Farm Horizons, December 2013

Nitrogen based fertilizers may be causing groundwater nitrate contamination

By Tara Mathews

In order to assess the levels of nitrate in drinking water, which may pose risks for infants and those with specific medical conditions, the Minnesota Department of Agriculture (MDA) is testing wells in rural Minnesota for elevated levels of nitrates, which are thought to occur in areas where nitrogen-based fertilizers are used more often.

Testing will be done in vulnerable townships with the cooperation of local government and other agencies that can provide field support.

The program was initiated in 2010 when MDA convened an advisory committee and conducted an analysis of the issues related to nitrates in groundwater.

The committee reviewed Minnesota’s nitrogen fertilizer management plan (NFMP), according to Annie Felix-Gerth, Minnesota Department of Agriculture’s state program administrator-principal fertilizer management unit. Revisions based on input from the committee concluded that testing needed to be done.

In August 2013, MDA released the revised draft of the NFMP for public comment and began testing. Target areas for testing are determined by the township’s groundwater vulnerability information (how many farms in the area may use nitrogen-based crop fertilizers), and the proportion of land used for row crops.

Well owners, in the target areas, are contacted through mail and encouraged to participate in the free testing. Then, they are sent a sample kit with instructions and a questionnaire about their well, which contains inquiries about the well’s construction type, depth, age, and other details.

Then, the well owners send the sample and questionnaire to a certified lab, or to MDA, where ultra violet spectrophotometers are used to analyze the water sample.

So far, wells have been tested in Dakota, Wadena, Morrison, and Benton counties, but samples are expected to be examined from all over the state.

The goal is to have all vulnerable areas tested within the next 10 years.

Results of the tests are made available to residents through their township, excluding the well owner’s name and personal information.

Counties with test results confirming a higher concentration of nitrates will be contacted and are welcome to meet with the MDA to discuss options.

MDA’s plans to correct nitrate issues in problem areas include:

• promoting nitrogen fertilizer best management practices to protect groundwater;

• monitoring private wells over a 10-year period;

• conducting detailed assessments of water quality to determine severity and priority of problem areas; and

• conducting mitigation actions in high priority areas, starting with voluntary actions and progressing to regulatory actions if necessary.

The US Environmental Protection Agency has established a drinking water standard of 10 milligrams per liter of nitrate-nitrogen for public water supply systems.

The EPA uses this standard as a health risk limit for public water supply systems and as a guideline for private wells.

The major issue with nitrates in water is “methemoglobinemia,” also known as “blue baby syndrome,” Felix-Gerth noted.

Babies under six months of age are most susceptible to nitrate issues because their gastrointestinal tract reduces the nitrates to nitrite, a bacteria that is absorbed into the bloodstream.

Nitrite, then, impairs the blood’s ability to carry oxygen and causes infants to look blue in color. If the nitrate level is high in water consumed by the infant, and prompt medical attention is not received, death can occur, according to Felix-Gerth.

Pregnant women, people with a reduced amount of stomach acid, or people with blood or oxygen disorders are also susceptible to methemoglobinemia.

According to Felix-Gerth, most healthy adults can consume large levels of nitrate with no ill-effects. In fact, the average adult in the US consumes about 20 to 25 milligrams of nitrate every day in food, largely from vegetables.

References and more information can be found at www.mda.state.mn.us/chemicals/fertilizers/nutrient-mgmt/nitrogenplan.aspx.

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