One of the latest chain mails deals with the hidden dangers behind the numbered recycling symbol found on plastic bottles. It's called a Mobius logo, and it has three arrows rotating clockwise to represent collecting, reprocessing and reusing.
Unverified sources say the number can be a sign of whether a plastic food container is safe for use. For example, plastic materials marked with the number one recycling symbol cannot be used more than once or they will produce carcinogens. Plastic bottles with the number four symbol will release cancer-causing substances if heated.
These chain e-mails may seem convincing, yet Dr Michael Lam Hon-wah, of the City University of Hong Kong (CityU), points out that the logos "are actually not for the 'average Joe', but for the recyclers to sort out plastic and determine the method of reprocessing".
Lam, associate head and associate professor at CityU's Department of Biology and Chemistry, said the alleged threats from plastic listed in the e-mails were exaggerated. "All kinds of plastic products are safe, as long as they are used in the right way," he says.
Lam noted that heat can indeed have a negative effect on the state of a plastic food container and the term "microwavable" is misleading. "Microwavable is a term used to show that a container will not deform under a high temperature [around 120-125°C], but it does not guarantee that the leaking of chemical additives from the plastic will not occur," he says. "But [we should bear in mind] the relationship between toxicity and exposure. Exposure to low levels of toxicity is inevitable and it is often the case when we talk about using plastic products."
We can protect ourselves by using plastic products the right way. Preventing plastic from being exposed to sunlight and heat is one way of doing just that.
The majority of plastic bottles are made out of PET (polyethylene terephthalate) and are meant to be used only once because their surface is porous, which makes it easy for bacteria to accumulate.
"Yet we can safely reuse the bottles after cleaning them with warm, soapy water," Lam says.
Oxidation of plastic is another problem. We should avoid exposing plastic bottles to direct sunlight which can cause their surfaces to crack.
Finally, all kinds of plastic will release chemicals when heated. So try to avoid heating food using a plastic container.