Nitrogen-based fertilizers applied to corn and other crops in Wisconsin is partially to blame for unsafe levels of nitrate found in wells around the state, researchers say. Credit: Jim Massey / The Country Today

Nitrate is a compound made up of nitrogen and oxygen. It is formed when nitrogen from ammonia or other sources combines with oxygen in water.

Nitrate is naturally found in plants and in vegetables and can be found in groundwater, depending on how much fertilizer and manure is applied to fields.

According to the U.S. Environmental Protection Agency, most adults who are eating a balanced diet may consume 10 to 25 milligrams of nitrate or nitrogen per day in their food. Most comes from leafy vegetables such as lettuce, cabbage, celery and spinach but also from cured meats such as bacon.

Additional exposure to nitrate from contaminated drinking water may pose significant health risks. Potentially fatal “blue baby syndrome” has been linked to the presence of nitrate in drinking water. It is also suspected of causing thyroid disease, diabetes and certain types of cancer.

Common sources of nitrate include nitrogen fertilizers, manure, septic systems and sewage treatment practices. Nitrate can be carried into the groundwater by rainwater and melting snow that percolates through the soil and bedrock into the underlying aquifer.

Nitrate can also run off fields and pollute surface water, causing overstimulation of aquatic plants and algae, resulting in unsightly scum and occasional fish kills.

Sources: Wisconsin Department of Natural Resources Nitrate in Drinking Water fact sheet and U.S. Geological Survey Water Science School website.

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Hall, a co-founder of the Wisconsin Center for Investigative Journalism, joined the staff as managing editor in June 2015. She worked at the Wisconsin State Journal for 24 years as an editor and reporter focusing on projects and investigations. Previously she was a reporter for eight years at The Arizona Republic in Phoenix, where she covered city government, schools and the environment. During her 35-year journalism career, Hall has won more than three dozen local, state and national awards for her work, and is a member of Investigative Reporters and Editors. She is based in Madison, Wisconsin. She can be reached at