From: Sil Horwitz (silh@earthlink.net)
Date: 05/09/01-11:07:59 AM Z
At 2001/05/08 08:30 AM -0400, Dan wrote:
>Sounds silly but I was wondering, is there any danger (toxic fumes,
>explosions, reproductive organ mutation, etc.) in mixing a chlorine-based
>bleach with EDTA? Seems like it could be a handy spray for both mildew
>and mineral buildup in showers.
In spite of many photographers thinking it's the best thing since Sodium
sulfite, EDTA has only one main function: it's a sequestering agent. That
is, it can prevent interaction between two otherwise reactive substances.
Its main use is in preventing many metals from reacting with others,
therefore, it is used in photography (and washing compounds) for minimizing
the effect of calcium in tap water from combining with sulfites and other
chemicals that form insoluble calcium compounds. Also used in bleach-fix
solutions to minimize reaction of iron compounds with thiosulfates (fixer)
which are otherwise incompatible. (Its use in some of the alternative
processes is highly questionable in value. But if the practitioner feels it
helps, fine, as it won't hurt!)
OK. EDTA, though the abbreviation translates to "ethylenediamine
tetra-acetic acid" is not an acid in the sense that most of us have
learned. It's an acid in the carbon-group, which means it can react to form
compounds. EDTA is rarely used in photography or anywhere else, as it is
difficult to dissolve. What we use is either the disodium salt or mostly,
the tetrasodium salt (remember: EDTA can form compounds as though it were a
true acid). Any sodium salt of EDTA is alkaline as the sodium is more
highly ionized than the weak EDTA radical.
Now, to answer your question (I'll bet you thought I'd never get to it):
household bleach is also alkaline, sodium hypochlorite, made by dissolving
chlorine gas in sodium hydroxide (lye). The only possible toxicity would be
the chlorine, which is normal with the bleach. Though I'm not familiar with
any testing, there is a possibility that the EDTA would actually inhibit
the action of the chlorine bleach because of its sequestering action. Look
on a bottle of one of the proprietary liquids used for the purpose you
describe and I don't think you will find EDTA. There are other materials
more efficient for this purpose. It's why I would stick to the spray
bottles available in every household cleaner department, as most of the
chemicals in the formulas are practically unavailable to us little guys.
Chlorox brand has a number of them that include sodium hypochlorite.
My late wife used to say if you ask me what time it is, I go into how a
watch works. Sorry if I'm longwinded about this, but otherwise I find I get
many additional questions. Hope I've answered them all in advance.
Sil Horwitz, FPSA
Technical Editor, PSA Journal
teched@psa-photo.org
silh@earthlink.net
Visit http://www.psa-photo.org/
Personal page: http://home.earthlink.net/~silh/
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