Fixation on Histology

Formalin Disposal


The discussion about how to dispose of histology chemicals is one that occurs frequently, both on The Block, NSH’s member community, and our Histology Professionals Facebook page. We have covered some waste related situations before in previous posts, including an Earth Day post on the difference between hazardous and biohazardous waste, but today’s post is focused on formalin disposal.


Formalin is an aqueous solution of formaldehyde used in the histology lab as a fixative. Because of the toxicity dangers associated with formaldehyde, it is usually not advised for formalin to go straight down the drain. Ultimately, these recommendations vary by where you live and the local/state water departments. Where you live also may impact whether or not you have the ability to send your waste off site by way of a third party.


One of the discussions surrounding formalin disposal on Facebook included this poll

The most popular method of formalin disposal is neutralization. So how do you neutralize formalin? There are several different companies manufacturing a product for this. Most come in a powder, others a liquid, that is added to the formalin. The formalin is then left to sit until it is neutralized and able to be poured down the drain. As with any safety related procedure in the histology lab, documenting that you have followed the processes necessary to make the formalin safe to dump, is essential.


Products such as aldehyde strips are available to make sure that the formaldehyde in the formalin has been sufficiently neutralized. When checking for neutralization before disposal, it is a good idea, and potentially required by your municipality, that you keep a log of the measured aldehyde in ppm (parts-per-million), as well as the pH and keep those records on hand for at least 3 years.


Depending on where you live, and your workplace’s budget, you may have the option of having your waste, including formalin taken off site. Companies like Stericycle and Clean Harbors offer various services including waste removal, that can be worth investing in if your lab generates a significant volume of waste.


For more information on what can and can not go down in the sink in your area, contact your local water department. Having a representative from the water department come to your lab can be a great way to get to know the regulations in your area and make sure your lab is compliant and doing all it can to be a good neighbor to the community you’re in.


For more on formalin safety, check out NSH’s formaldehyde checklist on The Block.