DES MOINES, Iowa -- The Raccoon River is the most nitrogen-polluted river in America's heartland. Each day in spring and summer, the Raccoon carries as much as 600 tons of nitrate, the biologically active form of nitrogen, past the Des Moines Waterworks' intake pipe.
To protect the people of Iowa's biggest city against a potentially dangerous overdose of nitrate, the waterworks has built the world's largest nitrogen removal system. Eight giant tanks use custom-made, electrically charged plastic particles to remove a half-ton of nitrate from each day's water supply.
Then, because they have no place else to put the stuff, the water engineers dump it back into the river, passing the health and environmental risks downstream.
How big are the health risks? Medical researchers have been trying to find out for more than 50 years, and so far they have few answers. But their questions are becoming more urgent as higher levels of nitrogen compounds turn up in drinking water all over the world, from Hungary to New Zealand.
When fertilizer or animal waste is spread on farm fields, natural processes in many soils transform it into a nitrogen-hydrogen-oxygen compound called nitrate. Some nitrate seeps into underground water supplies. Rain and snow sweep some of it into rivers and streams.
Nitrate is one of life's crucial building blocks. It's a key component of amino acids, the chemicals found in every one of the human body's 60 trillion cells. But scientists suspect that too much nitrate can damage those cells -- overdose them so they can no longer do the body's essential work or mutate them so they become cancerous.
World War II-era research showed baby formula mixed with nitrate-tainted water can cause "blue baby syndrome," a condition that can kill infants less than 6 months old. So the U.S. Environmental Protection Agency and the World Health Organization have set limits on nitrates in drinking water.
But more than one in six rural American families drink water that violates this standard, according to a 1997 study by the federal General Accounting Office.
On the Delmarva Peninsula in the early 1990s, between one in three wells in farming areas and one in six in residential areas had more nitrates than the standard, according to the U.S. Geological Survey (USGS). Nitrate contamination in Delmarva's shallow ground water has increased along with fertilizer use, says Robert Shedlock, associate director of the USGS Maryland-Delaware district.
In Iowa, about 40 percent of the state's private wells exceed the standard, says Rick Kelley, an environmental program consultant at the University of Iowa Hygienic Lab, which analyzes water samples for the state.
Blue baby syndrome is the best documented illness from nitrate pollution. When fertilizer-tainted water is given to infants, their digestive systems transform the nitrate into another nitrogen compound called nitrite, which drastically reduces blood's ability to carry oxygen.
Victims' skins take on a purple-blue tint. Their blood turns the color of melted chocolate, and their oxygen-starved organs can be damaged or fail. Most recover if the condition is treated promptly in a hospital, says Dr. Daniel J. Kobaugh, associate director of the American Association of Poison Control Centers.
No one knows how many American infants get blue baby syndrome from tainted well water. Health departments aren't required to track such cases.
From 1993 to 1997, 1,277 U.S. children under the age of 6 developed the condition because of some nitrate source -- not necessarily drinking water -- according to the poison control group. Over the past 20 years, medical journals record only two cases of the syndrome caused by high nitrate levels in farm wells and only one death.
Biologist Alex Avery of the Hudson Institute, a pro-business think tank, caused a furor in public health circles last summer by disputing that nitrates cause blue baby syndrome. If fertilizer contamination really caused the illness, there would be far more cases, Avery says. He believes bacteria in well water cause the syndrome.
Most nitrate experts disagree. But farm state epidemiologists say that, even if Avery is right, the nitrate standard is needed because there's too much uncertainty about its role in other illnesses. Nitrates are suspected of playing a role in cancer, but the evidence is inconclusive. And researchers have found links to central nervous system defects. But for almost every study connecting nitrates to a particular disease, there's a contrary study.
"I look at that kind of thing, and I think, geez, there's a lot of work to be done here," says Peter J. Weyer, associate director of the Center for Health Effects of Environmental Contamination, at the University of Iowa. "A lot of people will say, 'Don't drink the water.' I'm not saying that. The jury is out, and we need to do more studies. And that's the truth. That's all we can say right now."
PETER J. WEYER,
associate director of the Center for Health Effects of Environmental Contamination, at the University of Iowa