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Stanford, CA, United States

Boehm A.B.,Environmental and Water Studies | Boehm A.B.,Stanford University | Soetjipto C.,Environmental and Water Studies | Wang D.,Environmental and Water Studies
Journal of Water and Health | Year: 2012

Sunlight-mediated disinfection of water is of interest to both the drinking and recreational water quality community of researchers due to its potential to reduce microbial contamination and waterborne illness. Photo-inactivation of enteric bacteria has primarily been investigated using Escherichia coli and laboratory strains of model bacteria. The present study sought to document the photo-inactivation of environmental isolates of Salmonella in filter-sterilized natural seawater and freshwater and to test the hypothesis that diverse Salmonella serovars decay at similar rates both within and between water matrices. The inactivation of Salmonella enterica TyphimuriumLT2, Typhimurium ST19, Heidelberg, and Mbandaka was examined in sunlit and dark microcosms. First order decay was observed in sunlit microcosms; the time until 90% inactivation was of the order of 10 min. A significant shoulder, of the order of 1 hr in length, was observed in the freshwater microcosms during which concentrations were stable. Serovar Mdandaka decayed more slowly than other serovars in both seawater and freshwater. The serovarswere extremely stable in the darkmicrocosms showing little to no decay over 53 days. The results document intra-species variation in photo-inactivation, likely owing to differences in intracellular concentrations of photo-sensitizing molecules or molecules that quench reactive species. © IWA Publishing 2012.

Maraccini P.A.,Environmental and Water Studies | Wang D.,Environmental and Water Studies | Mcclary J.S.,Environmental and Water Studies | Boehm A.B.,Environmental and Water Studies
Journal of Applied Microbiology | Year: 2015

Aims: To investigate how the growth stage of Enterococcus faecalis affects its photoinactivation in clear water. Methods and Results: Enterococcus faecalis were grown in batch cultures to four different growth stages or grown in chemostats set at four different dilution rates, then harvested and exposed to full spectrum or UVB-blocked simulated sunlight. Experiments were conducted in triplicate in clear water with no added sensitizers. Decay curves were shoulder-log linear and were generally not statistically different in experiments conducted under full spectrum light. Shoulders were longer and first order inactivation rates smaller when experiments were seeded with cells grown to stationary as compared to exponential phase, and for slower growing cells when experiments were done under UVB-blocked light. Chemostat-sourced bacteria generally showed less variability among replicates than batch-sourced cells. Conclusions: The physiological state of cells and the method via which they are being generated may affect the photoinactivation experimental results. Significance and Impact of the Study: Photoinactivation experiments conducted with exponential phase cells may overestimate the photoinactivation kinetics in the environment, particular if UVB-independent mechanisms predominate. Chemostat-sourced cells are likely to provide more consistent experimental results than batch-sourced cells. © 2015 The Society for Applied Microbiology.

Russell T.L.,Environmental and Water Studies | Sassoubre L.M.,Environmental and Water Studies | Zhou C.,Environmental and Water Studies | French-Owen D.,Environmental and Water Studies | And 2 more authors.
Environmental Science and Technology | Year: 2014

Fecal indicator bacteria (FIB) are used to assess the microbial water quality of recreational waters. Increasingly, nonfecal sources of FIB have been implicated as causes of poor microbial water quality in the coastal environment. These sources are challenging to quantify and difficult to remediate. The present study investigates one nonfecal FIB source, beach wrack (decaying aquatic plants), and its impacts on water quality along the Central California coast. The prevalence of FIB on wrack was studied using a multibeach survey, collecting wrack throughout Central California. The impacts of beach grooming, to remove wrack, were investigated at Cowell Beach in Santa Cruz, California using a long-term survey (two summers, one with and one without grooming) and a 48 h survey during the first ever intensive grooming event. FIB were prevalent on wrack but highly variable spatially and temporally along the nine beaches sampled in Central California. Beach grooming was generally associated with either no change or a slight increase in coastal FIB concentrations and increases in surf zone turbidity and silicate, phosphate, and dissolved inorganic nitrogen concentrations. The findings suggest that beach grooming for wrack removal is not justified as a microbial pollution remediation strategy. © 2014 American Chemical Society.

Russell T.L.,Environmental and Water Studies | Sassoubre L.M.,Environmental and Water Studies | Wang D.,Environmental and Water Studies | Masuda S.,Environmental and Water Studies | And 4 more authors.
Environmental Science and Technology | Year: 2013

Consistently high levels of bacterial indicators of fecal pollution rank Cowell Beach as the most polluted beach in California. High levels of fecal indicator bacteria (FIB), E. coli and enterococci, are measured throughout the summer, resulting in beach advisories with social and economic consequences. The source of FIB, however, is unknown. Speculations have been made that the wrack accumulating on the beach is a major source of FIB to the surf zone. The present study uses spatial and temporal sampling coupled with process-modeling to investigate potential FIB sources and the relative contributions of those sources. Temporal sampling showed consistently high FIB concentrations in the surf zone, sand, and wrack at Cowell Beach, and ruled out the storm drain, the river, the harbor, and the adjacent wharf as the sources of the high concentrations observed in the surf zone. Spatial sampling confirmed that the source of FIB to the beach is terrestrial rather than marine. Modeling results showed two dominant FIB sources to the surf zone: sand for enterococci and groundwater for E. coli. FIB from wrack represented a minor contribution to bacterial levels in the water. Molecular source tracking methods indicate the FIB at the beach is of human and bird origin. The microbial source tracking (MST) approach presented here provides a framework for future efforts. © 2013 American Chemical Society.

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