"Many people are unaware of poisoning caused by re-using plastic bottles," reads a chain e-mail that's causing a stir among concerned consumers. The mail states that freezing water bottles could lead to dioxin leakage, and it's attributed to the John Hopkins Bloomberg School of Public Health in the US.
In reaction to the e-mail, the School's Public Affair's office did an interview with Dr Rolf Halden from the Johns Hopkins Department of Environmental Health Sciences.
"It's an urban legend," Halden says. "Freezing actually works against the release of chemicals. Chemicals do not diffuse as readily in cold temperatures, which would limit chemical release if there were dioxins in plastic."
"Dioxin" refers to a group of toxic chlorinated organic compounds, produced as a by-product of many industrial processes, such as waste incineration and fibre bleaching.
It's a known fact that traces of dioxins can be found in most places on earth. All of us carry a certain amount of the chemical in our cells, regardless of how and what we eat.
Dioxin can be poisonous
However, excessive exposure to dioxin has been linked to an array of negative health effects, including cancer, reproductive and developmental problems, birth defects, diabetes and immune system abnormalities.
But "pure forms of dioxin are not produced because they have no commercial usefulness by themselves. If someone had to ingest a pure form of dioxin, he or she would die within hours," says Prof Gerbus Muller, clinical toxicologist at Tygerberg Hospital.
The dangers that lurk in PVC
One of the types of plastic that has been implicated in the release of dioxins, is polyvinyl chloride (PVC).
This polymer is indeed a potential source of dioxins when it is incinerated, according to Prof Ronald Sanderson of the Institute for Polymer Science at the University of Stellenbosch. But as PVC has little chance of burning during recycling and it is not recycled to make new bottles in South Africa, consumers have nothing to worry about. They can use their mineral-water bottles over and over again.
Other types of plastic that are commonly used in the production of plastic bottles include polyethylene terephthalate (PET), polypropylene and polycarbonate. These plastics have all been extensively tested for safety by such regulatory bodies as the US Food and Drug Administration (FDA). And, according to Sanderson, there is no known link between these materials and dioxin leakage.
Heating can 'pull' chemicals out
However, Halden warns against the process of heating. "In general, whenever you heat something, you increase the likelihood of pulling chemicals out. Chemicals can be released from plastic packaging materials like the kinds used in some microwave meals."
The best thing to do when you are cooking with plastics, is to follow the directions and only use plastics that are specifically meant for cooking, Halden advises.
Note that plastics are by nature extremely sanitary materials. Therefore, consumers also needn't be worried that their plastic bottles are harbouring harmful bacteria. If bottles are re-used, they should simply be cleaned with soap and warm water.