Irradiating iceberg lettuce, spinach effective but not fail-safe; critics cite consequences

For many consumers, the prospect of eating produce zapped with ionizing radiation doesn't sound all that appetizing, conjuring up images of mushy fruits and wilted leaves -- not to mention fears over safety. Last month's ruling by the Food and Drug Administration that food manufacturers can now irradiate fresh spinach and iceberg lettuce to kill bacteria came with reassurances that the process wouldn't result in food any less appealing or healthful than non-irradiated varieties.

Research indicates that that may all be true. But critics say the new rule ignores the source of the problem -- sloppy agricultural practices -- and could give consumers a false sense of security.

One might imagine that washing would take care of most bacteria on a piece of fresh fruit or a vegetable -- including the forms of E. coli and salmonella implicated in recent food-borne disease outbreaks. But the microbes that spurred the Washington, D.C.-based Grocery Manufacturers Assn., an industry group, to request the current ruling are known as internalized bacteria -- so called because they've taken up inside the plant's tissues and can't just be washed off under the faucet.

Contrary to popular perception, the food doesn't retain radiation any more than, say, skin does after a day in the sun -- which is to say, not at all. It heats up a bit during treatment, then the radiation dissipates -- and no radioactive compounds enter the food.

When the radiation dose is kept low enough, the plant's own cells remain largely intact. When it's too high, however, the whole plant suffers. Irradiated food's reputation suffered a blow half a century ago, says Brendan Niemira, acting research leader with the U.S. Department of Agriculture's in Wyndmoor, Penn. Early experiments to develop an eternally shelf-stable head of lettuce resulted in leaves that were limp, colorless and bland.

Back then, scientists were dosing food with up to 10 grays of radiation. (A gray is a measure of how much energy is absorbed: It corresponds to one joule of energy per kilogram of matter.) The FDA's new rule allows food manufacturers to dose spinach and iceberg lettuce with up to 4 grays, enough to kill germs without withering plant material.