Scientists at the University of Cincinnati in the US say that when the same new and used polycarbonate drinking bottles were exposed to boiling hot water, BPA, an environmental estrogen, was released 55 times more rapidly than before exposure to hot water.
Their study sheds light on how BPA is released from plastic.
BPA is one of many man-made chemicals classified as endocrine disruptors, which alter the function of the endocrine system by mimicking the role of the body's natural hormones.
It has been shown to affect reproduction and brain development in animal studies although its effect on humans is not clear.
Nevertheless, the chemical is widely used in plastic packaging for food and beverages and the resin linings of food cans and some groups say it should be removed to protect human health.
Previous studies have found that the chemical migrates in small amounts into food and beverages from packaging containing the substance but it was not understood why.
The new study shows that it is not whether the container is new or old but the liquid's temperature that has the most impact on how much BPA is released.
"Previous studies have shown that if you repeatedly scrub, dish-wash and boil polycarbonate baby bottles, they release BPA.
But we wanted to know if 'normal' use caused increased release from something that we all use, and to identify what was the most important factor that impacts release," said Scott Belcher, associate professor of pharmacology and cell biophysics and corresponding study author.
Belcher's team analyzed used polycarbonate water bottles from a local climbing gym and purchased new bottles of the same brand from an outdoor retail supplier.
All bottles were subjected to seven days of testing designed to simulate normal usage during backpacking, mountaineering and other outdoor adventure activities.
The researchers found that the amount of BPA released from new and used polycarbonate drinking bottles was the same-both in quantity and speed of release-into cool or temperate water.
However, drastically higher levels of BPA were released once the bottles were briefly exposed to boiling water.
"Compared to the rate of release from the same bottle, the speed of release was 15 to 55 times faster," explains Belcher.
Prior to boiling water exposure, the rate of release from individual bottles ranged from 0.2 to 0.8 nanograms per hour.
After exposure, rates increased to 8 to 32 nanograms per hour.
"There is a large body of scientific evidence demonstrating the harmful effects of very small amounts of BPA in laboratory and animal studies, but little clinical evidence related to humans," said Belcher.
"There is a very strong suspicion in the scientific community, however, that this chemical has harmful effects on humans."
The scientists report their findings in the 30 January issue of the journal Toxicology Letters.