A Better Cancer Detox
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. Because it is an element, lead can’t be broken down into smaller components. It can exist by itself as a metal, but it is more often combined with other elements in a variety of compounds. These compounds are divided into 2 groups:
Lead and its compounds have many useful properties. Lead is soft and easily shaped, durable, resistant to some chemicals, and fairly common.
Humans have used lead since early history. Lead has been used in plumbing, tableware, and other products since the Roman Empire. It has been used in pipes and plumbing, pigments and paints, gasoline additives, construction materials, lead–acid batteries, and many other products. It has even been used in some medicines and cosmetics.
The use of lead in pipes, paints, and gasoline additives has resulted in large amounts of lead entering the environment. These uses have been limited or phased out in many countries, including the United States. The main use of lead today is to make lead–acid batteries. Lead metal is also used in ammunition, cable coverings, piping, to make brass and bronze, bearing metal in machinery, and to make sheet lead. Lead compounds have a wide variety of uses, such as in matches, some paints and ceramics, in soldering and building materials, in photography, as catalysts to help chemical reactions, and in a number of other products.
People are exposed to lead mainly by breathing it (from dust or fumes) or swallowing it. Because of its widespread use over the years, exposure to lead in the environment is now more likely to come from man-made rather than natural sources. Lead can change forms (for example from organic to inorganic) and can move around in the environment (for example, from the air to the soil to the water), but it does not break down and go away.
In the past, when lead was added to gasoline, breathing automobile exhaust was the major source of lead exposure for most people. Lead from exhaust also contaminated the soil near roads. The use of lead in gasoline for road vehicles was phased out in the 1980s and early 1990s, although it can still be used in some off-road vehicles and in airplanes. Much of the lead deposited decades ago still remain in the soil today.
Another major source of exposure is old paint that contains lead. Many houses and other buildings built before 1978 have lead-based paint in them. It can also be found on older structures such as bridges. Lead from paint in older homes can become part of the dust inside the home or the soil outside it, which people can inhale. This tends to be worse during renovation of an older home, when the lead paint is more likely to be disturbed. Children can also be exposed to lead in older homes if they pick off the lead paint chips and swallow them. More often, particles from worn painted surfaces mix with soil and household dust, and children unintentionally swallow lead from their contaminated toys or hands.
Drinking water is another potential source of lead exposure. Lead is rarely found in natural water sources, but it can enter drinking water as it travels through pipes containing lead. Homes built before 1986 are more likely to have lead pipes, fixtures, and solder. But even the “lead-free” plumbing found in newer homes may contain some lead.
Lead can also be found in food and alcoholic beverages. Levels in foods were higher before the 1980s, when lead-soldered food cans were taken out of use.
Cigarette smoke also contains lead.
Before the 1950s, lead was used in some pesticides applied to fruit orchards. Soil near old orchards may still contain some lead. Soils at old smelting and battery making industrial sites are also likely to be contaminated with lead. This has proven to be a particular problem where residential housing is built on previous industrial sites without first removing the heavy metals, including lead, that contaminate these soils.
Other sources of lead exposure include some folk remedies, 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 in a number of industries may be exposed to lead as part of their jobs. These include:
The amount of lead these workers are exposed to can vary depending on many different factors, including the particular tasks performed and how many years they worked at these tasks.
Researchers use 2 main types of studies to try to determine if a substance or exposure causes cancer. (A substance that causes cancer or helps cancer grow is called a carcinogen.)
In studies done in the lab, animals are exposed to a substance (often in very large doses) to see if it causes tumors or other health problems. Researchers may also expose normal cells in a lab dish to the substance to see if it causes the types of changes that are seen in cancer cells. But it’s not always clear if the results from these types of studies will apply to humans.
Another type of study looks at cancer rates in different groups of people. Such a study might compare the cancer rate in a group exposed to a substance versus the rate in a group not exposed to it, or compare it to what the expected cancer rate would be in the general population. But studies in people can sometimes be hard to interpret, because there may be other factors affecting the results that are hard to account for.
In most cases neither type of study provides definitive evidence on its own, so researchers usually look at both lab-based and human studies if they are available.
Overall, it has been hard to evaluate lead’s ability to cause cancer, in part because it is found in so many places and in many different forms.
Most of the studies looking for a possible link between lead exposure and cancer have focused on workers with high levels of occupational (work-related) exposure to inorganic lead. People with heavy workplace exposures to lead have been found to have blood lead concentrations many times higher than the average blood lead concentration in the general population.
Several studies have looked for a link between exposure to lead in the workplace (mainly among battery workers and smelter workers) and lung cancer. Some of these studies have found a small increase in lung cancer risk. However, most of these studies were limited in that they didn’t take into account other factors that might affect lung cancer risk, such as smokingor exposures to arsenic or other heavy metals that typically also occur along with lead exposures in industrial settings. Some studies looking at blood lead levels in the general population have also found a small increased risk of lung cancer in people with higher lead levels.
Several of these same workplace studies also looked at stomach cancer risk. Most of the studies found an increased risk of stomach cancer with higher lead exposure. Although it is unlikely these results would be affected by smoking or arsenic exposure, the studies didn’t take into account other factors that could also have affected stomach cancer risk.
Studies have also looked at possible links between workplace exposures to lead and other cancers, including cancers of the brain, kidney, bladder, colon, and rectum. The results of these studies have been mixed. Some studies have found links, while others have not.
The link between lead exposure and cancer is clearly a concern, and more research is needed to better define the possible link between lead exposure and a number of cancers.
Lead has not been found to damage the DNA in cells directly. (Substances that cause cancer often do so by causing DNA damage.) But lead might affect cells in other ways, such as by interfering with repair of DNA damage caused by other chemicals.
Several studies in lab animals have found that exposure to lead compounds (by swallowing or other means) can cause cancer. Kidney tumors have been linked with lead most strongly, but tumors of the brain, lung, and some other organs have also been linked to lead in different studies.
Several agencies (national and international) study different substances in the environment to determine if they can cause cancer. The American Cancer Society looks to these organizations to evaluate the risks based on evidence from laboratory, animal, and human research studies.
Based on the available evidence, some of these expert agencies have evaluated the cancer-causing potential of lead and lead compounds.
The National Toxicology Program (NTP) is formed from parts of several different US government agencies, including the National Institutes of Health (NIH), the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA). Exposures that are thought to be carcinogenic are included in the Report on Carcinogens, published every few years. The NTP classifies lead and lead compounds as “reasonably anticipated to be human carcinogens,” based on limited evidence from studies in humans and sufficient evidence from studies in lab animals.
The International Agency for Research on Cancer (IARC) is part of the World Health Organization (WHO). Its major goal is to identify causes of cancer. The IARC has classified inorganic lead compounds as “probably carcinogenic to humans,” based on limited evidence in humans and sufficient evidence in lab animals. Organic lead compounds are listed as “not classifiable as to their carcinogenicity in humans,” based on inadequate evidence.
The Environmental Protection Agency (EPA) maintains the Integrated Risk Information System (IRIS), an electronic database that contains information on human health effects from exposure to various substances in the environment. The EPA has classified lead and inorganic lead compounds as “probable human carcinogens.”
(For more information on the classification systems used by these agencies, see Known and Probable Human Carcinogens.)
Whether lead enters the body by breathing it in or swallowing it, it enters the bloodstream, from which it can reach other parts of the body. Most lead eventually ends up in the bones and teeth, but its main health effects are on other organs.
The main toxic effects of lead are on the brain and nervous system. In adults, high levels of lead can cause headaches and problems with mood, thinking, and memory. It may also damage peripheral nerves, which can cause tremors or weakness in fingers, wrists, or ankles. Adults whose work exposes them to lead have been shown to develop nervous system problems even at relatively low blood lead levels.
The effects of lead on the nervous system are even more of a concern in young children, whose brains are still developing and whose bodies take in lead more readily. Lead poisoning in children can lead to lower intelligence, stunted growth, impaired hearing, and behavioral and learning problems. These problems can even appear in children whose mothers were exposed to lead while pregnant with them.
High lead levels in the body can also cause:
At high enough levels of exposure, lead can severely damage the brain and kidneys in adults or children and ultimately cause death.
In fact, health issues other than cancer are the main reason exposure to lead is regulated.
A number of federal regulations are in place to help limit our exposure to lead. Some, such as the ban on lead additives in gasoline (except in off-road vehicles and airplanes) and the ban on lead solder in food cans, have been in effect for many years.
The Environmental Protection Agency (EPA) enforces limits on contaminants in drinking water, including lead. Source water does not usually contain much lead, but the pipes from the source water to your tap may allow some lead to enter the water. EPA requires public water suppliers to analyze water from a sample of household taps. If lead is consistently present above 15 micrograms per liter of water (mcg/L) in more than 10% of homes, the water supplier must take steps to reduce the amount of lead so that it is consistently below that level.
The Food and Drug Administration (FDA) has set a lead limit of 5 mcg/L for bottled water.
The Consumer Product Safety Commission (CPSC) enforces limits on the amount of lead allowed in consumer products such as paints and children’s toys. For more information on these limits, contact the CPSC at 1-800-638-2772.
The Occupational Safety & Health Administration (OSHA) is responsible for regulating exposure to potential hazards such as lead in most workplaces. OSHA allows a maximum level of 50 micrograms of lead per cubic meter of air (mcg/m3), averaged over an 8-hour period. The employer must provide protective equipment such as respirators if air levels are higher than this. OSHA also requires that employers provide medical monitoring of employees exposed to levels of 30 mcg/m3 or higher. For more information on the OSHA standards for lead, call 1-800-321-OSHA (1-800-321-6742).
In addition to the federal limits above, some states may have stricter limits.
Lead is a common presence in the environment from both man-made and natural sources, so it is not possible to completely eliminate your exposure to it. But because lead can cause health problems, even aside from its possible link to cancer, it is important to limit your exposure whenever possible.
One of the most important ways to lower your exposure to lead is to know about the sources of lead in your home and avoid exposure to these sources.
You may want to consider having your home tested for lead, especially if it was built before 1978 and you have children aged 6 or younger in the home. Lead-based paints were commonly used before 1978, and any areas where the paint is worn or damaged can allow lead to enter dust in the home or the soil outside it. Small children may also eat any flaking paint chips. To find a qualified professional to test for lead in your home, contact the National Lead Information Center at 1-800-424-LEAD (1-800-424-5323).
If you have your home tested and lead is found, there are ways to limit your exposure to it. One way is to have leaded paint removed from your home by a lead-safe certified contractor. The EPA requires all contractors doing renovations, repairs, or painting that may disturb lead-based paint to be certified and trained to follow lead-safe work practices. Children and pregnant women should not be in the home while renovations are being done.
Other options for people with lead in their homes or who have homes built before 1978 but haven’t been tested include:
If you get your drinking water from a public source, you can contact your water supplier to find out about lead levels in your system. Whether your water comes from a public or a private source (such as a well), lead may enter your water from the pipes in or leading into your home. The only sure way to know how much lead is in your water is to have it tested by a certified lab. Contact the EPA’s Safe Drinking Water Hotline at 1-800-426-4791 or your state or local drinking water authority to get a list of certified labs in your area.
If your home’s water tests positive for lead, the EPA recommends that you:
If you live in an older home and have very young children, talk to your child’s doctor about having their blood lead levels tested. Many doctors recommend testing at ages 1 and 2, especially if a child is at increased risk of lead exposure.
Other things you can do:.
The Occupational Safety & Health Administration (OSHA) is the federal agency responsible for health and safety regulations in most workplaces. OSHA has standards in place that limit the amount of lead you can be exposed to on the job and that require employers to make regular testing available to you if certain limits are exceeded.
If there is a chance you might be exposed to lead at work, important ways to reduce or prevent exposure include:
If you are concerned about lead exposure in your workplace, discuss the situation with your employee health and safety representative or your employer. If needed, OSHA can provide more information or make an inspection.
If you think you or your loved ones have been exposed to lead, talk to your doctor about a simple blood test to check lead levels. Long-term lead exposure can be measured by some other tests, including measuring lead in teeth or bones by x-ray techniques, but these methods are not widely available.
If you were only exposed to lead for a short time, or only at very low levels, you are not likely to be 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 but still relatively low, avoiding further exposure to lead as much as possible (see the section above) may reduce your lead level over time.
For children or adults with very high levels of lead in the blood, doctors sometimes recommend a medical treatment called chelation, in which you take a medicine that binds the lead so that it leaves your body in your urine. But chelation may not be able to reverse any damage that has already been done.