Do not eat fish caught in polluted waters, since the fish might also contain large amounts of the chemicals. Some people are exposed to carcinogens at work. The first link between occupation and cancer was noted in 18th-century England where physicians saw high rates of cancer in men who were chimney sweeps in their youth. The physicians determined exposure to soot in the chimneys had caused the cancer. Once the sweeps wore protective clothing and routinely cleaned the soot off their bodies, the cancer rate dropped.
Asbestos is another occupational carcinogen.
Occupational exposure might be related to up to 5 percent of cancer deaths. Diet Foods such as hot dogs, bacon, ham and pickled meats and fish have preservatives called nitrites. Nitrites convert to another chemical called nitrosamines, which are known cancer-causing agents. Researchers have linked an increased risk of stomach cancer to overconsumption of smoked or cured foods. Eating such foods only occasionally is not harmful.