Abstract
This study develops general predictive models for the ultraviolet (UV) radiation dose–response behavior of Bacillus subtilis spores to solar UV irradiation that occurs in the environment and broadband UV irradiation used in water disinfection systems. The approach is demonstrated using previously obtained experimental survival rates for B. subtilis spores deposited on dry surfaces as well as in water and exposed to both narrow band UV radiation as well as broadband UV irradiation from solar exposure and disinfectant lamps. Results are modeled to derive predicted survival rates for spores as a function of irradiance intensity and wavelength, capability for repair, and depletion of available sites for UV damage. The essential features of the approach are expression of the inactivation action spectrum in terms of the probability of an incident photon being absorbed and forming a dimer lesion, and expression of the spore survival as a cumulative binomial distribution for damage. The results provide increased accuracy in estimating dispersed biological hazards, and evaluating the effectiveness of UV air and water disinfectant systems. In addition, the approach for the first time explains the observed reduced inactivation rate in a repair-capable strain compared with a sensitive, repair-deficient strain by accounting for the depletion of available lesion-forming sites due to increasing DNA damage.
Highlights
The objective of this study is to demonstrate a mechanistic, predictive modeling approach that can accurately predict inactivation of both sensitive strain and wildtype, repair-capable bacillus spores by solar ultraviolet (UV) irradiation, as well as by broadband UV irradiation from disinfection lamps, based on measurements of inactivation of such spores under similar conditions by narrow band UV irradiation at wavelengths spanning the UV range of interest
This study develops general predictive models for the ultraviolet (UV) radiation dose–response behavior of Bacillus subtilis spores to solar UV irradiation that occurs in the environment and broadband UV irradiation used in water disinfection systems
An example comparison of the calculated SIDR with experimental results is shown in Table 3 for the data reported in Munakata et al (1996) from exposures to solar UV of repairdeficient B. subtilis made on July 28, 1993, and given in Fig. 3 and Table 2 of that reference
Summary
The objective of this study is to demonstrate a mechanistic, predictive modeling approach that can accurately predict inactivation of both sensitive strain and wildtype, repair-capable bacillus spores by solar ultraviolet (UV) irradiation (from *290 to 400 nm), as well as by broadband UV irradiation (from *200 to 400 nm) from disinfection lamps, based on measurements of inactivation of such spores under similar conditions by narrow band UV irradiation at wavelengths spanning the UV range of interest. The approach is designed to explicitly account for the accumulation of inactivating DNA damage (pyrimidine dimers) from exposure to multiple wavelengths of UV and the spore’s capability to repair damage from all wavelengths during germination. The intended application of these results is improved accuracy in predicting inactivation of Bacillus subtilis spores in air and in water by solar irradiation and broadband disinfectant lamps, since B. subtilis is used as a biodosimeter and an indicator. Predicting inactivation of B. subtilis spores from exposure to solar and broadband disinfection lamp UV irradiance is useful for several reasons. Exposure to UV, either to solar UV, during outdoor transport and dispersion (Handler and Edmonds, 2015), or to
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