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Better Drinking Through Chemistry - Rat Ramblings [entries|archive|friends|userinfo]
Nicodemus

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Better Drinking Through Chemistry [Jun. 14th, 2005|12:13 pm]
Nicodemus
[Current Mood |curiouscurious]

Sometimes bottled water gets a funny "plastic" taste. This seems to happen a lot if a bottle of water is left in the car (something I tend to do frequently). The water then gets a light aftertaste.

Now I know that the temperatures inside my car don't get high enough to even begin to melt the plastic of the bottle... So where is that flavor coming from? Well, I did a bit of web reading about some polymers today during lunch (what, you don't read about polymers for fun?) and came up with this theory:

The degradation of the bottle's PET (polyethylene terephthalate) is leeching out trace amounts of acetaldehyde into the water. This is that bottle taste. Any [armchair or pro] chemists out there who can chime in on this one?
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[User Picture]From: nicodemusrat
2005-06-14 07:29 pm (UTC)
Cool. I always wonder about these things... I like understanding the details of everything! I just happened to come across the right information today to put together a good guess. :)
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[User Picture]From: 14cyclenotes
2005-06-14 07:31 pm (UTC)
Yes. Acetaldehyde is harmless, but it isn't tasteless. It's produced as a natural part of the polymerization process and also as a degradation product, and over time it leeches into any water-based liquid that's stored in such bottles.
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[User Picture]From: nicodemusrat
2005-06-14 07:47 pm (UTC)
Cool. Thanks for the info!

Since it's part of the polymerization process, that some amount of acetaldehyde is present in the plastic from the beginning. I guess time alone would be enough for some of that to leech out (which would explain expiration dates on bottled water). PET degradation (due to heat) just speeds things along a bit.

(Also, since I'm curious, how did you find my entry/LJ?)
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[User Picture]From: 14cyclenotes
2005-06-15 06:25 pm (UTC)
I guess time alone would be enough for some of that to leech out (which would explain expiration dates on bottled water).

That's part of it: there is a constant leeching of plastic components into the water. Part of it also though is bacterial growth. Unless the water is sterilized in the bottle there's no way to make it free of bacteria, and bacteria can eventually use almost any source of carbon. So while bottled water has a very long shelf life (water in glass has the longest) it can "go bad" in time.

Also, since I'm curious, how did you find my entry/LJ?

artsykitten linked me to it, since she knows that I'm a chemist and enjoy this sort of thing. :)
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[User Picture]From: nicodemusrat
2005-06-15 09:06 pm (UTC)
Aha, should've thought of that.

Welcome. Thanks for providing the helpful info!
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[User Picture]From: brandywine93
2005-06-14 07:36 pm (UTC)
wow!! that is very cool!!! :-) thank you for sharing as i've always wondered that myself.
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[User Picture]From: xolo
2005-06-14 08:25 pm (UTC)
Ethyl aldehyde (acetaldehyde) occurs industrially as a byproduct in the polymerization of ethylene, which is where the traces in the plastic bottle come from. It's considered a CNS depressant, and acts on the body much like alcohol. Ethyl aldehyde is in fact produced as a breakdown product from any alcohol that you drink, so that if you've ever had a beer in your life, you probably generated more ethyl aldehyde in your liver right there than you'd get in a year of drinking out of plastic bottles. Your liver further reduces it to acetic acid, and it's excreted in the urine.

Most sources list it as highly toxic, but in all honesty, at the concentrations in which it occurs in the real world, it's nothing to worry about. Here's the MSDS.
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[User Picture]From: nicodemusrat
2005-06-15 09:11 pm (UTC)
Ooooo, an official MSDS. You get bonus points!

I figured that there was no real toxicity threat from the levels in bottled products. (Otherwise it surely would've been noted before now.) But I am satisfied that I finally figured out why bottled water gets that odd taste!

Thanks for the extra info.
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[User Picture]From: xydexx
2005-06-14 09:23 pm (UTC)
I've been wondering about this as well. When I've brought my water bottles to work, the plasticky taste starts to be noticeable towards the late afternoon (about 6 hours after filling). I counter this by simply emptying and refilling the bottles if I know they've been sitting around a while.
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[User Picture]From: sabercat
2005-06-15 03:40 am (UTC)

Darn it...

Xolo and 14cyclenotes beat me to it... I was hoping to finally put my Chemical Engineering degree to some use. :)
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[User Picture]From: shalora
2005-06-15 06:34 am (UTC)

Re: Darn it...

Well, then here's a question for ya. Someone who usually doesn't spout this stuff unless she knows what she's talking about told me once that you shouldn't refill and re-use plastic water bottles. Not the kind like you buy in a sporting goods store, but like Evian and such come in. Any truth to that theory? D'you suppose it was just because of this leeching? 'Cause frankly, it doesn't sound like too big a deal, if that's all it is. :)
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