Half of the ultra low temperature (ULT) freezers on the CU Boulder campus are at -70 ⁰C (~75 of ~150 freezers). In 2010, there were probably only 5 at -70 ⁰C. The CU Green Labs Program is very proud of this, and we hope to continue to encourage laboratories to switch their freezers to -70 ⁰C where it makes sense for their samples. This progress has been encouraged by the fact that we had a number of campus scientists that were already setting their ULT freezers to -70 ⁰C and had been for a very long time, before CU Green Labs even started. Knowing that colleagues had been successful storing samples at that temperature probably helped to convince some labs to change. Check out the labs and departments taking conservation actions with their ULT freezers!
Scientists at CU Boulder, UC Davis, and several other campuses have contributed to a database of cold sample storage practices to demonstrate sample types that are being stored at -70 ⁰C. Please note that this database is not science-based data on appropriate temperatures for samples, though these temperatures have been successful for various labs for years. You can access the CU Boulder and UC Davis cold sample storage practices database at this link.
Did you know that before any ULT freezers could be manufactured to reach -80 ⁰C, ULT freezers were only able to reach -70 ⁰C? To best of our knowledge, the switch from -70 ⁰C to -80 ⁰C was a result of marketing by manufacturers to sell ULT freezers rather than a demonstrated scientific need for -80 ⁰C for samples stored in ULT freezers.
At the International Institute for Sustainable Laboratories (I2SL) conference in September 2013, a presentation by the CDC included the fact that they raised 60 of their ULT freezers to -70 ⁰C from -80 ⁰C on one of their campuses as part of the freezer challenge. Click here for a link to the CDC's I2SL abstract.
The University of Edinburgh in the UK is currently conducting a study to scientifically address the question of what temperatures are most appropriate for certain sample types. They hope to store their samples at either -60 ⁰C, -70 ⁰C, or -80 ⁰C for a minimum of five years and then test their viability. This is an exciting study, and we look forward to learning about the results in a few years!
The 2012 article "Long term stability of paraoxonase-1 and high-density lipoprotein in human serum" tested the viability of this enzyme after storage at -20 ⁰C, -70 ⁰C, and -196 ⁰C for one year, and determined that PON1 activity is no different after storage at -70 ⁰C versus -196 ⁰C. Full article is in Lipids in Health and Disease, Beekhof, Gorshunska, Jansen.
A 2004 article from the Journal of Clinical Microbiology indicates that the majority of fungal isolates tested in the study (excluding dermatophyte and C. dubliniensis strains) are viable after storage at -70 ⁰C for four years. Full article is DOI: 10.1128/JCM.42.3.1257-1259.2004, "Long-Term Preservation of Fungal Isolates in Commercially Prepared Cryogenic Microbank Vials" by Espinel-Ingroff et al. 2004
An article from the Archives of Pathology & Laboratory Medicine, written in 1996, identifies ideal storage temperatures for DNA and RNA samples in a clinical setting, including the recommendation of -70 ⁰C in certain cases. Review the article for full details.
Two posters from the company SeraCare on the topic of sample stability are available below. The first poster indicates that -20 ⁰C and -80 ⁰C both are suitable freezer temperature for genomic DNA storage. The second poster indicates effective preservation of RNA at -70 ⁰C and effective preservation of antibodies and antigens at -20 ⁰C.
A representative from Thermo Fisher Scientific mentioned to Allison Paradise at My Green Lab that they have unpublished data supporting the fact that it takes 1 to 1.5 hours less time for an empty ULT freezer at -70 ⁰C to warm up to -50 ⁰C than if the freezer’s set point had been at -80 ⁰C. The representative reported that on average the warm up time went from about 300 minutes to about 235 minutes when you changed the setpoint from -80 ⁰C to -70 ⁰C. For a full freezer, the warm up difference between a freezer set at -80 ⁰C and one set at -70 ⁰C is only 30-40 minutes.
At the University of Copenhagen, freezers were evaluated on the basis of Total Cost of Ownership with focus on energy consumption. Four different models were tested at both -70 C and -80 C under controlled conditions at an external certified laboratory. Results of the tests include 20-22% lower energy consumption at -70C for new ULT freezers and inner temperature being more reliable at -70C than -80C. Additionally, upright freezers are in average 22% more efficient by volume than chest freezers, and large freezers are in average 13% more efficient by volume than small freezers.
Ashlyn Norberg gave a presentation at a recent I2SL conference highlighting how CU Green Labs was able to convice scientists to raise their freezer temperatures to -70 ⁰C from -80 ⁰C. Check out Ashlyn's presentation by following this link.
Join your colleagues by exploring whether -70 ⁰C is appropriate for your samples too!