Although it is generally thought to be safer, researchers from the University of Florida are warning consumers to be careful when drinking warm bottled water, based on their study that examined bottled water in China.

The researchers state that, when heated, plastic water bottles made from polyethylene terephthalate release the chemicals antimony and bisphenol A, commonly known as BPA.

FDA says BPA is not a major concern in the low levels found in beverage containers, but the agency is continuing to study its impact.

However, health officials, including those at the Mayo Clinic, say the chemical can negatively affect children’s health.

Furthermore, the study researchers say the International Agency for Research on Cancer, part of the World Health Organization, considers antimony to be a carcinogen.

Lena Ma, soil and water science professor at the university, led the study of chemicals released in 16 brands of bottled water kept at 158°F for four weeks. The researchers called this a worst case scenario for human consumption.

Of the 16 brands, only one exceeded the EPA standard for antimony and BPA; however, Ma says more research is needed to see if the other brands are safe. She adds that, as the bottles warmed over the four-week period, antimony and BPA levels increased.

 “If you store the water long enough, there may be a concern,” Ma says. Consequently, she warns against leaving bottled water in a hot garage for weeks on end or in a car all day during the summer.

Because of what Ma calls cultural differences and the fact Chinese citizens have less faith in their tap water, some leave bottled water in their car trunks for weeks. China consumed 9.6 billion gallons of bottled water in 2011, making that country the commodity’s largest market.

By comparison, Americans drank 9.1 billion gallons of bottled water that year, according to the International Bottled Water Association. While most Americans don’t store bottled water in their cars for extended periods, they often keep it there for a day or two. Drinking that water occasionally isn’t dangerous, but doing so regularly could cause health issues, Ma says. And it’s not just water containers that merit more study, she adds.

“More attention should be given to other drinks packaged with polyethylene terephthalate plastic, such as milk, coffee and acidic juice,” she says. “We only tested the pure water. If it is acidic juice, the story may be different.”

Although not part of the study, Ma touts tap water over bottled water. Both are regulated by the federal government— tap by the EPA and bottled by the U.S. Food and Drug Administration.

The study is published in this month’s edition of the journal Environmental Pollution.