Two soft-drink companies were sued Tuesday by parents complaining that there might be cancer-causing benzene in kids' drinks.

Attorneys filed class-action lawsuits against the companies in Suffolk Superior Court in Boston and Leon County Circuit Court in Tallahassee, Fla. They accused Polar Beverages Inc. and In Zone Brands Inc. of not taking steps to keep benzene from forming in their beverages.

Benzene, a chemical linked to leukemia, can form in soft drinks containing two ingredients: Vitamin C, also called ascorbic acid, and either sodium benzoate or potassium benzoate.

The presence of those ingredients doesn't mean benzene is present. Scientists say factors such as heat or light exposure can trigger a reaction that forms benzene in the beverages.

"It's impossible for parents to know which soft drinks are safe and which contain cancer-causing benzene," said Timothy Newell, one of the plaintiffs.

Atlanta-based In Zone makes BellyWashers, juice drinks that come in reusable bottles featuring Spiderman, Hello Kitty, Scooby Doo and dozens of other well-known characters. Worcester, Mass.-based Polar Beverages makes fruit-flavored sodas and seltzers as well as mixers.

The lawsuits allege that independent laboratory tests found benzene in the companies' drinks at levels above the federal drinking-water limit, which is 5 parts per billion.

Food and Drug Administration sampling from 1995 through 2001 found similar results in unidentified brands, and FDA is currently doing more tests. FDA officials maintain there is no safety concern and that levels are still relatively low compared with other sources of exposure to benzene.

Likewise, a soft drink industry group argues that the amount of soft drinks people consume is much less than the amount of tap water they are exposed to.

"Benzene is ubiquitous to the environment. It's in the air. It's in dozens of foods, including bananas, meat and eggs," said Kevin Keane, spokesman for the American Beverage Association, the industry group.

Keane called the lawsuit an attempt by trial lawyers to make money.

In a statement, Polar Beverages president and CEO Ralph D. Crowley Jr. said all of his company's products are safe.

"Polar is committed to ensuring the safety of our products through in-depth research and testing," Crowley said. Polar Beverages had an independent laboratory test its products as recently as February and no trace of benzene was found, he said.

The plaintiffs ask that companies be prohibited from selling drinks that may contain benzene in Massachusetts and Florida. They note that other companies have either removed one of the ingredients or added ingredients to keep benzene from forming.

Benzene forms naturally in forest fires, gasoline and cigarette smoke, among other things, and it's widely used industrially to make plastics, rubber, detergents, drugs and pesticides.