There are 35 metals that concern us because of occupational or residential exposure; 23 of these are the heavy elements or "heavy metals": antimony, arsenic, bismuth, cadmium, cerium, chromium, cobalt, copper, gallium, gold, iron, lead, manganese, mercury, nickel, platinum, silver, tellurium, thallium, tin, uranium, vanadium, and zinc (Glanze 1996). Small amounts of these elements are common in our environment and diet and are actually necessary for good health, but large amounts of any of them may cause acute or chronic toxicity (poisoning). Heavy metal toxicity can result in damaged or reduced mental and central nervous function, lower energy levels, and damage to blood composition, lungs, kidneys, liver, and other vital organs. Long-term exposure may result in slowly progressing physical, muscular, and neurological degenerative processes that mimic Alzheimer's disease, Parkinson's disease, muscular dystrophy, and multiple sclerosis. Allergies are not uncommon, and repeated long-term contact with some metals (or their compounds) may cause cancer (CIS 1999).
For some heavy metals, toxic levels can be just above the background concentrations naturally found in nature. Therefore, it is important to learn about heavy metals and take protective measures against excessive exposure. In most parts of the United States, heavy metal toxicity is an uncommon medical condition; however, it is a clinically significant condition when it does occur. If unrecognized or inappropriately treated, toxicity can result in significant illness and reduced quality of life (Ferner 2001). For persons who suspect that they or someone in their household might have heavy metal toxicity, testing is essential. Appropriate conventional and natural medical procedures may need to be pursued (Dupler 2001).
The association of symptoms indicative of acute toxicity is not difficult to recognize because they are usually severe, rapid in onset, and associated with a known exposure or ingestion (Ferner 2001). Symptoms include: cramping, nausea, and vomiting; pain; sweating; headache; difficulty breathing; impaired cognitive, motor, and language skills; mania; and convulsions. Symptoms of chronic exposure (impaired cognitive, motor, and language skills; learning difficulties; nervousness and emotional instability; and insomnia, nausea, lethargy, and feeling ill) are also easily recognized; however, they are much more difficult to associate with their cause. Symptoms resulting from chronic exposure are very similar to symptoms of other health conditions and often develop slowly over months or even years. Sometimes symptoms of chronic exposure subside; thinking the symptoms are related to something else, people postpone seeking treatment.
Definition of a Heavy Metal
"Heavy metals" are chemical elements with a specific gravity at least 5 times that of water. The specific gravity of water is 1 at 4°C (39°F). Specific gravity is a measure of density of a given amount of a solid substance when it is compared to an equal amount of water. Some well-known toxic metals with a specific gravity 5 or more times that of water are arsenic (5.7), cadmium (8.65), iron (7.9), lead (11.34), and mercury (13.546) (Lide 1992).
Beneficial Heavy Metals
In small quantities, certain heavy metals are nutritionally essential for a healthy life. Some of these are trace elements (eg, iron, copper, manganese, and zinc). These elements, or some form of them, are commonly found naturally in foodstuffs, fruits and vegetables, and in commercially available multivitamin products (CIS 1999). Diagnostic medical applications include direct injection of gallium during radiological procedures, dosing with chromium in parenteral nutrition mixtures, and the use of lead as a radiation shield around x-ray equipment (Roberts 1999). Heavy metals are also common in industrial applications such as the manufacture of pesticides, batteries, alloys, electroplated metal parts, textile dyes, steel, and so forth (CIS 1999). Many of these products are in our homes and add to quality of life when properly used.
Toxic Heavy Metals
Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissues. Heavy metals may enter the human body via food, water, air, or absorption through the skin in agriculture, manufacturing, pharmaceutical, industrial, or residential settings. Industrial exposure is common in adults. Ingestion is the most common route in children (Roberts 1999). Children may develop toxic levels from normal hand-to-mouth activity (ie, coming in contact with contaminated soil or eating objects that are not food such as dirt or paint chips) (Dupler 2001). Less common routes of exposure include a radiological procedure, inappropriate dosing or monitoring during intravenous (parenteral) nutrition, a broken thermometer (Smith 1997), or a suicide or homicide attempt (Lupton 1985).
As a rule, acute poisoning is more likely to result from inhalation or contact with dust, fumes or vapors, or materials in the workplace. However, lesser levels of contamination may occur in residential settings, particularly in older homes with lead paint or old plumbing (CIS 1999). The Agency for Toxic Substances and Disease Registry (ATSDR) in Atlanta, Georgia (a part of the U.S. Department of Health and Human Services) was established by congressional mandate to perform specific functions concerning adverse human health effects and diminished quality of life associated with exposure to hazardous substances. The ATSDR is responsible for assessment of waste sites and providing health information concerning hazardous substances, response to emergency release situations, and education and training concerning hazardous substances (ATSDR Mission Statement 2001). In cooperation with the U.S. Environmental Protection Agency, the ATSDR has compiled a Priority List for 2001 called the "Top 20 Hazardous Substances." The heavy metals arsenic (1), lead (2), mercury (3), and cadmium (7) appear on this list.
- Note: The ATSDR provides comprehensive protocols called Medical Management Guidelines for Acute Chemical Exposures in Volume III of the Managing Hazardous Material Incidents Series. These protocols have a Chemical Abstracts Service (CAS) number and give a description of toxic substances; routes of exposure; health effects; prehospital, triage, and emergency medical department care; antidotes and treatment; disposition and follow-up; and reporting instructions. The series may be viewed or downloaded from the ATSDR web site at no cost.