The nitrogen in chemical fertilizer does two things incredibly well. It supercharges crop growth, and it produces nitrate, a chemical that is ultra soluble in water and easily passes through soil to accumulate in the ground-water table. Once there, nitrates can persist for decades and increase in concentration as more fertilizer is added.
Ingestion of nitrates by infants has been shown to lower levels of oxygen in blood, leading to the potentially fatal blue-baby syndrome. And several studies have shown that consumption of nitrate-contaminated water can cause cancers in animals. But a recent report by a team led by Mary H. Ward of the National Cancer Institute for the first time links nitrates directly to thyroid cancer in humans.
This is bad news for more than half the nation’s population, both urban and rural, that drink water from wells, according to a study done by United States Department of Agriculture (USDA). And since chemical fertilizers only came into general use in the last 60 years, the problem could become much more severe.(Click here to read the full USDA report.)
Writing in the journal Epidemiology, Ward’s team reported that their examination of more than 20,000 older women in Iowa showed that those who had consumed water that had nitrate levels of five milligrams per liter or above were three times as likely to develop thyroid cancer as women who consumed water low in nitrates. Five milligrams per liter is half the nitrate concentration that the Environmental Protection Agency deems “safe.”
Organic fertilizers such as manure also produce nitrate, but because they break down slowly, plants are able to absorb more of the nitrogen, leaving less to percolate into the ground water. Nitrates can also enter the water table through polluted rainfall.
“But the largest problem is irrigated agriculture,” Jean Moran, professor of earth and environmental science at California State University, told Julia Scott of the San Francisco Chronicle. In some cases, crops absorb only one half of the applied nitrogen, leaving residues to pollute rivers, lakes and oceans as runoff, or to seep into sources of drinking water. And yet, there are no regulations on how much chemical fertilizers farmers can apply to their fields.
Michael Cahn of the University of California has shown that farmers can get by using far less nitrogen fertilizer than they now apply. He frequently tests soil in farmers’ fields for excess nitrogen, telling growers that the wasted chemicals represent dollars that are leaching out of their field.
They also represent proven carcinogens that are being absorbed into our bodies.