[Nhcoll-l] long-term storage of amphibian larvae in formalin

[Robert Waller]

Just to clarify, formalin is stable with respect to spontaneous
decomposition but not stable with respect to oxidation.  A buffer system, by
definition, will slow but not eliminate drift in pH levels. Different
containers and closures will lead to different rates of pH decline. I would
hesitate to adopt a fluid change schedule based on a different collection
unless that collection uses the same containers and the same buffer
formulation.

Robert Waller

 

From: nhcoll-l-bounces at mailman.yale.edu
[mailto:nhcoll-l-bounces at mailman.yale.edu] On Behalf Of A.J.van_Dam at lumc.nl
Sent: July-03-14 6:46 AM
To: simmons.johne at gmail.com; gregory.watkins-colwell at yale.edu
Cc: cahaas at vt.edu; nhcoll-l at mailman.yale.edu
Subject: Re: [Nhcoll-l] long-term storage of amphibian larvae in formalin

 

Formalin is not stable! We noticed in our fetus collection stored on
phosphate buffered formalin (pH 7.3) that after ten years pH is around 6,
after 20 years around 5, and after 30 years around 4 (close to unbuffered
formalin). Therefore, when using buffered formalin as a preservation fluid,
I recommend to change the fluid every 10 years.

Regards,

 

Andries J. van Dam, conservator

Museum of Anatomy
Leiden University Medical Center 
Building 3 (V3-32)
P.O.Box 9600 
2300 RC Leiden 
The Netherlands 
tel: +31 (0)71 52 68356
E-mail: A.J.van_Dam at lumc.nl <mailto:A.J.van_Dam at lumc.nl> 
Visiting address: Hippocratespad 21  

Scientific associate Natural History Museum London
http://www.nhm.ac.uk <http://www.nhm.ac.uk/> 

Directory Board member ICOM-CC
http://www.icom-cc.org <http://www.icom-cc.org/>  

Director Alcomon Company
http://www.alcomon.com <http://www.alcomon.com/>  

 

  _____  

Van: nhcoll-l-bounces at mailman.yale.edu
<mailto:nhcoll-l-bounces at mailman.yale.edu>
[nhcoll-l-bounces at mailman.yale.edu] namens John E Simmons
[simmons.johne at gmail.com]
Verzonden: donderdag 3 juli 2014 5:50
Aan: Watkins-Colwell, Gregory
CC: Carola Haas; nhcoll-l at mailman.yale.edu
<mailto:nhcoll-l at mailman.yale.edu> 
Onderwerp: Re: [Nhcoll-l] long-term storage of amphibian larvae in formalin

On Wed, Jul 2, 2014 at 11:36 AM, Watkins-Colwell, Gregory
<gregory.watkins-colwell at yale.edu <mailto:gregory.watkins-colwell at yale.edu>
> wrote:

...I have, however, found it difficult to maintain the pH properly and even
the best of formalin solutions can result in some specimen clearing
long-term.  

If buffer the solution with 4 g monohydrated acid sodium phosphate + 6.5 g
anhydrous disodium phosphate per liter of one part commercial formaldehyde
with nine parts deionized or distilled water, that should be a very stable
buffered system. The sources of error that can produce clearing include
failure to rinse out field buffers, using tap water to dilute the
formaldehyde, and not measuring carefully. You can purchase pre-buffered
formaldehyde but personally, I would not trust it for use with scientific
specimens. I have never seen clearing when this buffer system is used
properly.

 

I do not keep reptile eggs in formalin.  I fix them in formalin and then
transfer them to ethanol.  Long-term exposure to formalin can damage the
eggshell and cause issues with histology.  I treat reptile eggs as I would a
whole reptile specimen and transfer them to 70% ethanol for long-term
storage.

 

If the formaldehyde is properly buffered, it will not damage reptile eggs.
However, I would not bother fixing reptile eggs in formaldehyde unless it is
necessary in the field. Better to preserve them directly in 70% ethyl
alcohol.

But, as for amphibian larvae, we've started transferring them to 70% ethanol
for long-term storage.  This also makes them easier to work with from a
health and safety perspective, especially with a lot of student workers.  

Because formaldehyde solutions are essentially water ("10% buffered
formaldehyde" is really about 96% water), amphibian larvae in 1:9
formaldehyde and water solutions can be safely transferred to deionized or
distilled water when people use them, then returned to the buffered
formaldehyde for storage. Unless you rinse the specimens very thoroughly
when you transfer them to alcohol, you are still going to have trace amounts
of formaldehyde in the alcohol solution that can pose a safety issue. Wear
neoprene (nitrile) gloves when handling specimens in any case.

 

I think that no matter what you do, there will be a cost/benefit.
Understand your institutional priorities and weigh those against the rarity
of the specimen. This also might be a good reason to photograph examples of
each taxon/developmental stage PRIOR to changing storage fluid.  Even if you
only change to new formalin, you should document.  There's a chance that
your formalin isn't buffered the same way as what was used in the past.
That difference can cause some issues with the specimens.  So, really,
whatever you do there is a risk.    

 

I agree with you here, Greg. No solution is perfect for everyone, and
documentation of what is done to specimens is critical. However, you can
greatly reduce risks to specimens and to workers by controlling which
chemicals are used, how they are mixed, and how they are used with a set of
enforced SOPs (Standard Operating Procedures).

--John

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