Still, the agency is not ready to disclose its findings. The FDA started sampling soft drinks after a private study in November found small amounts of benzene in some beverages.
In the vast majority of drinks sampled, benzene either was not found or was present at levels below the federal limit for drinking water.
"Although the results to date are preliminary, they do not suggest a safety concern," Robert E. Brackett, director of the agency's Center for Food Safety and Applied Nutrition, wrote in a letter released Tuesday.
A "very, very few samples" had slightly elevated levels of benzene, Laura Tarantino, the agency's director of food additive safety, said in an interview.
The FDA is continuing the tests and will release results "when we have a more complete understanding of the current marketplace," Brackett said.
The letter was a pointed retort to an environmental group that is calling for benzene warnings on soft drinks.
The Environmental Working Group asked the FDA to warn the public about popular soft drinks containing two ingredients that can form benzene. The ingredients are ascorbic acid and benzoate preservatives, also known as Vitamin C and sodium or potassium benzoate.
"Notably, they don't give us the data," said Richard Wiles, the group's senior vice president.
"We simply asked for them to disclose the results of their testing. If there's nothing to hide, why won't they show us numbers? It might be a small percentage, but there is some percentage of drinks that have very elevated levels of benzene," he said.
Benzene is a cancer-causing chemical that has been linked to leukemia. It can form naturally; it's found in forest fires, gasoline and cigarette smoke. It also is widely used in industrial production to make plastics, rubbers, detergents, drugs and pesticides.
Benzene can form in soft drinks made with Vitamin C and sodium or potassium benzoate.
But the presence of those ingredients does not mean benzene is present, Tarantino said. Heat, light and shelf life can affect whether benzene will form, she said. That means benzene could be found in one can of soda, but not in another of the same brand, she said.
"To release all the data now could be confusing," she said. "It's not only not good for companies; it's not particularly good for consumers. It doesn't give them any useful information. One of the misperceptions is that anytime you see ascorbic acid and benzoate, you're going to automatically have high levels of benzene, and that just isn't so."
The Washington-based environmental group accused the FDA of suppressing information about benzene in soft drinks in 1990.
Brackett said the FDA did not suppress information; it published findings in 1993. Those findings showed that benzene was detected at insignificant levels and that trace levels could be found in foods without the two ingredients, Brackett said.
The environmental group said such findings were a clear threat to health. But Brackett said the U.S. and Canadian governments have agreed that low levels of benzene are not an "imminent health hazard."
Last week, a group of advocates and health professionals asked schools to ban soft drinks containing the two ingredients.
By Libby Quaid