NEW YORK (Reuters) -- Researchers have found a link between contamination of drinking water by nitrate fertilizers and the risk of developing non-Hodgkin's lymphoma (NHL), a cancer of the lymph nodes, which are the body's factories for making infection fighting cells.
"Drinking water nitrate may act as a carcinogen via the formation of N-nitroso compounds, many of which are animal carcinogens," the study authors explain.
The report in the September issue of the journal Epidemiology points to a 70% increase in NHL cases over the past 25 years in the U.S. The researchers say their findings reflect long-term exposure to high nitrate levels in community drinking water in farming areas, and do not implicate dietary nitrate (from vegetables) as a possible cause of NHL.
"This is one of the first epidemiological studies to suggest that there might be a link between drinking water and non-Hodgkin's lymphoma," said epidemiologist Dr. Mary H. Ward of the National Cancer Institute's occupational epidemiology branch in Bethesda, Maryland.
Ward and her co-authors note that, largely as a result of the increase in nitrogen fertilizer use over the past 40 years, nitrate levels in ground and surface waters in agricultural areas have risen.
The study looked at 156 people with NHL from counties in eastern Nebraska, and matched them with more than 500 healthy people from the same farming regions. The study participants were surveyed about their past exposure to nitrate in drinking water and in dietary sources, mainly vegetables. The researchers then estimated an average nitrate exposure for the years 1947 through 1979.
They found that people who drank community tap water with average nitrate levels in the highest percentages (at least 4 milligrams per liter of nitrate or nitrogen) over a long period had more than twice the likelihood of developing NHL, regardless of how much dietary nitrate they consumed.
"I would say our study is suggestive of a possible link [between NHL and nitrate in drinking water] but it deserves further evaluation," Ward said.
She added that similar studies are planned for other farming regions in Iowa and Minnesota to see if current findings can be confirmed for lymphoma and other cancers.
Source: Epidemiology (1996;7:465-471)
