I would suggest you check with your safety department and/or your city's
waste department. Silver salt is silver salt, and can not be disposed of
down the sink, per the EPA.
Chemically, by adding sodium chloride, the clear silver nitrate has been
made into silver chloride, which is now white and which is not very soluble
in water, hence the precipitation (turning visible). However, it is still a
silver salt which cannot be disposed down the sink.
Now, if you filter this through a filter paper, collect up the silver
chloride on the filter paper, you should at that point be able to throw a
away the clear water. You might wanted to have your safety department check
the water first, to see if you did remove all the silver salts from the
water. Safety department will send it out for analysis.
Then, let the filter paper with the silver chloride dry overnight (in a hood
is fine - dries faster and it's out of everyone's way). Put the dried filter
paper into a zippable plastic bag. As you collect more filter papers with
silver on it (such as from disposing solutions of silver stains like retic,
GMS, PAMS, etc.) you can put these filter papers together in the same
zippable plastic bag.
These plastic bags with filter paper with silver chloride can be hauled away
by your hazardous waste hauler. Now you are properly disposing silver
nitrate via EPA rules, and you are not paying for disposal of water which is
very heavy by weight.
Another method for disposal of silver nitrate solutions is to add equal
amount by volume of 1.0 N hydrocloric acid to the silver solution, and let
it set overnight. Again, silver chloride will precipitate out, collect on
the filter paper and dried as mentioned above, and the "water" part can now
be disposed down the sink (if tested and OK'ed to go this).
We take an old 1 gallon plastic alcohol bottle, pour all our silver staining
solutions in it until it is 1/2 full, the pour the 1 N Hydrochoric acid to
the top, let it set overnight, filter, etc. Then we reuse the plastic bottle
for the next collection, as the some silver does stick to the inside plastic
and turns black. There's no danger in this, it just looks ugly. After a few
times of collecting and precipitating, we have the waste hauler dispose of
the bottle too, and just start with a new plastic bottle. This bottle cannot
go into the regular trash, as it is contaminated with silver, and the EPA
won't like it in a regular land fill.
We are a large institution, and are doing lots of silver stains a day, so we
collect silver in large quantities. If you are a small institution, collect
the silver solutions in a smaller bottle. Ammoniacal silver (such as used in
the retic stain), if allowed to dry, can be explosive. So don't let the
silver solutions dry out when you are collecting them. Add some water, if
Peggy A. Wenk, HTL(ASCP)SLS
William Beaumont Hospital
Royal Oak, MI 48073
[mailto:firstname.lastname@example.org] On Behalf Of MaryAnn
Sent: Friday, April 27, 2007 6:47 AM
Subject: [Histonet] SILVER NITRATE
Our Pathologists have used silver nitrate for years a 5% solution and then
add NACL before discarding down the drain with water. We only use it on
large specimens, breast, lumpectomy etc.
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