Ammoniation of Aflatoxin-Contaminated Corn

Aflatoxins are toxic compounds produced in contaminated grains by the fungi Aspergillus flavus and Aspergillus parasiticus. Animals that consume high levels of these toxins may develop various health problems, depending on their susceptibility.

Treating Corn with Ammonia

Corn contaminated with aflatoxin can be treated with ammonia to destroy the toxin. This will maintain the food quality of the grain, at least for on-site use. Either anhydrous ammonia, NH₃ (gas), or aqua-ammonia, NH₄OH (liquid), can be used.

Ammonia treatment is economical for low volume feeding operations; however, proper equipment must be used and all safety precautions carefully observed. It should be noted that corn treated with ammonia turns dark because the sugar (altrose) is caramelized. Also, the grain temperature increases about 10 degrees at the time of treatment.

The FDA has not yet approved the interstate shipment of ammonia-treated grain. This does not prevent its use on the farm. The FDA has, however, approved the ammonia treatment of cottonseed meal to be used as a feed additive. Some questions still exist as to the possible side effects of ammoniation on livestock, although no problems have yet emerged in feeding trials. Cattle can utilize the ammonia in corn just as they do when urea is added as a feed supplement. Swine and poultry, however, cannot utilize the ammonia and may be reluctant (at least initially) to eat corn with an ammonia odor.

Safety Precautions with Ammonia

Ammonia can be deadly when used improperly. Always follow safety precautions.

Ammonia gas can irritate the eyes. Prolonged inhalation can cause suffocation and death. Anhydrous ammonia also can cause freeze burn on the skin because it is both caustic and has a low boiling point. A large supply of water should be close at hand for flushing eyes or skin if an accident occurs.

When handling anhydrous ammonia, always wear goggles, gloves and a long-sleeved shirt. Avoid breathing ammonia vapors. Never allow a spark, flame or electrical equipment near the ammonia.

Ammonia is corrosive to metal (copper and brass fittings cannot be used) and reacts with galvanized metal, making ammonia very corrosive to grain bins.

Ammonia cannot be forced into a grain-filled bin with a drying or aerating fan. Not only is the practice dangerous and destructive, but the ammonia readily escapes and has little benefit in detoxifying corn.

When handling corn with high levels of aflatoxin, always wear a dust mask. The contaminated dust is hazardous. Where dust is a major problem, as in grain cleaning, a self-contained respirator should be worn.

Government Regulations

All provisions of the Occupational Safety and Health Act (OSHA) regulations (29CFR 1910.111) must be followed when working with anhydrous ammonia.

• Children younger than 16 are not allowed to handle, transport or transfer anhydrous ammonia.

• Only equipment that is specially designed for use with anhydrous ammonia can be used. This includes tanks, valves, lines, etc.

• Rubber gloves and tight-fitting, unvented goggles must be worn when transferring anhydrous ammonia.

• At least 5 gallons of water must be carried on vehicles transporting anhydrous ammonia.

• Trailers transporting anhydrous ammonia on public roads must display SMV symbols.

Most agricultural uses of anhydrous ammonia are exempt from Texas Air Control Board permitting, provided it is used more than 1/4 mile from another residence or a recreation area, and provided that ammonia vapors are not released into the atmosphere. All vapor should be bled into an adequate volume of water and never released directly into the atmosphere. Always work downwind of residential areas and livestock in case of accidental releases.

A copy of the rules that govern the use of anhydrous ammonia may be obtained from OSHA headquarters in Washington, D.C. or from an anhydrous ammonia dealer.

Ammoniation of aflatoxin-contaminated corn is approved for Texas under certain conditions. The corn to be ammoniated must not have an initial aflatoxin level of over 1000 ppb. After the ammoniation process, the aflatoxin level must not exceed 200 ppb, and then can only be used for feedlot cattle in Texas. It is not legal for interstate transport. If the corn is to be used for deer corn, the aflatoxin level must not exceed 100 ppb. A permit to ammoniate corn must be obtained from the Office of the State Chemist (tel. 409-845-1121) before the process is attempted.

Ammonia Application Rate

The amount of ammonia needed to destroy aflatoxin depends on the temperature and moisture content of the grain, as well as the level of contamination. Ammonia has a strong affinity for moisture and readily combines with the moisture in grain at warm temperatures. For this reason, treatment is more effective when the moisture content of the grain is higher than 13% and the temperature is higher than 60 degrees F. Grain with less than 13% moisture and at cooler temperatures can be detoxified with ammonia, but a longer exposure time will be required. Corn kernels with more than 17% moisture will likely stick together when the ammonia caramelizes the sugar in the corn. Once it is broken apart the corn will flow freely.

The amount of ammonia needed for treatment can vary from 0.5% to 1.5% of the dry weight of the corn (48 pounds per bushel). The lower rate is recommended for corn with more than 15% moisture at grain temperatures higher than 80 degrees F and with aflatoxin levels below 200 ppb. The 1.5 % rate is recommended for lower temperatures and moisture levels, and/or higher aflatoxin levels. Treatment usually requires 5 to 7 days; then samples of the corn should be analyzed for aflatoxin levels.

The quantity of ammonia needed for various application rates is shown in Table 1.

Table 1. Quantity of ammonia at various treatment rates for corn with 15 percent moisture.

To accurately measure the ammonia used, the tank should be weighed before and after injecting the ammonia. An estimate of the amount of ammonia used can be made from the ammonia level indicator on the tank, or by calculating the amount of ammonia dispensed as a function of temperature/pressure relationship, as shown in Table 2.

Table 2. Properties of anhydrous ammonia (NH₃).

Treatment Methods

When treating corn with either anhydrous or aqua-ammonia, the grain must be sealed in an air-tight container to prevent vapor from escaping.

Anhydrous ammonia can be injected into the bottom of a hopper bottom wagon. If a large volume of corn is being treated the gas must be recirculated to uniformly distribute the gas throughout the corn. Sometimes the ammonia tank, lines or valves freeze when liquid ammonia (NH₃) converts to a gas. If this occurs, close the valve, wait for the ice to thaw, and then continue application. Using a cold-flow converter or an ammonia tank containing two or three times the quantity needed may prevent freezing of the lines.

Aqua-ammonia can be sprayed directly on corn when loading a sealed container with a grain auger. The application rate is determined by calculating the conveyor rate (bushels per minute) and flow rate (ounces per minute). The spray nozzles should be elevated above the auger housing to uniformly disperse ammonia into the flowing grain. No recirculation of the ammonia gas is required when corn is treated in this way, but the corn must be sealed until treatment is complete (about 7 days under favorable conditions) to prevent the ammonia from escaping. The application of aqua-ammonia will add about 2 % moisture to the corn for every percent of actual ammonia injected. This may also eliminate the need for rewetting dry corn.

Small Batches

Small batches of corn can be treated in sealed grain trailers or hopper bottom wagons. Before filling the wagon with grain, line it with a cylindrical, 6-milileter polyethylene bag. Put the bottom open end of the bag through the side discharge door to allow grain discharge after treatment. Insert a hose through the open end of the plastic and into the bottom of the hopper. A PVC pipe with holes in the sides can be attached to the supply hose and used to distribute vapor in the bottom of the bin. Gather the plastic and tie it tightly around the hose. Then close the door.

Drop the top portion of the bag over the sides of the wagon. After filling the wagon with grain, gather the plastic together and tie it tightly like a big sack, sealing the grain inside. Inject anhydrous ammonia through the hose until the desired rate has been applied. After 5 to 7 days, analyze a corn sample for aflatoxin level.

Large Batches

Large batches of corn, or corn in flat bottom containers, also can be treated with anhydrous ammonia. A 6-milileter polyethylene sheet totally encloses the grain to prevent ammonia from escaping. A central duct runs under the center of the grain pile and lateral ducts of 6-inch perforated plastic drain tile are connected at right angles to the central duct. The laterals are spaced 24 inches apart and extend to within 2 feet of the edge of the pile. A flexible return duct is sealed to the top of the plastic cover. A squirrel cage fan powered by an electric motor recirculates ammonia from the flexible duct at the top of the pile, forcing it under the corn through the central duct underneath.

Ammonia is injected into the pressurized duct beneath the grain pile. The fan and motor should be sized to deliver ½ cfm per bushel treated. Ammonia vapor should be recirculated for about 48 hours. After that time the fan can be turned off except for short periods when it is needed to distribute heat and moisture. The treatment time varies from 1 to 3 weeks, depending on grain temperature and moisture.

When sampling indicates that aflatoxin has been reduced to acceptable levels, the return hose can be disconnected and the fan operated to aerate the grain. Aeration removes some of the ammonia odor and makes the corn more acceptable to swine and poultry.

FIRST AID

FLUSHING WITH LARGE QUANTITIES OF WATER IS THE MAIN FIRST AID TREATMENT FOR EXPOSURE TO ANHYDROUS AMMONIA.

Inhalation. If ammonia gas is inhaled, the victim should immediately go or be assisted to an uncontaminated area. If the exposure was very brief or to a low concentration of ammonia, further treatment usually is unnecessary. However, medical assistance should be obtained if the victim has chest pains, pains when breathing or a persisting cough. A physician should be called immediately and thoroughly informed about the accident. If oxygen is available, it can be administered by a trained individual until medical help arrives. If the victim is not breathing, artificial respiration should be started immediately. The victim should be kept warm and at rest until medical help can be obtained.

Eye contact. Even if only a small amount of ammonia gets in the eyes they should be flushed for at least 15 minutes with clean, lukewarm water. The entire eye surface and inner linings of the eyelids must be flushed, so it is necessary to hold the eyes open. Begin flushing as soon as possible. One emergency method is to duck your head in a container of water and rapidly blink and move your eyes around. Or, as a precaution, workers can carry clean water with them in small, squeezable plastic containers. BUT THIS SMALL AMOUNT IS NOT SUFFICIENT. Eyes must be flushed for at least 15 minutes. If medical help is not available by then, flushing should continue.

Skin Contact. Skin exposed to ammonia also should be thoroughly flushed with water. If clothes become saturated with liquid ammonia they will probably freeze to the skin. With any skin exposure, immediately get in a shower or jump into a stock tank or any other water source. Jump in with your clothes on and only remove them after they are unfrozen and can be pulled freely from the skin. Do not apply medications to ammonia burns. Get medical help as soon as possible.

Swallowing. In the unlikely event ammonia is swallowed, call a doctor immediately. If the victim is conscious he should swallow large quantities of water. When vomiting begins, place the victim face down with the head lower than the hips to vent vomitus from entering the lungs. If a victim is in shock or pain or is unconscious, do not give him water or induce vomiting.

References

Hammond, Cecil. Treating Aflatoxin Contaminated Corn with Ammonia. Cooperative Extension Service, University of Georgia, Athens, Georgia. Bulletin 869, March 1987.

Mycotoxins in Feed and Food-Producing Crops. B-1279. Texas Agricultural Extension Service, The Texas A&M University System, College Station, Texas.

Glover, John W. Decontamination of Aflatoxin Corn with Ammonia. North Carolina Agricultural Extension Service, North Carolina State University, Raleigh, North Carolina. AG-233, December 1980.