The Use of Irradiation for Post-Harvest and Quarantine Commodity Control

In both domestic and international agricultural markets, expanding the use of irradiation can help to reduce the need for methyl bromide for the post-harvest control of insect pests. Currently, irradiation treatments have been approved for a variety of food use applications by the U.S. Food and Drug Administration (FDA). The United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine Service (PPQ) has outlined policy positions regarding the development and use of irradiation treatments for quarantine pest control, and is actively seeking ways to incorporate additional irradiation uses into their plant protection program (USDA 1995, USDA 1996a, 1996b, 1996c). Furthermore, research has been conducted to determine optimal irradiation dosages for controlling pests and maintaining produce quality, a variety of irradiation technologies have been commercialized worldwide, and there is extensive data available on the capital, operating, and per unit treatment costs associated with irradiation projects. In addition, recent market studies have generally found that consumers are willing to buy irradiated produce (Morrison 1992). In fact, research conducted in Florida indicated that consumer acceptance for such commodities is high, and many actually prefer the methods to traditional chemical fumigation (Marcotte 1992).

Food irradiation is a process by which products are exposed to ionizing radiation to sterilize or kill insects and microbial pests by damaging their DNA. The FDA permits three types of ionizing radiation to be used on foods: gamma rays from radioactive cobalt-60 and cesium-137, high energy electrons, and x-rays. Although all three have similar effects, gamma rays are most commonly used in food irradiation because of their ability to deeply penetrate pallet loads of food (Forsythe and Evangelou 1993, Morrison 1989). Gamma irradiation equipment irradiates packaged or bulk commodities by exposing the product to gamma energy from cobalt-60 in closed chambers, which range in size from single modular pallet irradiators to large research or contract irradiation facilities. Absorbed dose is measured as the quantity of radiation imparted per unit of mass of a specified material. The unit of absorbed dose is the gray (Gy) where 1 gray is equivalent to 1 joule per kilogram (ICGFI 1991, NAPPO 1996).

Benefits of Irradiation

There are several benefits of expanding the use of irradiation treatments to control pests infesting perishable and non-perishable commodities in the United States. First, irradiation may be useful for preventing the movement of quarantine species possibly present in trade commodities into areas where such pests are not established (USDA 1996b). From an economic standpoint, irradiation, therefore, has the potential to increase trade opportunities between nations, especially from major fruit and vegetable producing countries with high infestation rates (ICGFI 1994). Irradiation also can be used to reduce the risk of infection and disease caused by foodborne pathogens (Moy 1991). Although consumers have concerns associated with the safety of irradiation technology and its effects on food, research indicates that properly irradiated food does not pose a risk to consumers (Thorne 1983, OTA 1985). In fact, the potential for human health impacts from exposure to foodborne pathogens is believed to be substantially reduced through the use of irradiation (OTA 1985, Morrison et al. 1992).

In addition, by interfering with cell division, irradiation inhibits sprouting in tubers, bulbs, and root vegetables (potatoes, onions) and can delay ripening of some tropical fruits, resulting in an extended shelf life for many foods. In turn, longer shelf lives will enhance trade opportunities between nations by extending time constraints under which fresh produce must be delivered to more distant geographic markets or by allowing the use of slower and less expensive modes of transportation (Kader 1986, Moy 1991, OTA 1985).

Uses of Irradiation

Irradiation is used as a pest control tool in over 40 countries, including the United States, Russia, Great Britian and Brazil (Nordion 1995). The disinfestation of grain as it enters the Soviet Union at the Black Sea Port of Odessa, estimated at over 500,000 metric tons per year, is one of the largest documented commercial industrial applications (Giddings 1991). In the United States, the FDA approved low-doses irradiation for wheat, wheat flour, and potatoes in the early 1960s. In 1984 and 1985, the FDA approved irradiation of spices and pork, and in the following year, approved low-dose irradiation (up to 1 kGy) to control insects in foods and extend the shelf life of fresh fruits and vegetables (Kader 1986, Morrison 1989). Irradiation has also been used to sterilize food for U.S. hospital patients and astronauts (Morrison 1992). Further, irradiation disinfestation has been found to be effective for treatment of dried fruits, spices, nuts, cut flowers, lumber, and wood chips (ICGFI 1994, Marcotte 1992, Morrison 1989, OTA 1985). At doses below 1 kGy, irradiation is an effective treatment against various species of fruit flies, mango seed weevils, naval orange worms, potato tuber moths, codling moths, and other insect species of significance to quarantine situations (Kader 1986). For irradiation to be approved as a quarantine treatment in the United States, either as a single treatment, or as part of a combined approach (e.g., systems approach), USDA/APHIS/PPQ will require that the level of efficacy be scientifically demonstrated, and that efficacy be demonstrated under commercial settings (USDA 1996b).

Effective Dosages and Impact on Produce Quality

Because foods differ in their radiation dose requirements, densities, as well as specific packing configurations (Kunstadt et al. 1990), research has focused on insect mortality, morbidity, and sterilization, as well as the effects of ionizing radiation on fruit quality. The effects of irradiation depend on the dose absorbed. Low doses (up to 1 kGy) inhibit sprouting in tuber, bulb and root vegetables, inhibit the growth of asparagus and mushrooms, and delay physiological processes (ripening, etc.) in such fruits as banana, mango, and papaya. Medium doses (1 to 10 kGy) extend the shelf life of commodities, eliminate spoilage and pathogenic microorganisms, and improve the technical properties of food. Lastly, high doses (10 to 50 kGy) can be used for industrial sterilization and decontamination of certain additives or ingredients (Morrison 1992, ICGFI 1994, OTA 1985, Kader 1986).

In 1984, the International Consultive Group on Food Irradiation (ICGFI) convened in Washington, D.C., to develop a set of guidelines for the irradiation of fresh produce. The group established minimum doses that could provide effective treatments against most arthropod pests (ICGFI 1994). Doses used to disinfest foods and agricultural products are usually between 0.15 kGy (minimum dose for fruit fly sterilization and to prevent larval development) and 0.30 kGy (to control other species of insects and mites), but may go as high as 1 kGy (Forsythe and Evangelou 1993, Marcotte 1992). While research has proven irradiation to be effective at sterilizing pest insects, there is concern as to how quarantine inspectors would tell the difference between sterile and non-sterile insects that physically appear the same.

Unless already established, the correct dose required for a specific commodity infested with a specific pest must be determined through testing. Results of some of the studies that have investigated dose requirements include:

• Research on the mango seed weevil in the U.S. has shown that irradiation at doses of 0.30 kGy prevented adult emergence from infested fruit (ICGFI 1994).
• USDA researchers in Florida found that radiation doses as low as 0.30 kGy were effective in eliminating plum curculio (Conotrachelus nenuphar), and blueberry maggot (Rhagoletis mendax), without altering overall fruit quality (Hallman and Miller 1994).
• Researchers at Washington State University conducted a series of tests on 'Rainier' cherries and determined that irradiation levels as high as 0.30 kGy had no effect on composition, color, or taste. They also concluded that doses of 0.15 and 0.25 kGy were effective in controlling cherry fruit flies and codling moths, respectively (Drake et al. 1994).
• Studies done at the U.S. Horticultural Research Laboratory in Florida (USDA/ARS, Orlando) showed that irradiation doses up to 0.75 kGy were sufficient in controlling apple maggot (Rhagoletis pomonella), blueberry maggot (Rhagoletis mendax), and plum curculio (Conotrachelus nenuphar), without doing any damage to the fruit's composition or taste (Miller and McDonald 1994).

Factors influencing the response of fresh fruits and vegetables to irradiation include the type of commodity and cultivar, production area and season, maturity at harvest, initial quality, and post harvest handling procedures. Similarly, environmental conditions during irradiation (temperature and atmospheric composition), and dose rates are also influencing factors (ICGFI 1994, Kader 1986, OTA 1985, Morrison 1992). The relative tolerances of fresh fruits and vegetables to irradiation doses below 1 kGy are listed in Table 1 below.

Source: Kader 1986.

Costs

The actual cost of food irradiation is influenced by dose requirements, the food's tolerance of radiation, handling conditions (i.e., packaging and stacking requirements), construction costs, financing arrangements, and other variables particular to the situation (Forsythe and Evangel 1993, USDA 1989). Irradiation is a capital-intensive technology requiring a substantial initial investment, ranging from $1 million to $3 million (or possibly more for special applications). In the case of large research or contract irradiation facilities, major capital costs include a radiation source (cobalt-60), hardware (irradiator, totes and conveyors, control systems, and other auxiliary equipment), land (1 to 1.5 acres), radiation shield, and warehouse. Operating costs include salaries (for fixed and variable labor), utilities, maintenance, taxes/insurance, cobalt-60 replenishment, general utilities, and miscellaneous operating costs (Kunstadt et al., USDA 1989).

Based on a review of public information on the costs of treating a variety of food items with irradiation, Table 2 presents data on the per-unit costs for gamma irradiation and methyl bromide treatments for selected crops. Although irradiation is more expensive than fumigating with methyl bromide, the cost of irradiation may be offset by its many benefits, including reduced damage to fruits and vegetables and an extended shelf life. Furthermore, it is likely that irradiation costs will decrease in the future as the number of commercial irradiators and volumes of treated commodities increases. In addition, the relative proportion of the treatment cost is small when compared to the value of the commodity. Furthermore, other related costs (i.e., harvesting, packaging, storage, processing, and transportation costs to bring the commodity to market) further reduce the percent contribution of irradiation treatments, making it a relatively insignificant cost overall.

Sources: Forsythe and Evalgelou 1993 and 1994, Morrison 1989.

References

Drake et al. 1994. Effects of Low Dose Irradiation on Quality of 'Rainer' Cherries. Proceedings from the 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL.

 

Forsythe and Evangelou. 1993. Costs and Benefits of Irradiation and Other Selected Quarantine Treatments for Fruit and Vegetable Imports to the United States of America. Issue Paper. Proceedings of An International Symposium on Cost-Benefit Aspects of Food Irradiation Processing Jointly Organized by the International Atomic Energy Agency, The Food and Agricultural Organization of the United Nations, and the World Health Organization. Aix-En-Provence, Vienna. March 1-5, 1993.

 

Forsythe and Evangelou. 1994. Costs and Benefits of Irradiation versus methyl bromide fumigation for disinfestation of U.S. fruit and vegetable imports. U.S. Department of Agriculture, Economic Research Service, Agriculture and Trade Analysis Division, Washington, D.C., March 1994.

 

Giddings. 1991. Radiation Disinfestation of Agricultural Commodities. Nordion International, Inc. Kanata, Ontario, Canada.

 

Hallman and Miller. 1994. Irradiation as an Alternative to Methyl Bromide Quarantine Treatment for Plum Curculio in Blueberries. Proceedings from the 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL.

 

ICGFI. 1991. Facts About Food Irradiation. International Consultative Group on Food Irradiation, Fact Sheet Series, May 1991.

 

ICGFI. 1994. Irradiation as a Quarantine Treatment of Fresh Fruits and Vegetables. A report of the Working Group Convened by ICGFI, U.S. Department of Agriculture, Washington, D.C., March 22 to 25, 1994.

 

Kader 1986. Potential Applications of Ionizing Radiation in Post-harvest Handling of Fresh Fruits and Vegetables. Food Technology, Volume 40, Number 6, June, 1986, pp. 117-121.

 

Kunstadt et al. 1990. Economics of Food Irradiation. P. Kunstadt, C. Steeves, D. Scaulieu, Nordion Technical Paper. Market Development, Food Irradiation Division, Nordion International Inc. Kanata, Ontario, Canada.

 

Marcotte. 1992. The Practical Application of Irradiation Disinfestation for Food and Agricultural Commodities. Proceedings from the 1992 International CFC and Halon Alternatives Conference, Washington, D.C. September 1992.

 

Miller and McDonald. 1994. Irradiation as an Alternative Quarantine Treatment to Methyl Bromide for Blueberries. Proceedings from the 1994 International Conference on Methyl Bromide Alternatives and Emissions Reductions. Kissimmee, FL.

 

Morrison. 1989. An Economic Analysis of Electron Accelerators and Cobalt-60 for Irradiating Food. Rosanna Mentzer Morrison. U.S. Department of Agriculture, Economic Research Service, Technical Bulletin #1762, June, 1989.

 

Morrison. 1992. Food Irradiation Still Faces Hurdles. Food Review. October-December, pp. 11-15.

 

Morrison et. al. 1992. Irradiation of U.S. Poultry -- Benefits, Costs, and Export Potential. Food Review. October-December, 1992, pp. 16-21.

 

Moy. 1991. Plant Quarantine Treatment by Irradiation: Potential Benefits and Barriers in International Trade. Proceedings from the International Plant Quarantine Congress. Kuala Lumpur, Malaysia.

 

NAPPO. 1996. NAPPO Standards for Phytosanitary Measures. Guidelines for the Use of Irradiation as a Phytosanitary Treatment. Draft for the Secretariat of the North American Plant Protection Organization, Nepean, Ontario, Canada, July 1, 1996.

 

Nordion. 1995. World Suppliers of Contract Gamma Processing Services - 1995. Nordion International, Inc., Kanata, Ontario, Canada.

 

OTA. 1985. Food Irradiation: New Perspectives on a Controversial Technology. Rosanna Mentzer Morrison and Tanya Roberts, Office of Technology Assessment, Congress of the United States, Washington, DC. December 1985.

 

Thorne. 1983. Developments in Food Preservation. Applied Science Publishers Ltd., S. Thorne, ed., Essex, England. Chapter 2.

 

USDA. 1995. The application of irradiation to Phytosanitary problems. Position Discussion Document IV, U.S. Department of Agriculture, Animal Plant Health Inspection Service, Plant Protection and Quarantine, Washington, D.C., September 1995.

 

USDA. 1996a. Papaya, Carambola, and Litchi from Hawaii. Federal Register, U.S. Department of Agriculture, Animal Plant Health Inspection Service, Washington, D.C., Volume 61, No. 142, pp. 38108 - 38114.

 

USDA. 1996b. The application of irradiation to phytosanitary problems. Federal Register, U.S. Department of Agriculture, Animal Plant Health Inspection Service, Washington, D.C., Volume 61, No. 95, pp. 24433 - 24439.

 

USDA. 1996c. Methyl bromide alternatives newsletter. U.S. Department of Agriculture, Washington, D.C., January, 1996.

More information on the irradiation of agricultural products is available from the USDA Food Safety and Inspection Service .

Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.