Arsenic and Cancer

The simple versionExplain▾

Arsenic is a natural element found in soil, water, and air. The most harmful form, inorganic arsenic, can build up in drinking water — especially from private wells — and cause cancer over many years. Testing and treating your water is the main way to protect yourself.

What arsenic isExplain▾

Arsenic is a naturally occurring element. Its inorganic form is the most toxic and is released into groundwater from rock and soil, and by mining and smelting. Some foods, including rice, can contain small amounts absorbed from soil and water.

How people are exposedExplain▾

Common ways people come into contact with it:

• Drinking water from wells or areas with naturally high arsenic
• Eating foods, such as some rice products, grown in arsenic-rich conditions
• Working in or living near mining and smelting operations
• Older pressure-treated wood and some pesticides (largely phased out)

The cancer connectionExplain▾

Long-term arsenic exposure is linked to cancers of the bladder, skin, and lung. It is also associated with cancers of the liver, kidney, and digestive tract, and with non-cancer effects like skin changes.

The International Agency for Research on Cancer (IARC), the cancer arm of the World Health Organization, places arsenic in Group 1, carcinogenic to humans — the strongest evidence category, meaning there is enough evidence that it can cause cancer in people. In the United States, the National Toxicology Program's Report on Carcinogens lists it as known to be a human carcinogen.

Hazard is not the same as riskExplain▾

It helps to separate two ideas that are easy to mix up: hazard and risk. When an agency lists arsenic as a carcinogen, it is making a statement about hazard — whether the substance is capable of causing cancer under some conditions. It is not, by itself, a statement about your personal risk, which depends on how much you are exposed to, for how long, and other factors. Two substances in the same group can carry very different real-world risks. The label answers "can it cause cancer?" — not "how likely is it to cause cancer for me?"

How to lower your exposureExplain▾

• Test private well water for arsenic; public systems must meet the EPA limit of 10 parts per billion
• Use certified treatment (reverse osmosis or adsorption) or switch to a safer source if levels are high
• Vary your grains and rinse rice to modestly lower dietary arsenic
• Follow safety rules if you work around arsenic

If you are looking at your overall cancer risk, small, steady steps add up. See our overview of cancer prevention and what raises cancer risk to put any single exposure in context.

The bottom lineExplain▾

Arsenic is a known human carcinogen (IARC Group 1). The most important thing you can do is understand where exposure comes from and take reasonable steps to reduce it, without losing sleep over a single label. Focus your energy on the biggest, most controllable risks in your own life.