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As a heat wave bakes parts of the country this week, some experts believe there may be more than one reason to keep your bottle of water cool when the temperatures rise in the summer.
Some researchers who study plastics recommend against drinking water from plastic bottles that have been sitting in hot places for a long time — such as a car sizzling in the sun — concerned that the heat could help chemicals from the plastic leach into the water.
The industry disagrees, with the International Bottled Water Association maintaining that plastic bottled water containers are regulated and safe under a variety of conditions, including when they are left in hot cars.
But Cheryl Watson, a professor in the biochemistry and molecular biology department at the University of Texas Medical Branch in Galveston, advised people not to store bottled water in places that have a significant amount of heat, like a garage or a car parked outside.
“When you heat things up, the molecules jiggle around faster and that makes them escape from one phase into another. So the plastic leaches its component chemicals out into the water much faster and more with heat applied to it,” Watson told TODAY.
“It’s kind of like when you put mint leaves in your tea. The heat extracts the mint-tasting molecules and it happens faster in hot tea than it does in cold tea.”
If you’ve ever left a plastic water bottle in a hot car or another very warm environment for a while, you may notice the water tastes a little funny, Watson noted: “That’s everybody’s bottom-line sensing mechanism — you can even taste it,” she said.
A 2014 study analyzed 16 brands of bottled water sold in China that were kept at 158 degrees Fahrenheit for four weeks and found increased levels of antimony — listed as a toxic substance by the Centers for Disease Control and Prevention — and bisphenol A (BPA), a chemical in certain plastics that can mimic estrogen and has been under scrutiny for years
But of the 16 brands, only one exceeded the EPA standard for antimony and BPA, a University of Florida news release noted.
“I don’t want to mislead people, saying bottled water is not safe. Bottled water is fine. You can drink it — just don’t leave it in a hot temperature for a long time. I think that’s the important message,” Lena Ma, the study’s co-author and a professor of biogeochemistry of trace metals at the University of Florida, told Yahoo Health.
Another study, conducted in 2007 by Arizona State University researchers, found summertime temperatures inside cars, garages and enclosed storage areas “could promote antimony leaching from PET bottled waters.”
When it came to Ma’s research, the International Bottled Water Association said the study “misrepresents facts.”
The group noted that BPA is not a chemical component of polyethylene terephthalate (PET), the packaging material used to make single-serve bottles of water, and that the level of antimony found in the samples was minimal.
“Bottled water products that are packaged in PET plastic containers do not contain ingredients capable of producing dangerous substances under conditions of normal use,” said Jill Culora, a spokeswoman for the International Bottled Water Association, in a statement.
“Claims that plastic bottled water containers stored in warm environments — for example, a hot vehicle — ‘leach’ unnamed chemicals that cause breast cancer or other maladies are not based in science and are unsubstantiated.”
The U.S. Food and Drug Administration regulates the safety of bottled water, including the packaging, the group noted. As with any food product, bottled water should be stored in a cool dry place, away from household solvents, fuels and other chemicals, and away from direct sunlight, it added.
BPA, which is used to make polycarbonate beverage bottles, food storage containers, metal can coatings, and which also coats some register receipts, has long caused concern about its impact on human health.
But it’s unlikely to be harmful to people in typical doses, the FDA said in February.
Still, Watson, the University of Texas Medical Branch researcher, advised people to always stick to glass or stainless steel water containers — no matter the temperature. Those materials are very inert and don’t leach anything into the water, she said.
Her studies have found products labeled “BPA-free” may contain BPS instead, a chemical that’s very highly related to BPA in structure and appears to act much like BPA, causing the same disruptions of hormone signaling, Watson noted.
“It’s a shell game,” she said. “As we get the word out to the public that BPA is dangerous, they substitute other chemicals that are different, but only slightly different.”
She’s sticking to her trusty stainless steel bottle that she fills at home with filtered tap water.