Plasticisers - Good or Bad?

PLASTICISERS – GOOD OR BAD?


A reader commented recently that she had heard that the plasticiser used in water bottles could be toxic and find its way into the water. This is a very timely question and one that I had considered but was unable to fit into my previous column. Let’s take a more detailed look at this complicated story.

First, what is a plasticiser? Many polymers contain additives to give them desirable properties such as colour, resistance to UV and heat (the enemies of polymers) and sometimes more or better flexibility. For example, we have seen the turquoise pipe made in Prescott for water pipes. It is made of polyvinyl chloride, or PVC, and is very hard. PVC is the same material that your swimming pool liner and your raincoat is made of, but they contain a plasticiser to make them flexible. So a plasticiser acts as a lubricant between the very large polymer molecules, enabling them to move against and past one another, and giving flexibility to the finished product. Sometimes plasticisers are added to make a polymer easier to process, such as in making wire insulation.

These plasticisers take many different chemical forms, depending on what polymer is being processed and what end-use is sought. A very common plasticiser is called dioctyl phthalate, or DOP for short… we won’t worry about the formula for now. DOP is used extensively in flexible PVC polymer, the kind consumers encounter frequently in waterproof clothing, pool liners and many other applications. DOP is considered safe… more about that in a moment. For food handling and packaging applications, plasticisers are based on citric acid, the most common of which is called tributyl citrate.

As I mentioned above, most plasticisers are used in PVC plastics. Water bottles are made of polyester plastic, or PET, and according to my research and to the manufacturers, do not contain plasticiser. Most common food-packaging polymers, such as polyethylene (milk bags), polypropylene (yogurt and ice cream containers) and polystyrene (clear clam-shell containers and foam plastic containers) are made without plasticisers. There is a catch, of course. When a polymer is made and all those tiny molecules are linked to make a large polymer molecule, not all the small molecules become incorporated into the polymer. This material, called monomer, may be soluble in the food, or may be volatile (evaporates) and this could be a cause of concern to some consumers.

I have read about claims that freezing a water bottle to keep your lunchbox cool and enjoying ice water at 3:00PM can increase the amount of plasticiser in the water. This is wrong on two counts – first, there are no plasticisers in water bottles, and second, in almost all physical and chemical processes, a lower temperature slows things down. Researching this in the 70s regarding plastic milk bags, we placed milk in bags at 35 deg. F., (fridge temperature), at 70 deg. F., (room temp) and at about 150 deg. F., (microwave temp). In every case more monomer (not plasticiser) migrated to the milk as the temperature increased, although none at a level thought to be harmful. So freezing your water bottle is not going to cause any health risk.

Now we get to an interesting component of this story. Some of this information and misinformation has been swirling around the Internet for a while, and as you know it can gain a life of its own. A thesis by a student at the University of Idaho claimed that chemicals were leached from water bottles into the water, and this was widely quoted. The problem is that this was not a peer-reviewed scientific study, one in which scientists familiar with the subject examine the work and determine if it was done to the highest technical standards A subsequent review of the student’s lab work revealed significant gaps and unacknowledged sources of error, yet the so-called study continues to be cited.

Back to DOP, the common plasticiser in PVC. In the chemical world, there are many chemicals that have been in common use for years. As knowledge and better testing advances, some of these are removed as we realise their harm, such as asbestos for insulation and phenol as a disinfectant. Others we substitute using a less harmful equivalent material, such as using HCFCs instead of the original fluorocarbons. With others we change the amount or the application as we refine our understanding of how they work. DOP comes in the latter category. It has no known connection to cancer or any adverse health effects, but it is being monitored to determine if it is being over-used and a better substitute can be used. This is a long-winded way of saying that medical science knows of no long term serious effects of exposure to DOP, but that doesn’t mean they don’t exist.

So where does all this leave us? Food packaging material is extensively tested under a variety of conditions, and is very safe. It has significant benefit to the consumer by keeping food clean, maintaining freshness and minimising waste. If you as a consumer are concerned, you can of course purchase your food fresh and have it wrapped in paper or polyethylene bags and wrap. My guess is that you will not see a difference.