On Wed, 28 Mar 2001, ANATECH LTD wrote:

>                           ...  Most living tissue is at 
> leat 50% water, so such a specimen would contain 18,500 ppm 
> formaldehyde. ...
> You could wash the formalin out of the specimen with water, but now 
> you have a huge volume of hazardous waste liquid, so nothing has been 
> gained.

Is it really that huge or hazardous? To get the 
concentration of formaldehyde down to 100 ppm a specimen
needs to be washed in 185 times its own volume of 
water - say 200 times to be generous. If the average 
specimen has a volume of 10 ml, this means 2 litres of 
tap water per specimen. A five-gallon (25L) bucket will 
be enough for a dozen such specimens. After a few hours
(perhaps with stirring occasionally) the concentration 
of formaldehyde in the washed specimens and in the water 
will be below the 100 ppm limit., It should then be OK 
to send the tissues off to the not-chemically-hazardous
waste place, and empty the bucket of water down the loo.   

I can see that really large formalin-fixed objects might
pose a problem, but isn't 10 ml - a bit bigger than a 2cm
cube - a fairly generous average size for most labs?
If you work with 5 mm cubes of tissue, a 5 gallon
bucket would be big enough to dilute the formaldehyde 
from at least 2000 specimens to below 100 ppm. 

----------------------------------------
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