Carcinogen

Radioactive substances found in rocks and soil are also considered potentially carcinogenic. While most people do not come in contact with radioactive chemicals on a day-to-day basis, these substances can emit radioactive particles that can be dangerous. Radon, a radioactive substance emitted by uranium, can seep from rocks into buildings. In some areas of the country, radon can be emitted in relatively large amounts into buildings which should be tested for radon. If the levels are found to be high, changes should be made to the building's ventilation system to reduce the amount of radon in the building.

In 1993, the EPA designated second-hand smoke from cigarettes to be a known human carcinogen. It is estimated that 2,000 lung cancer deaths a year are caused by second-hand smoke, which has led to the designation of many public areas as smoke-free zones.