Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: thedoc on 12/03/2012 08:51:01
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Alan Cluett asked the Naked Scientists:
Chris,
I listen to your session with Redi (http://www.thenakedscientists.com/ask) on 702 on Fridays.
My wife and I differ on how we complete the dishwashing exercise.
I always rinse the cleaned but soapy dishes in clean water before stacking for drying, whilst my wife stacks the dishes directly from the soapy water.
We use biodegradable dish washing liquid.
My view is that the dishwashing liquids contains de-greasers and wetting agents that, if not rinsed off, will contaminate the next plate of food, cup of coffee or tea etc. Over many years this could impact on the internal linings of our mouths, throats and, especially, stomachs.
Am I being paranoid*?
Alan.
* in the sense of "unreasonably or obsessively anxious, suspicious, or mistrustful"?
What do you think?
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I say definitely yes because I find the taste of dish washing detergent to be disgusting. Even your nice biodegradable one.
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I'm all for a good rinsing... I suppose if you towel dry the dishes, that will take off most of the soap. Or, you could stack, then spray-rinse.
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any small traces of detergent in your mouth will be washed away when you eat and drink, they will get mashed to bits in the stomach full of hydrochloric acid and any surviving traces will be washed through your guts, eventually finding their way back into the drainage system via your toilet bowl. At least they may in some small way contribute to keeping the bowl clean
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Isn't the rinsing process just using hot water/steam drying?
There's usually a rinsing 'agent' in the dishwashing tablet but I had thought this just stopped smearing (just a softener?) and left no chemical residue behind anyway.
I have heard that washing-up liquid can have carcinogenic properties and I would always rinse suds off plates, etc before stacking. Although it's probably just an urban myth.
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"I have heard that washing-up liquid can have carcinogenic properties"
I can think of relatively few things that couldn't be substituted for "washing up liquid" in that sentence.
The detergents are of low oral toxicity (Gosh!).
They don't taste very nice (even the lemon scented ones).
On the other hand, if those detergents get into the bloodstream they are quite toxic. However if there's a big enough hole in your stomach lining for that to be an issue, then you already have a much bigger problem than soap.
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They do tend to have a laxative effect in many cases........
A case of them doing double duty, cleaning the plate and a while later doing the same to you from the inside.
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I'm not quite sure what is in the squeeze bottle of detergent.
However, you can make lye soap if you wish. 100% natural, and it should be safe to eat it too [;)]
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Aside from the chance of gaining a stomach ache and/or diarrhea, the basic mechanism of how soap works would be enough to get me to rinse off the dirty dishwater.
Soap removes grease and dirt(salty, sugary) things from your dishes. Each lauryl (soap) molecule has a non-polar end for greases and oils, and a polar end for salts and sugars. These soap molecules surround the oils and dirts by which ever end of the molecule is needed.
So when the dishes are not rinsed, those greases and dirts are being left on your dishes, with the 'bonus' of the soap as well. Hope this helps your proposal.
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I agree with you at this and I do it the same way you do. I usually use dishcloth or silicone sponges to rinse the dishes first, and then washing the dishes with clean water. Though they claim that dishwashing liquid is not harmful, I don't believe that, never.
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Though they claim that dishwashing liquid is not harmful, I don't believe that, never.
Well, that's what the evidence says, so why don't you believe it?
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I spent the most entertaining six months of my life as a detergent chemist. Like Colman's Mustard, the hand dishwashing detergent suppiers make their profit from the fact that everyone uses far more than necessary to do the job. Two lessons learned from a great job and a long life
1. Always rinse. That's what the chemicals are designed for.
2. Use a dishwasher. It's hotter than you can safely wash by hand, uses a more efficient surfactant (the stuff would degrease your hands) , and uses less water if it's reasonably full before you start.
Finally: what the heck is "micellular water" that ladies are now encouraged to splash on their faces? In my book, that's just weak detergent, and should not be left in prolonged contact with skin. Zillions of years of rigorous research and development (known as evolution) have determined that your skin, particularly on your face, is protected from bugs and ultraviolet by the natural oils it exudes for the purpose. If you rip them off, you'll have to pay for expensive cosmetics to replace them. Soap off the mud, then rinse with plain water only.
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To be fair, the skin could reasonably be described as "micellular water"- cells are pretty nearly micelles.
Perhaps more relevantly, most "cream" cosmetics are emulsified oil/ water mixtures of some description and are micelles.
Cream (as in, floats to the top of the milk) is too.
And the oil/ water mix that we call sweat probably is (I haven't checked).
The fatty acids that are present on our skin are (poor) surfactants so...
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I've been taught to distinguish between an emulsion, where a fundamentally hydrophobic liquid is held in suspension by the surface tension of its own droplets preventing coalescence, and a micellular complex where a surfactant molecule forms a stabilising link by having a hydrophobic head and a hydrophilic tail. But that was many years ago!
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It's a valid distinction, but I suspect that much of biology is more complicated than that. Cell walls have proteins stuck through them.
Not all emulsions have a high enough concentration of a surfactant that the whole surface is covered, but it's high enough that electrostatic repulsion stabilises them against "settling out".
None of this detracts form the term used in the advert being a prime example of "technobabble" for which I am grateful; I may use it in future.
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There is no doubt that the detergent should be rinsed off after washing. You can use another dish scrubber which is clean and hasn't absorbed any detergent to wipe the dishes during rinsing.