This article was co-published with Sierra.
Among all the contaminants in drinking water, nitrates are one of the most pervasive. They leach from chemical fertilizers and animal manure to pollute groundwater, rivers, and streams. Doctors have long known that, in infants, nitrates can lead to blue baby syndrome—a potentially fatal blood condition that starves the body of oxygen. But now scientists and health advocates are worried that nitrates could also cause cancer. They suggest it could be behind hundreds of cases in farming states across the U.S.
To address these concerns, the US Environmental Protection Agency (EPA) began a crucial and long-awaited assessment of the health risks of nitrates in 2017. Scientists and public health advocates hope the assessment will spur the EPA to tighten restrictions on nitrates in drinking water. Legal limits were set over thirty years ago, but scientists and advocates warn that the limits are outdated and don’t protect against cancer. They point to spiking cancer rates in farming states like Iowa and Minnesota, where nitrate contamination can reach sky-high levels. They also highlight studies that suggest the risk of dying is higher by 73 percent compared to water without nitrates, even when nitrates are at low levels in drinking water.
“Nitrate pollution from industrial-scale agricultural practices… poses an imminent and substantial endangerment to communities across the country,” wrote a coalition of environment and community advocates in a letter to the EPA in October 2024.
Other researchers are concerned that the existing standards don’t even protect infants from blue baby syndrome. David Belluck, a retired state toxicologist for Wisconsin and an expert on nitrate pollution in groundwater, writes that the EPA overlooked key information when calculating safe levels of nitrates. The missed data could dramatically lower the levels of nitrates considered safe, he wrote in a public comment submission to the EPA. Belluck called on the EPA to reconsider nitrates’ potential harm to infants.
But representatives from the food and agricultural industry are downplaying the health risks. They hired a consulting firm to produce a study that dismisses the need for tighter nitrate controls. In public comments to the EPA, they argue that stricter controls would be prohibitively expensive without providing any health benefits. They also assert that nitrates can be beneficial to health when present in food such as fruits and vegetables. However, independent scientists say these arguments overemphasize the benefits of nitrates in food and draw attention away from the risks of nitrates in drinking water. The researchers said the industry’s strategy is an attempt to muddy the debate and delay further controls.
Elizabeth Southerland, former director of the EPA’s Office of Science and Technology in the Office of Water, is troubled by industry’s tactics to derail the assessment and fight tighter controls. “The objective is to paralyze so that you cannot move forward until you have many more years of study,” she said. “This is always the industry playbook. There’s never enough data.”
The objective is to paralyze so that you cannot move forward until you have many more years of study. This is always the industry playbook. There’s never enough data. – Elizabeth Southerland
Flawed standards
In the 1940s and 50s, researchers began reporting on a spate of infants with a blue discoloration of their skin. Some were also vomiting. Others struggled to breathe. Several didn’t survive. The infants were suffering from blue baby syndrome, also known as methemoglobinemia (MetHb). They likely developed the condition after being fed with infant formula made with nitrate contaminated well water, concluded researchers and health professionals. But the condition can also occur as a genetic disorder.
MetHb occurs when bacteria in the body convert nitrate—a compound of nitrogen and three oxygen atoms—into nitrite—a compound of nitrogen and two oxygen atoms. The nitrite interacts with hemoglobin molecules in red blood cells to form methemoglobin. In this form, blood is less able to bind oxygen and deliver it around the body. Infants are particularly vulnerable to adverse effects of excess nitrate because their bodies are more sensitive to nitrate and nitrite and are not yet able to correct the problem. The condition can be treated with an intravenous dose of methylene blue, a blue-colored solution.
In 1991, the EPA set legal limits on nitrates in drinking water to protect infants from the condition. Largely based on two key studies, the EPA determined that restricting nitrates in drinking water to 10 milligrams per liter (mg/L) of nitrate–nitrogen (a measure of the amount of nitrogen in a sample of nitrate) would protect infants from harm.
However, some toxicologists say infants are still at risk of MetHb at this level.
Belluck, who spent much of his career writing drinking water standards for Wisconsin, asserts that the nitrate limits are based on a false premise. The EPA assumes that infants develop the condition at concentrations of 11 mg/L nitrate-nitrogen or above. He identified several cases where infants developed the condition at much lower levels. These include five cases in the state of Iowa where infants developed MetHb at concentrations as low as 0.4 mg/L. These cases were reported in studies that the EPA considered directly and indirectly when developing its standards.
Lots of uncertainty
There are also other problems with the EPA’s nitrate standards. The limits don’t take account of differences in the way infants respond to nitrate or their susceptibility to MetHb, writes Belluck in comments to the EPA. Factoring in this variation would lower the limits to ensure that the most vulnerable individuals are protected.
“There is no scientific justification to assume that all infants are the same in their response to nitrate ingestion…,” wrote Belluck.
Anna Fan, a toxicologist and former chief of the pesticide and environmental toxicology branch of California’s Environmental Protection Agency, wrote that there is little buffer between the legal limit of 10 mg/L and the level the EPA says can harm infants.
In addition, the studies that the EPA standard relies on are poor quality and scientifically unreliable, suggested Fan and Belluck. “Every day that goes by, infants are exposed to unacceptable levels of nitrate and nitrite… because of math and science errors,” wrote Belluck. The EPA needs to cut its safe levels by “one or more orders of magnitude”, he suggested.
Catherine Zeman, an environmental health scientist and expert in infant methemoglobinemia at James Madison University in Virginia, agrees that standards don’t protect all infants. “I think it’s right at the edge of where it needs to be. But there are cases where it’s not going to protect [infants],” she says.
The EPA did not respond to questions about the concerns regarding MetHb and the safe levels of nitrates in drinking water.
In a statement, an EPA spokesperson said the agency is required to review drinking water regulations every six years to determine whether any need revisions are needed. In its review published last year, the agency noted that it is conducting a health assessment for nitrates and nitrites.
Assessing nitrates’ links to cancer
In June 2023, the EPA announced it would reassess the health risks of nitrates and nitrites in drinking water. However, it will not review the risks of MetHb. The agency said it only plans to look at possible links to cancer and some other health effects, such as thyroid disease, that were not considered when the EPA developed the nitrate standards.
Fifteen years ago, EPA scientists recommended the agency evaluate growing evidence of cancer and other health effects from nitrates in drinking water. Meanwhile, other EPA scientists have long called for changes to the nitrate regulations. In an email from 2017, Kimberly Harris, who at the time was a health effects specialist at a regional EPA branch that serves states, including Wisconsin and Minnesota, wrote that her office had been “advocating for updates to the nitrate/nitrate drinking water regulations for some time”. But they were told that the risk assessment must precede any reforms, she writes. The email was obtained through a Freedom of Information Act request.
In 2017, the EPA started the risk assessment, but it was suspended two years later by the previous Trump administration due to changes in EPA leadership priorities. The Biden administration restarted the program, but the nitrate assessment could take several years to complete. The EPA says it will decide whether regulatory reforms are needed once the assessment is finished.
All the while, nitrate pollution continues to grow. In July last year, the EPA released data showing that it found nitrates in over 71 percent of water systems it surveyed nationwide between 2012 and 2019. Of these, 2.8 percent exceeded legal limits, with some nitrate concentrations reaching over 90 times the limit. An earlier EPA survey between 2006 and 2011 found nitrates in 63 percent of water systems surveyed.
Researchers and health advocates say the assessment and better protection for citizens are past due. Michael Schmidt, staff attorney for the Iowa Environmental Council, said, “We have endured drinking water contamination for decades, and action to ensure our health is overdue.”
We have endured drinking water contamination for decades and action to ensure our health is overdue.
– Michael Schmidt, staff attorney, Iowa Environmental Council
Studies sound alarm bells
The National Cancer Institute, part of the National Institutes of Health, says that ingested nitrates and nitrites react with other substances in the body to form N-nitroso compounds, which are known to cause cancer in animals and may cause cancer in humans.
Studies show that people who ingest nitrate in drinking water can develop colorectal and stomach cancer even at concentrations below the legal limits. A 2022 analysis found that the risk of stomach cancer linked to nitrate in drinking water nearly doubles as the concentration increases from 0 to 2.26 mg/L. With each additional 2.26 mg/L, the risk grows at a faster rate.
Roberto Picetti, an epidemiologist at the London School of Hygiene and Tropical Medicine and lead author of the study, said, “For stomach cancer and colorectal cancer, the direction is clear. It looks like there might be an association.”
Other research showed that across the US, people who ingested drinking water with nitrates at mostly low levels were at a 73% higher risk of dying from cancer over a 13-year period compared to people whose drinking water had no detectable nitrates.
“The magnitude of the effect size was shocking,” said Angelico Mendy, an epidemiologist at the University of Cincinnati in Ohio and coauthor of the study.
But although there is strong evidence of a link between stomach cancer and colorectal cancer, it is not yet conclusive, Picetti said. This is because there aren’t enough high-quality studies confirming the connection.
There is even less certainty around possible links between nitrates in drinking water and other kinds of cancers, such as those of the brain and pancreas, Picetti added. There are fewer studies of these cancers, and the outcomes sometimes conflict. Also, their quality is not always high. This is also true of studies on other health concerns, such as thyroid disease and birth defects.
There are not yet enough well-designed studies to draw firm conclusions, Mary Ward, scientist emerita at the National Cancer Institute, concluded. Ward, who investigated links between nitrates in drinking water and cancer, added that the increased risk for some cancers from nitrates at levels below the legal limits “raises concerns and points to the need for additional well-designed studies to clarify risks.”
Nonetheless, environmental and health advocates say regulators don’t need to wait for further scientific certainty. The studies are sounding an alarm that people need better protection, they say. “We know enough now to justify taking action,” Schmidt said.
Schmidt and a coalition of 23 environmental and health advocacy groups say state agencies that oversee local nitrate limits for drinking water have failed to control nitrate pollution. Consequently, people’s health is suffering. In Wisconsin, for example, research estimates that annually up to 298 cancer cases identified between 2010 and 2017 may be due to nitrate-contaminated drinking water.
According to Schmidt, voluntary and regulatory efforts to cut nitrate pollution have not succeeded in curbing excessive use of chemical fertilizers and animal manure from large animal feeding operations.
For example, between 2013 and 2023, the Iowa Department of Natural Resources recorded 179 incidents in which animal agriculture operators discharged manure into waterways, violating the law, according to an analysis by Food and Water Watch, a non-governmental organization pursuing corporate and government accountability.
“No area of the state is safe from manure discharging into waterways,” stated the analysis.
Industry fights back
Meanwhile, representatives from the food and agricultural industries are fighting back to deter stricter nitrate controls. They argue that nitrates aren’t all bad because consuming them in food can boost health. In addition, they say people get most of their nitrate from food, only a small amount comes from drinking water.
The Fertilizer Institute, a trade organization, and 21 other agriculture groups, including the National Pork Producers Council, wrote to the EPA arguing that the current nitrate standard should stay as it is. The agriculture and food groups argue that tighter controls would be expensive and not provide any health benefits. They point to estimates that halving the permissible levels of nitrates in drinking water could burden customers with additional costs of over $ 400 million each year.
To clarify the risks of exposure to nitrates, the industry groups urged the EPA to focus its review on the benefits of nitrates in people’s diets. Some fruits and vegetables, such as spinach and beetroot, are high in nitrates. Research shows that these vegetables can reduce the risk of heart disease and prevent some cancers. The public might get confused if the benefits of nitrates are not addressed, they wrote.
Similar arguments are made in separate comments by Daniele Wikoff, chief scientific officer of ToxStrategies, a science consulting firm, which was paid for by PepsiCo. ToxStrategies has offices across the country and performs work that minimizes the risks of products for industrial clients. For example, its scientists have run studies paid for by an energy industry think tank that questioned some of the dangers of hexavalent chromium, a carcinogenic compound used by the steel industry and others and a byproduct of electricity production.
Independent scientists agree that nitrate and nitrite from food and water should be considered when assessing the overall risk. But nitrates in drinking water are more of a health concern, they said. This is partly because of a crucial difference between nitrate and nitrite ingested in drinking water and that from fruits and vegetables. The latter also contains antioxidants and phytochemicals, which can offset some of the negative effects of nitrates and nitrites, studies suggest. Drinking water lacks these health-boosting compounds.
“Drinking water is just a straight shot of nitrate, nothing in opposition,” Zeman said.
Zeman was an expert witness in a lawsuit brought by more than 800 residents of Millsboro, Delaware, against a local chicken processing plant that polluted their groundwater with nitrate from manure. In 2021, residents won $205 million in a settlement.
In addition, nitrates and nitrites, which are used to cure meats and as preservatives, are linked to cancer. In 2010, the International Agency for Research on Cancer (IARC) found that nitrate and nitrite are probably carcinogenic to humans in some circumstances. In 2015, the IARC concluded that processed meats are carcinogenic to humans.
The industry comments “overemphasize the benefits of dietary nitrates and downplay drinking water risks,” Zeman said.
The Fertilizer Institute did not respond to requests for comment.
“Drinking water is just a straight shot of nitrate, nothing in opposition”. – Catherine Zeman
Pushing industry funded research
To assess the risks and benefits of nitrates, the industry groups suggest that the EPA use an analysis performed by Wikoff and colleagues at ToxStrategies that was funded by PepsiCo.
The analysis published in 2018 suggests that the acceptable daily intake of nitrates in food, as recommended by an international expert committee, is too low and could be quadrupled for people aged 12 weeks and older.
Zeman said the proposed higher dietary intake is “based on a blatant untruth” that the expert committee’s recommendations were not supported by robust research.
Furthermore, the ToxStrategies analysis repeats a “disproven” idea that minimizes nitrate’s role in the development of methemoglobinemia in infants, says Zeman. The analysis suggests that bacteria infections causing diarrhea could be the main cause of MetHb in infants. Zeman says there is some evidence suggesting that diarrhea-causing bacteria can make infants more susceptible to developing methemoglobinemia if they consume or drink nitrates in water or infant formula . But nitrates are the main problem.
The argument that bacteria contamination is the main cause of MetHb is “science denialism” aimed at “manufacturing doubt” to downplay the risks of nitrate in drinking water, says Zeman.
Wikoff and ToxStrategies did not respond to requests for comment.
Fears of further delays
The EPA is considering the comments from industry and others as it develops a draft assessment for nitrate and nitrite. It is not yet clear when it will be published.
The returning Trump presidency is sparking fears of further delays. Southerland worries that the Trump administration will derail the nitrate and nitrite review. She says the previous Trump administration was “very opposed” to the EPA’s Office of Research and Development, which oversees the health risks assessments.
In addition, the Project 2025 manifesto from the conservative think tank, the Heritage Foundation, proposes scrapping the EPA program that runs the health risk assessments.
But likely the biggest hurdle will be enforcing changes in farming practices, such as cutting fertilizer use and manure application, that are needed to tackle nitrate and nitrite pollution.
To ensure progress, the EPA and state agencies will have to overcome the “enormous power of the agribusiness”, says Southerland.
“Shifting from voluntary practices to some basic standards of care has faced a lot of resistance from industry,” Schmidt said. It “has gone largely unregulated, at least in terms of water, for many years.”
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