Estimating solar and nonsolar inactivation rates of airborne bacteria

ABSTRACT Land application of biosolids is a wide spread practice in the US, Canada and Western Europe. Fundamental information to characterize the relationship between atmospheric conditions, source concentration, transport, and airborne fate of bioaerosols emitted during the application of biosolids is needed to assess exposure to workers and the public. Pilotscale bioaerosol reactor experiments that independently measure the solar and nonsolar (absence of solar radiation) inactivation rates of airborne Mycobacterium parafortuitum and Escherichia coli were performed. Direct fluorescent microscopy measurements for total airborne bacteria and culture-based assays were used to measure concentrations in a one m 3 reactor that was transparent to UV-A and UV-B wavelengths and to produce decay curves of airborne bacteria under moderate and high ranges of relative humidity (RH). Relative humidity strongly influenced airborne inactivation rates in both bacteria. In addition, E. coli was more susceptible to solar and nonsolar airborne decay than M parafortuitum. Results demonstrate, at moderate RH, that nonsolar mechanisms dominate the inactivation of airborne E. coli while solar mechanisms dominate M. parafortuitum inactivation