JERROLD SCHARNINGHAUSEN
Directorate of Assessments and Prevention, 
Workplace Safety Division
U.S. Army Combat Readiness Center
Fort Rucker, Alabama

What are heavy metals? The answer depends upon who you ask. A metallurgist would define heavy metals based upon the density of the material. A physicist would classify them by their atomic number on the periodic table. A chemist would base the definition upon the chemical behavior of the element. While there are differences in opinion over what should be included in the group when referring to heavy metals, the one thing everybody agrees upon is that they are toxic at low concentrations and can create severe health hazards. 

Some of the most common heavy metals exposures on military installations include lead, chromium, cadmium and beryllium. In very low concentrations, heavy metals can be essential in maintaining various biochemical and physiological functions in living organisms. Common sources of heavy metals in the workplace include mining and industrial wastes; vehicle emissions; lead-acid batteries; fertilizers; paints; treated timber; and the aging water supply infrastructure. 

Heavy metals tend to bioaccumulate. Bioaccumulation occurs when an organism absorbs a substance at a faster rate than it is excreted from the body. The accumulation in your body can occur through a variety of routes, including ingesting contaminated food and water; breathing contaminated air; and absorption through the skin. Toxicity will depend upon the route of exposure, the amount absorbed by the body and the duration of exposure (i.e., acute or chronic). 

Numerous public health measures have been undertaken to control and prevent heavy metal toxicity occurring as a result of occupational exposures. Heavy metal toxicity is involved in a variety of physical processes, some of which the exact mechanism is not clearly understood. Each metal, however, is known to have unique features and properties that conform to specific toxicological mechanisms of action.

Lead
Overexposure to lead is one of the most prevalent occupational exposures worldwide. Activities with high potential for lead exposure include construction work, smelter operations, vehicle repair and weapons firing. Non-workplace exposures can occur from deteriorating lead paint or older water systems. Lead exposure in humans can result in a wide range of biological effects depending on the level and length of exposure. Effects vary over a broad range of doses, with infants and small children being more sensitive than adults. 

High levels of exposure may result in toxic effects in humans, which in turn cause problems in the formation of hemoglobin, damage to the kidneys, gastrointestinal tract, joints, reproductive system, and acute or chronic damage to the nervous system. Lead exposure can occur from inhalation of lead dust during range maintenance operations, deteriorating lead paint or through ingestion from eating or drinking in areas where lead is present. 

Chromium 
The Occupational Safety and Health Administration estimates that more than 558,000 workers are potentially exposed to chromium and chromium-containing compounds in the workplace annually. Chromium is used in paint pigments, cement, paper, rubber, metal alloys and other materials. Calcium chromate, lead chromate, strontium chromate, zinc chromate and chromium trioxide are known human carcinogens. 

Chromium exposure can also occur when involved in processes that include the burning of oil and coal; working with pigments, oxidants and fertilizers; welding stainless steel; oil well drilling; and metal plating. Exposure at low levels can irritate the skin and cause ulceration. Long-term low-level exposure can damage kidney, liver, circulatory and nerve tissue. Breathing higher levels of chromium (VI) can irritate the lining of the nose and cause nasal ulcers. Ingestion of chromium (VI) compounds may cause irritation and ulcers in the stomach and small intestine, anemia and male reproductive system damage. 

Some individuals can become extremely sensitive to chromium, developing allergic reactions consisting of severe redness and swelling of the skin. Ingestion of extremely high doses of chromium (VI) compounds has resulted in severe respiratory, cardiovascular, gastrointestinal, hematological, hepatic, renal and neurological effects leading to death. 

Cadmium
Cadmium is an extremely toxic metal commonly found in industrial workplaces. Cadmium compounds are classified as human carcinogens by the National Toxicology Program of the U.S. Department of Health and Human Services. Occupational or environmental cadmium exposure has been associated with development of cancers of the lungs, prostate, kidney, liver and stomach and interference with the formation of red blood cells. 

Cadmium and cadmium compounds are not combustible but may decompose when heated and release corrosive and toxic fumes. Deaths have occurred from acute exposure among welders who have unsuspectingly welded on cadmium-containing alloys. Additional exposure may occur through con¬sumption of contaminated food and drinking water, inhalation of cadmium-containing particles from ambient air or cigarette smoke, and ingestion of contaminated soil and dust. 

Current research indicates that adverse health effects from cadmium exposure may occur at lower levels than previously anticipated, primarily in the form of kidney damage. Cadmium is used by the military for surface treatment (corrosion protection) in aerospace and weapon systems. Exposures can potentially occur while grinding, filing, conducting welding operations or by heating the metal to release fumes. 

Beryllium
Beryllium is crucial to national defense. It is considered essential for defense systems and unique in the function it performs. Military systems depend heavily on electronics for navigation, target acquisition and firing solutions, making the rigid and lightweight nature of beryllium ideal. Beryllium metal and metal alloys may be found in aircraft disc brakes, X-ray transmission windows, space vehicles optics and instruments, aircraft/satellite structures, missile guidance systems, nuclear reactor neutron reflectors, nuclear warhead triggering devices, fuel containers, precision instruments, rocket propellants, navigational systems, heat shields, mirrors, high speed computers, ceramics, electronic heat sinks, electrical insulators, microwave oven components, gyroscopes, military vehicle armor, rocket nozzles crucibles, thermocouple tubing, laser structural components, substrates for high-density electrical circuits, automotive ignition systems, radar electronic countermeasure systems and special non-sparking tools. The use of beryllium in electronic and electrical components, aerospace and defense applications accounted for more than 80 percent of its consumption.

Occupational exposure to beryllium occurs at places where workers engage in machining metals containing beryllium, recycling beryllium from scrap alloys or use beryllium products. Contact with beryllium metal and metal alloys is usually unlikely, since the material is typically enclosed to prevent exposure. Breathing large amounts of soluble beryllium compounds can result in lung damage resembling pneumonia. The damage to the lungs may heal if beryllium exposure is eliminated. Some people can become sensitive to beryllium, developing an immune or inflammatory reaction to small amounts. The U.S. Department of Health and Human Services has determined beryllium and beryllium compounds are human carcinogens.

Conclusion
The Department of Defense is currently researching strategies to develop new and innovative technologies to replace heavy metals. These strategies include reduction, substitution and elimination of these materials wherever possible. The Department of the Army has established and implemented Installation Restoration Programs to clean up contaminated areas that occurred from past Army-related operations. If your occupation could potentially expose you to heavy metals, ensure that you are using the appropriate personal protective equipment for the job and it is serviceable.