American food producers will soon be allowed to expose fresh spinach and iceberg lettuce to low levels of radiation in order to kill E. coli, salmonella, listeria and other dangerous bacteria.

The U.S. Food and Drug Administration has ruled that the technique, known as irradiation, can be used on the produce starting Friday.

The FDA already allows the use irradiation on meats and spices. In Canada, producers can irradiate onions, potatoes, wheat, flour, spices and seasonings.

"What it does is give producers and processors one more tool in the toolbox to make these commodities safer and protect public health," said Dr. Laura Tarantino, the director of the FDA's office of food additive safety.

Dole Food Co. has already indicated it's testing irradiation techniques and considering using them.

The change comes after a 2006 E. coli outbreak in spinach that killed three people in the U.S. and sickened 200. There were numerous lettuce recalls in the U.S. over the same time period.

The U.S. Grocery Manufacturers Association has petitioned the FDA to loosen irradiation rules on many types of produce, but asked that the ruling on leafy greens come first.

Process is safe, FDA says

When food is irradiated, Gamma rays, X-rays or electron beam radiation are used to penetrate food, killing micro-organisms without raising the temperature of the food significantly, according to the Canadian Food Inspection Agency.

The agency says the technique dramatically reduces bacteria levels, which prevents spoiling, increases shelf life and lowers the risk of food poisoning. E.coli is fairly sensitive to small amounts of radiation, although bacteria such as salmonella require larger doses.

The FDA notes that food can become contaminated after the irradiation takes place, so it still must be properly stored and washed before being consumed.

The process is not harmful, the FDA says, because the food doesn't harbour the radiation once the treatment has taken place.

"There is no residue," Tarantino said. "There's nothing left and certainly no radioactivity left."

Canada considers irradiating meat, mangoes

A leading food safety expert said irradiation can kill certain bacteria safely, but she said the FDA also needs to address other sources of food contamination — such as the way farmers handle manure, or the safety of their irrigation systems.

"We are not opposed to the use of irradiation, but it's expensive and it doesn't really address the problem at the source," said Caroline Smith DeWaal of the U.S. Center for Science in the Public Interest.

In Canada, the government specifies exactly how high the energy level can rise when irradiating food, and how much radiation the food can absorb. All irradiated foods must be marked as such when sold.

Health Canada, which reviews all applications for irradiation, is proposing to expand the list of permitted irradiated foods to ground beef, poultry, shrimp and mangoes.

With files from the Associated Press