Plastic water bottles release the toxic chemical bisphenol A at a rate 55 times greater when filled with boiling water than when filled with room temperature water, according to a study conducted by researchers from the University of Cincinnati College of Medicine and published in the journal Toxicology Letters.

"Previous studies have shown that if you repeatedly scrub, dish-wash and boil polycarbonate baby bottles, they release bisphenol A," said researcher Scott Belcher. "But we wanted to know if 'normal' use caused increased release."

Bisphenol A is used to make the hard, transparent polycarbonate plastics that are used in a wide variety of consumer products, including water and baby bottles. But concerns have been raised that the chemical might leach into water or infant bottles from the normal use of such bottles.

"There are a lot of concerns surrounding bisphenol A," said David Santillo a scientist at the Greenpeace research laboratory in Exeter, England. "It is a hormone disrupter able to mimic and interfere with hormone systems in animals. Newborn babies are at a very sensitive stage of their development and the last thing you want to be doing is dosing them with a very potent hormone disruptor."

Hormone disruptors can interfere with the development of infants, as well as causing reproductive problems and cancers in adults.

Researchers tested reusable polycarbonate water bottles for seven days with room temperature water and then with boiling water. The bottles were shaken in such a way as to simulate regular outdoor activities such as backpacking.

When filled with room temperature water, bisphenol A leached from the bottles at a rate of 0.2 to 0.8 nanograms per hour. After being exposed to boiling water, the bottles leached the chemical at a rate of 8 to 32 nanograms per hour.

"A nanogram is a fairly small amount, but given that a lot of hormones work at levels far below that ... you are in the range there which could be contributing to adverse effects," Santillo said.