Radiation has a very bad reputation. There is something about it that scares the daylights out of people. This is understandable since the devastation of Hiroshima and Nagasaki produced graphic images of the devastation that radiation could cause. The Cold War generated additional fears of radiation silently killing off large numbers of people. Even today, one sees the fears generated by the phrase ‘dirty bombs’ that kill by nuclear radiation.
The latest issue of Physics Today (February 2012, p. 66) has an article by James W. Dixon, professor of animal science at Iowa State University, that looks at a question that troubles a lot of people: Should we be concerned that the food we purchase and eat nowadays may have been irradiated?
Not surprisingly, the effect of radiation on food is related to the amount of ionizing energy absorbed. That quantity is measured in grays (Gy), named after physicist Louis Harold Gray, with 1 Gy being an absorbed dose of 1 joule per kilogram of material. Doses of less than 1 kGy prevent sprouting in potatoes and delay ripening of fruits. Such doses also serve to disinfect foods by killing insects in grains and fruits and inactivating parasites in meat—in particular, they can knock out the worm responsible for trichinosis.
Slightly higher doses of 1–5 kGy serve to pasteurize foods—that is, to kill many of the microorganisms that reside therein. Radiation pasteurization, or radurization, significantly reduces or eliminates bacteria of public health significance in the food. Salmonella, the most often reported bacterial agent of foodborne illness, Listeria monocytogenesi, and the harmful bacterial strain Escherichia coli O157:H7 are all very sensitive to irradiation.
What are the usual concerns that people have?
Perhaps the more prevalent concerns relate to the quality of the food after irradiation. Some consumers worry that irradiation will be used to “salvage” spoiled food, others are concerned that irradiated food is poor in nutrients, and still others express anxiety about compounds generated in food during the irradiation process.
Since irradiation reduces the amount of bacteria in the food, it increases shelf life. As noted earlier, though, the organisms responsible for food spoilage are not as sensitive to radiation as are more lethal bacteria such as Salmonella. In any event, spoilage results from bacterial byproducts, not simply bacterial presence; radurization, like conventional pasteurization, does not get rid of those byproducts. If irradiation were used in an attempt to salvage spoiled milk, for example, the process would not fool the consumer; the milk would still smell and taste bad.
For 30 years now, food scientists have been trying to determine whether irradiation creates any byproducts that are not caused by other common (and, by the way, rarely tested) processes. After three decades, we haven’t found any, though we can’t say with certainty that they don’t exist.
The scientific evidence to date indicates that irradiation does not produce any toxicity in foods. Still, consumers have the right to make their own informed choices. For the foreseeable future, consumers will retain the option to select nonirradiated foods; indeed, at present it’s the irradiated meat, poultry, or produce that is hard to find. In any case, shoppers can readily distinguish between the irradiated and nonirradiated varieties in the supermarket: Those foods that have been irradiated must, by US law, display the internationally recognized Radura symbol shown in the figure, accompanied by the words “treated by irradiation” or “treated by ionizing radiation.”
Although such food is required by law to display the ‘Radura’ symbol, I must admit that I personally have never seen it on any food I have purchased. Either irradiation of food that I happen to buy is rare or I am remarkably unobservant and incurious about the packaging of the things I buy and eat.
It is an interesting and informative article, though, that clearly lays out the issues.