The Food and Drug Administration (FDA) demanded reformulation after tests on more than 100 drinks found four contaminated with benzene above the World Health Organisation's (WHO) 10 parts per billion limit for benzene in drinking water.
The offenders were batches of Safeway Select Diet Orange, AquaCal Strawberry Flavored Water, Crystal Light Sunrise Classic Orange and Giant Light Cranberry Juice Cocktail. A fifth drink, Crush Pineapple, had benzene above the US' five parts per billion water limit.
Benzene is a known carcinogen, although authorities have set no specific limit for it in soft drinks.
The FDA has been under pressure to release results of its tests on soft drinks since one of its own scientists first revealed to BeverageDaily.com in February that some drinks had been found contaminated with benzene above water limit.
The news prompted testing on drinks in several countries, and recently led to the recall of four drinks contaminated with benzene in the UK. All authorities have assured there was no health risk to consumers.
The suspected source of benzene is a reaction between two common ingredients in drinks: benzoate preservatives and ascorbic acid (vitamin C).
Erythorbic acid and citric acid are also thought to play a similar role to ascorbic acid, and the reaction is enhanced if drinks are exposed to higher temperatures.
Both the FDA and the US soft drinks association have known this for 15 years, an investigation by BeverageDaily.com found earlier this year.
Top drinks, including those owned by Cadbury Schweppes, were reformulated after private industry testing in late 1990 revealed a problem. No public statement was ever made, with the FDA allowing industry to "get the word out".
Now, the re-emergence of that problem indicates a communication breakdown in industry and government, although the FDA re-iterated Friday that there was no risk to consumers' health from benzene levels found so far in drinks.
The FDA added it intended to test more drinks for benzene in the near future. It was unclear whether it had tested drinks after exposing them to heat.
Lawyer Ross Getman criticised the agency for not testing enough 'high risk' drinks. Getman and a former food scientist for the soft drinks industry, Larry Alibrandi, re-alerted the FDA to the ongoing presence of benzene in drinks last autumn.
The two men sent the FDA independent lab tests they commissioned, which showed two drinks with benzene above the WHO water limit. The FDA made no mention of these drinks on Friday.
The drinks, BellyWashers 2/3 Less Sugar, made by In Zone Brands, and Polar Diet Orange, made by Polar Beverages, have since been hit by lawsuits in the US over alleged benzene content. Lawsuits have also been filed against PepsiCo and Talking Rain drinks groups.
The FDA said in its statement on Friday that all the producers of affected drinks had agreed to reformulate.
The American Beverage Association said it was sending out a new guidance document across the industry on how to minimise benzene in drinks.
"Repeated reviews by the FDA over the years continue to turn up the same answer: there is no threat to the health of consumers," it said.
Michael Knowles, director of scientific and regulatory affairs at Coca-Cola Europe, said soft drinks makers had learnt to control benzene formation. Consumers must understand, he added, that sodium benzoate's strong ability to kill off bacteria in drinks hugely outweighed the risks.
Other scientists were not so sure, however.
"What are we to tell consumers? 'Product contains cancer-causing substance, drink immediately, do not store in a warm environment or near sunlight?' Preferably benzoate should not be used in combination with Vitamin C (ascorbic acid) or added juice," said a scientist involved in industry testing for benzene 15 years ago.
Glen Lawrence, a scientist who helped the FDA understand the chemical reaction in drinks back then, agreed that sodium benzoate and vitamin C should not be used together."It is really very easy to avoid the problem," he said.