Heavy metal ingestion

Overview
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 accidental human poisoning are lead, mercury, arsenic, and cadmium. More recently, thallium has gained some attention in the media as the poison used in several murder cases in the 1990s. 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.

A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. There are several different definitions concerning which elements fall in this class designation. Alternative terms are 'metal' or 'semi-metal' (according to the element in view). Some of the nearly 40 known definitions are:


 * According to one definition, heavy metals are a group of elements between copper and bismuth on the periodic table of the elements—having specific gravities greater than 4.0.


 * A more strict definition increases specificity to metals heavier than the rare earth metals, which are at the bottom of the periodic table. None of these are essential elements in biological systems and additionally, most of the better known elements are toxic in fairly low concentrations. Thorium and uranium are occasionally included in this classification as well, but they are more often referred to as "radioactive metals". See actinides in the environment for further details of these radioactive metals.


 * Also, often the elements beyond mercury, e.g., the actinides such as uranium and plutonium, are not excluded from the heavy metals. In the context of nuclear power plants, tHM means tons of heavy metal.


 * In astronomy, which defines any element heavier than helium a metal, a heavy metal or heavy element includes all elements that were not formed in the big bang; all but hydrogen (and deuterium), helium, and lithium.


 * Any toxic metals may be called "heavy metals", whether or not they are heavy.

Living organisms require trace amounts of some heavy metals, including iron, cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium (with one exception for the latter) are toxic metals &mdash; they have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness. The pathway for toxic effects on humans is normally:
 * for the entry of heavy metals into the atmosphere as industrial stack gas
 * to enter the soil as a soil contaminant
 * to enter groundwater as a water pollutant
 * to be deposited in ocean bottoms or bay mud, which materials at a later time be dredged to the surface

In medical usage, the definition is considerably looser and includes all toxic metals irrespective of their atomic weight: "heavy metal poisoning" can include excessive amounts of iron, manganese, aluminium, or beryllium (the seventh-lightest metal) as well as the true heavy metals.

Heavy metals in a hazardous materials (or "hazmat") setting are for the most part classified in Misc. on the UN model hazard class but, they are sometimes labeled as a poison when being transported. 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. Lead poisoning in adults has been traced to the use of lead-based glazes on pottery vessels intended for use with food, and contamination of Ayurvedic and other imported herbal remedies. Arsenic and thallium have been mixed with food or beverages to attempt suicide or poison others.

Another form of mercury poisoning that is seen more and more frequently in the United States is self-injected mercury under the skin. Some boxers inject themselves with mercury in the belief that it adds muscle bulk. Metallic mercury is also used in folk medicine or religious rituals in various cultures. These practices increase the risk of mercury poisoning of children in these ethnic groups or subcultures.

Occupational History
The healthcare provider should take a thorough patient history with particular emphasis on the patient's occupation.

Symptoms
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.

Signs
Depending on the metal, there may be blue-black lines in the gum tissues. In severe cases, patients exhibit obvious impairment of cognitive, motor, and language 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.

Laboratory Evaluation
Heavy metal poisoning may be detected using blood and urine tests, hair and tissue analysis, or x ray. The diagnosis is often overlooked, however, because many of the early symptoms of heavy metal poisoning are nonspecific.

In childhood, blood lead levels above 80 ug/dL generally indicate lead poisoning, however, significantly lower levels (&gt;30 ug/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 ug/dL or higher in children a cause for concern. In adults, symptoms of lead poisoning are usually seen when blood lead levels exceed 80 ug/dL for a number of weeks.

Blood levels of mercury should not exceed 3.6 ug/dL, while urine levels should not exceed 15 ug/dL. Symptoms of mercury poisoning may be seen when mercury levels exceed 20 ug/dL in blood and 60 ug/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 ug/dL in people with arsenic poisoning. If acute arsenic or thallium poisoning is suspected, an x ray may reveal these substances in the abdomen (since both metals are 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 ug/dL of creatinine and blood levels exceed 5 ug/dL.

Thallium poisoning often causes hair loss (alopecia), numbness, and a burning sensation in the skin as well as nausea, vomiting, and dizziness. As little as 15-20 mg of thallium per kilogram of body weight is fatal in humans; however, smaller amounts can cause severe damage to the nervous system.

Treatment
When heavy metal poisoning is suspected, it is important to begin treatment as soon as possible to minimize long-term damage to the patient's nervous system and digestive tract. Heavy metal poisoning is considered a medical emergency, and the patient should be taken to a hospital emergency room.

The treatment for most heavy metal poisoning is chelation therapy. A chelating agent specific to the metal involved is given either 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 is not useful in treating cadmium poisoning. To date, no treatment has been proven effective for cadmium poisoning. Thallium poisoning is treated with a combination of Prussian blue (potassium ferric hexacyanoferrate) and a diuretic, because about 35% of it is excreted in the urine; however, if treatment is not started within 72 hours of ingesting the poisoning, damage to the patient's nervous system may be permanent.

In cases of acute mercury, arsenic, or thallium ingestion, vomiting may be induced. Activated charcoal may be given in cases of thallium poisoning. Washing out the stomach (gastric lavage) may also be useful. The patient may also require treatment such as intravenous fluids for such complications of poisoning as shock, anemia, and kidney failure.

Patients who have taken arsenic, thallium, or mercury in a suicide attempt will be seen by a psychiatrist as part of emergency treatment.

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

Primary Prevention
Because arsenic and thallium were commonly used in rat and insect poisons at one time, many countries have tried to lower the rate of accidental poisonings by banning the use of heavy metals in pest control products. Thallium was banned in the United States as a rodent poison in 1984. As a result, almost all recent cases of arsenic and thallium poisoning in the United States were deliberate rather than accidental.

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. Exposure to environmental sources of lead, including lead-based paints, plumbing fixtures, vehicle exhaust, and contaminated soil, should be reduced or eliminated.

People who use Ayurvedic or traditional Chinese herbal preparations as alternative treatments for various illnesses should purchase them only from reliable manufacturers.

Books

 * 1) Beers, Mark H., MD, and Robert Berkow, MD., editors. "Poisoning." Section 23, Chapter 307 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
 * 2) Beers, Mark H., MD, and Robert Berkow, MD., editors. "Psychiatric Emergencies." Section 15, Chapter 194 In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
 * 3) Wilson, Billie A., Margaret T. Shannon, and Carolyn L. Stang. Nurses Drug Guide 2000. Stamford, CT: Appleton &amp; Lange, 2000.

Periodicals

 * 1) Boyarsky, Igor, DO, and Adrain D. Crisan, MD. "Toxicity, Thallium." eMedicine August 3, 2004.
 * 2) Centers for Disease Control and Prevention (CDC). "Adult Blood Lead Epidemiology and Surveillance-United States, 2002." Morbidity and Mortality Weekly Report 53 (July 9, 2004): 578-582.
 * 3) Counter, S. A., and L. H. Buchanan. "Mercury Exposure in Children: A Review." Toxicology and Applied Pharmacology 198 (July 15, 2004): 209-230.
 * 4) Ferner, David J., MD. "Toxicity, Heavy Metals." eMedicine May 25, 2001.
 * 5) Prasad, V. L. "Subcutaneous Injection of Mercury: 'Warding Off Evil'." Environmental Health Perspectives 111 (September 2004): 1326-1328.
 * 6) Schilling, U., R. Muck, and E. Heidemann. "Lead Poisoning after Ingestion of Ayurvedic Drugs." [in German] Medizinische Klinik 99 (August 15, 2004): 476-480.
 * 7) Thompson, D. F., and E. D. Callen. "Soluble or Insoluble Prussian Blue for Radiocesium and Thallium Poisoning?" Annals of Pharmacotherapy 38 (September 2004): 1509-1514.

Patient Resources

 * 1) American Society of Health-System Pharmacists (ASHP). 7272 Wisconsin Avenue, Bethesda, MD 20814. (301) 657-3000.
 * 2) Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. (800) 311-3435, (404) 639-3311.
 * 3) Food and Drug Administration. Office of Inquiry and Consumer Information. 5600 Fisher Lane, Room 12-A-40, Rockville, MD 20857. (301) 827-4420.
 * 4) National Institutes of Health. National Institute of Environmental Health Sciences Clearinghouse. EnviroHealth, 2605 Meridian Parkway, Suite 115, Durham, NC 27713. (919) 361-9408.