Decontamination of naturally contaminated liquid nitrogen storage tanks

The objective of this study was to evaluate the efficacy of cleaning and decontamination procedures in liquid nitrogen tanks. We evaluated 151 canisters and 133 bottoms from 133 nitrogen tanks of companies or farms for the presence of bacteria and fungi. Samples were collected from the canisters and the bottom of tanks containing liquid nitrogen. Tanks were divided into Group 1 (G1): tanks decontaminated with 2% glutaraldehyde - Glutaron® II (n = 16 canisters in 8 tanks); Group 2 (G2): decontamination with 70% ethanol (n = 20 canisters in 10 tanks); and Group 3 (G3): decontamination with 70% ethanol (n = 115 canisters in 115 tanks). Tanks in Groups 1 and 2 belonged to companies; Group 3 tanks belonged to farms. The culture of canisters showed twelve genera of bacteria and five genera of fungi. Bacillus cereuswas the most prevalent bacterial contaminant (42/133) in liquid nitrogen tanks (31.57%). Decontamination by 2% glutaraldehyde plus 70% ethanol was effective and no difference was found between the decontamination methods of Groups 1 and 2. In Group 3 the decontamination method was considered effective. Handling procedures with high hygienic standards should be recommended to avoid contamination of liquid nitrogen tanks on farms.