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Issues: Growing and Production

PMA Overview: Irradiation

On August 21, 2008, the U.S. Food and Drug Administration announced a final rule amending the food additive regulations to provide for the safe use of ionizing radiation for the control of foodborne pathogens and extension of shelf-life in fresh iceberg lettuce and fresh spinach. FDA has determined that this use of ionizing radiation will not adversely affect the safety of the food. Accompanying this final rule were questions and answers about FDA's decision.

Prior to this rulemaking, in 2007, PMA submitted comments on the FDA's proposed rule on irradiated foods and issued a press release.

What is food irradiation?
Food irradiation is a food safety technology that can eliminate disease-causing germs from foods. Like pasteurization of milk and pressure cooking of canned foods, treating food with ionizing radiation can kill bacteria and parasites that would otherwise cause foodborne disease. The food that NASA astronauts eat has been sterilized by irradiation to avoid getting foodborne illness in space. The effects of irradiation on the food and on animals and people eating irradiated food have been studied extensively. These studies show clearly that when irradiation is used as approved on foods: disease-causing germs are reduced or eliminated; the food does not become radioactive; dangerous substances do not appear in the foods; and the nutritional value of the food is essentially unchanged.

Irradiation is a safe and effective technology that can prevent many foodborne diseases.

Which foodborne diseases could be prevented with irradiation?
As of August 2008, irradiation has been approved in the United States to control pathogens, such as E. coli O157:H7, and extend shelf life of Iceberg lettuce and spinach. Irradiation could also eliminate parasites such as Cyclospora and bacteria such as Shigella and Salmonella from fresh produce, though that application is not approved now.

What is the actual process of irradiation?
Three irradiation technologies exist, using three kinds of rays: gamma rays, electron beams, and x-rays.

The first technology uses the radiation given off by a radioactive substance. This can be either a radioactive form of the element cobalt (Cobalt 60) or of the element cesium (Cesium 137). These substances give off high energy photons, called gamma rays, which can penetrate foods to a depth of several feet. These particular substances do not give off neutrons, which means they do not make anything around them radioactive. This technology has been used routinely for more than 30 years to sterilize medical, dental, and household products, and it is also used for radiation treatment of cancer. Radioactive substances emit gamma rays all the time. When not in use, the radioactive "source" is stored in a pool of water, which absorbs the radiation harmlessly and completely. To irradiate food or some other product, the source is pulled out of the water into a chamber with massive concrete walls that keep any rays from escaping. Medical products or foods to be irradiated are brought into the chamber and are exposed to the rays for a defined period of time. After it is used, the source is returned to the water tank.

Electron beams, or e-beams, are produced in a different way. The e-beam is a stream of high energy electrons, propelled out of an electron gun. This electron gun apparatus is a larger version of the device in the back of a TV tube that propels electrons into the TV screen at the front of the tube, making it light up. This electron beam generator can be simply switched on or off. No radioactivity is involved. Some shielding is necessary to protect workers from the electron beam, but not the massive concrete walls required to stop gamma rays. The electrons can penetrate food only to a depth of three centimeters, or a little over an inch, so the food to be treated must be no thicker than that to be treated all the way through. Two opposing beams can treat food that is twice as thick. E-beam medical sterilizers have been in use for at least 15 years.

Another technology is X-ray irradiation. This is an outgrowth of e-beam technology, and is still being developed. The X-ray machine is a more powerful version of the machines used in many hospitals and dental offices to take X-ray pictures. To produce the X-rays, a beam of electrons is directed at a thin plate of gold or other metal, producing a stream of X-rays coming out the other side. Like cobalt gamma rays, X-rays can pass through thick foods, and require heavy shielding for safety. However, like e-beams, the machine can be switched on and off, and no radioactive substances are involved. Four commercial X-ray irradiation units have been built in the world since 1996.

How does irradiation affect foods?
The foods are not changed in nutritional value, and they are not made dangerous as a result of the irradiation. The high energy ray is absorbed as it passes through food, and gives up its energy. If the food still has living cells (such as seeds, or shellfish, or potatoes), they will be damaged or killed just as microbes are. This can be a useful effect. For example, it can be used to prolong the shelf life of potatoes by keeping them from sprouting. Irradiated foods need to be stored, handled, and cooked in the same way as unirradiated foods. They could still become contaminated with germs during processing after irradiation, if the rules of basic food safety are not followed. Because the irradiated foods have fewer microbes of all sorts, including those that cause spoilage, they may have a longer shelf life.

Which foods can be irradiated?
At low doses, irradiation could be used on a wide variety of foods to eliminate insect pests and as a replacement for chemical fumigation that is routine for many foods now. It can also inhibit the growth of molds, inhibit sprouting, and prolong shelf life. This application has been approved for produce for years at a dose not exceeding 1.0 kiloGray (kGy).

At higher doses, irradiation could be used on a variety of foods to eliminate parasites and bacteria that cause foodborne disease. Many foods can be irradiated effectively, including meat, poultry, grains, and many seafoods, fruits, and vegetables. On August 21, 2008, the U.S. Food and Drug Administration approved the use of ionizing radiation for control of foodborne pathogens, and extension of shelf-life, in fresh iceberg lettuce and fresh spinach at a dose up to 4.0 kGy. After extensive research, FDA concluded that irradiation of iceberg lettuce and spinach as approved does not present a hazard, nor does it harm the nutrition value.

How can I tell if the food has been irradiated?
A distinctive logo has been developed for food labeling to identify the product as irradiated. This symbol is called the "radura" and is used internationally to mean that the food so labeled has been irradiated. A written description may also be present, such as "Irradiated to destroy harmful microbes." It is not required to label a food if a minor ingredient of the food, such as a spice, has been irradiated itself.

Who makes sure that the irradiation facilities are operated safely?
In the United States the effectiveness of the treatment in eliminating pathogens will be regulated as a food safety process, by either the U.S. Department of Agriculture or the Food and Drug Administration, often in concert with state authorities, just as is the case now for milk pasteurization.

The safety of operations of irradiation facilities is regulated separately. This requires extensive worker training, supervision, and regulatory oversight. U.S. facilities using radioactive sources are regulated by the Nuclear Regulatory Commission (NRC). To be licensed, the facility must have been designed with multiple fail-safe measures and must establish extensive and well-documented safety procedures and worker training. The safe transport of the radioactive sources is regulated by the Department of Transportation.

E-beam and X-ray sources are not monitored by the NRC, but rather by the part of the FDA that regulates medical X-ray devices, and by the same state authorities that regulate other medical, dental, and industrial uses of these technologies.

What radioactive waste is generated? Is waste storage or transport a problem?
Cobalt 60 is manufactured in a commercial nuclear reactor, by exposing nonradioactive cobalt to intense radiation in the reactor core. Cesium 137 is a by-product of the manufacture of weapons-grade radioactive substances. Thus the supply of these two substances, like that of other radioactive materials used in medicine, science, and industry, is dependent on the nuclear industry.

The food irradiation facilities themselves do not become radioactive and do not create radioactive waste. The cobalt sources used in irradiation facilities decay by 50% in five years and therefore require periodic replacement. The small radioactive cobalt "pencils" are shipped back to the original nuclear reactor, where they can be recharged for further use. The shipment occurs in special hardened steel canisters that have been designed and tested to survive crashes without breaking. Cobalt is a solid metal, and even if somehow something should break, it will not spread through the environment. Cobalt 60 may also be disposed of as a radioactive waste. Given its relatively short half life (5 years) and its stable metallic form, the material is not considered to be a problematic waste.

In contrast to metallic cobalt, cesium is a salt, which means it can dissolve in water. Cesium 137 sources decay by 50% in 31 years, and therefore are not often replaced. When they are replaced, the old cesium sources are sent to a storage site in the same special transport canisters. If a leak should occur, there is the possibility that the cesium salts could dissolve in water and thus spread into the environment.

Do other countries irradiate their food?
Food irradiation is allowed in nearly 40 countries, including the United States, France, the Netherlands, Portugal, Israel, Thailand, Russia, China, and South Africa. It is endorsed by the World Health Organization, the American Medical Association, and many other organizations.

PMA Position
The Produce Marketing Association believes that sound science must be the basis for decisions about all food issues. Based on extensive scientific research and review by the U.S. government and international food and science experts, irradiation has been deemed to be a safe and viable technology. PMA supports the government's decision allowing the irradiation of fresh fruits and vegetables. PMA also believes in providing consumers the choice in the marketplace, including the choice of irradiated and nonirradiated produce.