Heavy Metal Toxins

Even at a very low level, heavy metal ions can cause serious health effects, including reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death. The most common heavy metal toxins are aluminum, arsenic , cadmium, lead, and mercury. Once emitted from their sources, they have the property of accumulating in the environment for many years. They enter the human body through breathing, drinking, and skin absorption. They also can accumulate in the bodies of animals and humans before they even cause damage.

The sources of heavy metal ions are diverse and specific to each element. Aluminum is mostly found in canned food, cookware, antacids, aluminum foils, and drinking water. Arsenic is encountered through air pollution and in drinking water, meat from commercial farms, and wood preservatives. Cadmium originates mainly from cigarette smoke, air pollution, batteries, fish, paint, and food grown in cadmium-laden soil. The major sources of lead are gasoline, house paints, lead pipes, mines, and batteries. "Silver" dental fillings constitute the most important source of mercury. Other sources of mercury are from gold mining and fish. In general, the increased use of coal favors exposure to major heavy metals. What then is the mode of action of heavy metal ions?

The heavy metal ions form complexes with proteins, in which carboxylic acid (–COOH), amine (–NH 2 ), and thiol (–SH) groups are involved. These modified biological molecules lose their ability to function properly and result in the malfunction or death of the cells. When metals bind to these groups, they inactivate important enzyme systems, or affect protein structure, which is linked to the catalytic properties of enzymes. This type of toxin may also cause the formation of radicals, dangerous chemicals that cause the oxidation of biological molecules.

Some diseases associated with heavy metal ions are as follows:

  • Aluminum has been associated with Alzheimer's and Parkinson's disease, senility, and presenile dementia.
  • Arsenic exposure can cause, among other illnesses or symptoms, cancer, abdominal pain, and skin lesions.
  • Cadmium exposure produces kidney damage and hypertension .
  • Lead and mercury may cause the development of autoimmunity, in which a person's immune system attacks its own cells. This can lead to joint diseases and ailments of the kidneys, circulatory system, and neurons. At higher doses, lead and mercury can cause irreversible brain damage.

Heavy metal poisoning or intoxication can be diagnosed through analysis of samples from certain parts of the body. For example, lead poisoning is diagnosed by analyzing blood samples from affected individuals. The maximum allowed concentration of lead is 10 micrograms (3.5 × 10 −7 ounces) per deciliter of blood. At exposures above this level, action must be taken to treat the victim.

A common treatment for metal intoxication is the use of chelators. A chelator is a flexible molecule with two or more electronegative groups that can form stable complexes with cationic metal atoms. The complexes are then eliminated from the body. The most widely used chelator is ethylenediaminetetraacetic acid (EDTA). It has four binding positions (two nitrogen atoms and two oxygen atoms) that focus on the metal ion. It works very well on many metals, the most notable being calcium, magnesium, and lead.

SEE ALSO Enzymes ; Proteins ; Tertiary Structure ; Toxicity .

Joseph Bariyanga


Dhar, Sanat K. (1973). Metal Ions Biological System. New York: Plenum.

Internet Resources

World Resources Institute. "Heavy Metals and Health." Available from http://www.wri.org/wr-98-99/metal2.htm .

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