From: robert (robert@RobertSchaller.net)
Date: 01/11/02-04:12:26 PM Z
I am interested in the recent observations on the toxicity of Chrome VI,
which occurs in Dichromate, which is used in gum printing among many other
processes. I would like to minimize (eliminate?) any adverse effects either
to my health, any one else's, or to the environment. If one is going to use
a known carcinogen, how does one handle it?
In my gum printing procedure, I place the exposed material into a "dirty"
water bath for a few minutes immediately after exposure. Most of the
dichromate comes off here, and so is contained. I then transfer the exposed
print to a "clean" bath, which generally does not develop the characteristic
orange color of dichromate, and which I thereafter pour down the drain
(since it appears not to contain dichromate).
The "dirty" bath gets reused over and over, until it gets very orange. The
question is, what do I do with it? I have previously taken jugs of it to a
household hazardous waste disposal site, but I can't help feeling that I am
merely passing the buck. Is there some way to effectively detoxify (at
least in part) this solution by converting the Chromium VI to Chromium III?
Or, can I reclaim and reuse the Dichromate?
I have seen references to the use of UV light to reduce the Chromium VI to
Chromium III (e.g., Kieber, R. J. and Heiz, G. R., Indirect photoreduction
of aqueous chromium (VI), Environ. Sci. Technol., 26, 307-312, 1992., or
Selli, E., Giorgi, A., and Bidoglio, G., Humic acid-sensitized
photoreduction of Cr(VI) on ZnO particles, Environ. Sci. Technol., 30,
599-604, 1996, niether of which I've actually seen, and an even more direct
reference that i can't find just now), which makes me wonder whether the
process of exposing the gum emulsion has already achieved this effect, or
whether I could expose the solution to UV light and transform it completely.
This would be a good solution for a small-scale operation, if it would work.
There are also numerous references to bio-remediation, which likewise
changes the oxidation of chromium to the trivalent state, but these sound
like large in situ environmental processes (using native bacteria) and not
easily applicable in any way I can see to my situation -- or does anyone
sell a bacterial culture that I could cultivate that would do this?
Passages like " According to the EPA's 1998 Toxicological Review of
Hexavalent Chromium, Cr(VI) found in the soil is generally converted to
Cr(III) by organic matter" (found in Alberto's link to
http://www.mindfully.org/Pesticide/Hexavalent-Chromium-Health-Hazards.htm)
are suggestive of some such possibility. Kodak recommended years ago for
Dichromate reversal bleach to add an excess of NaOH and precipitate Chromium
Hydroxide, which could then be removed as a solid, but isn't this compound
hexavalent?
I also wonder whether there is a lab I could send a sample of my "dirty"
bath to -- or any other solution I produce in trying to remediate it -- and
see what's really in it.
Any information or guidance anyone might offer would be greatly appreciated.
Nor am I the only one using Dichromate -- so, how do others handle it? The
days of just blithely pouring everything down the drain are over, I think,
if we want to survive in this world. What can we do?
What, by the way, is the mechanism of the cross-linking of a colloid that
Dichromate has on exposure? Is it a photoreduction from the hexavalent
state to the trivalent? It would be nice if the photographic processes
which use chrome VI also made it less toxic...
Thanks,
Robert Schaller
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