The limit set for a cancer-causing compound found in tap water may be too high, putting women at increased risk for bladder cancer, results of a study suggest, Reuters Health reports. According to the study, carried out by Dr. Peter J. Weyer of the University of Iowa, women who drank tap water that contained levels of nitrates below the maximum level of 10 milligrams (mg) per litre set by the US Environmental Protection Agency (EPA) were still nearly three times more likely to develop bladder cancer compared with women who consumed much lower levels of the contaminate. The study compared women who drank water with more than 2.46 mg of nitrate per litre for more than 10 years with those who consumed less than 0.36 mg of nitrate per litre of water. "Our study suggests that nitrate levels much less than (the EPA's maximum limit) could be a serious health concern," Dr. Peter J. Weyer said in a prepared statement. Nitrate is a pollutant that can leak into municipal water supplies from commercial fertilisers, as well as human and animal waste. In the stomach, about 20 per cent of nitrates can be transformed into nitrites, which can be converted into "some of the strongest known" cancer causing compounds, the authors write. The study included nearly 22,000 Iowa women aged 55-69 years who had used the same water supply for more than 10 years - with most drinking the water for more than 20 years. About 75 per cent used a municipal supply and the remainder used a private well when the study began in 1986. The researchers found that the risk of bladder cancer rose in tandem with nitrate levels in the communities' water supplies regardless of smoking, intake of vitamins C and E, and nitrates in the diet. Smoking can increase nitrate exposure, as can certain vegetables, while the vitamins C and E can counteract the carcinogenic effects of nitrates. While the association between nitrate contamination in drinking water and bladder cancer supports previous research, the findings warrant further study, Dr. James R. Cerhan, a co-author from the Mayo Clinic in Rochester, Minnesota, said in a prepared statement. The researchers did not collect data on the volume of tapwater consumed by the women, or how much water they consumed outside their home. Full findings are published in the May issue of Epidemiology 2001;11:327-338.