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Arsenic is known to cause cancer, as well as many other serious health problems. Here we review the hazards of arsenic exposure and ways people can protect themselves from these hazards.

What is arsenic?

Arsenic is an element in the environment that can be found naturally in rocks and soil, water, air, and in plants and animals. It can also be released into the environment from some agricultural and industrial sources.

Arsenic has no taste or smell. Although sometimes found in its pure form as a steel grey metal, arsenic is usually part of chemical compounds. These compounds are divided into 2 groups:

  • Inorganic compounds (combined with oxygen, iron, chlorine, and sulfur)
  • Organic compounds (combined with carbon and other atoms)

Inorganic arsenic compounds are found in industry, in building products (in some "pressure-treated" woods), and in arsenic-contaminated water. This is the form of arsenic that tends to be more toxic and has been linked to cancer.

Organic arsenic compounds are much less toxic than the inorganic arsenic compounds and are not thought to be linked to cancer. These compounds are found in some foods, such as fish and shellfish.

How is arsenic used?

Arsenic compounds have many uses, including:

  • As a preservative in pressure treated lumber (although US residential use ended in 2003)
  • In pesticides (although the use of inorganic arsenic in US agriculture ended in 1993)
  • As a preservative in animal hides
  • As an additive to lead and copper for hardening
  • In some glass manufacturing
  • As arsine gas to enhance electrical junctions in semiconductors

Although it can be poisonous in higher doses, arsenic has also been used in some medicines. In the 1800s and early 1900s, arsenic was commonly used in treating diseases such as syphilis and psoriasis. A form of arsenic is still used to treat an uncommon blood cancer known as acute promyelocytic leukemia.

How are people exposed to arsenic?

We normally take in small amounts of arsenic in the air we breathe, the water we drink, and the food we eat. People may also be exposed to arsenic in other ways. Very high doses have been used in murder or suicide attempts. Some jobs may expose workers to high levels over long periods of time when they breathe in or swallow dust that contains arsenic compounds, but such exposures are now rare in the United States. People who live near current or former industrial or agricultural sources of arsenic may be exposed by inhaling fumes or eating contaminated food. People may also take in higher levels of arsenic if they live in areas where arsenic is naturally high in drinking water or if they eat a lot of seafood (although the organic form found in seafood is likely to be much less harmful).

At work

Arsenic has not been produced in the United States since 1985, although it is imported from other countries. In the past, workers in smelters and in plants that made, packaged, or distributed pesticides that contained arsenic had high exposures from breathing in arsenic fumes and dust. Today workplace exposure to arsenic may still occur in some occupations that use arsenic, such as copper or lead smelting, wood treating, or pesticide application. Regulations are in place to limit workplace exposure.

In the community

Communities near previous or current agricultural or industrial sources may be exposed to arsenic. Facilities such as wood preservative and glass factories may contaminate nearby air, soil, and water. Communities near smelters, or near fields or orchards where arsenic pesticides were used, may also have contaminated soil. Burning fossil fuels (such as coal) and tobacco can also release small amounts of arsenic into the air.

In drinking water

Drinking water is an important and potentially controllable source of arsenic exposure. In fact, drinking water accounts for most human arsenic exposures worldwide. In parts of Taiwan, Japan, Bangladesh, and western South America, high levels of arsenic occur naturally in drinking water.

Water in some areas of the United States, especially in the West, also naturally contains arsenic. Most US areas with higher levels of arsenic in drinking water are rural communities. Albuquerque, New Mexico, is the only urban area in the US with substantial natural arsenic concentrations in drinking water.

Arsenic levels tend to be higher in drinking water that comes from ground sources, such as wells, as opposed to water from surface sources, such as lakes or reservoirs.

Arsenic levels in public drinking water are regulated in the United States by the Environmental Protection Agency (EPA). As of January 2006, the maximum contaminant level for inorganic arsenic permitted in US drinking water is 10 μg/L (micrograms per liter), or 10 ppb (parts per billion).

In pressure-treated wood

Chromated copper arsenate (CCA) is a chemical preservative that helps protect wood from rot and insects. It was used to pressure treat lumber used for some home foundations, decks, fences, playgrounds (play sets), and other structures for many decades. In fact, starting in the 1970s, the majority of the wood used in residential settings was CCA-treated wood.

The use of CCA in pressure-treated lumber for residential uses was stopped at the end of 2003 (although it is still used for industrial purposes). This was done because of concerns that some of the arsenic might leach out of the wood and enter the soil or be absorbed through the skin when the wood is touched. Wood that is frequently touched by children, such as that found in some playground equipment, is a special concern.

People can also be exposed to arsenic by breathing in sawdust from cut arsenic-preserved wood or by breathing the smoke from burning this wood.

Pressure-treated lumber for residential uses is now made with other compounds that do not contain arsenic. However, any structures built from lumber that was pressure treated in 2003 or before may contain CCA. (For more information, see the section, "How can I limit my exposure to arsenic?")

In food

For most people, food is usually the largest source of arsenic, although most of this is likely to be in the less dangerous, organic form. The highest levels of arsenic (in all forms) in foods can be found in seafood, rice, rice cereal, mushrooms, and poultry, although many other foods may contain low levels of arsenic.

Does arsenic cause cancer?

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. It's not always clear if the results from these types of studies will apply to humans, but lab studies are the best way to find out if a substance could possibly cause cancer in humans before widespread exposure occurs.

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.

Studies in people

Many studies have looked at the potential of arsenic to cause cancer. People can be exposed to arsenic in different ways (inhaling, ingesting, or through skin contact) and in different settings (in the workplace, in drinking water, in medical treatments, etc.), so it has been important to study different routes of exposure.

Workplace exposures

A number of studies have looked at cancer occurrence among workers who manufactured pesticides containing arsenic and those who worked in mines and copper smelters. These workers' inhaled exposures were often very high. All together, these studies have followed thousands of workers for as long as 40 or 50 years. They have consistently shown an increase in lung cancer risk with higher and more prolonged exposures. Some studies have also suggested that workers exposed to arsenic might be at higher risk for other cancers, including cancers of the skin, stomach, and kidneys, as well as leukemias and lymphomas. However, the results from these studies have not been consistent.

Exposure from drinking water

Studies of people in parts of Southeast Asia and South America with high levels of arsenic in their drinking water have found higher risks of cancers of the bladder, kidney, lung, skin, and, less consistently, colon and liver.

In most of these studies, the levels of arsenic in the water were many times higher than those typically seen in the United States, even in areas where arsenic levels are above normal.

There have not been as many studies looking at arsenic exposure and cancer in the United States. This is largely because for most Americans who are on public water systems, drinking water is not a major source of arsenic. The studies that have been done have generally not found a strong link between cancer and the lower levels of arsenic exposure typically seen in the US.

Exposure from medicines

In older studies, some cancers have been linked to exposure to arsenic in medicines. The strongest link has been found with skin cancer.

Studies done in the lab

Arsenic is rather unusual in that the evidence for it causing cancer is actually stronger in human studies than it is in studies done in the lab. Some studies have found higher rates of stomach and lung cancers and lymphomas in certain species of animals exposed to high levels of inorganic arsenic. But many other studies have not found an excess of tumors in lab animals exposed to arsenic.

What expert agencies say

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 human and animal evidence, several expert agencies have evaluated the cancer-causing potential of arsenic.

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. Based on the data available, IARC classifies arsenic and arsenic compounds as "carcinogenic to humans". IARC notes that this evaluation applies to the group of chemicals as a whole and not necessarily to all the individual chemicals in the group.

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). In its most recent Report on Carcinogens, the NTP has classified inorganic arsenic compounds as "known to be a human carcinogen".

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 classifies inorganic arsenic as a "human carcinogen".

(For more information on the classification systems used by these agencies, see our document, Known and Probable Human Carcinogens.)

Does arsenic cause any other health problems?

Both short- and long-term exposure to arsenic can cause health problems.

Short-term exposure

Breathing in high levels of arsenic may cause a sore throat and irritated lungs. Swallowing high levels of arsenic can cause things like:

  • Stomach ache
  • Nausea and vomiting
  • Diarrhea
  • Muscle weakness and cramping
  • "Pins and needles" sensations in hands and feet
  • Skin changes or rashes
  • Bruising (caused by blood vessel damage)

Exposure to high enough amounts of arsenic can be fatal.

Contact with the skin can cause redness and swelling, although it's not known if it can cause other health problems.

Long-term exposure

Exposure to lower levels of arsenic over longer periods of time can cause many of the same health problems listed above. It can also result in:

  • Irregular heartbeat
  • Liver and kidney damage
  • A shortage of red and white blood cells, which can lead to fatigue and an increased risk of infections

Skin changes are a common sign of chronic arsenic exposure. The changes can include darkened patches of skin and the appearance of areas of thickened skin, usually on the palms and soles.

Are arsenic levels regulated?

Several government agencies regulate arsenic levels and exposures.

The EPA limits concentrations of arsenic in drinking water to 10 ppb (parts per billion). The Food and Drug Administration (FDA) has set a limit of 5 ppb in bottled water.

The EPA has also set limits on the amount of arsenic that industrial sources can release to the environment and has restricted many of the uses of arsenic in pesticides.

The Occupational Safety & Health Administration (OSHA), the federal agency responsible for health and safety regulations in most workplaces, limits workplace exposure to inorganic arsenic to 10 micrograms per cubic meter of air, averaged over an 8-hour period. When working at potentially higher exposure levels, OSHA requires employers to provide personal protective equipment such as respirators.

How can I limit my exposure to arsenic?

Arsenic is a naturally occurring element, so it is not possible to completely eliminate exposure to it. But there are some things you can do that may lower your exposure.

In drinking water

Public drinking water systems in the United States are required to test for arsenic and to keep it below a certain level (10 parts per billion). If your drinking water comes from a public source, you can find out about the levels of certain substances in your drinking water, including arsenic, by contacting your local water system. Each system is also required to provide its customers with an annual report on water quality known as a Consumer Confidence Report. This report lists the levels of certain chemicals and other substances in the water. You can also contact the EPA's Safe Drinking Water Hotline at 1-800-426-4791 for information about drinking water safety.

If you get your water from a private source such as a well, you may want to have your water tested for arsenic levels by a reputable laboratory. People who live in areas with high levels of arsenic in the water may consider using alternative sources of drinking water, such as bottled water. (The US Food and Drug Administration [FDA] sets the standards for allowable levels of arsenic in bottled water.) Common household water filters do not effectively remove arsenic.

At work

If there is a chance you may be exposed to arsenic at work, important ways to reduce or prevent exposure include:

  • Making engineering changes, such as substituting safer materials for more hazardous materials, enclosing a process that may expose workers to hazards, or ventilating a work area.
  • Using good work practices, such as changing clothes after work, washing work clothes regularly, and keeping food out of the work area.
  • Using personal protective equipment, such as gloves and respirators, as part of a workplace protective program.

If you are concerned about arsenic exposure in your workplace, discuss the situation with your employee health and safety representative or your employer. If needed, OSHA, the federal agency responsible for health and safety regulations in most workplaces, can provide more information or make an inspection.

In wood

Some pressure-treated lumber products contain an inorganic arsenic compound known as CCA that helps protect the wood against rot and insects. The sale of CCA-treated lumber for residential use was stopped at the end of 2003. However, many structures such as home foundations, decks, fences, or playground play sets that contain CCA-treated lumber are still in use.

It is not clear if skin contact with arsenic from pressure treated lumber can cause health problems, other than skin irritation in some people. However, a larger concern has been raised with its use around children, especially in play sets. Children might swallow small amounts of arsenic if they put their hands in their mouths after touching the wood or the soil around it.

A child's exposure to arsenic in CCA-treated playground equipment could vary based on many factors, including the amount of arsenic released from the CCA-treated wood, the amount of arsenic picked up on the hands, the number of days the child plays on the wood, and the amount of arsenic transferred to the mouth by hand-to-mouth activity.

If you aren't sure if a wooden play set contains arsenic, calling the play set manufacturer might help you find out. But if this information isn't available, it is safest to assume that it does. To reduce exposure, parents and caregivers should make sure children's hands are thoroughly washed with soap and water after playing on all pressure-treated wood playground equipment. It has also been suggested that children not eat while on wooden playground equipment.

People concerned about arsenic exposure at home from wooden decks or play sets may want to consider applying a sealant on existing CCA-treated lumber surfaces each year. This may lower the amount of arsenic released from the wood.

Arsenic can also be released into the air when cutting or burning CCA-treated lumber. If you are cutting pressure-treated lumber, it is important to use proper safety equipment, including a mask, to limit your exposure, and to clean up any sawdust promptly. Do not burn pressure-treated lumber.

The EPA does not currently recommend that CCA-treated lumber has to be removed, but if you decide to remove CCA-treated wood in a play set, deck, or other structure, contact the EPA or your state or local solid waste management offices to get instructions on how to dispose of it safely.

Contact an expert

If you are concerned about arsenic exposures at work, from drinking water, from treated wood, or from other sources, contact the EPA or your state or local health department for more information. You can also contact specialists in environmental and occupational medicine. They can assess exposure levels, evaluate current health problems that may be related to the exposures, and give you information concerning future risk and how to minimize it. You can locate such qualified professionals and facilities by checking with the Association of Occupational and Environmental Clinics (www.aoec.org).

What should I do if I think I've been exposed to arsenic?

Laboratory tests can measure arsenic levels in your blood, urine, hair, and fingernails. These tests are not routinely done – they require sending the samples to a special laboratory.

A urine test is the most reliable method for identifying arsenic exposure within the past several days. But it can't detect long-term exposure because most arsenic is excreted in urine within a few days. This test can also sometimes be misleading, because the organic forms of arsenic in fish and shellfish can give a high reading even if you have not been exposed to more toxic, inorganic forms of arsenic. For this reason, labs sometimes use a more complicated test to separate "fish arsenic" from other forms.

Tests of hair and fingernails can detect high-level arsenic exposures during the previous 6 to 12 months, but these tests are not as good at detecting lower levels of exposure.

These tests can only measure arsenic levels. Unless the levels detected are very high, none of these tests can tell for certain if you are likely to have health problems in the future.

In cases where a person is exposed to very high amounts of arsenic over a short time, treatment to lower arsenic levels in the body may be recommended, especially if the levels are potentially life-threatening. But in cases of chronic exposure to lower levels of arsenic, the most important thing may be to remove the source of the arsenic and allow the body to get rid of what remains. Some health problems caused by arsenic may improve over time, but others may not.

Because arsenic exposure may increase the risk of skin, bladder, kidney, and lung cancer, people who have been exposed should learn about other risk factors for these cancers and about things they can do that may help lower their risks.

Not smoking is especially important if you have been exposed to arsenic. Both arsenic exposure and smoking can increase your risk of lung, kidney, and bladder cancer. Tell your doctor if you develop symptoms that could be caused by these cancers, including a new cough (especially if it is bloody), hoarseness, blood in the urine, or a change in your urine habits (having to go more often, having pain when going, etc.). These symptoms are more likely to have causes other than cancer, but it is important to have them checked out.

Arsenic exposure and too much sun can increase your risk of skin cancer. Practice sun safety and tell your doctor about any signs and symptoms such as new skin bumps or sores, or changes in old skin problems.

If you have been exposed to arsenic, ask your doctor about a proper schedule for skin exams. Based on your arsenic exposure and other factors, your doctor might consider using other early detection testing, such as urine cytology (checking urine for cancer cells under a microscope), although it's not clear how helpful such testing is.

Additional resources

More information from your American Cancer Society

The following related information may also be helpful to you. These materials may be viewed on our web site or ordered from our toll-free number, at 1-800-227-2345.

Known and Probable Human Carcinogens

National organizations and Web sites

In addition to the American Cancer Society, other sources of information and support include*:

Agency for Toxic Substances and Disease Registry (ATSDR)
Toll-free number: 1-888-422-8737 (1-888-42-ATSDR)
Web site: www.atsdr.cdc.gov
Public Health Statement for Arsenic: www.atsdr.cdc.gov/toxprofiles/phs2.html
ToxFAQs™ for Arsenic: www.atsdr.cdc.gov/tfacts2.html

Association of Occupational and Environmental Clinics
Web site: www.aoec.org

Environmental Protection Agency (EPA)
Safe Drinking Water Hotline: 1-800-426-4791
Web site: www.epa.gov
Arsenic in Drinking Water: www.epa.gov/safewater/arsenic/index.html

Occupational Safety & Health Administration (OSHA)
Toll-free number: 1-800-321-6742 (1-800-321-OSHA)
Web site: www.osha.gov
Arsenic page: www.osha.gov/SLTC/arsenic

US Geologic Survey
Arsenic in Ground Water of the United States: http://water.usgs.gov/nawqa/trace/arsenic

*Inclusion on this list does not imply endorsement by the American Cancer Society.

No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-227-2345 or visit www.cancer.org.


Agency for Toxic Substances and Disease Registry (ATSDR). Public Health Statement for Arsenic. 2007. Accessed at www.atsdr.cdc.gov/toxprofiles/phs2.html on April 26, 2010.

Agency for Toxic Substances and Disease Registry (ATSDR). Case Studies in Environmental Medicine: Arsenic Toxicity. 2009. Accessed at www.atsdr.cdc.gov/csem/arsenic/index.html on April 26, 2010.

Frumkin H, Thun MJ. Arsenic. CA Cancer J Clin. 2001;51;254-262.

International Agency for Research on Cancer. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Supplement 7: Overall Evaluations of Carcinogenicity: An Updating of IARC Monographs Volumes 1 to 42. 1987. Accessed at http://monographs.iarc.fr/ENG/Monographs/suppl7/Suppl7-19.pdf on April 20, 2010.

International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 84: Some drinking-water disinfectants and contaminants, including arsenic. 2004. Accessed at http://monographs.iarc.fr/ENG/Monographs/vol84/index.php on April 20, 2010.

Mead MN. Arsenic: in search of an antidote to a global poison. Environ Health Perspect. 2005;113(6):A378-A386.

US Consumer Product Safety Commission. Fact Sheet: Chromated Copper Arsenate (CCA) -Treated Wood Used in Playground Equipment. Accessed at www.cpsc.gov/phth/ccafact.html on April 26, 2010.

US Department of Health and Human Services. Public Health Service, National Toxicology Program. Report on Carcinogens, Eleventh Edition. 2005. Accessed at http://ntp.niehs.nih.gov/ntp/roc/eleventh/profiles/s015arse.pdf on April 20, 2010.

US Department of Labor, Occupational Safety & Health Administration. Arsenic Standards. 2008. Accessed at www.osha.gov/SLTC/arsenic/standards.html on April 26, 2010.

US Environmental Protection Agency. Integrated Risk Information System: Arsenic, inorganic (CASRN 7440-38-2). 1998. Accessed at www.epa.gov/ncea/iris/subst/0278.htm on April 22, 2010.

Last Medical Review: 02/17/2011
Last Revised: 02/17/2011