The positive association we found between nitrate contamination in drinking water and bladder cancer is consistent with some previous data. Minn. The researchers assessed nitrate exposure from drinking water for 21,977 women who were participants in the Iowa Women's Health Study. Since no individual water consumption data were available, the researchers assigned each woman an average level of exposure to nitrate based on data collected between 1955 and 1988 on nitrate levels in her community's water supply. No nitrate data were available for women using private wells. Using cancer incidence data from the Iowa Cancer Registry for 1986 to 1998, and after adjusting for factors such as smoking and nitrate in the diet, the researchers found a greater risk for bladder cancer as the nitrate levels in the communities' water supplies increased.
Drinking water can account for a substantial proportion of the total nitrate intake.
Up to 20 percent of ingested nitrate is transformed in the body to nitrite, which can then undergo transformation in the stomach, colon and bladder to form N-nitroso compounds. These compounds are known to cause cancer in a variety of organs in more than 40 animal species, including higher primates. The U.S. Environmental Protection Agency drinking water standard is 10 mg per liter nitrate-nitrogen. Weyer emphasized that additional studies are needed to look at possible links between nitrate levels in drinking water and cancer, particularly with respect to refining exposure assessments. From a public health perspective, source water protection is a main concern.