The treatment of food with ionizing radiation has been in practice for nearly a century since the first irradiation process patents were filed in 1905. Regular use of the technology in food processing started in 1963 when the U.S. Food and Drug Administration (FDA) approved the sale of irradiated wheat and wheat flour. Today irradiation treatment is used on a wide variety of food products and is regulated in the United States by the FDA under a Department of Health and Human Services regulation.
Irradiation of food has three main applications: extension of shelf life, elimination of insects, and the destruction of bacteria and other pathogens that cause foodborne illness. This final goal may have the most far-reaching implications for Americans; the U.S. Centers for Disease Control (CDC) estimate that seventy-six million Americans get sick, and five thousand die each year from illnesses caused by foodborne microorganisms, such as E. coli, Salmonella, the botulism toxin, and other pathogens responsible for food poisoning.
Irradiation technology involves exposing food to ionizing radiation. The radiation is generated from gamma rays emitted by cobalt-60 (60Co) or cesium-137 (137Cs), or from x rays or electron beams. The amount of radiation absorbed during irradiation processing is measured in units termed radiant energy absorbed (RADs). One hundred RADs is equivalent to one Gray (Gy). Depending on the food product being irradiated, treatment can range from 0.05 to 30 kGy. A dosimeter, or film badge, verifies the kGy dose. The ionizing radiation displaces electrons in the food, which slows cell division and kills bacteria and pests.
The irradiation process itself is relatively simple. Food is packed in totes or containers, which are typically placed on a conveyer belt. Beef and other foods that require refrigeration are loaded into insulated containers prior to treatment. The belt transports the food bins through a lead-lined irradiation cell or chamber, where they are exposed to the ionizing radiation that kills the microorganisms. Several trips through the chamber may be required for full irradiation. The length of the treatment depends upon the food being processed and the technology used, but each rotation takes only a few minutes.
The FDA has approved the use of irradiation for wheat and wheat powder, spices, crustaceans including lobsters, shrimp, and crab, enzyme preparations, vegetables, pork, fruits, poultry, beef, lamb, molluscan shellfish, sprouts, and goat meat. The FDA also approved the use of irradiation to control salmonella in fresh eggs.
Labeling guidelines introduced by the Codex Alimentarius Commission, an international food standards organization sponsored jointly by the United Nations Food and Agricultural Organization (FAO) and the World Health Organization (WHO), requires that all irradiated food products and ingredients be clearly labeled as such for consumers. Codex also created the radura, a voluntary international symbol that represents irradiation. In the United States the food irradiation process is regulated jointly by FDA and the U.S. Department of Agriculture (USDA). Facilities using radioactive sources such as cobalt-60 are also regulated by the Nuclear Regulatory Commission (NRC). The FDA regulates irradiation sources, levels, food types and packaging, as well as required recordkeeping and labeling. Records must be maintained and made available to FDA for one year beyond the shelf-life of the irradiated food to a maximum of three years. These records must describe all aspects of the treatment, and foods that have been irradiated must be labeled with the radura symbol and by the statement "treated with radiation" or "treated by irradiation." Food irradiation is endorsed as safe by the World Heath Organization and other international organizations.
Food that has been treated with ionizing energy typically looks and tastes the same as non-irradiated food. Just like a suitcase going through an airport x-ray machine, irradiated food does not come into direct contact with a radiation source and is not radioactive. However, depending on the strength and duration of the irradiation process, some slight changes in appearance and taste have been reported in some foods after treatment. Some of the flavor changes may be attributed to the generation of substances known as radiolytic products in irradiated foods.
When food products are irradiated, the energy displaces electrons in the food and forms compounds termed free radicals. The free radicals react with other molecules to form new stable compounds termed radiolytic products. Benzene (C6H6), formaldehyde (CH2O), and hydrogen peroxide (H2O2) are just a few of the radiolytic products that may form during the irradiation process. These substances are only present in minute amounts, however, and the FDA reports that 90 percent of all radiolytic products from irradiation are also found naturally in food.
The chemical change that creates radiolytic products also occurs in other food processing methods, such as canning or cooking. However, about 10 percent of the radiolytic products found in irradiated food are unique to the irradiation process, and little is known about the effects that they may have on human health. It should be noted, however, that the WHO, the American Medical Association (AMA), the American Dietetic Association (ADA), and a host of other professional healthcare organizations endorse the use of irradiation as a food safety measure.
Treating fruit and vegetables with irradiation can also eliminate the need for chemical fumigation after harvesting. Produce shelf life is extended by the reduction and elimination of organisms that cause spoilage. It also slows cell division, thus delaying the ripening process, and in some types of produce irradiation extends the shelf life for up to a week. Advocates of irradiation claim that it is a safe alternative to the use of fumigants, several of which have been banned in the United States.
Nevertheless, irradiation removes some of the nutrients from foods, particularly vitamins A, C, E, and the B- complex vitamins. Whether the extent of this nutrient loss is significant enough to be harmful is debatable. Advocates of irradiation say the loss is insignificant, and standard methods of cooking can destroy these same vitamins. However, research suggests that cooking an irradiated food may further increase the loss of nutrients.
Although research studies have shown that consuming irradiated foods does not cause carcinogenic, mutagenic, or toxic effects, critics of irradiation question the long-term safety of consumption of irradiated food and their associated radiolytic products. The changes in texture, flavor, and odor as well as the reduction in nutritional content in irradiated foods are also issues that critics cite in opposing irradiation. These critics charge that the technology does nothing to address the unsanitary food processing practices and inadequate inspection programs that breed foodborne pathogens. Additionally, a potential type of carcinogen termed 2-alkylcyclobutanone (2-ACB) has been identified in foods as a product of irradiation and is being studied with regard to health effects.
Even if irradiation is 100 percent safe and beneficial, there are numerous environmental concerns. Many opponents of irradiation cite the proliferation of radioactive material and the environmental hazards. The mining and on-site processing of radioactive materials are devastating to regional ecosystems. There are also safety hazards associated with the transportation of radioactive material, production of isotopes, and disposal.