A top environmental group has sued the U.S. Food and Drug Administration over its failure to regulate bisphenol A, a ubiquitous chemical linked to reproductive harm, cancer and obesity in studies.

The Natural Resources Defense Council filed a lawsuit Tuesday in the U.S. Court of Appeals for the D.C. Circuit arguing that millions of Americans have been unnecessarily exposed to the substance - found in everything from soda bottles and tuna cans to children's sippy cups - in the two years since it first petitioned the agency to outlaw bisphenol A.

Under the FDA's own rules, it was required to approve, deny or otherwise respond to the October 2008 petition within 180 days, the lawsuit said. After maintaining for decades that bisphenol A was safe, the FDA reversed position in January, saying exposure to the chemical was of "some concern" for infants and children. The FDA also said it would further study bisphenol A over the next two years.

"More research is always welcome and interesting, but at some point you have to say, 'We know enough,' and take action. We've reached that point," said Sarah Janssen, senior scientist at the NRDC's Environment and Public Health program in San Francisco.

The American Chemistry Council, the trade group representing makers of bisphenol A, said in a statement that "the scientific process and the public interest are both best served by allowing the U.S. Food and Drug Administration to complete its ongoing review of the science surrounding the safety profile of bisphenol A."

Doubts About the Chemical

Officials at the Food and Drug Administration said the agency does not comment on lawsuits.

First developed as a synthetic form of estrogen in the 1930s and later transformed into a plastic used in food containers, bisphenol A has come under increasing scrutiny not just for its connection to early puberty and other reproductive harms, but also to suppressed immune function, cancer, neurological delays and diabetes in studies of laboratory animals.

Most bisphenol A exposure in humans occurs when the substance leaches out of everyday plastics, such as the coatings on pizza boxes or in reusable water bottles.

Urine, Breast Milk

In 2004, the Centers for Disease Control and Prevention found bisphenol A in the urine of 93 percent of 2,500 test subjects, with the highest levels in those 6 to 11 years old. The chemical has also been detected in amniotic fluid, breast milk and umbilical cord blood.

A handful of governments around the world have moved to phase out and otherwise curb bisphenol A. But efforts to ban the chemical in the United States have had limited success.

In 2006, San Francisco became the first city in the country to prohibit bisphenol A in children's products. But the city backpedaled on the ordinance after legal pressure from retailers and chemical manufacturers.

A similar state bill sponsored by Sen. Fran Pavley, D-Agoura Hills (Los Angeles County), passed the Senate but was defeated in the Assembly on Monday.

According to some estimates, makers of bisphenol A have spent $5 million campaigning against the California measure.