Before bagged leafy greens wind up on your plate, they are washed, often three times, in a potent chlorine bath. But new research shows that the steps that California companies rely on to protect consumers do not kill dangerous bacteria inside the leaves.

The debate over how to protect consumers from E. coli and other potentially deadly microbes has intensified since the fall of 2006, when at least 200 people across the U.S. became ill and three died after eating tainted spinach grown in California.

Irradiation, which involves bombarding food with high-energy gamma or electron beams to disrupt the DNA of pathogens, has its supporters and critics. But the new research suggests that it might be the only way to penetrate leafy greens and kill bacteria hiding inside.

While some hamburger meat, poultry and spices are irradiated to kill bacteria, its use on fruits and vegetables to enhance food safety is not permitted in the U.S. Currently, some produce is irradiated only for insect control and shelf-life extension. The Food and Drug Administration is considering whether to allow it for killing pathogens, which would make irradiation much more widespread.