The Environmental Protection Agency (EPA) has backed off its reassessment of cancer-causing nitrates despite decades of research suggesting the contaminant is more harmful than previously thought and that nitrate pollution is at crisis levels in U.S. drinking water.
The agency would not confirm the assessment was canceled, but the work has been stagnant for more than two years and the department responsible for it was eliminated. And scientists and health advocates say regardless of whether it has been canceled or is locked in a lengthy delay, Americans are paying the price with their health.
The EPA set a threshold for nitrates in drinking water more than 30 years ago at a level designed to avoid harming babies after research showed that ingesting nitrates could trigger dangerously low oxygen in babies’ blood, what’s known as “blue baby syndrome.” The EPA announced it would reassess nitrates — and nitrites — in 2017 to look at other potential health impacts, including cancer, but the work was suspended in 2019 by the first Trump administration.
The Biden administration restarted the work, and the EPA accepted public comments on the planned assessment in 2023 but the agency hasn’t provided an update since. Earlier this year, the Trump administration eliminated the EPA’s Office of Research and Development, which housed the Integrated Risk Information System (IRIS) and was responsible for such health assessments.
“The assessment was intended to do the hard science to support appropriate human health protections,” said Tyler Lobdell, a senior staff attorney with Food & Water Watch. “It’s alarming that the Trump administration has decided to undermine that process.”
Independent research has significantly advanced since the EPA set its drinking water threshold in 1991. Nitrates can be naturally occurring, but nitrate pollution in waterways has been tied to heavy use of nitrogen-based fertilizers and the spreading of large amounts of livestock manure on farm fields as fertilizer. Nitrate contamination has been linked to cancer and other health problems, particularly in prominent farm states.
The current EPA nitrate threshold for nitrates under the Safe Drinking Water Act is 10 parts per million (ppm) — a level that researchers and health advocates say is far too high to protect health. Studies have linked nitrate exposure below 10 ppm to increased risk of colorectal cancer, bladder cancer, thyroid disease and other health problems.
“We need IRIS to go and do another health assessment on nitrates because links to cancer and birth defects keep popping up in the scientific literature,” said David Cwiertny, a researcher and director of the University of Iowa’s Center for Health Effects of Environmental Contamination.
IRIS assessments don’t create legal standards but inform the EPA when it sets drinking water limits.
The EPA’s delayed assessment is particularly troubling because the agency itself has acknowledged increasing evidence that nitrates contribute to cancers and birth defects, Cwiertny said. The EPA cited new science on cancer and birth defects in the 2010 drinking water standards review as well as in its 2017 scoping review.
“That’s the EPA saying ‘this is science worth paying attention to,’” Cwiertny said. “They’ve opened the door acknowledging the need for more assessment and then just left it ajar.”
Brigit Hirsch, a spokesperson for the EPA, did not comment on the status of the assessment, but said that research on nitrate in drinking water was “largely transitioned to the Office of Water … as part of the agency’s strategic reorganization to better align scientific research with policy development and program implementation.”
Hirsch also pointed to the agency’s six-year review of nitrate completed in 2024 that concluded the current health threshold did not need to be revised.
Nitrates pervasive in U.S. drinking water
The stalled assessment comes as nitrate pollution becomes more pervasive: an April report from the Environmental Working Group (EWG) found more than 60 million Americans get their water from sources contaminated with elevated levels of nitrate pollution. The report found that the majority of the pollution is likely coming from agricultural manure or fertilizer runoff.
The water systems with the highest and most frequent nitrate levels were in heavy agricultural states. And federal research is key to bolstering drinking water protections in those states, said Nancy Stoner, a senior attorney at the Environmental Law & Policy Center.
“States rely upon the EPA to be able to do deep science. Whether it’s drinking water standards or water quality standards, most of that is done at the federal level,” Stoner said.
The nitrate problem is particularly bad in Iowa, which is the nation’s top corn and hog producer and has loads of nitrates washing into waterways from manure and fertilizer. Iowa also has the second-highest rate of cancer in the nation and is only one of three states where cancer is rising, according to the National Institutes of Health. For many types of cancer, the state’s numbers dwarf national averages — and nitrates are a key culprit.
“In science, we’re unfortunately not going to get something very definitive that this contaminant is causing this,” Cwiertny said. “The point is that there are now enough converging lines of evidence out there.”
Central Iowa Water Works, the state’s largest water utility, has frequently asked residents to cut back on water use over the past few years because nitrate levels are so high in drinking water supplies that the utility is having a hard time treating it. The Des Moines and Raccoon rivers in Iowa are in the top 1 percent of rivers nationwide for nitrate concentration, with an estimated 80 percent of the contamination coming from agriculture.
“Even for places like this where the current nitrate drinking water standard applies … we’ve seen such high levels of nitrate in source water that municipal water utilities are struggling to remove it,” said Stacy Woods, a research director for the Food & Environment program at the Union of Concerned Scientists.
Woods added that nitrates’ health impacts extend beyond farming states.
“Nitrate pollution can travel hundreds of miles through streams and rivers and groundwater and other connected water bodies,” she said. “That water-to-water pathway is how fertilizer in the Midwest creates pollution all the way down in the Gulf of Mexico.”
Pressing the EPA for information
In May, Stoner and Woods co-authored a letter, which was signed by more than 80 health and environmental groups, sent to Health and Human Services (HHS) Secretary Robert F. Kennedy Jr. and EPA administrator Lee Zeldin urging the officials to protect Americans from a “public health emergency” driven by nitrate pollution.
“It is imperative that EPA and HHS act now to address this public health emergency in Iowa and across the country,” the letter states. “Your agencies should immediately identify and eliminate sources of nitrate pollution in drinking water and provide funds to communities to reduce nitrate to safe levels.”
Stoner said she and others met with some officials at the EPA about the letter, but haven’t received an official response from the agency, nor have they heard from HHS.
Food & Water Watch sued the EPA in June alleging the agency has failed to release records under Freedom of Information Act (FOIA) requests about the stalled nitrate assessment. Food & Water Watch requested such records in August 2025 after the EPA had cut staffing and announced plans to eliminate the Office of Research and Development.
Tyler Lobdell said he worked with EPA staffers for several months to get the records and they told him “scientists were being reassigned.”
“That’s pretty vague but it’s clear that the teams, the department, and the organizational structure that supported this kind of work is gone,” he said.
This story was originally published by The New Lede.
