Abstract
Fecal indicator bacteria concentrations, a measure of water pollution, do not remain static in the environment and can fluctuate both temporally and spatially. Diurnal variation, partially resulting from the effects of UV light, may decrease the density of E. coli, resulting in lower concentrations in the afternoon. Previous studies conducted at 63rd Street Beach in Chicago, IL [1] and North Beach in Racine, WI [2] demonstrated significant diurnal variation using an E. coli standard and culture-based assays. Subsequent studies conducted at sewage-impacted Great Lakes beaches employing molecular assays (qPCR) found that the signal remained stable; it is unknown whether a similar scenario exists at non-sewage impacted beaches. During the summer of 2011, surface water samples were collected in the morning and afternoon (0700 and 1200) and analyzed by both IDEXX/Colilert and qPCR/BioGx SmartBeads/OmniMix HS to determine if temporal variation in E. coli was occurring (n = 29/23, culture/qPCR). Analysis of log-converted data (independent t-test/one-way ANOVA) indicated no significant difference in mean E. coli concentration as determined by morning and afternoon sampling via either method (Colilert/qPCR, p = 0.49/0.09, α = 0.05). Although not statistically significant (p = 0.09) there were 5 of 23 (22%) instances where afternoon qPCR values exceeded morning counterparts; two (10%) when culture-based assays did not show a similar response. The utility of rapid assays lies in their ability to generate results prior to beach opening; temporal or event-based fluctuations should be considered when using molecular assays at non-sewage impacted beaches for regulatory purposes.
Highlights
High levels of fecal indicator bacteria (FIB), a measure of water pollution and surrogates for waterborne pathogens, have been monitored for decades to ensure the public health and safety of those participating in recreational water activities [3,4]
The purpose of this study was: 1) to determine if significant diurnal variation was occurring at a nonsewage impacted beach (North Beach, Racine WI); 2) whether the detection of diurnal variation varied significantly based on the analytical method; and 3) what impact early morning (0700 vs. 1200) sample collection would have on regulatory decisions
A survey of morning (0700) and afternoon (1200) surface water samples collected from North Beach (Racine, WI) was conducted in order to determine if diurnal variation existed prior to implementation of qPCR assays
Summary
High levels of fecal indicator bacteria (FIB), a measure of water pollution and surrogates for waterborne pathogens, have been monitored for decades to ensure the public health and safety of those participating in recreational water activities [3,4]. Exceedance of single sample limits, or 5-day rolling geometric mean values, indicate that the risk to human health may be elevated. During these periods, beach managers are required to either prohibit swimming or issue a water quality advisory, allowing the public to make an informed decision on whether or not to swim [5,6]. The US EPA agreed to complete critical research related to human health effects and rapid analyticcal assays for the enumeration of FIB in recreational waters by December 2010 and publish revised water quality criteria in October 2012. The implementation of more rapid analytical methods will result in greater protection of public health in the context of full body contact water-related recreational activities [7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
