The American Dental Association and the US Food and Drug Administration (FDA), among other health agencies, have issued position statements supporting the continued use of mercury fillings because there are no conclusive studies that correlate its use to mercury poisoning. However, most dentists offer alternative materials for people who are concerned about mercury fillings.
By far the most significant source of mercury among Americans is seafood. In 2004 the FDA issued a health advisory regarding mercury levels in four kinds of fish: swordfish, king mackerel, shark, and tilefish. These fish are at the top of the food chain; they live for many years, subsisting on a diet of other fish. Methylmercury levels in the flesh of these kinds of fish are higher than in other kinds of fish. The advisory recommends that pregnant women and women who are breastfeeding avoid eating these kinds of fish. Salmon, cod, albacore tuna, pollock, haddock, ocean perch, tilapia, and fresh-water trout have the lowest levels of mercury.
Thimerosal, a common preservative in vaccines and some other biologic agents, contains mercury. Though pharmaceutical manufacturers are moving away from its use, thimerosal remains a concern especially with childhood vaccinations. Individuals should ask for thimerosal-free vaccines and other biologic agents for themselves and for their children. US health agencies have called for the complete eradication of thimerosal as a medicinal preservative.
Though copper occurs in nature, the most common source of human exposure to copper is through water supplies that travel through copper pipes. Water that is highly acidic corrodes the pipes, drawing copper into the water. Excessive copper accumulations in the body can cause irreversible liver and kidney damage. Copper also can accumulate in the brain, causing cognitive dysfunction. People who have Wilson’s disease, a hereditary disorder in which the body cannot metabolize copper, are especially vulnerable to copper in the food supply and the environment because copper accumulates in their bodies. The body needs only a very small amount of copper, which it uses to make certain enzymes and to facilitate iron metabolism for hemoglobin production.
The body needs iron to produce hemoglobin, the protein in the blood that binds with oxygen. Iron deficiency is fairly common, and many people take iron supplements. These supplements are the most frequent source for iron poisoning, especially among young children. Excessive amounts of iron in the body slow the heart rate and force of contractions, reducing the flow of blood. Other chemical changes that take place at the molecular level affect the ability of cells throughout the body to function. People who have the hereditary condition HEMOCHROMATOSIS cannot properly metabolize iron, resulting in toxic accumulations over years to decades. Iron is also highly toxic to the liver, resulting in hepatonecrosis (death of hepatocytes, the primary functional cells in the liver).
See also DRINKING WATER STANDARDS; POISON PREVENTION.
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