Background: Nitrate contamination of drinking water has been documented in many areas of the United States. The source of the nitrate has been attributed to widespread use of commercial fertilizers as well as animal and human wastes. In Iowa, the use of fertilizers in both rural and urban settings has resulted in 30-40% of the public water supply with nitrate concentrations greater than 5 mg/liter. The EPA limit for nitrate in drinking water is 10mg/liter primarily to prevent methemoglobinemia in infants. However, other health risks of nitrate exposure have not been fully evaluated against this standard.
These investigators were interested in evaluating nitrate consumption and cancer risk. Nitrates are converted to highly carcinogenic N-nitroso compounds in the digestive track. An epidemiologic study was conducted using the Iowa Women's Health Study cohort. Drinking water source is but one of the many issues this study tracks and with over 40,000 women enrolled, it is an excellent resource for this type of investigation.
Advance: As in previous studies, these investigators found a positive association between nitrate exposure and bladder cancer. Unexpectedly, they also found a positive association for ovarian cancer. In addition, they reported a negative association for uterine and rectal cancer. All associations appear to be dose dependent. There were no associations for all other cancer types examined.
Implication: Results from these studies correlate with earlier studies that show increased risk for bladder cancer as nitrate level in drinking water rises. The unexpected positive association with ovarian cancer and the even more unexpected negative associations for uterine and rectal cancer suggest that nitrate levels below the current EPA standard in municipal water supplies are of significant public health concern. Additional research is necessary to fully understand this issue and to make standards to protect public health.
Publication: Weyer PJ, Cerhan JR, Kross BC, Hallberg GR, Kantamneni J, Breuer G, Jones MP, Zheng W, Lynch CF. Municipal drinking water nitrate level and cancer risk in older women: the Iowa women's health study. Epidemiology. 2001 May;11(3):327-338.