Nitrate (NO3-) is a water-soluble molecule made up of nitrogen and oxygen. It is formed when nitrogen from ammonia or other sources combines with oxygenated water. Nitrate is a natural constituent of plants and is found in vegetables at varying levels depending on the amount of fertilizer applied and on other growing conditions. According to the World Health Organization, most adults ingest 20-70 milligrams of nitrate- nitrogen per day with most of this coming from foods like lettuce, celery, beets, and spinach. When foods containing nitrate are eaten as part of a balanced diet the nitrate exposure is not thought to be harmful.
Water naturally contains less than 1 milligram of nitrate-nitrogen per liter and is not a major source of exposure. Higher levels indicate that the water has been contaminated. Common sources of nitrate contamination include fertilizers, animal wastes, septic tanks, municipal sewage treatment systems, and decaying plant debris.
The ability of nitrate to enter well water depends on the type of soil and bedrock present, and on the depth and construction of the well. State and federal laws set the maximum allowable level of nitrate-nitrogen in public drinking water at 10 milligrams per liter (10 parts per million). These laws apply to all city and village water supplies and are used as an advisory for private wells.
Infants who are fed water or formula made with water that is high in nitrate can develop a condition that doctors call methemoglobinemia. The condition is also called "blue baby syndrome" because the skin appears blue-gray or lavender in color. This color change is caused by a lack of oxygen in the blood.
All infants under six months of age are at risk of nitrate poisoning. Some babies may be more sensitive than others. Infants suffering from "blue baby syndrome" need immediate medical care because the condition can lead to coma and death if it is not treated promptly.
When nursing mothers ingest water that contains nitrate, the amount of nitrate in breast milk may increase. Although no confirmed cases of "blue-baby syndrome" have been associated with nitrate in breast milk, it may be advisable for nursing women to avoid drinking water that contains more than 50 milligrams per liter nitrate-nitrogen.
Some scientific studies have found evidence suggesting that women who drink nitrate-contaminated water during pregnancy are more likely to have babies with birth defects. Nitrate ingested by the mother may also lower the amount of oxygen available to the fetus.
People who have heart or lung disease, certain inherited enzyme defects, or cancer may be more sensitive to the toxic effects of nitrate than others. In addition, some experts believe that long-term ingestion of water high in nitrate may increase the risk of certain types of cancer.
When laboratory tests determine that water contains more than 10 milligrams per liter nitrate-nitrogen, the following actions are recommended:
The only way to determine the nitrate level in water is to have a water sample tested by a certified laboratory. Public water supplies are tested regularly for the presence of nitrate. A nitrate test is recommended for all newly constructed private wells and wells that have not been tested during the past five years. Testing is also recommended for wells used by pregnant women and is essential for wells that serve infants under six months of age.
Wells with nitrate-nitrogen levels below five milligrams per liter should be retested every few years. If the levels are between five and 10 milligrams per liter, owners should consider testing more often to check for seasonal changes. Additional testing may also be useful if there are any known sources of nitrate or if high nitrate levels are detected in nearby wells.
Wisconsin Department of Natural Resources (WDNR)
WDNR - What is Nitrate Brochure