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Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries
Citation:
Zepp, R., Mike Cyterski, K. Wong, O. Georgacopoulos, Brad Acrey, G. Whelan, R. Parmar, AND M. Molina. Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries. ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 52(22):13068-13076, (2018). https://doi.org/10.1021/acs.est.8b02191
Impact/Purpose:
One approach to predictive modeling of biological contamination of recreational waters and drinking water sources involves applying process-based models that consider microbial sources,hydrodynamic transport, and microbial fate. Coliphages can indicate contamination of recreational waters. Previous studies indicate that sunlight plays an important role in altering densities of coliphages, other indicator microorganisms, and pathogens in aquatic environments. Here, we report laboratory studies of the light-induced inactivation of representatives of two coliphage groups, f-specific and somatic coliphage, under various conditions in phosphate buffered water (PBW). The groups were isolated from wastewater treatment facilities or were individual viruses, MS2 and phiXl 74 bacteriophages, that have been widely used as surrogates for enteroviruses. Directly exposing the phages to simulated solar radiation in buffered waters resulted in rapid inactivation with half-lives of just a few hours. Dark controls exhibited no detectable decay during the periods of time used for irradiations. Inactivation rates of the coliphages were determined in a series of irradiations using simulated solar radiation passed through light filters that blocked different parts of the ultraviolet and visible spectral region. Inactivation rates and spectral irradiance were then analyzed by the Runde! technique to develop biological weighting functions (BWFs) for the light-induced inactivations. BWFs were then used to model the light-induced inactivation of phage over a range of conditions in aquatic environments. The results show that near-surface inactivation rate constants are sensitive to atmospheric parameters such as solar zenith angle and, thus, latitude and time-of-day, as well as total ozone.
Description:
Coliphages can indicate contamination of recreational waters and previous studies show that sunlight is important in altering densities of coliphages, other indicator microorganisms, and pathogens in aquatic environments. Here, we report on laboratory studies of light-induced inactivation of two coliphage groups—male-specific (F+) and somatic coliphage—under various conditions in phosphate-buffered water (PBW). Strains isolated from wastewater treatment facilities and laboratory strains (MS2 and phiX174 coliphages) were evaluated. Inactivation rates were determined in a series of irradiations using simulated solar radiation passed through light filters that blocked different parts of the ultraviolet spectral region. Inactivation rates and spectral irradiance from these experiments were then analyzed to develop biological weighting functions (BWFs) for the light-induced inactivation. BWFs were used to model the inactivation of coliphages over a range of conditions in aquatic environments that included two beach sites in Lake Michigan and one in Lake Erie. For example, modeled effects of sunlight attenuation, using UV absorption data from the three Great Lakes beach sites, inferred that direct photoinactivation rate constants, averaged over a one-meter water column in swimmable areas, were reduced 2- to 5-fold, compared to near-surface rate constants.
URLs/Downloads:
DOI: Biological Weighting Functions for Evaluating the Role of Sunlight-Induced Inactivation of Coliphages at Selected Beaches and Nearby Tributaries