关键词：饮用水 硝酸 硝酸盐 硝酸盐氮 用水
Many Nebraskans have questions about the impact of nitrate in their drinking water. Water quality monitoring shows that nitrate is present in groundwater throughout much of Nebraska and that concentrations are increasing in some areas.
Nitrogen is essential for all living things as it is an essential component of protein. Nitrogen exists in the environment in many forms and changes forms as it moves through the nitrogen cycle. However, excessive concentrations of nitrate-nitrogen in drinking water can be hazardous to health, especially for infants and pregnant women.
Sources of Nitrate in Drinking Water
Nitrogen is the nutrient applied in the largest quantities for lawn and garden care and crop production. Feedlots, animal yards, septic systems, and other waste treatment systems are additional sources of nitrogen. Nitrogen occurs naturally in the soil in organic forms from decaying plant and animal residues.
Bacteria in the soil convert various forms of nitrogen to nitrate, a nitrogen/oxygen ion (NO3-). This is desirable as the majority of the nitrogen used by plants is absorbed in the nitrate form. However, nitrate is highly leachable and readily moves with water through the soil profile. If there is excessive rainfall or over-irrigation, nitrate will be leached below the plant's root zone and may eventually reach groundwater.
Nitrate-nitrogen (NO3-N) in groundwater may result from point sources such as sewage disposal systems and livestock facilities, from nonpoint sources such as fertilized cropland, parks, golf courses, lawns, and gardens, or from naturally occurring sources of nitrogen. Proper site selection for the location of domestic water wells, upslope and with adequate separation distances between wells and possible contamination sources, can reduce potential nitrate contamination of drinking water. Proper well construction and maintenance also reduces potential drinking water contamination.
Indications of Nitrate
Nitrate in water is undetectable without testing because it is colorless, odorless, and tasteless. A water test for nitrate is highly recommended for households with infants, pregnant women, nursing mothers, or elderly people. These groups are the most susceptible to nitrate.
Nitrate-nitrogen occurs naturally in groundwater, usually at concentrations far below a level of concern for drinking water safety. An initial test of a new water supply is needed to determine the baseline nitrate concentration. In addition, if the water supply has never been tested for nitrate, it should be tested.
Activities near the well potentially can contaminate the water supply, changing the nitrate concentration. Domestic wells near potential point sources of contamination, such as livestock facilities or sewage disposal areas, should be tested at least once a year to monitor changes in nitrate concentration. Depending on the location of the well relative to areas where nitrogen fertilizer is applied, follow-up testing to monitor changes from nonpoint sources may be conducted less often. All drinking water supplies should be checked at least every two or three years to assure that significant increases in nitrate concentrations are not occurring.
If a fertilizer or manure spill occurs, the spill should be cleaned up immediately and any wells near the spill should be tested. Unfortunately, any nitrate from the spill may not move through the soil profile quickly and annual testing is recommended to monitor the effects of the spill.
Potential Health Effects
The primary health hazard from drinking water with nitrate-nitrogen occurs when bacteria in the digestive system transforms nitrate to nitrite. The nitrite oxidizes iron in the hemoglobin of red blood cells to form methemoglobin, which lacks the oxygen-carrying ability of hemoglobin. This creates the condit
| 
