Lead is a naturally occurring bluish-gray metal found in small amounts in the earth’s crust. Lead can also be found in plants, animals, air, water, dust, and soil. As an element, lead is indestructible. But lead compounds can be changed by air, sunlight, and water. Once lead is released into the air, it lasts, and can move from one medium to another. For example, lead in dust can be carried long distances, dissolved in water, and find its way into soil where it can remain for years.

Like many metals, lead exists in different chemical forms.

• Metallic lead is the pure metal. 
• Inorganic lead compounds, such as lead oxide and lead acetate are combinations of lead with other elements. 
• Organic lead compounds, such as tetraethyl lead, those where lead is combined with carbon, are especially toxic.

Lead has many useful properties. It is soft and easily shaped, durable, resistant to some chemicals, and fairly common. Humans have used lead since early history. Lead is in batteries, paints, ceramics, and soldering and building materials. Until recently, lead was added to automobile gasoline. It has even been used in medicines and cosmetics. Because of its many uses, lead is now a common contaminant in waste sites. It is found in over half of the nation’s Superfund sites. Superfund is the federal government's program to evaluate and clean up uncontrolled or abandoned sites where hazardous waste is located and may pose a risk to local ecosystems or people. For more information about the Superfund program, visit their Web site: http://www.epa.gov/superfund/index.htm.

How Are People Exposed to Lead?

People are exposed to lead by swallowing or breathing it. In the past, when lead was added to gasoline, this was the major source of exposure. Automobile exhaust contained lead and people breathed it in contaminated air. Lead from automobile exhaust also contaminated soil near busy roadways and this soil continues to contaminate many yards.

Since lead has been taken out of gasoline, the major source of exposure is old paint that contains lead. This can be found in older homes and on structures such as bridges. Although the amount of lead used in paint has been regulated since 1978, it is estimated that 38 million homes in the US still have lead paint. That's about 40% of all US housing. During renovation of an older home, (built before 1978) swallowing or breathing lead paint dust can increase your body’s lead content. Some children pick off the lead paint chips to chew on and swallow. More often, particles from worn painted surfaces mix with soil and household dust, and children unintentionally swallow lead from their contaminated toys or hands.

Tap water that runs through old lead pipes and soldered joints in older homes can also be contaminated with lead. So can the water that runs through the water service lines that contain lead in many older US cities. The EPA estimates that 10% to 20% of human lead exposure comes from drinking water.

Other sources of lead exposure include cosmetics (especially the Asian cosmetics surma and kohl), ceramics (especially imported hand-painted ceramics which can contaminate food and drinks stored in and eaten from them), and bullets (which may expose people who prepare their own shot and/or who practice shooting in indoor firing ranges). Workers who make or recycle lead batteries, who process other metals that may be contaminated by lead, who weld or solder, and who repair automobile radiators may be exposed to lead.

Occupations With Exposure To Lead

Does Lead Cause Cancer?

There is some evidence showing that lead may cause cancer, but this evidence is weak. Still, lead has been loosely linked with cancers of the lung and stomach, and more weakly linked to brain and kidney cancers.

What Do Scientific Studies Show?

Like most metals, it is difficult to evaluate lead's ability to cause cancer because it is found in so many forms. Most of the evidence linking lead exposure and cancer comes from studies of workers with high levels of occupational (work-related) exposure to inorganic lead. People who have worked in heavily lead-exposed industries have been found to have blood lead concentrations of 40 to 100 micrograms per deciliter (mcg/dL). In comparison, in 1991, the average blood lead concentration in US males in the general population was 4 mcg/dL (10 mcg/dL is considered a low lead level). In 2000, Steenland and Boffetta summarized results from 8 studies of workers exposed to lead, using standard methods to compute combined relative risk estimates for the cancer sites of concern. The results of their study are reviewed here.

Lung cancer

All 8 studies of highly exposed workers reported results for lung cancer, with 2 showing an increased risk of lung cancer (at least 50% higher than people not exposed). In all studies combined, the risk was about 30% higher than in people not exposed. But, the results depended heavily on one study where a very high (3-fold) excess risk of lung cancer was found.

Workers in the highest risk study may have been exposed to arsenic as well as lead in the early years of plant operation. Because arsenic is known to cause lung cancer, it is not clear whether the increase in lung cancer was due to lead, arsenic, or the combination of the two.

More studies are being done to find out if lead or arsenic is responsible for the increase. Without the one highest risk study, all studies combined estimate the risk of workers exposed to lead at about 14% higher than unexposed persons. And, these studies could not determine whether this increase was because of lead exposure or if it happened because the lead-exposed workers tended to smoke more than the comparison groups.

Stomach Cancer

The combined analysis of 8 groups of lead-exposed workers showed a 34% increase in their risk of developing stomach cancer. A case-control study in one of the groups found that workers with the highest exposure levels were no more likely to develop stomach cancer than were workers with lower exposure levels. But many case-control studies in the general population found higher rates of stomach cancer among people who worked in jobs likely to have exposed them to high levels of lead. The evidence from studies does not agree, and stomach cancer among people exposed to lead is still a concern.

Brain Cancer

A case-control study of lead-exposed workers in Finland compared 26 patients who had brain cancer to 200 control subjects who did not, and found that the brain cancer patients had higher blood lead levels. In a death-certificate based study in the United States, researchers looked at the occupations of more than 27,000 people who died of brain cancer and more than 108,000 who died of other causes. The brain cancer cases were about twice as likely to have worked in an occupation that exposed them to lead. When combined data from all 7 studies of brain cancer among lead-exposed workers was reanalyzed, it did not show evidence of increased risk. But this finding was limited by the small number of brain cancer cases available to study. More recently, a 2006 study found that brain cancer risk was highest among people with the highest likelihood and intensity of lead exposure, which gives further support to the link between lead exposure and brain cancer. And so, research continues and the link between lead exposure and brain cancer is still a concern.

Kidney Cancer

In animal studies, kidney cancer is the most common cancer linked to lead exposure. Still, the combined results from all 7 studies of lead-exposed workers showed no evidence of an increased risk. Two of the studies did show about a 2-fold excess of kidney cancer, so kidney cancer remains a concern.

Colon and Rectal Cancer

A 1991 study found that workers in tetraethyl lead manufacturing industries were nearly 4 times as likely as unexposed people to develop rectal cancer, and workers with higher estimated exposure had higher risk. Less tetraethyl lead is produced today because it is no longer used as a gasoline additive.

What Do Animal Studies Show?

Lead by itself does not cause DNA mutations (changes) in animal cells. But studies suggest that lead exposure can interfere with repair of DNA damage caused by other chemicals. Lead acetate and lead phosphate, two inorganic lead compounds, cause kidney tumors in mice and rats. Most human exposures are to lead oxide and lead fumes, which have not been evaluated for carcinogenicity (the ability to cause cancer) in animals.

What Do the Expert Agencies Say?

National Toxicology Program

The National Toxicology Program evaluates exposures that may be carcinogenic. Those that are thought to be carcinogenic are included in the Reports on Carcinogens, which is published every 2 years. Each exposure is assigned to a category: "known to be human carcinogens" or "reasonably anticipated to be human carcinogens." The first category includes substances for which human studies show "sufficient evidence" of carcinogenicity in humans. The second category includes substances for which there is limited evidence of carcinogenicity in humans and/or sufficient evidence of carcinogenicity in experimental animals. Using this system, the National Toxicology Program classifies lead acetate and lead phosphate as "reasonably anticipated to be human carcinogens."

International Agency for Research on Cancer

The International Agency for Research on Cancer (IARC) also evaluates exposures that may be carcinogenic. IARC classifies exposures into 4 categories:

• Group 1 exposures are those "known to be carcinogenic to humans," usually based on "sufficient" human evidence, but sometimes based on "sufficient" evidence in experimental animals and "strong" human evidence. 
• Group 2 exposures are divided into 2 categories. Group 2A (probably carcinogenic to humans) has stronger evidence, and Group 2B (possibly carcinogenic to humans) has weaker evidence. 
• Group 3 exposures are not considered classifiable, because available evidence in limited or there is not enough evidence. 
• Group 4 exposures are "probably not carcinogenic to humans," based on evidence suggesting lack of carcinogenicity in humans and in experimental animals.

In 2006 the IARC rated lead and inorganic lead compounds as probably carcinogenic to humans (Group 2A).

Environmental Protection Agency

The Environmental Protection Agency (EPA), through its Integrated Risk Information System, uses a classification scheme very much like that of IARC. It classifies exposures in 5 categories:

(A) Human carcinogen
(B) Probable human carcinogen
(C) Possible human carcinogen
(D) Not classifiable as to human carcinogenicity
(E) Evidence of non-carcinogenicity for humans

The EPA has classified lead and lead compounds (inorganic) as probable human carcinogens.

Does Lead Cause Any Other Health Problems?

Lead is a well-known toxin. Severe lead poisoning can cause death. One of lead's primary targets is the nervous system. It lowers intelligence, stunts growth, impairs hearing, and causes behavioral difficulties and learning disabilities in children. It also causes problems with mood and thinking in adults. Adults whose work exposes them to lead have been shown to develop nervous system problems even at relatively low blood lead levels.

Lead harms the peripheral nerves causing weakness and sensory disturbances. Wrist weakness was a common symptom found among persons with severe lead poisoning in the early 20th century. Other forms of lead toxicity include:

• kidney damage, which can lead to high blood pressure and stroke 
• bone marrow damage, which can cause anemia 
• reproductive problems, such as miscarriage and stillbirth among exposed women 
• low sperm counts and hormone disturbances in highly exposed men 
• gastrointestinal symptoms such as nausea, constipation, and abdominal pain 
• bone and joint pain

In fact, these other symptoms of lead toxicity are usually of greater concern than its ability to cause cancer, and are the reason to regulate exposure to lead.

After lead enters the body, it travels in the blood reaching the soft tissues and bone. About 75% to 90% of lead in the body is found in the bones and teeth. Studies have shown that it can stay in the bones for decades. Then, when bone conditions such as osteoporosis cause loss of minerals from bones, lead can reenter the bloodstream and affect the nervous system and other organs, causing delayed side effects. Blood lead levels can show recent exposure to lead or lead released from bone. Bone lead levels show exposure over a lifetime. The amount of lead in bone can be measured using a method called x-ray fluorescence.

What Should I Do If I’ve Been Exposed to Lead?

Talk to A Doctor

If you think you have been exposed to lead, it is important to look at the amount of your exposure. You can do this by having a doctor do a blood test. There are also other ways to measure long-term lead exposure, including chelation challenge testing and x-ray fluorescence. Ask your doctor about these tests.

If a high level of lead is found in your blood there is a medical treatment, called chelation, (using a substance to bind with a metal so that it loses its toxic effect and/or is excreted). Although there is no convincing evidence that chelation helps with low-level lead exposure, many doctors recommend it.

If you were only exposed for a short time, or only at very low levels, your blood lead level will most likely stay low, and you are not at risk of lead-related disease. But, if you were exposed at higher levels, you may have a higher risk of the health problems discussed above. Children are especially at risk for lead’s effects on the nervous system.

If your blood lead level is increased, you should avoid any further exposure to lead. For example, a child who is exposed to lead from paint in an older home should not stay in the home until the lead is removed.

Protect Yourself and Your Family

Take the following steps to protect your health and the health of those around you:

• Avoid lead exposure at home by using lead-free paint, ceramics, and other products. Have leaded paint removed from your home by a qualified contractor. In older homes, built before about 1980, you should find out if the paint has lead in it. 
• Wipe dust from floors, windowsills, and other surfaces with water and detergent. Cloths and sponges that have been used to clean lead dust shouldn’t be used to wash dishes or wipe down food preparation areas. 
• Move cribs and playpens away from areas where paint is chipped or peeling. 
• Children should wash their hands often, especially before eating. Pacifiers and toys that children put in their mouths should be washed every day. 
• If you live in a building with old pipes or an old hot water heater, use cold tap water for cooking and drinking. Run it for at least 30 seconds or until it’s as cold as it can get. 
• Any product labeled as containing lead should be kept out of the reach of children. Hands should be washed right after handling such products to avoid accidental ingestion. 
• Nutrition plays a role in lead absorption, so make sure you and your children eat balanced diets with recommended amounts of iron, calcium, zinc, and vitamin C. The amount of lead absorbed also increases when your diet is high in fat or your stomach is empty.

Protect Yourself at Work

If there is a possibility that you will be exposed to lead on your job, your employer should follow the requirements of the OSHA Lead Standard, which is intended to protect workers from the harmful effects of lead exposure. Precautions to minimize exposure to lead include using careful personal hygiene such as hand-washing, showering and changing clothes before leaving work, and not smoking or eating near work. Your employer is required to make facilities available to do this.

The employer is also required to maintain air levels of lead below 50 µg/m³ averaged over an 8 hour period, and to provide respirators if air levels are higher than this. The OSHA standard also requires free, full medical monitoring which includes blood lead levels if employees are exposed to lead levels above 30 µg/m³ for more than 30 days per year. For more information on the OSHA standard for lead see http://www.osha.gov or call 1-800-321-OSHA (1-800-321-6742).

What’s the Bottom Line About Lead?

Lead causes cancer in animals, and there is some evidence of carcinogenicity in humans. Lead is also toxic to humans in many other ways. You should make every effort to minimize your exposure to lead.

Where Can I Get More Information?

Agency for Toxic Substances and Disease Registry
Division of Toxicology and Environmental Medicine
Toxic Substances Resources
Web site: http://www.atsdr.cdc.gov/2p-toxic-substances.html
Toll-free telephone: 1-888-422-8737

Environmental Protection Agency
Web site: http://www.epa.gov/ttn/atw/
Lead in drinking water Web page: http://www.epa.gov/safewater/lead/
Toll-free telephone: 1-800-424-LEAD (1-800-424-5323)

International Agency for Research on Cancer
Web site: http://www.iarc.fr/

National Institute for Occupational Safety and Health
Web site: http://www.cdc.gov/niosh/topics/lead/

National Safety Council
Provides access to a lead dust kit
Lead Poisoning Web page: http://www.nsc.org/issues/lead/
Toll-free telephone: 1-800-621-7619

References

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Agency for Toxic Substances & Disease Registry. ToxFAQs for: Lead. Updated 9/11/2007. Available at http://www.atsdr.cdc.gov/tfacts13.html#bookmark01. Accessed October 16, 2007.

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Environmental Protection Agency. Lead in Drinking Water. 2006. Available at http://www.epa.gov/safewater/lead/basicinformation.html. Accessed on October 15, 2007.

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National Safety Council. Lead Poisoning Happens More Than You Think. Available at: http://www.nsc.org/issues/lead/. Accessed October 15, 2007.

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Vig EK, Hu H. Lead Toxicity in Older Adults. J Am Geriatrics Soc. 2000;48 (11):1501-150.

Van Wijngaarden E, Dosemeci M. Brain cancer mortality and potential occupational exposure to lead: Findings From the National Longitudinal Mortality Study, 1979–1989. Int J Cancer. 2006;119:1136-1144.

Revised: 12/05/2007