Irradiation for Safety and Performance
Your day goes like this. You emerge from beneath your feather-filled comforter, eat some buttered toast and drive to work. After work, you get a flu shot, buy some fresh spinach, a bunch of bananas and chew treats for your dog. Arriving home, you notice your mail order steaks have arrived and decide to have one for supper.
Nothing unusual has happened, yet throughout your day you've been exposed to irradiated products: the feathers in your comforter\; the inks on the butter package\; the tires and other components of your car\; the syringe and cotton swab used during your flu shot\; the vegetables, fruit and dog chews at your grocery store and the beef you had for dinner. None of the products has become radioactive. They contain no residues and haven't been exposed to any heat or chemicals during the irradiating process. But the food, feathers and medical products are safer and less likely to harbor potentially harmful bacteria, microorganisms or insects, and the ink and automobile components have enhanced performance.
"Irradiation is an extremely safe process that enhances the safety and performance of the products we use and see every day," explains Emily Craven, manager, sterilization science, at Nordion Inc., headquartered in Ottawa, Ontario, Canada, and an ASTM International member since 2009.
Irradiating products dates back to the 1950s when Johnson &\; Johnson first used the process to sterilize medical devices. Since then, according to Gary Pageau, a long-time ASTM International member and CEO and president of GEX Corp. in Centennial, Colo., the radiation processing industry, which includes irradiating and dosimetry services and equipment to measure the exact dose of radiation absorbed, has grown by about 5 to 6 percent a year, accounting for some $1 billion worth of irradiated products annually.
As the industry has grown, so has its profile as an ASTM International standards development activity. Since the mid-1980s, standards and guidelines have been addressed by ASTM Subcommittee E10.01 on Radiation Processing: Dosimetry and Applications, under the jurisdiction of ASTM Committee E10 on Nuclear Technology and Applications. In April 2012, the focus on radiation processing sharpened as ASTM's board of directors approved new ASTM Committee E61 on Radiation Processing to manage existing standards and develop new ones.
Irradiated products are exposed to ionizing radiation in the form of highly penetrating gamma rays, X-rays or a stream of high energy electrons from an electron beam irradiator. Gamma rays are produced by radioactive isotopes of cobalt-60 and sometimes cesium-137, while X-rays and electron beams are produced by electron accelerator machines powered by electricity. The choice of irradiator depends on the density and thickness of the product being irradiated.
Ionizing radiation packs so much energy density as it bombards a product that molecules and atoms break apart, liberating electrons and producing ions, or atoms or molecules with positive and negative charges that are especially chemically reactive. In irradiated food, the DNA of insect pests (such as fruit flies and seed weevils), spoilage-causing microorganisms, bacteria (including salmonella and E. coli) and viruses is destroyed beyond their ability to repair and reproduce. Food-borne pathogens are killed, sprouting is inhibited and ripening is delayed, enhancing food safety and extending shelf life. In medical devices, radiation penetrates through final product packaging and the products themselves, ensuring sterilization. In materials using polymers, irradiation initiates cross-linking chemistry, changing the physical nature of the product to enhance performance or appearance.
The irradiating process is done in a shielded environment - usually a concrete room with walls at least six feet (2 m) thick. Calibrated dosimeters measure the amount of radiation absorbed within a product. The recorded dose is evaluated to ensure that the desired results have been achieved.
ASTM Subcommittee E10.01, which had absorbed another E10 subcommittee, focused on food irradiation and developed a number of standards instructing industry users how to safely irradiate prepackaged meat and poultry products, fresh frozen meat, fin fish and aquatic invertebrates, fresh agricultural produce and dried spices, herbs and vegetable seasonings. But with consumer perceptions limiting the acceptance of irradiated foods, despite support from the U.S. Department of Agriculture, attention focused on the sterilization of medical devices and developing a number of dosimetry standards for this purpose. Today, says Craven, "single-use medical disposable products such as syringes, gloves, gowns and swabs are the number one commercially irradiated product in the world." This area also accounts for about 90 percent of dosimeter sales, notes Pageau.
The idea of having the subcommittee continue its work as a free-standing main committee surfaced in the fall of 2011. Subcommittee membership numbered more than 125, accounting for nearly half of all membership in Committee E10. About 43 percent of these members come from outside the United States. Also, the group currently oversees 36 completed standards and, due to its size, has had its own executive team. Perhaps more indicative of the need to form a separate committee, "When we put up a standard for ballot and asked for comments, we wouldn't receive any from outside our own subcommittee, since Committee E10 is based on the nuclear industry," says John Logar, chairman of the new committee and associate director of sterilization science and technology at Ethicon Inc., Somerville, N.J. "Having a separate committee puts a new focus on standards for the radiation processing industry."
Two current standards are considered especially significant in terms of their usefulness to the industry: ISO/ASTM 51261, Guide for Selection and Calibration of Dosimetry Systems for Radiation Processing, and ASTM E2628, Practice for Dosimetry in Radiation Processing. The first "helps users understand what a dosimeter can do and shows them how to use a dosimeter to reach a standard," explains David Pymer, general manager, Harwell Dosimeters Ltd., Didcot, Oxfordshire, England, who joined ASTM last year. The second is really the "road map for all other standards, since all other standards refer back to it," says Logar, citing ISO/ASTM 51276, Practice for Use of a Polymethylmethacrylate Dosimetry System, as an example.
As new applications for radiation processing emerge and as perceptions of the industry change, ASTM Committee E61 on Radiation Processing will revise existing standards and develop new ones covering the entire irradiation process, from dosimetry selection to the analysis of routine processing results.
Food irradiation may regain emphasis as more and more food is shipped around the world. Some 50 countries now permit food irradiation, although the range in number and types of foods varies widely. Additionally, according to the USDA Food Safety and Inspection Service, consumers, when educated about the significant safety benefits of irradiated food, are more inclined to purchase it even though it generally costs more.1 A Radura logo on the packaging of irradiated foods, required by the U.S. Food and Drug Administration, may also increase consumer awareness and understanding of irradiated foods.
"If irradiated food really takes off, it will mean huge growth for the industry," says Logar. Having international standards that assure food has been safely irradiated, regardless of its origins, would make the job of inspectors easier. "Food might also be irradiated at lower and lower doses, requiring new dosimeters and new standards for measuring dosages," offers Craven.
Prescribing the appropriate radiation dose for sterilization could impact standards for irradiating medical devices. "If a large dose is given to a surgical drape that doesn't come near the wound on a patient, some in the industry are asking if that dose is really relevant," points out Mark Bailey, senior research scientist at the National Physical Laboratory, Teddington, Middlesex, England, and an ASTM member. He adds that in an effort to lower costs, some hospitals now wash, sterilize and reuse single-use devices, such as catheters. Standards could eventually be required to ensure the sterilization, functionality and safety of medical products that are re-irradiated.
Then, there are the new irradiating applications: everything from laminating membranes for clothing that more efficiently wicks away moisture, to sterilizing human tissues and medicinal preparations created by biological processes, to increasing the switching speed of semiconductors.
An ongoing challenge for the industry is overcoming public misunderstanding and fear. "We're exposed to radiation all the time and a little bit from artificial sources makes no appreciable difference," says Bailey.
Logar anticipates adding more value to existing standards by being more prescriptive or definitive and developing industry-specific standards, such as guidelines for the wastewater treatment industry that explain how to decontaminate water using irradiation.
"Standards are born out of necessity," Logar says. "Now is the time to start creating international processes to ensure that best practices are being utilized around the world." He adds, "As we look to globalize standards for radiation processing, there's no better place to start than a committee within ASTM."
1. Conley, S.T., "What do Consumers Think About Irradiated Foods," FSIS Food Safety Review, Fall 1992, pp. 11-15.
Subcommittee E10.01 on Radiation Processing: Dosimetry and Applications has sponsored several workshops to share scientific and technical information and contribute to the state of the art. First held in 1989, the workshops will continue under the sponsorship of Committee E61 on Radiation Processing.The Seventh International Workshop on Dosimetry for Radiation Processing, the most recent in the series, took place June 24-28 and included lectures, practical hands-on exercise and roundtable discussions designed to increase understanding of dosimetry principles, applications and standards. Geared toward researchers, irradiator operators, dosimeter suppliers, regulators, quality assurance personnel, medical product manufacturers and food processors, the program has emphasized the application of ASTM and joint International Organization for Standardization (ISO)/ASTM standards.Adele Bassett is a freelance writer who has covered everything from youth gangs in Colorado to earthquakes in Connecticut while working for a variety of corporations and publications. She holds a B.A. in English, an M.S. in journalism and an M.B.A.