Histology FAQ

Staining, Histochemistry and Histotechnology

(Frequently Asked Questions)


Dr. John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London, Canada



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Disposal of waste from "special stains."


How should I safely dispose of the waste chemicals generated in a variety of special staining porcedures?

There is no consensus here, especially about the use of "copious running water" for dilution. A sample of the opinions stated in replies to the HistoNet listserver in the Summer of 1998 follows.

Answer 1.

Identify the substances that are dangerous in quite small amounts, such as mercuric chloride or sodium cacodylate, and follow your institution's guidelines for collection and disposal. Most substances used in special stains (dyes, acetic acid etc) can be flushed down the sink with plenty of running water.

John A. Kiernan
London, Canada.

Answer 2.

There are disposal practices that are forbidden for "Industrial" users that are allowed for "Educational" users.

The last time (some years ago) I took a Hazardous Waste Disposal course, I found out that Industry has strict regulations on e.g. Osmium tetroxide disposal, but it was *recommended* that university labs dump it down the sink. This was allowed, as long as the Os concentration didn't exceed some specified level at the sewage treatment plant. Storing the Os for disposal (even using corn oil and kitty litter) was more likely to result in legal troubles because of laws on how waste must be stored, for how long, and whether at a "local" site (your lab) or a central collection site, etc.

Hazardous waste laws change frequently.

Philip Oshel

Answer 3.

Here is a brief synopsis of advice appropriate for the USA, and to a great extent, Canada. Further details can be found in our book, Hazardous Chemicals in the Histopathology Laboratory, 3rd ed.

First and foremost, never mix different wastes together unless directed to do so by a licensed waste hauler, or until you have determined that it is safe and proper to do so. Why? You could easily create something far more hazardous. You might be mixing a low-hazard solution that could go down the drain with a high-hazard solution that could only be hauled away; that creates a far larger volume of high-hazard material that you have to pay to get rid of. A good example would be mixing mercury waste from B-5 or de-Zenkerization with a trichrome solution. Remember, too, that alcoholic waste is burnable and thus less expensive to haul away than aqueous waste. Don't dilute alcoholic waste with a lot of aqueous waste, or you will be billed at the aqueous price.

Second, ALWAYS contact your local wastewater authority for advice.  In many cases, they can assist in determining disposal procedures, particularly in those communities with proactive outreach programs.  Have information ready for them: type of waste (flammable, toxic, etc.), components (don't say Mallory's trichrome, rather list the ingredients), volume and how often. Include MSDS's. Every community has its own unique set of limits for certain chemicals. Chromium, silver and mercury are stringently regulated, so keep those wastes separate from others.

Third, use common sense. Stain waste that does not contain heavy metals, and is of small volume (few hundred ml) is so insignificant that in most sewer districts it can be trickled down the drain.  NEVER pour waste down the drain if silver, chromium or mercury is present. This includes rinses following those solutions in the staining program.

Do not pour waste down the drain all at once. Trickle it from a small carboy outfitted with bottom spigot.  Never use "copious amounts of water" to flush waste; it is against EPA regulations anywhere in the United States.

Finally, use what others are doing as a guide only. They may or may not have opted for legitimate means of disposal, and even then, their constraints or lack thereof almost certainly will not pertain to you unless you are in the same community.

Richard W. Dapson
Battle Creek, MI  49015

Answer 4.

I have to ask why using copius amounts of water is bad when disposing of waste. I can understand arguments about wasting water, but that would preclude putting solutions down the drain in the first place. So, if you are allowed to put something down the drain, I would think the volume would be beneficial for dilution.

Tim Morken,
Centers for Disease Control
Atlanta, GA 30333, USA