Peggy,
What an intriguing question!  Even so, I bet someone comes up with
the answer!
Apart from the fact that tissue, etc need not and should not come
into contact with the liquid nitrogen (only liquid nitrogen cooled
carrier fluid).
I've just asked a colleague who runs my tissue culture lab.  and she
says "let it evaporate"
Me "What if there are bacteria or viruses in it? If it had become
contaminated"
 She "I would autoclave the container"
Me "What about bugs carried into the atmosphere by convection?"
She "We may have a problem there, perhaps we ought to look into it"
Me "Do you reckon it's real problem?"
She "I'll bet some of our storage containers are contaminated.  I
visited my GP (sorry, is that physician in US?) for treament to a
verruca and he dipped a swab into liquid nitrogen and applied it to
my verruca.  I decided to treat myself thereafter, using "fresh"
liquid nitrogen, in a "fresh" container each time."
Me "Great!  What did you do with the nitrogen you contaminated?"
She "I used a fresh swab each time!  So there!"
Smart Ass kids!!
As I said, interesting problem Peggy.  What about all those stored
tissues worldwide? Foetuses, embryos, sperm, spare cells, serum in
virology labs, etc, etc, any or all of which could be contaminating
the storage dewars.


Russ Allison, Wales