Answer to Question #7989 Submitted to "Ask the Experts"

Q

My question is in regard to irradiation of food. I purchased some beef steaks recently, only to find out after the fact that the company irradiates food. A Web search turned up pro and con commentary on food irradiation—to the degree that I'm now more confused than enlightened. My concerns are not just that irradiated food could be a health hazard but also the possibility of any radioactive contamination from the irradiation process itself onto the food or its packaging. I don't know what company or process this company uses, but what is the likelihood that some aspect of the process could lead to contamination? Is the food checked for any radioactivity before it is shipped to consumers? Could other items, such as nonirradiated food or cookbooks or knives, shipped along with the irradiated food be contaminated? These, I'm sure, seem silly questions, but there is a wealth of conflicting information on the Web about the subject. I thought you, the experts, could help shed some light.

A

This is a very good question and it has not been so clearly asked or answered before now. Food irradiation, using radioactive material as the radiation source, is done with a strong gamma ray-emitting radionuclide, like cobalt-60. The gamma rays from cobalt-60 are the same as very high-energy medical x rays and will not make the irradiated food radioactive.

Now, to specifically answer your questions. The cobalt-60 sources, used in commercial irradiators to sterilize medical equipment and for food irradiation, are designed, built, and tested to not leak. Leaking is defined as the release of  radioactive dust or liquid (contamination) from the "encapsulated" cobalt-60. Encapsulation of the cobalt-60 is done within two stainless-steel containers. The cobalt-60 is first placed into a pretested stainless-steel container and welded shut. Then this first encapsulation is cleaned and tested for pinholes in the welded area. The first encapsulation is then placed into a similar second stainless-steel container, and it too is welded shut. This final encapsulation is cleaned, inspected for pinholes, and then "wipe tested" to assure that there is no leaking contamination from the finished source, which is a double-encapsulated "special-form" source of radioactive material. The wipe test must show that there is less than the limit of 5.0 x 10^-9 curies (0.005 microcuries) on a source (for a commercial irradiator) that has at least 1,000 curies. This is a very sensitive test to show if a source is leaking.

For the design and production of each model (type) of a special-form source, it must be rigorously tested to assure that it will not leak radioactive material (contamination) in normal-use or in severe-use (accident) conditions. The higher the amount of radioactive material contained in a special-form source, the more aggressive are the severe-use conditions that a special-form source must survive without releasing (leaking) its radioactive material.

Also, while in use, each special-form source is wiped tested at least every six months to confirm that the sources used in the irradiation process are not leaking contamination. Again, the wipe test must show that there is less than the limit of 5.0 x10^-9 curies (0.005 microcuries) on a source that contains at least 1,000 curies. This is a very sensitive test to show if a source starts to show any signs of leaking. If any source is found to be leaking, all irradiation processes must be stopped and the problem corrected. I don't know if any specific commercial irradiation facility checks the irradiated food, as it exits the irradiator's shielding area, for contamination. However, the routine wipes taken directly on the sources will detect any leakage from the sources in the most efficient manner.

Also, before any product is irradiated, it is wrapped or packaged in a container to prevent new bacteria or insects from infecting the product after irradiation. If a special-form source did leak, which is highly unlikely, only the food packaging could be contaminated and not the food itself. This would greatly reduce anyone's "degree" of ingesting the contamination. The degree of ingestion is very small because (1) only a small percent of the contamination on a package will be transferred to a person's hands, the countertop, cookbooks, knives, or other items that contact the packaging and (2) only a small percent of that contamination can then be transferred to the food that will be eaten. The greatest risk from contamination is the ingestion of contamination.

I hope this has reassured you regarding the safety of eating irradiated steaks. If not, please send the steaks to me and I will start warming up my grill!

John P. Hageman, MS, CHP