Definition
Heavy metal poisoning is the toxic accumulation of heavy metals in the soft tissues of the body.
Description
Heavy metals are chemical elements that have a specific gravity (a measure of density) at least five times that of water. The heavy metals most often implicated in human poisoning are lead, mercury, arsenic, and cadmium. Some heavy metals, such as zinc, copper, chromium, iron, and manganese, are required by the body in small amounts, but these same elements can be toxic in larger quantities.
Heavy metals may enter the body in food, water, or air, or by absorption through the skin. Once in the body, they compete with and displace essential minerals such as zinc, copper, magnesium, and calcium, and interfere with organ system function. People may come in contact with heavy metals in industrial work, pharmaceutical manufacturing, and agriculture. Children may be poisoned as a result of playing in contaminated soil.
Demographics
Heavy metal poisoning is relatively uncommon. In children, lead ingestion is the major culprit of heavy metal poisoning. In 2000, an estimated one in 22 American children had high levels of lead in their blood. Children in urban areas with old lead water pipes and lead-painted homes are especially at risk. Mercury poisoning is possible from eating contaminated fish.
Causes and Symptoms
Symptoms will vary, depending on the nature and the quantity of the heavy metal ingested. Affected people may complain of nausea, vomiting, diarrhea, stomach pain, headache, sweating, and a metallic taste in the mouth. Depending on the metal, there may be blue-black lines in the gum tissues. In severe cases, people exhibit obvious impairment of cognitive, motor, and language skills. The expression "mad as a hatter" comes from the mercury poisoning prevalent in seventeenth-century France among hat makers who soaked animal hides in a solution of mercuric nitrate to soften the hair.
When to Call the Doctor
A healthcare professional should be contacted whenever exposure to any heavy metal is suspected. The Centers for Disease Control and Prevention (CDC) recommends testing all children for lead exposure at 12 months of age and, if possible, again at 24 months. Testing should start at six months for children at higher risk for lead poisoning.
Diagnosis
Heavy metal poisoning may be detected using blood and urine tests, hair and tissue analysis, or x ray.
In childhood, blood lead levels above 80 mg/dL generally indicate lead poisoning; however, significantly lower levels (>30 mg/dL) can cause mental retardation and other cognitive and behavioral problems in affected children. The Centers for Disease Control and Prevention considers a blood lead level of 10 mg/dL or higher in children a cause for concern. In adults, symptoms of lead poisoning are usually seen when blood lead levels exceed 80 mg/dL for a number of weeks.
Blood levels of mercury should not exceed 3.6 mg/dL, while urine levels should not exceed 15 mg/dL. Symptoms of mercury poisoning may be seen when mercury levels exceed 20 mg/dL in blood and 60 mg/dL in urine. Mercury levels in hair may be used to gauge the severity of chronic mercury exposure.
Since arsenic is rapidly cleared from the blood, blood arsenic levels may not be very useful in diagnosis. Arsenic in the urine (measured in a 24-hour collection following 48 hours without eating seafood) may exceed 50 mg/dL in people with arsenic poisoning. If acute arsenic poisoning is suspected, an x ray may reveal ingested arsenic in the abdomen (since arsenic is opaque to x rays). Arsenic may also be detected in the hair and nails for months following exposure.
Cadmium toxicity is generally indicated when urine levels exceed 10 mg/dL of creatinine and blood levels exceed 5 mg/dL.
Treatment
The treatment for most heavy metal poisoning is chelation therapy. A chelating agent specific to the metal involved is given orally, intramuscularly, or intravenously. The three most common chelating agents are calcium disodium edetate, dimercaprol (BAL), and penicillamine. The chelating agent encircles and binds to the metal in the body's tissues, forming a complex; that complex is then released from the tissue to travel in the bloodstream. The complex is filtered out of the blood by the kidneys and excreted in the urine. This process may be lengthy and painful and typically requires hospitalization. Chelation therapy is effective in treating lead, mercury, and arsenic poisoning, but it is not useful in treating cadmium poisoning. As of 2004, no treatment had been proven effective for cadmium poisoning.
In cases of acute mercury or arsenic ingestion, vomiting may be induced. Washing out the stomach (gastric lavage) may also be useful. The affected person may also require treatment such as intravenous fluids for complications of poisoning such as shock, anemia, and kidney failure.
Prognosis
The chelation process can only halt further effects of the poisoning; it cannot reverse neurological damage already sustained.
Prevention
Because exposure to heavy metals is often an occupational hazard, protective clothing and respirators should be provided and worn on the job. Protective clothing should then be left at the work site and not worn home, where it could carry toxic dust to family members. Industries are urged to reduce or replace the heavy metals in their processes wherever possible. For the sake of children's health along with everyone else's, exposure to environmental sources of lead, including lead-based paints, plumbing fixtures, vehicle exhaust, and contaminated soil, should be reduced or eliminated.
Nutritional Concerns
Parents should avoid preparing or serving food in containers that have lead in their glazing.
Parental Concerns
Parents living in homes built prior to 1978 should be vigilant in removing flaking or peeling paint because it might contain lead. Simply repainting such surfaces will not solve the problem. Parents must monitor the environments in which their children play and the objects that go into their children's mouths. Cleanliness is a must if old paint is in a child's environment. Removal (stripping paint to bare metal or bare wood) of lead is the best way to prevent lead exposure in children. Areas where removal is taking place should be sealed off from the rest of the house. In addition, children should be kept away from occupational sources of other heavy metals. Parents who are concerned about their child's exposure to lead should have the child tested.
See also Lead poisoning.
Resources
Books
Goto, Collin S. "Heavy Metal Intoxication." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman, et al. Philadelphia: Saunders, 2003, pp. 2355–7.
Gupta, S. K., et al. Emergency Toxicology: Management of Common Poisons. Boca Raton, FL: CRC Press, 2003.
Klaasen, Curtis D., and John Doull. Casarett and Doull's Toxicology: The Basic Science of Poisons, 6th ed. New York: McGraw Hill, 2001.
Markowitz, Morrie. "Lead Poisoning." In Nelson Textbook of Pediatrics, 17th ed. Edited by Richard E. Behrman, et al. Philadelphia: Saunders, 2003, pp. 2358–61.
Periodicals
Clark S, et al. "The influence of exterior dust and soil lead on interior dust lead levels in housing that had undergone lead-based paint hazard control." Journal of Occupational and Environmental Hygiene 1, no. 5 (2004): 273–82.
Counter, S. A., and L. H. Buchanan. "Mercury exposure in children: a review." Toxicology and Applied Pharmacology 198, no. 2 (2004): 209–30.
Dorea, J. G. "Mercury and lead during breast-feeding." British Journal of Nutrition 92, no. 1 (2004): 21–40.
Yassin, A. S., and J. F. Martonik. "Urinary cadmium levels in the U.S. working population, 1988–1994." Journal of Occupational and Environmental Hygiene 1, no. 5 (2004): 324–33.
Organizations
American Academy of Clinical Toxicology. 777 East Park Drive, PO Box 8820, Harrisburg, PA 17105–8820. Web site: www.clintox.org/index.html.
American Academy of Family Physicians. 11400 Tomahawk Creek Parkway, Leawood, KS 66211–2672. Web site: www.aafp.org/.
American Academy of Pediatrics. 141 Northwest Point Boulevard, Elk Grove Village, IL 60007–1098. Web site: www.aap.org/default.htm.
American Association of Poison Control Centers. 3201 New Mexico Avenue NW, Washington, DC 20016. Web site: www.aapcc.org/.
American College of Occupational and Environmental Medicine. 55 West Seegers Road, Arlington Heights, IL 60005. Web site: www.acoem.org/.
Multiple Sclerosis Foundation. 6350 North Andrews Ave., Fort Lauderdale, Fl 33309–2130. Web site: www.msfacts.org/.
National Multiple Sclerosis Society. 733 Third Avenue, New York, NY 10017. Web site: www.nmss.org/.
Web Sites
"Heavy Metal Poisoning." Med Help International. Available online at www.medhelp.org/HealthTopics/Heavy_Metal_Poisoning.html (accessed November 10, 2004).
"Heavy Metals (Toxicology)." National Multiple Sclerosis Society. Available online at www.nationalmssociety.org/Sourcebook-Heavy%20Metals.asp (accessed November 10, 2004).
Hoekman, Theodore. "Heavy Metals Toxicology." Available online at www.luminet.net/~wenonah/hydro/heavmet.htm (accessed November 10, 2004).
"Toxicity, Heavy Metals." eMedicine. Available online at www.emedicine.com/emerg/topic237.htm (accessed November 10, 2004).
[Article by: L. Fleming Fallon, Jr., MD, DrPH]
