Several other environmental factors have been the source of speculation over their potential cancer risk. However, to date none of these have been positively linked to a higher cancer risk. They include:

• Pesticides. Insecticides, herbicides and other chemicals are widely used in agriculture. High doses of such chemicals sometimes have been associated with cancer in animals. But concentrations found in foods are low, and have not been tied to increased cancer risk in humans. People in industry or farming who are exposed to higher levels of pesticides may be at increased risk of cancer. Research is ongoing to ensure that foods are safe and that alternative pest-control measures are developed that lower cancer risk.
  
  
• Toxic wastes. Some toxic chemicals found at dump sites can be carcinogenic in high doses. Air, water and soil pollution are the chief avenues of exposure. However, most communities enforce rules to ensure that these sites emit very low or negligible levels.
  
  
• Nuclear power plants. These plants emit ionizing radiation, which has been shown to cause cancer. These emissions are tightly controlled, which keeps exposure levels negligible for those in the surrounding community. Studies have shown that clusters of cancer are no more likely to occur near nuclear power plants than they do in other areas.