LN2 Sterilization to Avoid Cross Contamination

Liquid nitrogen (LN2) and its gaseous form nitrogen vapor (NV) are key cryogenic agents for cooling and freezing in the healthcare and food industries. They can, however, become contaminated by viruses, bacteria, and fungi (Tedder et al., Lancet 346:137–140, 1995, Morris, Cryobiology 50:231–8, 2005). Human assisted reproductive technology (ART) is the only medical discipline where human gametes and embryos with the potential to produce live births are routinely stored in LN2/NV. The risk of infection is real, especially when new, highly infective agents arise. Airborne contaminants come into contact with LN2/NV and are cryopreserved. While some industrial sectors (drug manufacturing, food and beverage sterile packaging) carry out raw filtration of LN2 before use, this precaution is not yet mainstream, although it is increasingly used in human ART. During the COVID-19 pandemic, manufacturers of drugs/disposables/culture media were trying to mitigate risk by sourcing raw materials from low-risk regions, but this is not applicable to LN2/NV, which can thus become potential vectors of contamination. The use of contaminated LN2/NV risks virus awakening and the contamination of thawing cells, environment, and operators. This chapter seeks to warn practitioners of the potential risk of LN2/NV-mediated contamination and outline strategies for preventing this.