Weigh the pros and cons of a study done to see if there was an association between nitrate levels in drinking water and bladder cancer. In the Midwestern US state of Iowa, large amounts of nitrogen...

Weigh the pros and cons of a study done to see if there was an association between nitrate levels in drinking water and bladder cancer. In the Midwestern US state of Iowa, large amounts of nitrogen fertilizer have been used on agricultural fields for many years. Nitrate runoff from these fields has reached the drinking water of many municipalities; it is in drinking water at greater than 5 ppm in many cases. In 2001, University of Iowa researchers reported the results of a study on 21 977 women in Iowa. The women studied had drunk from the same water supply for more than ten years, and only communities where at least 90% of the water supply came from a single source were included in the study. Each woman’s nitrate exposure was estimated on the basis of the level in the water she drank. Results were adjusted for confounding factors (smoking, age, education, physical activity, and quantities of fruits and vegetables consumed). Researchers found a statistical link between nitrate in drinking water and an increased risk of bladder cancer. Women who drank water containing more than 2.5-ppm nitrate had a risk factor of 2.8 – they were almost three times more likely to develop bladder cancer than women whose drinking water contained less than 0.36-ppm. One author of the study noted that because there were only 47 cases of bladder cancer among the 21 977 women, the association must be considered moderate. Still, the authors believed that the results are biologically plausible as the body can convert nitrate into N-nitroso compounds, known carcinogens. The results raised concern because they associated bladder cancer with nitrate levels as low as 2.5-ppm whereas the US EPA standard for nitrate in drinking water is 10-ppm. The 10-ppm standard was set 50-years ago to avoid cases of blue baby syndrome. 11 At that time, possible chronic effects of nitrate such as cancer were not considered. Based on these results, some persons suggest that EPA should lower its drinking-water standard for nitrate. However, other epidemiologists evaluating the study did not believe that the study showed a meaningful association between nitrate at the levels studied and bladder cancer. If you had to come to a tentative conclusion as to whether there is an association between nitrate in drinking water at 2.5 ppm and bladder cancer, what would you conclude? Explain.