UV-C Decontamination of Aerosolized and Surface-Bound Single Spores and Bioclusters

Biological particles are rarely individual organisms, but are clusters of organisms physically bound to one another, or bound to other material present in the environment. The size and composition of these bioclusters contribute to the protection of the organisms within the core of cluster from the harmful effects of ambient UV light. The use of ultraviolet irradiation has been evaluated in the past as an option for decontaminating surfaces and air; however, previous studies were conducted with single spores, or poorly characterized polydispersed aerosols making comparisons between studies difficult. This study is intended to evaluate the effect of UV-C irradiation on monodispersed particles of spore clusters with mean diameters of 2.8 mu m and 4.4 mu m, and single spores of Bacillus atrophaeus var. globigii on fixed surfaces and as aerosol. The D-90, the UV-C irradiation doses at which 90% of the colony forming units were rendered nonculturable, for single spores and spore clusters of 2.8 and 4.4 mu m on surfaces were 138, 725, and 1128 J/m(2), respectively. The respective values for airborne spores were 27, 42, and 86-94 J/m(2). The first-stage decay rate constant for the surface exposure ranged from 0.012 for single spores to 0.003 for 4.4 mu m clusters. Similarly, the aerosol decay rate constant ranged from 0.12 for single spores to 0.04 for 4.4 mu m clusters. The results of this study demonstrate that the decay rate of spores contained in clusters is proportional to the overall particle size, and that it is harder to inactivate large clusters on surfaces. Copyright 2014 American Association for Aerosol Research