Re: "Disposal" of Osmium Tetroxide "Waste"

From:"J. A. Kiernan" <>

On Thu, 23 Nov 2000, stephen asquith wrote:

> disposal of this wonderful material but it still ...
> ... containers full of osmium in alcohol or corn oil ...
> ... what should be done with it then?

Osmium tetroxide is indeed wonderful stuff. Os is a rare
element, so disposal of used solutions should consist of
recycling, not dumping, even though osmium compounds are
not considered environmentally hazardous (Smith et al., 1978
Trace Metal in the Environment, vol 4. Ann Arbor Science
Publishers). The colourless soluble toxic tetroxide is rapidly 
reduced by almost any kind of dirt to a black, insoluble dioxide,
usually in a colloidal form that's readily dispersed by moving
water if it isn't firmly stuck to the solid organic matter that
brought about the reduction.

If OsO4 slops are collected in alcohol, the osmium (now in 
the form of crude, harmless, insoluble osmium dioxide) can 
be reoxidized, purified, re-reduced to pure OsO2 and stored. 
OsO2 is easily re-oxidized to give a buffered solution of
osmium tetroxide (2% or less). See J Microsc 113:77-82
(1978); the procedure does involve certain hazards, so
it must be done carefully. 

Recovered OsO4 can also be used to make osmeth, which is 
a beautiful golden crystalline solid that contains osmium 
tetroxide complexed with methenamine (= hexamethylene tetramine
or hexamine (Hanker et al., 1976 Histochemistry 49:263-291).
It costs next to nothing to make your own osmeth from
recycled OsO4, but osmeth is very expensive to buy. Osmeth
does not emit osmic fumes. When it is dissolved (in DMF
followed by dilution in an aqueous buffer) it becomes a
dilute (0.25%) working osmium tetroxide solution. I can vouch
for the excellence of home-made osmeth for post-osmication (for 
EM). It may also be OK as a primary fixative or for LM staining,
but I haven't encountered (personally, by anecdote or in the
literature) any use of osmeth other than for postosmication.
Perhaps someone reading this message will put me right on this.

Osmium tetroxide collected into vegetable oil could not be
recycled by the simple method cited above, and the recovery
methods used by chemists (which use apparatus etc not found 
in histology labs) would be made more difficult by the presence 
of the oil.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1

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