How Does Food Irradiation Work?

Ever since the FDA approved the use of irradiation on leafy greens last week, I've been curious to find out how irradiation works as well as its drawbacks. Where does anyone start when they want to find basic information on any topic? Wikipedia, of course.

Food irradiation is the process of exposing food to ionizing radiation in order to destroy micro-organisms, bacteria, viruses, or insects that might be present in the food.

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The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. Micro-organisms can no longer proliferate and continue their malignant or pathogen activities.

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By irradiating food, depending on the dose, some or all of the harmful bacteria and other pathogens present are killed. This prolongs the shelf-life of the food in cases where microbial spoilage is the limiting factor.

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Food irradiation using Cobalt-60 is the preferred method by most processors, because the deeper penetration enables administering treatment to entire industrial pallets or totes, reducing the need for material handling. A pallet or tote is typically exposed for several minutes to hours depending on dose. Radioactive material must be monitored and carefully stored to shield workers and the environment from its gamma rays. During operation this is achieved by substantial concrete shields.

Does food become radioactive after its irradiated?

No. The only way it becomes radioactive is if the source (Cobalt-60) gets on the food, which doesn't happen.

What are the criticisms?

Gristmill and Treehugger (reasonable go-to sources for anti-nuclear claims) published their thoughts last week on the FDAs recent approval.

Gristmill didn't really have complaints on irradiation itself, only that "the FDA is missing the fundamental key to "food safety" -- the prevention of contamination from happening in the first place." Well, people had the same concerns when pasteurization was first introduced (pdf, p. 15), now pasteurization is widely accepted. If you could make food safer and last longer, why not? No amount of prevention will get rid of all the organisms living on the food. Irradiation does.

Treehugger had more interesting comments, most of them in favor of irradiation. Here's one of the criticisms:

Irradiation works by splitting chemical bonds in molecules with high energy beams to form ions and free radicals. When sufficient critical bonds are split in organisms contaminating a food, the organism is killed. Comparable bonds are split in the food. Ions are stable; free radicals contain an unpaired electron and are inherently unstable and therefore reactive. ... I am opposed to consuming irradiated food because of the abundant and convincing evidence in the referred scientific literature that the condensation products of the free radicals formed during irradiation produce statistically significant increases in carcinogenesis, mutagenesis and cardiovascular disease in animals and man.

Sounds scary. Here's what the IAEA says about free radicals (pdf, p. 26):

The fact that irradiation causes the formation of free radicals - which in scientific terms are atoms or molecules with an unpaired electron - and that these are quite stable in dry foods has often been mentioned as a reason for special caution with irradiated dry foods. However, free radicals are also formed by other food treatments, such as toasting of bread, frying, and freeze drying, and during normal oxidation processes in food. They are generally very reactive, unstable structures, that continuously react with substances to form stable products. Free radicals disappear by reacting with each other in the presence of liquids, such as saliva in the mouth. Consequently, their ingestion does not create any toxicological or other harmful effects.

So I haven't found any real drawbacks to irradiation, only a lot of benefits. As irradiation becomes more and more accepted, hopefully more and more people will become less afraid of radiation. Radiation needs to be understood, not feared. Like I said before, radiation saves lives.