Most plastics are made of long chains of hydrocarbon molecules built from simpler blocks called monomers. When plastics break down they release small amounts of monomer chemicals and ingredients. This process happens more quickly when plastic is heated; for example, when a bottle is left in a car or put in a microwave.

Recently, attention has focused on whether such breakdown processes can occur in plastics after relatively short periods. Experts say it is possible, as are health risks associated with plastic degeneration.

Chris Winder, professor of toxicology at the Australian Catholic University, says the only well-established risk from reuse of plastic bottles is bacterial contamination. This can be resolved with proper washing and rinsing after each use. Given that heat aids the breakdown of chemicals, it's best if this is done in cold water.

Plastic bottles are generally made of two sorts of plastics – polycarbonates (made from Bisphenol A or BPA) and PET (made from polyethylene terephthalates).

Polyethylene is generally considered safe; it's BPA, which has been in commercial use for making plastics since the 1950s, that is getting a lot of bad press in toxicology and science circles.

BPA is known to leach from plastic containers into their contents. The chemical was detected in the urine of 95 per cent of humans sampled in the US (including pregnant women), with higher levels in children, so we are all exposed. This should raise a giant red flag, experts say.

BPA is structurally similar to some sex hormones and has, since the '30s, been recognised as an oestrogen mimic and disruptor. Professor Winder says BPA has been linked (in animal studies) to health problems including developmental and reproductive concerns, infertility, obesity/hypertension, diabetes, thyroid concerns and central nervous system problems such as attention deficit disorder. Breast and prostate cancer have also been reported in some animal studies, he says.

Opinions vary about the health risks of BPA. In some quarters, toxic effects in high-dose animal studies are not considered suitable for human risk characterisation.

That said, action is ramping up to ban the chemical. Canada's food regulator has banned its use, calling it a toxic chemical, and the US and the EU are looking to reduce the level of BPA products being sold. In Australia, Food Standards Australia New Zealand does not consider their use a health risk but has introduced a voluntary phase-out of polycarbonate bottles.

Bad press is causing drink manufacturers to look for other plastics, Winder says. “People who put their drink in this type of plastic are looking for alternatives . . . this chemical is on its way out. Within 10 years most regulators will have taken steps to do something about it and within 20 it will be gone,” he says.