National Institutes of Health
U.s. Dept of Health and Human Services: Cancer and the Environment [Pdf]
Document provides information on the causes and nature of cancer and particularly the substances in the environment that are known to cause or may cause cancer in humans such as tobacco, ultraviolet radiation, pesticides, and metals.
American Cancer Society
American Cancer Society: Stay Healthy
This large site from the American Cancer Society offers comprehensive information on many kinds of cancer. From the left navigation bar, click to Prevention, Early Detection, Nutrition and Prevention, or Environmental Risks.