What is nitrate?
Nitrate (NO3) is a naturally occurring form of nitrogen (N) which is very mobile in water. Because nitrate is tasteless and odorless, water must be chemically tested to determine nitrate contamination. Nitrogen is essential for plant growth and is often added to the soil in fertilizer to improve plant productivity. Nitrate is easily dissolved in water, which means that it is difficult to remove from water.
What happens to nitrate when it enters the environment?
Water moving down through the soil after a rainfall or irrigation carries with it dissolved nitrate down into the ground water table. This is one way that nitrate enters the water supplies of many homeowners who use wells or springs, and many of these residential wells contain nitrate at levels exceeding the safe drinking water standards.
How might I be exposed to nitrate?
Potential sources of nitrate include septic systems, animal waste, commercial fertilizer, and decaying organic matter. Often the nitrate is in the form of ammonia or protein first, which through contact with oxygen and certain bacteria, converts it to the oxidized form we know as nitrate. Sources of nitrate from wastewater include urea, ammonia cleaners, food solids and bacterial cells. It may also result from the breakdown of organic matter buried in the soil.Surface water which comes in contact with a source of nitrate and then moves downward through the soil will carry nitrate into the groundwater. Shallow wells are very susceptible to nitrate contamination because there is less soil and rock to serve as a natural filter between the soil surface and the ground water supply. Nitrate contamination levels may also vary with the time of year depending on the source of the pollutant. The best method for limiting nitrate in well water is source control.
Several measures may be taken to protect your well from direct contamination by surface water.
- Earth berms should be built to divert surface runoff away from the wellhead.
- The well casing should extend above the ground. If the casing was cut off below ground, an extension may be welded onto the the top of the existing casing.
- Proper well protection also includes grouting around the outside of the well casing and placing a concrete slab around the wellhead.
- Avoiding overdosing of fertilizer near the well and maintaining the required separation distances between septic tank leach fields and the well.
- Ideally, drinking water supplies (wells or springs) should be up hill and at least 100 feet away from all possible sources of contamination. Remember that any fertilizers or organic materials which are placed near a well are potential contamination sources for your water. It takes only a very small quantity of nitrate entering your water supply to raise the concentration to an unsafe level.
Due to its solubility in water and negative ionic charge, nitrate is not readily removed by filtration and other common home water treatment systems, such as softening or iron filtration. The source of nitrate contamination should be identified and eliminated whenever possible because the treatment of drinking water to remove nitrate is expensive. Take into consideration not only the initial purchase price of the treatment system, but also the cost of regular maintenance to that system. Nitrate can be removed by a special anion exchange filter which contains a media with a strong affinity for negatively charged ions in water, or by a reverse osmosis treatment system or distillation.
- Ion exchange introduces another substance, normally chloride, to "trade places" with nitrate in water.
- Reverse osmosis forces water under pressure through a membrane to filter out contaminants.
- Distillation boils water, then catches and condenses the steam while nitrate and other minerals remain in the boiling tank.
- Simple household treatment procedures such as boiling, filtration, disinfection, and water softening do not remove nitrate from water.
For more information on well protection, water quality testing and water treatment systems, contact your local Alaska Department of Environmental Conservation (ADEC) office.
How can nitrate affect my health?
Nitrate is generally not toxic to adults or children over the age of two or three years, however, infants under six months of age are susceptible to nitrate poisoning. This is due to the bacteria that live in the digestive tracts of newborn babies. These bacteria convert the nitrate (NO3) to nitrite (NO2) which can pass through the intestinal wall and into the blood stream. There the nitrite reacts and combines with the hemoglobin (he-moe-globe-bin) and interferes with the ability of the blood to carry oxygen and thus forms methemoglobin (meth-theme-oh-globe-in). Methemoglobin cannot carry oxygen, thus the affected baby suffers oxygen deficiency. The resulting condition is referred to as methemoglobinemia (meth-theme-moe-globe-in-knee-me-ah) commonly called "blue baby syndrome." The most noticeable symptom of nitrate poisoning is a bluish skin coloring, called cyanosis, particularly around the eyes and mouth. A baby with bluish skin should be taken to a medical facility immediately and tested for nitrate poisoning. The blood sample of an affected baby is chocolate brown instead of the normal bright red due to lack of hemoglobin.
Methemoglobinemia is relatively simple to treat, and in most reported cases, the affected baby makes a full recovery. Within several months after birth, the increasing level of hydrochloric acid in a baby's stomach kills most of the bacteria which convert nitrate to nitrite. By the age of six months, the digestive system is fully developed, and the risk of nitrate-induced methemoglobinemia is greatly reduced.
Consumption of high-nitrate water by pregnant women and nursing mothers is not as likely to be harmful to babies as direct consumption. The health effects in these cases are not completely understood, so it is recommended that pregnant women and nursing mothers limit nitrate consumption. Possible connections between nitrate and other health problems such as nervous system disorders, cancer, and heart damage are not well documented and are currently being researched.
ADEC limits the concentration of nitrate in public drinking water supplies to 10 ppm (parts per million or mg/l milligrams per liter) or 10,000 parts per billion µg/l (micrograms per liter) as nitrate-nitrogen (NO3-N). Ruminant animals (cattle and sheep) and infant monogastrics (baby pigs and baby chickens) are also susceptible to nitrate poisoning because of bacteria living in their digestive tracts. Horses, even though they are monogastric, are susceptible to nitrate poisoning throughout their lives. Livestock may be exposed to large quantities of nitrate in their feed as well as in contaminated water. Animals which are treated in time can recover fully from nitrate poisoning. Scientific studies indicate that water with greater than 25 mg/L NO3-N can be harmful to animals.