Arsenic and Cancer Risk

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 a natural element that can be found 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.

Although it is 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 (arsenic combined with elements other than carbon): These compounds are found in industry, in building products (such as 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 compounds (arsenic combined with carbon and other elements): These 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 been used in many ways, including:

  • As a preservative in pressure-treated lumber
  • In pesticides
  • As a preservative in animal hides
  • As an additive to lead (such as in lead-acid batteries) and copper
  • In some glass manufacturing
  • As arsine gas to enhance electrical junctions in semiconductors

Some of these uses have been discontinued in the United States, as described in later sections.

Although arsenic can be poisonous in higher doses, it has also been used in some medicines. In the 1800s and early 1900s, arsenic was commonly used to treat 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?

Arsenic occurs naturally in the environment, as well as being present in some man-made products. We normally take in small amounts in the air we breathe, the water we drink, and the food we eat. Most arsenic compounds have no smell or taste, so usually you can’t tell if arsenic is in your air, food, or water.

People can also be exposed to higher levels of arsenic in some 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 can be exposed to higher levels by inhaling fumes or eating contaminated food. People can also take in higher levels of arsenic if they live in areas where arsenic levels are naturally high in the drinking water or if they eat a lot of rice or seafood (although the organic form found in seafood is likely to be much less harmful).

In food

For most people, food is the largest source of arsenic, although much 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 (and other rice products), mushrooms, and poultry, although many other foods can contain low levels of arsenic.

Rice is of particular concern because it is a major part of the diet in many parts of the world. It is also a major component of many of the cereals eaten by infants and young children. (Nearly all rice products have been found to contain at least some arsenic, although the levels can vary widely.)

In drinking water

Drinking water is an important and potentially controllable source of arsenic exposure. In fact, drinking water is a major source of arsenic exposure in some parts of the world. 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 levels 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). Since January 2006, the maximum level of arsenic allowed in US drinking water is 10 μg/L (micrograms per liter), or 10 ppb (parts per billion).

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 manufactured, packaged, or distributed products that contained arsenic had high exposures from breathing in arsenic fumes and dust.

Arsenic was a common ingredient in many pesticides and herbicides in the past. People who made, transported, applied, or worked around these products may have been exposed to higher levels of arsenic. Inorganic arsenic compounds have not been used in pesticides in the US since 1993, and organic compounds have been phased out of pesticides (with one exception used on cotton plants) as of 2013.

Today workplace exposure to arsenic can still occur in some occupations that use arsenic, such as copper or lead smelting, and wood treating. Regulations in place can help limit this workplace exposure.

In the community

Communities near previous or current agricultural or industrial sources may be exposed to arsenic. Industrial buildings such as wood preservative and glass factories can contaminate nearby air, soil, and water. Communities near smelters, or near farm 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 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 that was used in some home foundations, decks, fences, playgrounds (play sets), and other structures for many decades. In fact, starting in the 1970s, most of the wood used in residential settings was CCA-treated wood.

The use of CCA in pressure-treated lumber for most residential (home) 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 before 2004 may still contain CCA. (For more information, see the section “How can I limit my exposure to arsenic?”)

Does arsenic cause cancer?

Exposure to high levels of arsenic has been linked to several types of cancer.

Researchers use 2 main types of studies to try to figure out 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 to 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 sometimes it can be hard to know what the results of these studies mean, because many other factors that might affect the results are hard to account for.

In most cases neither type of study provides enough evidence on its own, so researchers usually look at both lab-based and human studies when trying to figure out if something causes cancer.

Studies in people

Many studies have looked at arsenic’s potential 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 rates among people who worked with pesticides containing arsenic and those who worked in mines and copper smelters. These workers’ inhaled exposures were often very high. 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 as convincing.

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, prostate, 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 in drinking water 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, bladder, and lung cancers, leukemias, and lymphomas in certain species of animals exposed to high levels of inorganic arsenic. But other studies have not found an excess of tumors in lab animals exposed to arsenic.

What expert agencies say

Several national and international agencies study 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, 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.

  • IARC classifies arsenic and inorganic arsenic compounds as “carcinogenic to humans”, based on evidence from human studies that it can cause cancer of the lung, bladder, and skin. IARC also notes possible links between exposure to arsenic in drinking water and cancers of the kidney, liver, and prostate, although the evidence for these is not as strong.
  • IARC classifies the organic arsenic compounds dimethylarsinic acid (also known as cacodylic acid) and monomethlyarsonic acid as “possibly carcinogenic to humans.”
  • IARC classifies other organic arsenic compounds as “not classifiable as to their carcinogenicity in humans.”

The US National Toxicology Program (NTP) is formed from parts of several different 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 classifies arsenic and inorganic arsenic compounds as “known to be human carcinogens,”

The US 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,” based on evidence in human studies of links to lung, bladder, kidney, skin, and liver cancers.

(For more information on the classification systems used by these agencies, see 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:

  • Stomachache
  • 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 US government agencies regulate arsenic levels and exposures, a few of which are described here.

The EPA limits concentrations of arsenic (in all forms) in drinking water to 10 ppb (parts per billion). The Food and Drug Administration (FDA) has set a limit of 10 ppb in bottled water, and has also proposed a limit of 10 ppb in apple juice. There are no federal limits for arsenic in most foods.

The EPA has also set limits on the amount of arsenic that industrial sources can release into the environment and has restricted the use 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’s 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 give its customers 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.

In foods

Some foods naturally contain more arsenic than others. As mentioned above, rice and rice products are a particular concern because they are a major food source in many parts of the world and are included in the diets of many infants and children. The levels of arsenic in these products and their possible health effects are areas of active study. At this time, neither the FDA nor the American Academy of Pediatrics (AAP) recommend specific limits on how much rice or rice products should be eaten, but they do recommend that families eat a wide variety of foods for a well-balanced diet that includes grains other than rice, such as wheat, barley and oats. This can help limit any possible health effects from eating too much of any one type of food.

Concerns have also been raised about arsenic levels in some fruit juices (particularly apple juice). The FDA has tested the arsenic levels in many apple juice products and has stated that it is confident in the overall safety of apple juice for children and adults. The AAP does not have specific recommendations regarding arsenic in fruit juices, but it has stated that children don’t need to drink fruit juice to have a well-balanced, healthy diet. The AAP recommends limiting the intake of all sweet beverages, including juice, because of the risk for poor nutrition, obesity, and childhood cavities.

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 ones, enclosing a process that could expose workers to hazards, or ventilating a work area.
  • Using personal protective equipment, such as gloves and respirators, as part of a workplace protective program.
  • Using good work practices, such as changing clothes after work, washing work clothes regularly, and keeping food out of the work area.

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 pressure-treated 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 most residential (home) uses 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 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, contacting 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, the US Consumer Product Safety Commission (CPSC) recommends that parents and caregivers make sure children’s hands and other exposed body parts 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.

The CPSC also recommends that CCA-treated wood not be used where routine contact with food or animal feed can occur, such as in areas used to plant vegetables, fruits, or herbs. If you have a garden vegetable planter made with CCA-treated wood, put a plastic liner in it before filling it with soil to reduce exposure to CCA.

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 removal of CCA-treated lumber, 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 limit it. You can find qualified professionals and facilities by checking with the Association of Occupational and Environmental Clinics (

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. But these tests are not done routinely – 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 leaves the body in urine within a few days. This test also can sometimes be misleading, because the organic forms of arsenic in fish and shellfish can give a high reading even if you haven’t been exposed to the 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 past 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.

If a person has been 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 to stop further exposure 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 can increase the risk of skin, bladder, lung, and possibly some other cancers, 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 be caused by something other than cancer, but it is important to have them checked out.

Arsenic exposure and too much sun can both 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.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

Along with 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)
Public Health Statement for Arsenic:
ToxFAQs™ for Arsenic:

Association of Occupational and Environmental Clinics

Environmental Protection Agency (EPA)
Safe Drinking Water Hotline: 1-800-426-4791
Arsenic in Drinking Water:

Food and Drug Administration (FDA)
Foodborne Illness and Contaminants – Arsenic:

Occupational Safety & Health Administration (OSHA)
Toll-free number: 1-800-321-6742 (1-800-321-OSHA)
Arsenic page:

US Geologic Survey
Arsenic in Ground Water of the United States:

*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

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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. Volume 100C: Arsenic, Metals, Fibres, and Dusts. 2012. Accessed at on May 30, 2014.

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 on May 30, 2014.

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. Chromated Copper Arsenate (CCA) -Treated Wood: Guidance for Outdoor Wooden Structures. 2011. Accessed at on May 30, 2014.

US Department of Health and Human Services. Public Health Service, National Toxicology Program. Report on Carcinogens, Twelfth Edition. 2011. Accessed at on May 30, 2014.

US Department of Labor, Occupational Safety & Health Administration. Arsenic. 2012. Accessed at on May 30, 2014.

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Last Medical Review: July 9, 2014 Last Revised: July 18, 2014

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