Arsenic and Cancer: Water, Food, and Risk

This page is for anyone wondering about arsenic in water, food, or the workplace. It explains how people are exposed, the link to cancer, and how to lower exposure.

Arsenic is a natural element found in soil, water, and air. It comes in two forms, and the inorganic form is the more toxic one. It can build up in drinking water, especially in private wells. Over many years, that exposure can cause cancer. Testing and treating your water is the main way to protect yourself.

Arsenic occurs naturally in air, water, and soil. Mining and metal smelting can release it into the environment, and so can some farming processes. In parts of the United States and other countries, groundwater is naturally high in inorganic arsenic.

Common ways people come into contact with it:

• Drinking water that is contaminated with arsenic.
• Smoking tobacco, or being around tobacco smoke.
• Eating food from plants watered with contaminated water.
• Older pesticides and medicines. Arsenic pesticides were widely used until the mid-1900s. Some medicines contained arsenic until the 1970s.

Arsenic in drinking water is generally thought to be more harmful than arsenic in food.

Drinking arsenic-contaminated water for years is linked to bladder cancer and skin cancer. Medical exposure to arsenic has been clearly tied to skin cancer in population studies. Cancers of the lung, digestive tract, liver, kidney, and the blood and lymph systems have also been linked to arsenic.

The International Agency for Research on Cancer (IARC) studies the causes of cancer on behalf of the World Health Organization. It places arsenic in Group 1, carcinogenic to humans. That is the strongest evidence category. It means there is enough evidence that arsenic can cause cancer in people. The US National Toxicology Program agrees, listing arsenic in its Report on Carcinogens as known to be a human carcinogen.

Hazard and risk are not the same thing. Calling arsenic a carcinogen is a claim about hazard. It means arsenic can cause cancer under some conditions. Your own risk is a separate question. It depends on the dose you take in, how long you take it in, and other factors. Two agents in one group can carry very different real-world risks. A listing answers "can it cause cancer?" It leaves "how likely is it for me?" open.

Safe water for drinking, cooking, and watering food crops is the most important step.

• Test private well water for arsenic. Public systems must meet the EPA limit of 10 parts per billion.
• If levels are high, treat the water or switch to a safer source.
• Do not smoke, and stay away from secondhand smoke.
• Follow safety rules if you work around arsenic.

Any one exposure is easier to judge in context. Our overview of cancer prevention and what raises cancer risk give you that context.

Arsenic is a known human carcinogen (IARC Group 1). Your water supply is the piece you can most easily check and fix. Test a private well, treat it if levels are high, and then move on. A single label is not worth losing sleep over.