Introduction

Nitrates are chemicals made up of nitrogen and oxygen. They occur naturally in certain vegetables, preserved meat and soil, and are present in both commercial fertilizers and manure. The presence of nitrates in soil is necessary for plant growth. However, excess soil nitrates can contaminate water supplies, creating a potential health concern.
 

Nitrates in Soil

There are several processes that may lead to the presence of nitrates in soil:

• fixation of nitrogen by soil bacteria, as part of the nitrogen cycle.
• decay of organic matter in the soil.
• application of commercial fertilizers or manure to fields.
• leakage from domestic septic fields, municipal sewage systems, manure storage and livestock housing facilities.

The presence of nitrates in soil is essential for crop production. However, excess nitrates in soil can increase the risk of contamination of ground or surface water. This risk can be reduced through careful application of commercial fertilizers and manure at rates matching plant needs. Proper storage of fertilizers and manure is also required.

Livestock producers should exercise care to ensure that their operations do not contribute to excess soil nitrates.
 

Nitrates in Water

High nitrate levels in water may be encountered in agricultural areas, often in wells located near a long established barn site. Nitrates can leach from the soil into underground aquifers, contaminating well water. The extent of nitrate contamination, and how quickly it occurs, depends both on soil type and on depth of the water source. Nitrates can leach more easily in light sandy soils than in clay-based soils.

Contamination is more common in shallow wells than in wells drilled into deeper aquifers. Heavy rains and flooding also affect the amount of nitrate that reaches both ground and surface water.

There are two main concerns arising from the presence of nitrates in water:
 

• High nitrate levels in rivers and lakes can increase algae growth, degrading habitat for fish, other aquatic organisms, and wildlife.
• High nitrate levels in drinking water can have adverse effects on human health.
   

Health Concerns

Methemoglobinemia (also known as "Blue Baby Syndrome") is a health problem associated with nitrate ingestion. Most cases occur in infants under one year of age. Therefore, water high in nitrates should not be used to prepare infant formula or food, and should not be given to infants to drink. As nitrates may be present in breast milk, nursing mothers also should avoid ingestion of water high in nitrates. Pregnant women should also avoid using water with excess nitrates.

Nitrate is converted to nitrite in the stomach, then absorbed into the bloodstream. There it interferes with the ability of red blood cells to carry oxygen. Symptoms of "Blue Baby Syndrome" include cyanosis (bluish discoloration of the skin and mouth), shortness of breath and fatigue.

Evidence that other health problems are associated with nitrate ingestion is conflicting. Some studies suggest the possibility of association with stomach cancer, birth defects, hypertension, enlarged thyroid gland, and lymphoma, whereas other studies do not. There is not enough evidence at this time to draw firm conclusions.
 

Water Testing

In Manitoba, the recommended limit for nitrate in drinking water is 10 mg/L (nitrate measured as nitrogen). This is the same limit set by Health Canada, as well as by the U.S. Environmental Protection Agency and the World Health Organization.

Municipal water supplies are tested for nitrates to ensure that they are within recommended limits. Private wells should also be tested, by sending a sample to a private laboratory (look in the Yellow Pages under "Laboratories – Testing").

After an initial test is done, well water should be retested annually if someone using the well is under one year of age, or is pregnant, or a pregnancy is planned.

Otherwise, retesting should be carried out every 10 years. Owners of private wells with intermediate levels (greater than 2 mg/L but less than 10 mg/L nitrate measured as nitrogen) may wish to test more frequently.
 

Water with High Nitrate Levels

Boiling water does not reduce nitrates; instead it concentrates them, which increases the problem. Avoid using water with high nitrate levels for drinking; this is especially important for infants, nursing mothers and pregnant women. Do not use it for preparing infant formula or food. It is preferable not to use the water for cooking. Switch to bottled water or to a known safe source (such as a municipal supply) for these purposes. Water with high nitrate levels can be used safely for bathing, and for washing clothes and dishes.

Water treatment equipment  including reverse osmosis and ion exchange technology are available to reduce water nitrate levels. Sometimes the best long-term solution is to drill a new well. Contact Manitoba Water Resources for information on whether this may be a practical option in your situation.
 

• Excess soil nitrates can contaminate water supplies.
• High nitrate levels in drinking water can cause health problems, particularly for infants and in pregnancy.
• Because agricultural activities can contribute to excess nitrates, livestock producers and others involved in providing agricultural services must follow applicable guidelines and regulations to prevent this problem.

For further information about public issues refer to other titles in the series: "Living with Livestock Production" available from Manitoba Agriculture, Food and Rural Initiatives offices. More detailed information can be found on the Internet at www.gov.mb.ca/agriculture/livestock. Copies of the Farm Practices Guidelines for Hog Producers in Manitoba are available from Manitoba Agriculture, Food and Rural Initiatives offices in rural Manitoba and from Agriculture Publications at 8^th floor, 401 York Avenue, Winnipeg MB R3C 0P8 (FAX: 204-948-2498)