Comparison of the occurrence and survival of fecal indicator bacteria in recreational sand between urban beach, playground and sandbox settings in Toronto, Ontario
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abstract
While beach sands are increasingly being studied as a reservoir of fecal indicator bacteria (FIB), less is known about the occurrence of FIB in other recreational sands (i.e., sandboxes and playgrounds). In this study, different culture-based FIB enumeration techniques were compared and microbial source tracking assays were conducted on recreational sand samples from beaches, playgrounds and sandboxes around Toronto, ON. FIB were detected in every sand sample (n=104) with concentrations not changing significantly over the five month sampling period. Concentrations of FIB and a gull-specific DNA marker were significantly higher in foreshore beach sands, and indicated these were a more significant reservoir of FIB contamination than sandbox or playground sands. Human- and dog-specific contamination markers were not detected. All culture-based FIB enumeration techniques were consistent in identifying the elevated FIB concentrations associated with foreshore beach sands. However, significant differences between differential agar media, IDEXX and Aquagenx Compartment Bag Test were observed, with DC media and Enterolert being the most sensitive methods to detect Escherichia coli and enterococci, respectively. To better understand the elevated occurrence of E. coli in foreshore sands, microcosm survival experiments were conducted at two different temperatures (15 °C and 28 °C) using non-sterile saturated foreshore beach sands collected from two urban freshwater beaches with different sand type (fine grain and sand-cobble). Microcosms were inoculated with a mixture of eight sand-derived E. coli strains and sampled over a 28-day period. E. coli levels were found to decline in all microcosms, although survival was significantly greater in the finer sand and at the cooler temperature (15 °C). These results indicate that FIB can be widespread in any type of recreational sand and, while E. coli can survive for many weeks, it is most likely to accumulate in cooler fine-grain sand as occurs below the foreshore sand surface.
