Fact check: Plastic water bottles left in hot cars don't release dioxins, do leach other chemicals

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The claim: Heat reacts with the chemicals in plastic water bottles and releases harmful dioxin

Do water bottles leach a cancer-causing chemical when exposed to extreme heat?

A Facebook user shared an image of a warning sign on Oct. 3, 2019, that had the words, "Bottled water in your car is very dangerous!"

The two-year-old post generated nearly 160,000 shares, most of them early this October as the post found renewed life online.

According to the post, singer Sheryl Crow said on "The Ellen Degeneres Show" that she got breast cancer from dioxin from a water bottle that had been left in a hot car.

"Dioxin is a toxin increasingly found in breast cancer tissue. So please be careful and do not drink bottled water that has been left in the car," the post says.

"I posted that 2 years ago, it was sent from a family member so I decided to post," the Facebook user told USA TODAY. "Didn’t double check the info, but up until 3 days ago, it had thousands of shares and comments and likes."

The same warning was posted by an Instagram user on Oct. 7, and it generated more than 15,000 likes in less than a day. That post has since apparently been removed.

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But, the claim is off the mark. Heat does react with the plastic of the bottle to release chemicals in a process known as "leaching." However, dioxin is not one of those chemicals, experts say.

USA TODAY reached out to social media users who shared the post for comment.

No dioxins in water bottles

Dioxins are not found in plastic, nor do plastic water bottles left in hot cars release dioxin, experts say.

Dioxins are a group of toxic chemical compounds that share certain chemical structures and biological characteristics, according to the Environmental Protection Agency.

They are formed from industrial activity and combustion processes such as burning trash or fuel, and they then make their way from the air into lakes and soil, according to the EPA.

"People should not be concerned about carcinogenic dioxins in drinking containers. But there are other chemicals that potentially could cause harm," said Rolf Halden, director of the Center for Environmental Health Engineering at Arizona State University. "Therefore, it is better to use inert materials for storage, glass rather than plastic."

Halden debunked a similar urban legend with the Johns Hopkins Bloomberg School of Public Health in 2004 that said freezing water bottles releases dioxins.

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"The main way people are exposed to dioxins is through our food system. Dioxins are industrial pollutants that persist in the environment and tend to build up in the fatty tissue of animals," Nicole Deziel, associate professor of epidemiology and the environment at the Yale School of Public Health, told USA TODAY. "So, consuming animal products like meat, dairy, various fish is one of the main ways people get exposed to these chemicals."

She said dioxins can cause cancer in many parts of the body, and links to breast cancer specifically are still being studied.

Plastic water bottles exposed to heat undergo 'leaching'

Plastic water bottles are known to leach chemicals into water, and the process of leaching is facilitated by heat, according to Halden.

"So the hotter it is, the more readily the transfer occurs of things from the plastic polymer into the water that's stored in the plastic container," he told USA TODAY.

The type of chemicals released depends on the type of bottle, according to Halden. Polycarbonate reusable plastic water bottles are made of bisphenol A, which has been associated with a range of adverse health effects, including functioning like a hormone mimic and as an "obesogen," or fattening chemical, in animal studies.

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Polyethylene terephthalate, which is commonly used for single-use disposable plastic bottles, is known to leach a harmful metal, antimony, that can cause lung, heart and stomach problems.

Nature of Crow's comments unclear

USA TODAY was unable to find evidence of Crow talking about plastic bottles, dioxin and breast cancer on "The Ellen Degeneres Show."

Crow did an interview with DeGeneres in 2008, which was uploaded to YouTube, but it doesn't show her discussing plastic water bottles or dioxin. Crow was also a guest on the show in 2006, but USA TODAY wasn't able to locate a recording to establish what she talked about.

Crow did not respond to USA TODAY's request for comment.

Crow did post about bottled water on her website in 2006, where she says, "Don't drink water from a bottle that has been sitting in your car. Heated plastic will bleed toxic substances that can be carcinogenic."

Our rating: Partly False

Based on our research, we rate PARTLY FALSE the claim that heat reacts with the chemicals in plastic water bottles and releases harmful dioxin. Plastic water bottles left in hot cars do not release dioxin, according to an expert, but plastic water bottles are prone to leach other chemicals.

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This article originally appeared on USA TODAY: Fact check: Plastic water bottles leach chemicals, but not dioxins