| MadSci Network: Chemistry |
Most plastic beverage bottles are made of polyethylene terephthalate, or PET, which has the chemical structure shown below, where the number ‘n’ is large and varies from one molecule to another.
D. Lilya, at the University of Idaho (ref. 1), has found the organic molecules shown below in water stored in used PET beverage bottles under different conditions; there is little toxicity data for any of these, though di(2-ethylhexyl) adipate is a suspected carcinogen in high concentrations. It is present in beverage bottles as a plasticiser, to make the bottles more elastic and less brittle.
Over 48 hours at 60 C, the amount of di(2-ethylhexyl) adipate extracted from PET bottles from a number of sources was found to be almost the same as the background concentration found in water stored in glass bottles, suggesting it is not a serious health risk (ref. 2).
The USFDA and similar organisations in other countries are fanatical about protecting our health from non-natural chemicals, so the ‘use by’ date on the bottles is probably not a bad guide. If the bottle is designed to store one beverage for a certain number of months, then there seems no reason why it shouldn’t be able to keep any other beverage for the same length of time. However:
* UV light from sunlight will speed up the degradation of PET, so it is better not to leave full bottles in the sun for extended periods of time.
* Heat will speed up the motion of small contaminant molecules from the plastic into the contents of the bottle, another reason to keep them out of the sun.
* Recycled PET containers contain significantly more small molecular by-products, and are probably less wise to re-use.
Washing PET bottles with dishwashing detergent with the rest of the dishes should have little effect on them; hot, concentrated dishwashing detergent may well accelerate the degradation of the bottle faster than hot water alone, but should not be significant.
Some references:
(2) www.sodis.ch
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