This story was originally published by Sentient . In the early 20th century , scientists discovered how to produce nitrate from air. This was key to the development of factory farming because nitrate is a very efficient fertilizer that is readily absorbed by crops . But the following decades revealed significant downsides to the use of nitrogen-based fertilizers. Because the compounds in fertilizer can make their way into soil, groundwater and nearby waterways, nitrogen-based fertilizers have emerged as the main source of nitrate contamination in drinking water. Now, a new report from the Environmental Working Group (EWG) finds that around 18% of the United States population relies on drinking water with elevated nitrate levels in drinking water , which the EWG defines as levels above 3 milligrams per liter (mg/L). Related The Moms Vs. The Multinational Nitrate is a naturally occurring compound that exists in plants , rainwater and groundwater . However, the rise of industrial agriculture after World War II has accelerated nitrate contamination in the environment to levels far beyond those found naturally in the nitrogen cycle. And that’s a problem, because high levels of nitrate have been linked to increased risk of cancer, birth defects and thyroid disease .
One study found that if Americans reduced their meat consumption by just 10%, nitrate levels in groundwater would fall by up to 20% due to less livestock manure and less fertilizer needed for feed crops. Corn is a prime example: It requires nitrogen to grow , but unlike many other plants, “there’s no amount of nitrogen that can hurt the crop.” This, Anne Schechinger, who led the EWG analysis as the group’s senior director for agriculture and climate research, says, can lead to farmers overapplying nitrogen-based fertilizers to corn, resulting in nitrogen-saturated soil and, eventually, nitrate in drinking water.
“When you have a lot of animal facilities in a small area, there’s just not enough farm fields to apply the manure to dispose of it without it being overapplied,” Schechinger tells Sentient. “So you will see manure often being overapplied to the same farm fields, like in Iowa, here in Minnesota, and that can definitely contribute to nitrate in drinking water .”
In the United States, the problem is exacerbated by the federal government’s massive financial incentives for corn farmers, she adds. Corn, most of which goes to livestock feed or ethanol fuel , was the most heavily subsidized crop in 2024 , according to USAFacts. “When we have government policies like farm subsidies and crop insurance that really pay farmers to grow corn, you’re going to have more corn on the landscape,” Schechinger says. “So that’s a big driver of this problem.”
There’s little question that high nitrate levels can cause health problems in human health, but research and public policies have not provided clear or consistent guidance on how much is too much. High levels of nitrate have been linked to increased risk of cancer, birth defects and thyroid disease. The EPA’s legal limit for nitrate in drinking water is 10mg/L , known as the maximum contaminant limit, or MCL. The agency established this threshold in 1962 to reduce the risk of acute blue baby syndrome, a condition that’s most common in babies, in which excess nitrate leads to blood without enough oxygen . However, more recent studies show there are other serious health risks at much lower levels of nitrate than the MCL. The Technical University of Denmark’s National Food Institute recently issued a report for the Ministry of Environment and Gender Equality of Denmark advising that a nitrate level of 1.4 mg/L should reduce the risk of colon cancer and developmental issues from long-term exposure to nitrate in drinking water. The Minnesota Department of Health states that nitrate levels above 3mg/L suggests the water is contaminated from human activities, and those levels could rise over time. The Environmental Working Group looked at water systems with that level or more in its most recent analysis.
The EWG reports that almost one in five people in the United States may be drinking nitrate-contaminated tap water, but that’s likely an understatement, as the analysis included only public water systems . Although the majority of tap water in the U.S. comes from public water, many people living in rural regions with high nitrate pollution use well water, which wasn’t included in the EWG analysis
In Iowa, for example, in 2022, 7.6% of residents rely on well water, and in 2020, more than 96,000 wells were in use in the state. That could be significant given that Iowa has one of the highest cancer rates in the country, and a March study found that this is in part linked to — you guessed it — elevated nitrate levels in the state’s drinking water .
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