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 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 can be toxic in larger quantities. Heavy metals may enter the body through 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.
Sources of exposure for some heavy metals
lead: old paint, leaded gasoline, old pipes
mercury: contaminated fish, industrial and agricultural wastes
cadmium: industrial waste, insecticides, old galvanized pipes
arsenic: insecticides and industrial processes, some drinking water
Causes & symptoms
Symptoms will vary, depending on the nature and quantity of the heavy metal, and whether it was ingested or inhaled. Patients who ingest a heavy metal may complain of cramps, nausea, vomiting, diarrhea, stomach pain, headache, sweating, and a metallic taste in the mouth. Mercury can cause skin burns if it has touched the skin, and inhaled mercury vapor can cause severe inflammation of the lungs. If lead is inhaled in the form of lead dust, insomnia, headache, mania, and convulsions may occur. In severe cases of heavy metal poisoning, patients 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 hatmakers who soaked animal hides in a solution of mercuric nitrate to soften the hair.
Heavy metal poisoning may be detected using blood, urine, and stool tests, hair and tissue analysis, or x rays. In children, blood lead levels above 80 mcg/dl generally indicate lead poisoning; however, significantly lower levels (>.30 mcg/dL) can cause mental retardation and other cognitive and behavioral problems in chronically exposed children. The Centers for Disease Control and Prevention considers a blood lead level of 10 mcg/dl or higher in children a cause for concern. In adults, symptoms of lead poisoning are usually seen when blood lead levels exceed 80 mcg/dl for a number of weeks. Blood levels of mercury should not exceed 3.6 mcg/dl, while urine levels should not exceed 15 mcg/dl. Symptoms of mercury poisoning may appear when mercury levels exceed 20 mcg/dl in blood and 60 mcg/dl in urine. Mercury levels in hair may be used to gauge the severity of chronic mercury exposure, but a 2002 report says that these tests have questionable validity.
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 mcg/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 mcg/dl of creatinine and blood levels exceed 5 mcg/dl.
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