Heavy metal poisoning

Heavy metal poisoning is the toxic accumulation of heavy metals in the soft tissues of the body.

Heavy metals are chemical elements that have a specific gravity (a measure ofdensity) at least five times that of water. The heavy metals most often involved 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 essential minerals such aszinc, copper, magnesium, and calcium, and interfere with the function of theorgans. 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.

Symptoms will vary, depending on the nature and the quantity of the heavy metal ingested. Patients 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 gums. In severe cases, patients exhibit obvious impairment of awareness, judgment, language and motor skills. The expression "mad as a hatter" comes from the mercury poisoning prevalent in 17th century France among hatmakers who soaked animal hides in a solution of mercuric nitrate to soften the hair.

Heavy metal poisoning may be detected using blood and urine tests, hair and tissue analysis, or x ray. If acute arsenic poisoning is suspected, an x ray may reveal arsenic in the abdomen (since arsenic is opaque to x rays).

The treatment for most heavy metal poisoning is chelation therapy. A chelating agent specific to the metal involved is given either by mouth, injection orintravenously. The three most common chelating agents are calcium disodium edetate, dimercaprol, and penicillamine. The chelating agent binds to the metal in the body's tissues, forming a complex; which is then released to 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 is not useful in cadmium poisoning. To date, no treatment has been proven effective for cadmium poisoning.

In cases of acute mercury or arsenic ingestion, vomiting may be induced. A health professional may decide to wash out the stomach (gastric lavage). The patient may also require treatment such as intravenous fluids for complicationsof poisoning such as shock, anemia, and kidney failure.

The chelation process can only halt further effects of the poisoning; it cannot reverse neurological damage already sustained.

Because exposure to heavy metals is often an occupational hazard, protectiveclothing 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. Exposure to environmental sources of lead, including lead-based paints, plumbing fixtures, vehicle exhaust, and contaminated soil, should be reduced or eliminated.

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