Which plastic bottles are safe to re-use?

Canada's ban on plastic baby bottles containing the chemical bisphenol A - the first clampdown of its type - has reawakened the debate on what plastics are safe.

Bisphenol A, or BPA, is used to make polycarbonate plastic, a clear shatter-resistant material, in products ranging from plastic baby and water bottles to sports safety equipment and medical devices. 

The jury is still out on how dangerous BPA is. It's in the dock because it mimics estrogen, the female hormone, and may cause neural and behavioural problems in fetuses, infants and children. Given that these plastics can all be replaced by something else, the Canadian government has decided better safe than sorry.

What is not in dispute is that BPA is enterning the human body. In a 2007 study by the Centers for Disease Control and Prevention, 93% of Americans were found to have BPA in their urine.  

The reason is that contrary to what we've often been told, plastic does not last for ever. The chemicals can start leaching out as the plastic gets older and/or is and washed and/or heated repeatedly. Warning signs on bottles include cracks or cloudiness in the plastic.

How safe are your plastic bottles? You can check the plastic in your bottle by looking at the labelling on the bottom. There should be the name of the type of plastic (eg PET) and/or a number.

• The two categories which are most dangerous are probably number 3 (Vinyl/PVC: polyvinylchloride) and number 6 (PS: polystyrene) both can leach cancer-causing chemicals.
• PET or PETE (polyethylene terephthalate) is number 1. It's fine for one-off use but may leach cancer-causing chemical and endocrine-disruptors as it degrades. Whether these are in dangerous quantities or not is not clear. To be on the safe side, the general advice is not to reuse PET bottles.
• Category 7 is miscellaneous and may include bisephonal A. All tin can linings include BPA. But Tetrapak type 'brick' cartons do not.
• Safer plastics include: number 2 - HDPE (high-density polyethylene; number 4 - LDPE (low-density polyethylene); and number 5 - PP (polypropylene)