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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">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.<br>
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Regards,<br>
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<p class="MsoNormal"><span style="font-size:8.0pt; font-family:"Verdana","sans-serif"" lang="EN-US">Andries J. van Dam,
<span style="color:#FF8000">conservator</span><br>
<br>
Museum of Anatomy<br>
Leiden University Medical Center <br>
Building 3 (V3-32)<br>
P.O.Box 9600 <br>
2300 RC Leiden <br>
The Netherlands <br>
tel: +31 (0)71 52 68356<br>
E-mail: <u><span style="color:#0000FE">A.J.van_Dam@lumc.nl<br>
</span></u>Visiting address: Hippocratespad 21</span><span style="font-size:8.0pt; font-family:"Verdana","sans-serif"" lang="EN-US"> </span>
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<p class="MsoNormal"><span style="font-size:8.0pt; font-family:"Verdana","sans-serif"; color:#FF8000" lang="EN-US">Scientific associate</span><span style="font-size:8.0pt; font-family:"Verdana","sans-serif"" lang="EN-US"> Natural History Museum London<br>
<a href="http://www.nhm.ac.uk/" target="_blank"><span style="color:blue">http://www.nhm.ac.uk</span></a><br>
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<span style="font-size:8.0pt; font-family:"Verdana","sans-serif"; color:#FF8000" lang="EN-US">Directory Board member</span><span style="font-size:8.0pt; font-family:"Verdana","sans-serif"" lang="EN-US"> ICOM-CC<br>
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</u><span style="color:#FF8000">Director</span> Alcomon Company<br>
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<div style="direction: ltr;" id="divRpF447714"><font color="#000000" face="Tahoma" size="2"><b>Van:</b> nhcoll-l-bounces@mailman.yale.edu [nhcoll-l-bounces@mailman.yale.edu] namens John E Simmons [simmons.johne@gmail.com]<br>
<b>Verzonden:</b> donderdag 3 juli 2014 5:50<br>
<b>Aan:</b> Watkins-Colwell, Gregory<br>
<b>CC:</b> Carola Haas; nhcoll-l@mailman.yale.edu<br>
<b>Onderwerp:</b> Re: [Nhcoll-l] long-term storage of amphibian larvae in formalin<br>
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<div dir="ltr">On Wed, Jul 2, 2014 at 11:36 AM, Watkins-Colwell, Gregory <span dir="ltr">
<<a href="mailto:gregory.watkins-colwell@yale.edu" target="_blank">gregory.watkins-colwell@yale.edu</a>></span> wrote:<br>
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<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1f497d">...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.
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<div>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.<br>
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<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1f497d">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.</span></p>
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<div>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.<br>
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<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1f497d">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. </span></p>
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<div>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.<br>
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<p class="MsoNormal"><span style="font-size:11.0pt; font-family:"Calibri","sans-serif"; color:#1f497d">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.
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<div>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).<br>
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<div>--John<br>
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