Handling Hazardous Chemical Waste


The US Environmental Protection Agency (EPA) defines waste as any solid, liquid or contained gas that is no longer used and is designated for disposal or recycling.  If the waste can cause injury or death, or pollute land, water or air, it is deemed to be hazardous.  The EPA regulates hazardous waste at the federal level, and state regulation must be at least as stringent as the EPA.

In 1976, the Resource Conservation and Recovery Act (RCRA) was passed to track hazardous chemicals “from the cradle to the grave”.  RCRA defines two categories of hazardous waste:

  • Listed waste is any substance appearing on any one of RCRA’s four lists.
  • Characteristic waste is any substance having one or more of the following characteristics:
  • This includes liquids with a flash point of less than 140 F (i.e. nearly all clearing agents and dehydrants/alcohols).
  • This includes liquids with a pH less than or equal to 2.0, or greater than or equal to 12.5.
  • Substances that are unstable or undergo violent chemical reaction with water or other materials (i.e. picric acid).
  • TCLP toxicity. Substances that can leach from a secure landfill.

Strategies for Waste Handling


Recycling makes the most sense.  Alcohols, xylenes, xylene substitutes and formalin are examples of chemicals found in the histology laboratory that can be recycled.  The laboratory can keep smaller quantities on site and recycling is very cost effective.  Most recycling units pay for themselves in approximately two years.

Scaling Down

Try to “scale down” the quantities of chemicals that you use.  For example, if you are performing an iron stain on two slides (i.e. patient and control) instead of using 50 ml in a Coplin jar, use 10 ml in a plastic slide holder.  This decreases the amount of hazardous chemical waste you generate for this stain by more than half.

Re-use or “treat and release”

Non-mercury Harris’ hematoxylin is an excellent candidate to be re-constituted and re-used after the first use. Then, once it is depleted, hematoxylin can be treated for drain disposal (with permission from the owner of your sanitary sewer).

Store for legal transport and disposal

This is the method of last resort.  Alcohol tainted with xylene and special stains fall into this category.  These chemicals should be stored safely in drums for legal pick up and disposal by a licensed facility.  Remember, even after the facility comes to pick up your waste – you still own it.  If the waste hauler flips his truck over on the interstate, and your waste is on board – your laboratory helps pay for the clean up.  If you are found negligent in handling your hazardous waste, there can be criminal charges, and you – yes you – can go to jail.

Substituting for Hazardous Chemicals


One strategy for decreasing the laboratory use of hazardous chemicals is to find substitutes for them.  Ideally, a “safe” substitute is the best alternative.  However, a “less hazardous” chemical also can help in this regard.


Fixation.  Formaldehyde (i.e. formalin) has been the fixative of choice in histology laboratories for many years.  However, you can see from the Formaldehyde Standard that many parameters must be met to insure employee safety when handling formalin.  Spent formalin is a hazardous waste; however, it can be recycled.

Today, many formalin substitutes are available for fixation of tissue.  One must be aware, however, that many of these substitutes are alcohol based.  Formalin is a cross-linking fixative.  Alcohol fixes tissue by denaturation.  It is important to work with your pathologist to validate any changes in processing chemicals that are made, to ensure that the final slide is acceptable.

Dehydration.  Dehydration of tissues during processing is still carried out by a graded alcohol series.  Laboratories usually employ ethanol for this procedure.

Clearing.  Xylene has been the clearing agent employed by laboratories for many years.  It is like formalin in that proper ventilation must be used when handling it.  Xylene is also easy to recycle.

Also like formalin, there are many xylene substitutes available for use.  Some are limonene based (i.e. citrus based).  These are considered safe, however there are some reports indicating that some personnel may be allergic to them.  Additionally, there are xylene substitutes that are short-chain and long-chain aliphatic hydrocarbons.  Whatever substitute is chosen, the laboratory should make certain to perform validations to insure specimen integrity.  Additionally, all xylene substitutes can be recycled.

The most important aspect of using xylene substitutes (whether in processing or staining) is that they all are very water intolerant.  Xylene can dissolve up to 3% water with no deleterious effect on processing or staining.  Tissues and slides must be completely dehydrated prior to the xylene substitute stations on the tissue processor and stainer to insure optimum quality.  This requires a strict regimen of changing and rotating the 100% alcohols that precede the clearing step.

Incorporating some of these ideas may be time consuming, however, they will make your laboratory a safer place to work.


  1. Theory and Practice of Histological Techniques. JD Bancroft, A Stevens ed.  Churchill   Livingstone, NY.  Fourth edition. 1996
  2. Theory and Practice of Histotechnology. DC Sheehan, BB Hrapchak.  CV Mosby Company, St. Louis. First edition. 1980.
  3. Luna L.  AFIP. Manual of Histologic Staining Methods.  Third Edition. McGraw-Hill. p39. 1968.  As modified by CM Chapman
  4. Dermatopathology Laboratory Techniques.  CM Chapman, I Dimenstein.  2016.  CreateSpace/Amazon.com.