Cobalt-60 is a common source of medical and industrial radiation. In medicine its primary use is in cancer radiotherapy. In industry it is used to test welds and casings and a variety of measuring instruments. It is also used to sterilize instruments and as a radiation source for laboratory use.

Cobalt-60 does not occur naturally and does not persist in the environment because of its short, 5.2-year half-life. It is produced by neutron activation of naturally occurring cobalt-59, which is not radioactive.

The most controversial use of cobalt-60 is in agriculture to irradiate food to kill microbes and retard spoilage.

Opponents refer to a number of supposedly scientific studies that reported significant effects from irradiated food. In virtually all cases those results could not be verified in later experiments, could not be clearly attributed to radiation or could be attributed to flawed experimental design.

As with many issues over which emotions run high, there are many myths surrounding irradiation, most of which are not supported or are directly contradicted by good scientific studies.

Myth 1: Irradiation destroys the nutritional content of food, and irradiated foods taste "different."

All food preservation processes affect taste and nutritional content to some degree, but the FDA concluded that such changes are insignificant for irradiation.

Studies have shown that the loss of vitamins is comparable to cooking, canning and freezing. In fact there is less vitamin loss in fruits because they can be harvested ripe.

Claims of high nutrient loss refer to high doses of radiation not permitted in the United States or cite older, inaccurately measured nutritional values.

Numerous tests have shown that the organoleptic qualities (taste, smell, sight and touch) are unaffected or are improved because irradiated food retains freshness longer and can be harvested when quality is most desirable.

Myth 2: Irradiation is not safe, control is not adequate and the scientific community opposes its use.

In fact all respected national and international health organizations support irradiation, including the American Medical Association, the U.S. Centers for Disease Control, the American Dietetic Association and the World Health Organization. All countries adopt standards established by an international panel of experts.

Other myths also have been disproved. These include fears that irradiated food will glow or become radioactive, that activist groups reflect public views and are protecting the public interest, that consumers do not want and will not accept irradiated food, that the public will not know what food is irradiated and what is not, that irradiation facilities will add significant amounts of radioactive waste to the environment, that organic food is healthier and safer, that there have been no long-term studies on the safety of irradiated food. In addition, opponents claim that irradiation produces unique compounds, and specifically cite benzene and formaldehyde as hazardous byproducts of the irradiation process.

There is no scientific evidence to back up these claims, and all have been found to be without merit.

One criticism is true: Science has been unable to prove that irradiation is safe.

How would one formulate the null hypothesis for "X is safe"? Think about it, and then name anything that has been proved safe.

Richard Brill is a professor of science at Honolulu Community College. Email questions and comments to brill@hawaii.edu.