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Epidemiologic Notes and Reports Ammonia Contamination in a Milk Processing Plant -- Wisconsin

On October 30, 1985, the Wisconsin Division of Health was informed by the state poison control center of two elementary schoolchildren who presented with severe burning of the mouth and throat, as well as nausea. The symptoms developed within 1 hour of drinking milk packaged in half-pint containers with an expiration date of 11/9 from a Wisconsin milk processor. An investigation into the source of the milk determined that, 5 days previously, the milk processor had noted an ammonia leak in one of its cooling chambers, where approximately 250,000 half-pint milk containers with an expiration date of 11/9 were stored. The liquid ammonia, used to cool the tanks and stored under pressure, had sprayed about the storage tank for an undetermined number of hours. On discovery of the leak, the milk processors destroyed those cartons with obvious external damage to the paper and polyethylene containers. After tasting and smelling approximately 75 of the remaining 250,000 cartons, they determined the milk was safe and began distributing the product throughout the state.

Thirty milk containers with expiration date 11/9 were retrieved from the index elementary school. An analysis of these 30 containers by the Wisconsin Department of Agriculture identified seven (23%) that were contaminated with ammonia at levels ranging from 530 ppm to 1,524 ppm (normal = less than 15 ppm). The pH levels of these contaminated samples ranged from 9.1 to 10.0 (normal milk pH = 6.7-6.9).

On the basis of the initial reports of adverse symptoms associated with ingestion of the implicated milk, a case definition was established: the development of symptoms of irritation of the gastrointestinal tract, including the mouth, throat, or stomach, with onset within 1 hour of ingesting milk with expiration date 11/9 from the implicated processing plant.

Over the next 24 hours, 268 schools that had received milk with expiration date 11/9 from the implicated plant were contacted and instructed to withdraw these milk products from their schools. Additionally, each school was requested to inform the Wisconsin Division of Health if any child developed symptoms consistent with the case definition.

This surveillance effort identified approximately 520 cartons of milk ingested before notification. Twenty children fulfilling the case definition were identified (attack rate 3.9%). None required hospitalization, and no deaths occurred. Schools were instructed to return the unused cartons to the milk processer, where they were destroyed. This is the first reported incident of acute ammonia poisoning associated with contaminated milk. Reported by M Ziarnik, W Otto, T Sieger, MS, C Gannon, H Anderson, MD, Section of Environmental and Chronic Disease Epidemiology, Wisconsin Div of Health; Div of Field Svcs, Epidemiology Program Office, Div of Environmental Hazards and Health Effects, Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Ammonia (NH((3))) is a colorless gas with a characteristic strong, pungent, penetrating odor. It is one of the more common industrial chemicals; an estimated 20-30 million tons are used per year in the United States (1,2). It is widely used in fertilizer manufacture; other uses include dye, synthetic fiber, plastic, and nitric acid production, as well as refrigeration (2). In its aqueous form as ammonium hydroxide (NH((4((0H), it is extremely alkaline and can be highly caustic (2). Aqueous ammonia is 28% (280,000 ppm) ammonia, whereas household ammonia is 10% ammonia (100,000 ppm) (3). Mild to moderate ammonia exposures can produce headaches, salivation, burning of the throat, anosmia, nausea, vomiting, and substernal pain. Moderate doses may produce laryngospasm or bronchospasm (1).

The Occupational Safety and Health Administration standard for ammonia inhalation is 50 ppm as an 8-hour time-weighted average, but the National Institute for Occupational Safety and Health has recommended that 50 ppm be a 5-minute ceiling for exposure. The characteristic ammonia odor is readily perceptible below toxic levels. Most persons can detect an odor at 30 ppm, and eye and nose irritation become more severe as the levels increase to 50 ppm (4). The students involved in this incident were unable to smell the ammonia probably because the milk cartons were closed. The students first became aware of a problem when they felt burning in their throats.

Outbreaks of ammonia poisoning of milk, other beverages, or food have not been previously documented. The ammonium hydroxide apparently penetrated the milk cartons when the refrigerant tank leaked. Additional studies need to be done to determine how the ammonia contaminated the milk, and criteria need to be established to prevent contaminated milk from being distributed.

Recommendations for ammonia spills are as follows (1,5):

  1. Following ammonia ingestion, a conscious person should immediately be given large quantities of water to dilute the ammonia.

  2. Persons who have inhaled ammonia should be observed closely for visual disturbances, upper airway obstruction, and hypoxia.

  3. The area of the ammonia spill or leak should be ventilated to disperse the gas. A flow of gaseous ammonia should be stopped; liquid ammonia should be allowed to vaporize.

  4. Persons not wearing protective equipment and clothing should be restricted from areas of spills or leaks until the clean-up has been completed.


  1. Rom WN, Barkman H. Respiratory irritants. In: Rom WN, ed. Environmental and occupational medicine. Boston: Little, Brown and Company, 1983:273-4.

  2. Anderson HA. Irritant gases and fumes. In: Last JM, ed. Public health and preventive medicine, 11th ed. New York: Appleton-Century-Crofts, 1980:760-70.

  3. Wands RC. Alkaline materials. In: Clayton GD, Clayton FE, eds. Patty's industrial hygiene and toxicology. Third revised edition. New York: John Wiley & Sons, 1981:3045-70.

  4. National Institute for Occupational Safety and Health. Criteria for a recommended standard . . . occupational exposure to ammonia. Washington, D.C.: Public Health Service, CDC, 1974; publication no. (NIOSH) 74-136.

  5. Occupational health guidelines for ammonia. U.S. Department of Health and Human Services, U.S. Department of Labor, September 1978.

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