U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

April 2021

Nitrogen runoff leads to preventable health outcomes, experts say

The Environmental Health Matters Initiative took a detailed look at farm and watershed-level solutions, as well as policies and markets.

The time is ripe for reducing health impacts of drinking water contaminated by nitrogen runoff from farms and feedlots. But there is no single solution that can do the trick, according to experts at a winter workshop series. The Environmental Health Matters Initiative (EHMI), supported by NIEHS, organized the five-session workshop, which was held Jan. 28 – Feb. 25.

creek winding through a green pasture The EHMI workshop explored actions that can be taken on several levels to address nitrogen contamination from agricultural activities. (Photo courtesy of Weldon Schloneger / Shutterstock.com)

Catherine Kling, Ph.D., an environmental economist from Cornell University, chaired the organizing committee. New technologies and changes to policies and behaviors could speed up reduction of health risks, she explained.

During the course of the meetings, experts in engineering, agronomy, economics, cancer, developmental biology, and more explored the scope of the problem and examined potential solutions.

Catherine Kling, Ph.D. Kling gave a heartfelt thank-you to the EHMI and NASEM staff for doing the heavy lifting to make the multi-session, online symposium a success. (Photo courtesy of Catherine Kling)

Drinking water hazards

Human exposure to chemically active nitrogen compounds occurs largely through drinking water from both public systems and private wells. According to Kling, reported violations of drinking water standards for nitrates have nearly doubled in the past decade.

Regulatory action cannot solve the problem, because the Clean Water Act excludes agricultural sources, and the Safe Drinking Water Act does not cover private wells. Although some states do regulate nitrogen, voluntary action is the primary approach nationwide.

Harming bodies, ecosystems

Elena Austin, Sc.D. Austin said that we ingest nitrogen through drinking water and foods in which it occurs naturally or is added, such as sodium nitrate in certain cured meats. (Photo courtesy of Veronica Brace / University of Washington)

Elena Austin, Sc.D., from the University of Washington, described harmful algae blooms and other ecological damage. Excessive nitrogen is also linked to cancers, reproductive impacts, hypothyroidism, and methemoglobinemia — blue baby syndrome — from inadequate oxygen in body tissues.

Other speakers displayed maps of areas with intensive farming, which overlapped with high nitrogen concentrations in surface and groundwater. Several expressed concerns for private well owners, who must bear the cost of testing and cleanup.

To complicate matters, Austin explained, epidemiological studies of outcomes such as colorectal cancer may exclude participants on private wells because water quality data are not available.

Why so much nitrogen?

Nitrogen, a critical nutrient for crops, is applied through fertilizers. It is also present in livestock manure, which may be stored in ponds or piles and applied to fields. When fields are fallow, such as in winter, excess nutrients run off into surface water and seep into groundwater.

Because it is so difficult to determine the exact amount of nitrogen needed, farmers may over-apply fertilizers, according to Steve Hoffman, from InDepth Agronomy in Wisconsin. For more precise application, farmers need multiple tests of factors that accurately measure availability, not just concentration. “It’s not enough to know what the soil is telling us, we also have to know what the plants are telling us,” he cautioned.

Measure, reduce, solve

Hoffman compared the scenario of a farmer getting through the growing season with just enough available nitrogen to that of taking a car trip and trying to reach the destination precisely as the gas gauge reaches empty. Measurement approaches include sensors and other tools and evaluating soil microbes.

Kenneth Cassman, Ph.D. Cassman explained that because nitrogen drives the biomass creation, producing more food for growing populations means applying more nitrogen, risking further degradation of water quality. (Photo courtesy of Kenneth Cassman)

When the discussion turned to ways to moderate runoff, such as financial or regulatory incentives, further complexities arose. Kenneth Cassman, Ph.D., from the University of Nebraska–Lincoln, said that progressive growers optimize 10 to 20 different crop and soil management practices, such as tillage, rotation, irrigation, pest management, and nutrients. “To come up with the impact of one factor out of everything else is almost impossible,” he said.

Cassman imagined a database to which every grower could anonymously report their yields and management practices. The potential payoff from such data, in terms of identifying what practices work best to improve both yields and efficiency of nitrogen use, would be comparable to that from thousands of field experiments every year, he explained.

During a discussion of incentives and other behavioral approaches (see sidebar), Thomas Hertel, Ph.D., from Purdue University, shared a global perspective. Economic drivers such as government subsidies, tariffs, and exports influence crop choice, he emphasized.

“If economic drivers dictate more intensification, [behavioral] tools won’t have much impact,” Hertel predicted. Population growth in Africa and income growth in Asia contribute to worsening nitrogen contamination even more than effects of climate change, he argued. “Our projections suggest the problem will get worse, not better,” said the agricultural economist.

These comprehensive discussions — including innovative ideas for nitrogen measurement, reduction, alternatives, and more — will be included in a summary document to be released by the National Academies of Sciences, Engineering, and Medicine (NASEM) later this summer.

Meanwhile, videos of each session are being posted to the workshop website as they are finalized.

nitrate concentrations in groundwater in the U.S.

Nitrate concentrations exceeding the 10 mg/L maximum contaminant level (MCL) are a nationwide concern. Concentrations are predicted to be lower in deeper groundwater, right, than in shallow, recently recharged groundwater. (Image courtesy of U.S. Geological Survey)

Back To Top