[Nhcoll-l] Fluid preparation, exhibition of large-scale wet specimens in neutral buffered formalin or otherwise

[Mikkel Ege Bartholdy]

Dear Nhcoll-l list members and contributors,

I am looking for input on the subject matter, which is large volume formalin tanks to be on exhibit at our museum that opens in a couple of years.

Most of our wet specimens across the exhibit galleries are ethanol-based. Specific mixture depending on age, contents, and home collection. We will however have four larger fluid specimens on display, ranging from a 3000L tank with a Greenland shark, Somniosus microcephalus, the heart of a bowhead whale, Balaena mysticetus, in a tank with ~1000l, as well as two smaller tanks containing about 200-300l each, with various fish species connected to Danish and Arctic habitats. These four tanks are to contain a formalin solution as storing agent for the specimens.

I am specifically looking for input regarding a discussion on the benefits of buffering this solution and the method for this. Or from museums with data or experience regarding large tanks of formalin on display and their behavior over time, how they're sealed and accessed, etc.

Both specimens being thoroughly fixed already and with no danger of decalcification I have suggested that we do not initially buffer these solutions. This is partly because they are currently placed in unbuffered formalin, and their installation being scheduled for the next 5-7 months. One of my worries is that the buffer salts will need time to penetrate the tissue, or crystallization of insoluble salts (for the shark containing a more saline solution, while being fixed in a freshwater solution) as a risk if we try to rush this prior to installation, resulting in an additional fluid change before opening due to precipitation etc.
I do have the possibility of adding buffering salts to the two temporary tanks in the next month, and to mix the buffered formalin solution the specimens will be displayed in, in advance instead of mixing it into the display tank with the specimen present of course.
The display tanks are to be built and sealed well enough to allow for so little formaldehyde fumes to escape (due to ours and visitors safety, and regulations for measurable VOC levels), which in turn will hopefully allow for very little oxygen exchange and thus a slow rate of oxidation of the formaldehyde and lipid compounds.
I've suggested that we monitor the tanks in regular intervals (anything from every 3-5 years or out of sequence in relation to visible change) for changes to the fluid, with the argument that even using a neutral buffered formalin would realistically only postpone the fluid reaching a lower acidity at a later point, and only increase the intervals between monitoring and potential action. Earlier in the process of planning this display it was suggested to use buffered formalin and design tanks that are not meant to be opened, but I find the ability to access and monitor the fluid of great importance. Even if this means a tank that is in theory not as well sealed, or a tank that will require lots of resources to open and re-seal.
For buffering; Sodium dihydrogen phosphate and sodium hydrogen phosphate buffering system as mentioned in the excellent reference book on fluid preservation published by SPNHC (ISBN 979-8-218-01102-4) is currently my go to for a potential buffering as it seems affordable and doable for us regarding the large volumes to work with, I have not been able to find accounts from people using this, so any input on this specific buffering system is also very welcome!

If you're still reading along here's some context on the two specimens this project revolves around:
The Greenland shark is a juvenile 200kg specimen entering our collections from fresh in February 2024. Immediately upon having taken tissue samples we started fixing the specimen with formaldehyde injections and submersion in 1000l 3,5% formalin (custom tank which allowed the whole specimen to be submerged in this relatively small volume). The contents of the fluid have some natural minerals (using tap water) as well as the saline fluid contents of the shark. Initially the monitored pH levels sat at ~7-7,5, reaching a pH of 5 in September 2024 where it has settled since with no changes (so far). Throughout the fixing we have also had a clear fluid with no visible opacity in the water that could suggest formation of paraformaldehyde in the colder months. The shark is mostly liver (slight exaggeration) and thus very fatty, as well as Greenland shark tissue containing high amounts of urea and trimethylamine N-oxide which might be relevant, if you wonder that this might also have an effect on the fluid please let me know (the shark will only be about 7-10% of the collected mass of the fluid and specimen).
The whale heart weighing a bit over 150kg was fixed in 2010 when arriving at the collections, been on display in formalin, then transferred to ethanol, and recently phased from the ethanol fluid (~40% at the time of emptying the tank!) to formalin in preparation for the new exhibits. Currently sitting between 6 and 5,5 pH suggested by pH indicator strips. Rough treatment with the differing storage methods. But the heart is thankfully in good shape, probably in part due to the tough muscle tissue and a suspected thorough initial fixing (no logs available to me, but visible stitches where the heart has been bled out and rinsed and likely fixated internally as well). As expected, the whale tissue still bleeds lipids and fat here 15 years later. Potential for scheduled change of storage solution due to lipids bleeding out of the specimen is unrelated to formalin solution monitoring but would be combined with the monitoring effort when relevant.

Thank you for your time, I'm looking forward to learning from your experience. Feel free to write me directly if you have specific questions.
All the best,
Mikkel
Mikkel Ege Bartholdy
Conservator



Natural History Museum Denmark
University of Copenhagen

Conservation unit
Universitetsparken 15
2100 Copenhagen
Denmark

Telephone: +45 27 624 162
Mail: mneb at snm.ku.dk<mailto:mneb at snm.ku.dk>

www.snm.dk<http://www.snm.dk/>


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