Your Drinking Water: Nitrates
Mary Lou Dixon
Former Extension Clothing & Textiles Specialist
Drinking water supplied by municipal water systems is monitored for many contaminants. As authorized by the 1974 Safe Drinking Water Act and its amendments, the United States Environmental Protection Agency (EPA) has established the concentration of certain drinking water contaminants allowed in public water supplies. However, if your water comes from a private well or a system that serves fewer than 25 people or has fewer than 15 service connections, it is not covered by these standards. The safety of the water from these sources is your responsibility.
Health Effects in Humans
Infants under six months of age are most affected by excess nitrates in the water. They may develop a condition called "methemoglobinemia" (blue baby syndrome), which causes a bluish color around the lips, spreads to the fingers, toes and face, and eventually covers the entire body. If the problem is not dealt with immediately, the baby can die.
This problem occurs because human infants have bacteria in their digestive systems that convert nitrate to nitrite, a very toxic substance. When nitrites are absorbed into the blood, they make the hemoglobin (red oxygen-carrying blood pigment) incapable of releasing the oxygen and mild symptoms of asphyxiation appear.
Babies consume large quantities of water in relation to their body weight. This is especially true when water is used to mix powdered or concentrated formulas or juices. Some feeding practices will minimize the intake of nitrate and nitrite. Breast feeding reduces risk, since little if any nitrate gets into breast milk. Formula that does not need to be diluted or formula mixed with low-nitrate water is also safe. Feed vegetables only as advised by your physician, since some of them are high in nitrates.
Health Effects in Livestock
Ruminant animals (such as cows and sheep) and infant monogastrics (such as baby pigs and chickens) also have nitrate-converting bacteria in their digestive systems. For this reason, nitrate poisoning affects them the same way it affects human babies. Because adult animals that are monogastric generally do not have nitrate-converting bacteria, they are not affected by methemoglobinemia. Horses, however, are an exception. They are monogastric, but they also have a cecum, which is similar to a rumen. The nitrate-converting bacteria living in the cecum increase the risk of nitrate poisoning.
Livestock are exposed to nitrate in feed as well as in water. Crops harvested after weather stress (such as drought) may have high nitrate contents. To protect livestock, feeds can be tested for nitrate before being used. High nitrate water is generally a health hazard to animals only when it adds to high nitrate concentrations already present in some feeds.
Symptoms of methemoglobinemia in animals include: lack of coordination, labored breathing, blue coloring of mucous membranes, vomiting and abortions. Dairy cows, however, can have reduced milk production without showing any other symptoms. If animals show signs of nitrate poisoning or a problem is suspected, consult a veterinarian immediately. If the problem is diagnosed in time, animals can be treated and will usually recover fully.
Reducing Nitrate Risk: Sources of Nitrogen Contaminants
Nitrate can get into ground water from the natural ecosystem, runoff from lawns and gardens, intensely-fertilized farm areas, livestock facilities, municipal and livestock waste treatment systems, septic systems, stored chicken litter systems, stored chicken litter and manure and lagoons.
Nitrogen is necessary for plant growth. It is present in native ecosystems and farming ecosystems. Anima manure, human wastes, compost, sewage sludge, legume crops and green manure crops are organic sources of nitrogen. Before this nitrogen can be used by plants, it must be converted to ammonium (NH4+) or nitrate (NO3-). Some nitrogen fertilizer contains nitrogen already in nitrate form. In other fertilizer, nitrogen is in the ammonium form, which is rapidly converted to nitrate by soil bacteria at soil temperatures above 50F. When any nitrogen is added to the soil, either from organic or inorganic sources, it becomes a part of the soil nitrogen cycle. The total amount of nitrogen generated through the processes of the nitrogen cycle is not necessarily used by plants. When the nitrogen supply is greater than the amount used by plants, potential for accumulation of nitrates in the soil and loss from the system exists, regardless of the original source.
Nitrates can be lost from the system by leaching, denitrification, volatilization and immobilization. From the standpoint of ground water quality, leaching of nitrates is the primary concern. Leaching is the downward movement of water and nitrates through the soil. The potential for nitrate leaching varies with soil type and rainfall or irrigation amounts. Sandy soils under high rainfall or irrigation have high leaching potential.
Nitrates, moved downward by leaching, can come from many sources, not necessarily just from fertilizers. Since the downward movement of nitrate through soils was taking place before the presence of humans, it's unrealistic to expect to stop or eliminate this movement. Careless use of fertilizer or improper management of the other nitrogen sources, however, can increase the rate of movement and magnitude of loss and must be avoided.
The use of nitrogen fertilizers, animal wastes and legume crops will continue to supply the nitrogen necessary for crop growth. However, there is no question that improved nitrogen management can reduce the potential for ground water contamination. Several practices are important to this goal.
First, growers need to have realistic yield goals. This may be the most effective means of decreasing nitrogen losses and reducing potential ground water pollution. Yield goals are the heart of fertilizer rate recommendations, especially nitrogen. Setting unrealistically high yield goals results in over-fertilization and a greater potential for nitrate carryover and potential contamination of ground water. To arrive at an optimum nitrogen fertilizer rate, growers must consider the crop being grown, the productive capacity of the soil and the moisture availability.
A second important point is to consider all potential nitrogen sources for a crop. These sources (previous legume crops, manure and residual nitrate already in soil) can all contribute to the total nitrogen needs of that crop. A third management practice is timing of nitrogen fertilizer application. On course-textured, highly permeable soils, split or sidedress applications of nitrogen generally result in increased nitrogen efficiency and decreased potential for nitrogen loss because of the shorter time between fertilizer application and crop uptake.
The last point to consider is the placement of nitrogen fertilizers or organic nitrogen sources such as sludges and manure. Any management practice that results in more of the applied nitrogen being taken up by the crop lessens the potential for nitrate contamination of ground water. Proper placement near the plant roots may increase efficiency of nitrogen uptake by the plants.
Many farmers overlook the nutrient value of their livestock manure and poultry litter. Both are very high in nutrient value and should be considered and subtracted from calculations of fertilizer needs. Manure and litter can reduce fertilizer costs and still provide enough nitrogen for crops, while leaving little nitrate to leach into the ground water.
Application practices an also affect the leaching of nitrate into the ground water. For instance, if the manure is applied sooner than the crop can use it, a large portion of the nitrate can be lost by leaching. Nitrogen sources should always be applied as near as possible to the time of most rapid plant growth. To save litter and manure for the best application time, a well-engineered and constructed storage unit should be used. It must be large enough to contain the waste without overflowing and must be properly designed to prevent seepage of nitrates to the ground water.
Properly sited and well-maintained septic systems prevent problems and greatly lower the risk of ground water contamination.
Because a septic system contains nitrate, one way to prevent an excessive buildup in ground water is to limit the number of septic systems in an area. Ideally, in new subdivisions, there should be one septic system per 1.5 acres where drinking water is supplied by individual wells; with some soils, even larger lots are desirable. Some older subdivisions with three or more septic systems per acre have ground water so polluted with nitrate that shallow wells can no longer be used for drinking water. The present solution is to drill a well deep enough to reach an unpolluted aquifer.
Septic systems are needed in areas not served by municipal or regional sewer systems. Septic systems typically consist of two parts: a tank and a drain field. Waste flows first to a septic tank. The solids settle and scum is held at the top of the tank by baffles. Liquid flows to the second part, the drain field. Bacteria in the septic tank convert part of the solids to liquid, which then flows on to the drain field. The drain field is a system of perforated piping that allows waste water to seep into the ground.
Proper design is important for a septic system. Minimum tank capacity is based on the number of bedrooms and the maximum number of persons served. The size of the drain field or the length of the drain field trenches must be able to handle the water generated by the household. Soil conditions at the home site are very important in designing the system. A percolation test determines the soil permeability, a measure of the potential for water movement through the soil.
A septic system may develop operative or maintenance problems due to several causes. A clogged drain field is the most common problem. This is caused by too much wastewater entering the tank, solids from the septic tank entering the drain field or roots growing into the pipes and stopping the flow. You can protect your system against premature failure by keeping damaging materials out of the system and having the tank pumped out regularly.
Poultry and Livestock Operations
The location of a well in relation to poultry and livestock operations is important. Nitrogen can leach through the soil or be carried in runoff from animal pens, poultry houses, stored litter and manure. Small lagoons must be located and constructed according to guidelines of the Natural Resources Conservation Service.
Proper well siting is important for safe drinking water. The Georgia Water Well Standards Act of 1985 requires that wells be located uphill as well as minimum distances from potential pollutant sources. These minimum horizontal distances are as follows:
|Animal or fowl enclosure
|Cesspool or seepage pit
|Septic tank absorption field
The Georgia Cooperative Extension Service recommends minimum horizontal distances for location of the following:
|Nitrogen storage tanks
|Poultry litter storage
The Georgia Water Well Standards Act also established minimum standards for well construction. These standards were designed to ensure that wells are constructed in such a manner that contaminants cannot directly enter a well and pollute the water. Among the standards is one that requires all domestic wells to be grouted in at least the top 10 feet below the ground surface. This means that the open annular space between the casing the borehole shall be filled with sand-cement grout or other impervious material to prevent the entrance of pollutants or contaminants to the well.
The well must also be protected by a sanitary seal or cover to prevent entrance of pollutants to the well. In addition, a four-inch thick concrete curbing should extend two feet in all directions from the well casing and slope away from the casing.
How to Check Your Water for Nitrate
A water test will determine if your well water is contaminated with nitrate. Tests are available through your county Extension office and private laboratories. The laboratory will provide instructions for collecting the sample. The charge is relatively low.
Shallow wells (100 feet or less) should be tested for nitrates annually. Other wells should be tested at least every three years.
Samples taken from Georgia wells show that nitrate contamination is usually limited to shallow wells. Contamination seldom occurs in deep wells. If you have a shallow well, take extra precautions for wellhead protection.
If Your Water Contains Nitrates
Once a water supply becomes contaminated with nitrate, it is very difficult and costly to treat. One solution is an alternate water source; either connect to a public water source or bore or drill a new well. Bottled water is a short-term solution to meet needs of drinking water and food preparation. It may be practical to treat household drinking water, but it would be very costly to treat the large volumes of water consumed by livestock.
There are two possible treatment methods to reduce or remove nitrates from water: demineralization and ion exchange. Demineralization removes nitrates and other minerals from the water and can be accomplished in two ways: distillation and reverse osmosis.
The distillation process involves boiling the water and capturing and condensing the steam back into water. Since the minerals do not evaporate, they remain concentrated in the boiling tank.
In reverse osmosis, the water is forced, under pressure, through a membrane that filters out minerals and nitrates.
Both of these methods are expensive and consequently they are usually employed to treat drinking water only. Water for other household uses should be left untreated.
The ion exchange system operates on the same principle as a water softener. The water passes through a column of resin beads in which nitrate and sulfate ions are exchanged for chloride ions. The resin is recharged by backwashing with a brine solution (sodium chloride) just as with a water softener. Since this process also removes sulfates, any sulfate in the water supply may interfere with nitrate removal. The resin may also make the water corrosive, requiring the water to go through a neutralizing system after going through the ion-exchange unit.
Lamond, Ray E., John S. Hickman, & G. Morgan Powell. 1989. Nitrates and Ground water. Cooperative Extension Service, Manhattan, Kansas: MF-857. Revised.
McCasland, Margaret, Nancy M. Trautmann, Keith S. Porter, & Robert J. Wagenet. Nitrate: Health Effects in Drinking Water. Cornell Cooperative Extension Service, Fact Sheet Page 400.02.
Nitrate in Drinking Water. Ohio Cooperative Extension Service, The Ohio State University, Columbus, OH: Bulletin 744, Agdex 750.
Georgia Water Well Standards Act of 1985.
Tyson, Anthony, & Kerry Harrison. Water Quality for Private Water Systems. Cooperative Extension Service, The University of Georgia, College of Agricultural & Environmental Sciences. Athens, GA: Bulletin 939, Revised 1989.
This material is based upon work supported by the U.S. Department of Agriculture Extension Service under special project number 90-EWQI-1-9235.
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