Examination of ultraviolet germicidal radiation for inactivating microorganisms in melted snow and ice samples

The storage of melted snow and/or ice samples from snow pits and ice cores in a refrigerator for long durations may be limited by an increase in particle concentration caused by microbial growth after approximately 1–2 weeks. In this study, we examined an ultraviolet (UV) disinfection method for the storage of melted snow and/or ice samples. Surface snow obtained from Glacier No. 31 in the Suntar-Khayata Range, eastern Siberia, Russia was divided into two portions for UV treatment and untreated controls. Particle concentrations in the samples were measured using a Coulter counter (Multisizer 4e; Beckman Coulter, USA). Whereas the particle concentration in untreated samples increased, no obvious increase was observed over 53 days in the samples subjected to UV treatment. In addition, the original particle concentrations were unaffected by UV treatment. These findings indicate that the antimicrobial effect of UV radiation is effective for long-term sample storage of melted water samples. A detailed analysis of the particle size distribution for untreated samples indicated that particles of 0.7–1.2 µm appeared within the first 7–14 days. Measurements using a viable particle counter (XL-10BT2 and XL-28A1; RION Co. Ltd., Japan) confirmed that these were biological particles, suggesting that microbial growth occurs during this period. Subsequently, the particles shifted to a smaller size and a higher concentration, suggesting that the decomposition of microorganisms occurred in the water samples. Therefore, the size distribution of particles in untreated samples reflected the growth and decomposition of microorganisms over time.