Experts: Nitrate Water Contamination Is Now a Public Health Threat

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Key Takeaways

  • A new study estimates that nitrate exposure causes many cases of cancer and poor birth outcomes in Wisconsin annually. 
  • Nitrates are toxic chemicals that contaminate much of the state’s groundwater, due to agricultural runoff.
  • A component of many fertilizers, nitrates are present almost anywhere and everywhere farming is practiced.

If you’re based in Wisconsin, you might want to inquire into the source of your drinking water. Much of the state’s water supply appears to be contaminated with nitrates, naturally occurring ions that can pose a risk to human health when consumed in concentrations that exceed—or, it turns out, even meet—federal standards. The October study that revealed the extent of the problem was published in the journal Environmental Monitoring and Assessment.

Nitrates are chemical compounds that are endemic to soil, water, certain foods, and bodily waste. In the springtime, they can also be found blanketing the fields of farms and ranches in the West and Midwest, where nitrate-containing substances such as nitrogen-based fertilizer and animal manure have been a staple of agricultural production since the postwar era.

But their prevalence, according to the new study, comes at a cost to the surrounding communities. 

What This Means For You

High levels of nitrate in drinking water can have detrimental health effects. If you suspect your drinking water may be contaminated and it comes from a private well, you may contact your state certification officer for a list of laboratories in your area that will perform tests on drinking water for a fee, according to the Centers for Disease Control and Prevention.

The Financial Toll 

Conducted by researchers affiliated with the organizations Clean Wisconsin and the Environmental Working Group, the study aimed to put a number on the healthcare costs incurred by nitrate exposure in Wisconsin between January 1, 2010, and December 31, 2017, by quantifying associated disease diagnoses and adverse birth outcomes.

By reviewing data compiled by the Wisconsin Department of Natural Resources and the Wisconsin Department of Agriculture, Trade and Consumer Protection, the researchers determined that between 111 and 298 cancers, 137 and 149 low fetal birth weights, 72 and 79 premature births, and up to two neural tube birth defects could be attributed to ingesting water contaminated with nitrates each year.

Several recent studies have also found increased health risks from "nitrate levels below the federal drinking water standard” of 10 parts per million, lead study author Paul Mathewson, PhD, staff scientist at Clean Wisconsin and associate scientist in the department of integrative biology at the University of Wisconsin-Madison's College of Letters and Science, tells Verywell. The standard's evident inadequacy, he says, can be explained by the fact that it was "established to protect against methemoglobinemia rather than carcinogenic or birth effects." Methemoglobinemia is a condition caused by impaired oxygen transportation that is known as “blue baby syndrome” in infants.

Mathewson and his co-authors estimated that nitrate exposure-associated cancers and adverse birth outcomes run Wisconsinites up a minimum of $23 million and a maximum of $80 million annually. If nothing is done, that figure will likely only increase with time, but if local, state, or federal authorities manage to reduce nitrate concentrations in drinking water by 40%, it could be slashed by more than one-fifth.

However, the estimate did not factor in the indirect costs of diagnosis and treatment, which can be significant. Premature babies, for example, are more likely to have health problems and less likely to attain academic and financial success than their peers, “even after additional confounders and socioeconomic factors are considered,” Mathewson and his co-authors wrote.

Why Wisconsin?

While nitrate contamination is not exclusive to Wisconsin, the Midwestern state is particularly hard-hit because two-thirds of its residents source their drinking water from groundwater stores, often via private wells. Most of these wells, Chloe Wardropper, PhD, assistant professor in the department of natural resources and society at the University of Idaho's College of Natural Resources, tells Verywell, serve fewer than 25 people and are accordingly exempt from federal oversight under the Safe Drinking Water Act of 1974.

That means that users “could be unknowingly ingesting high concentrations of nitrates since they are colorless and odorless,” Mathewson says. 

When nitrogen-based fertilizer or animal manure is distributed to promote plant growth, according to Wardropper, the excess inevitably bleeds into the earth and contaminates the groundwater. Once ingested, the nitrates combine with amines and amides already present in the body to form what the National Cancer Institute describes as carcinogenic, or cancer-causing, “N-nitroso compounds” (NOCs). The NOCs eventually pass into the small intestine and other tissues, impairing the function of these organs along the way.

“High levels of nitrates in a human body can cause respiratory problems, particularly in babies with ‘blue baby syndrome,' reproductive complications for women, and have been connected to several types of cancer, including colorectal cancer and kidney cancer,” Wardropper says.

The prevalence as well as the severity of these side effects in affected populations, Mathewson and his co-authors wrote, means that nitrate contamination should be considered a public health threat—not only in Wisconsin but everywhere nitrogen-based fertilizer is in widespread use.

That includes every other U.S. state as well as foreign nations with industrial economies. In many European rivers, nitrate concentrations are 10 to 15 times higher than they were a century ago. In parts of the Baltic Sea, the Yellow Sea, the Adriatic Sea, the Chesapeake Bay, the Gulf of Thailand, and the Gulf of Mexico, nitrate overload has indirectly created marine “dead zones”—regions of the ocean so devoid of oxygen they can no longer support aquatic life—that can span thousands of square miles.

A Way Forward

Both Mathewson and Wardropper say that one way to reduce the nitrate burden would be by taking steps to combat fertilizer and manure overapplication and sewage leaks. 

“It is well understood that manure and fertilizers are commonly over-applied to many fields, so working to address this overapplication and encouraging farming practices that reduce runoff would go a long way towards addressing this contamination," Mathewson says. "Septic systems are also a source of nitrates to the environment, so ensuring septic codes are up to date and folks are in compliance would help."

One Wisconsin county, Dane County, has already set an example for others by developing what Wardropper, who attended graduate school there, describes as an "innovative" program that ensures safe and effective waste management. Home to many dairy farms, Dane has "invested in community manure storage facilities to take some of that excess manure, as well as biodigesters, which turn manure into energy,” Wardropper says.

But as with most solutions, money is an object. Both she and Mathewson seem to believe that an increase in federal funding for initiatives developed to monitor or improve water safety would streamline the process of curbing nitrate contamination significantly. 

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Mathewson PD, Evans S, Byrnes T, et al. Health and economic impact of nitrate pollution in drinking water: a Wisconsin case study. Environ Monit Assess. 2020;192:724. doi:10.1007/s10661-020-08652-0

  2. National Cancer Institute. Chemical and environmental exposures: nitrate. Cancer Trends Progress Report.

  3. Ward, MH. Too much of a good thing? Nitrate from nitrogen fertilizers and cancer. Rev Environ Health. 2009;24(4):357-363. doi:10.1515/reveh.2009.24.4.357

  4. Evans S, Mathewson P. Study: nitrate in Wisconsin’s drinking water linked to cancer, preterm births and up to $74 million in yearly healthcare costs. Environmental Working Group.

  5. Fields, S. Global nitrogen: cycling out of control. Environ Health Perspect. 2004;112(10):A556-A563. doi:10.1289/ehp.112-a556

By Caroline Tien
Caroline Tien is a journalist with degrees in English and biology. She has previously written for publications including Insider and Cancer Health.