The New York Times said it is the first time the U.S. government has allowed produce to be irradiated at levels high enough to kill E. coli and salmonella.

Critics have expressed concern that irradiation could lower nutritional value and create unsafe chemicals.

Dr. Laura Tarantino, director of the Office of Food Additive Safety at the FDA, told the newspaper the agency found no serious health or safety issues with irradiated spinach or lettuce.

"These irradiated foods are not less safe than others," Tarantino said, "and the doses are effective in reducing the level of disease-causing micro-organisms."

Food processors were already allowed to irradiate beef, eggs, poultry, oysters and spices, the newspaper said.