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Plastic bottles

Plastic bottlesWhat do the claims about plastics involve?

A group of hoax emails have been doing the rounds for a few years warning about the so-called dangers of plastic bottles, containers and films. The emails generally warn people about one or more of the following:

  • freezing water in plastic bottles
  • reusing plastic water bottles
  • leaving plastic bottles in cars
  • microwaving food in plastic containers or covered with plastic films

However, there is no convincing scientific evidence to back up these claims or to suggest that any of these products could cause cancer.

Where do the claims come from?

A health scare began in 2002 when a scientist voiced concerns about the safety of freezing water in plastic bottles on a Japanese television programme. This same programme also warned against microwaving food in plastic containers. The scientist’s opinions subsequently appeared widely on the Internet.

The emails claim that reusing, heating or freezing water bottles releases cancer-causing chemicals called dioxins. Some also mention a chemical called DEHA, a chemical found in plastics that the emails claim could potentially cause cancer.

Some of these emails credit the warnings about plastics to Johns Hopkins University in America, but the university denies any involvement. On their website, they say:

“The Internet is flooded with messages warning against freezing water in plastic bottles or cooking with plastics in the microwave oven. These messages, frequently titled “Johns Hopkins Cancer News” or “Johns Hopkins Cancer Update,” are falsely attributed to Johns Hopkins and we do not endorse their content.”

Other versions of the emails say that the claims are endorsed by the Walter Reed Army Medical Center. Again, this is not true.

Is there any truth in the claims?

There is no convincing scientific evidence to substantiate these health warnings against plastics. In the UK, there is legislation in place to ensure that all materials that come into contact with food, such as containers for pre-packed food, are thoroughly tested before they can be used.

Can I freeze or reuse plastic bottles?

Professor Rolf Halden of Johns Hopkins' Bloomberg School of Public Health has said that freezing actually works against the release of chemicals. He also says that it is not even clear if plastics contain dioxins, the group of chemicals specifically mentioned in the hoax email. Halden stressed that people should not be afraid of drinking water because of “miniscule amounts of chemical contaminants present in [their] water supply."

There is nothing to suggest that storing water in plastic bottles is unsafe or that a metal bottle would be any better. The types of plastic bottles in which drinking water is typically sold are safe to re-use as long as their condition hasn’t deteriorated and you can clean them. They should be cleaned with hot, soapy water and thoroughly dried every time you refill them, to prevent bacteria from growing.

Can I microwave food in plastic containers or covered in plastic film?

There is no scientific evidence that microwaving food in plastic containers or wrapped in clingfilm can affect the risk of cancer.

According to the Food Standards Agency you can use cling film in the microwave, but make sure the cling film doesn’t touch the food. Whenever you heat something, including plastics, you increase the likelihood of pulling chemicals out. This doesn't include the specific chemicals mentioned in the hoax emails, and there is no evidence that this process could affect the risk of cancer. Even so, it is a good idea to minimise any potential risks by using plastics and clingfilm correctly.

You also shouldn’t use cling film if it could actually melt into the food, like in the oven or on pots and pans on the hob.

Not every type of cling film is suitable for using with all foods. For example, only let cling film touch high-fat foods when the packaging says it is suitable for this. High-fat foods include some types of cheese, raw meat with a layer of fat, pies, and cakes with butter icing or chocolate coatings. You should check the description on the packaging to see what foods the cling film can be used with.

Likewise, it is best to only use plastics that are specifically meant for cooking. As Johns Hopkins University recommends, “In general, it is best to follow the manufacturer’s recommendations when using any plastic products. When cooking with plastics, only use those plastic containers, wraps, bags and utensils for their intended purposes.”

Do plastics release dioxins and are they harmful?

Dioxins are a group of chemicals that are formed unintentionally by industrial processes such as burning fuels and incinerating waste. Only one dioxin, known as TCDD, has been shown to cause cancer in people.

Burning some types of plastic, such as PVC, at very high temperatures can release dioxins into the atmosphere. But there is no evidence to support the idea that dioxins are produced when plastics are heated in a microwave oven, as opposed to actually burned in an incinerator. And it is not even clear if plastics used in water bottles or films contain dioxins in the first place.

Do plastics release DEHA, and is it harmful?

DEHA is a chemical found in some plastics. The email claims about DEHA are based on the work of an American student who supposedly showed this chemical can migrate from plastic wraps into food at high temperatures.

However, this work was never published, and there is no convincing evidence that DEHA is actually present in plastic bottles or plastic wraps. Even if it was, in the late 1990s, the US Environmental Protection Agency (EPA) removed DEHA from its list of toxic chemicals. It said that DEHA "cannot reasonably be anticipated to cause cancer" as well as a number of other health problems.

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Updated: 16 March 2010