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Process Relationships for Evaluating the Role of Light-induced Inactivation of Enterococci at Selected Beaches and Nearby Tributaries of the Great Lakes
Citation:
Zepp, R., Mike Cyterski, M. Molina, AND C. Fitzgerald. Process Relationships for Evaluating the Role of Light-induced Inactivation of Enterococci at Selected Beaches and Nearby Tributaries of the Great Lakes. Presented at Workshop on Sunlight Degradation of Biomolecules and Microorganisms, Stanford, CA, April 02, 2013.
Impact/Purpose:
Invited talk at the Workshop on Sunlight Degradation of Biomolecules and Microorganisms at Stanford University
Description:
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. Fecal indicator bacteria such as enterococci have been used to assess possible contamination of recreational waters. Past studies indicate that sunlight plays an important role in altering densities of culturable enterococci, as well as other indicator microorganisms and pathogens in aquatic environments. Here, we report laboratory studies of the light-induced inactivation of one species of enterococci, Enterococcifaecalis, in Nanopure and natural waters under various conditions. In all waters, exposing the bacteria directly to solar radiation resulted in rapid inactivation of the enterococci, with half-lives of only a few minutes. In the dark, inactivation half-lives were much longer -- on the order of several days. Inactivation rates of E. faecal is 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 regions. Inactivation rates and spectral irradiance were then analyzed by the Rundel technique to develop biological weighting functions (BWFs) for the light-induced inactivations. To model the light-induced inactivation of enterococci in selected recreational waters, BWFs were combined with other data related to underwater solar spectral irradiance. We report on this approach to aid in evaluating enterococci densities observed in field studies of the Manitowoc River basin, Burns Ditch and near-coastal regions of Lake Michigan close to these contaminated tributaries.