On Fri, 25 May 2001 JMeade0710@aol.com wrote:

> What is the proper method to use when disposing of expired unused 
> gluteraldehyde.  Our lab keeps a small portion of GLUT for the possibility of 
> EM fixation. When this expired without use, it needs to be disposed of.

First off, it's glutAraldehyde. Same root as glutarate & glutamate.
Food for thought:
Are there any words that contain the letter sequence GLUTE ?

Common sense says, "Use it to disinfect your sewer, along with
the detergents and sodium hypochlorite that you use at home."
Glutaraldehyde and formaldehyde are both disinfectants. 
Labs are expected to justify their disposal methods, even for
smaller and less toxic amounts of chemicals than those that
go down nearly every domestic drain.

You don't state the quantity; let us assume it is a few grams
of glutaraldehyde dissolved in a few hundred ml some buffer,
and containing also some formaldehyde (i.e. a Karnovsky-type
fixative). If the buffer is cacodylate, this is the most toxic
ingredient because it releases inorganic arsenic-containing ions
when digested in the stomach. (It is less toxic intravenously
than orally!).

Glutaraldehyde is used industrially for tanning leather (the
best quality stuff, I'm told by someone in the trade). They must
have to get rid of large quantities safely. I'm guessing now,
but the obvious way to do this would be to add an excess of
scrap protein until all the glutaraldehyde is permanently 
incorporated into cross-links between macromolecules. The
lab equivalent would be to put the old fixative solution
in an old plastic bottle, spoon in some skimmed milk powder,
shake well and leave overnight. Repeat if there is still a smell
of glutaraldehyde. This process should produce a plastic
bottle containing a single enormous molecule incorporating all
the carbon atoms that were in the glutaraldehyde and formaldehyde.
There will also be unreacted buffer salts and excess milk
proteins etc in the gel. Such a bottle would not contain
anything toxic derived from the fixative solution. The only
unpleasantness would be from bacteria eating up the leftover
milk protein. At a garbage dump they wouldn't be unduly
bothered by a few more grams of this, especially if the bottle
had a cap on it.

Another thing to remember is that glutaraldehyde polymerizes all
on its own, and the polymers combine rapidly with proteins. Simply 
storing the old fixative for a few months will greatly reduce its
glutaraldehyde content, and less protein will be needed to make
a great big cross-linked polymer. 10 yr-old 50% glutaraldehyde
is a solid transparent plastic, in a bottle with an unremovable
screw-cap. 

There obviously isn't any serious hazard with lab quantities, but 
for satisfying the safety police it would be sensible to find out
what's done in the tanning industry and do some scaled-down lab
equivalent, along the lines suggested above. 

----------------------------------------
John A. Kiernan
Department of Anatomy & Cell Biology
The University of Western Ontario
London,  Canada   N6A 5C1
   kiernan@uwo.ca
   http://publish.uwo.ca/~jkiernan