Distribution and Significance of Fecal Indicator Bacteria in Beach Sand and Seawater in a Sub-Tropical Environment

Gastroenteritis, upper respiratory complaints and dermatological infections can all result from swimming in sewage polluted waters. Current United States Environmental Protection Agency (EPA) guidelines require that recreational beaches are routinely tested for the presence of sewage contamination. Fecal indicator bacteria, such as Escherichia coli, fecal coliforms, and enterococci, are all intestinal microflora of warm-blooded animals and are the indicators of choice. It is assumed that high concentrations of these organisms in water imply fecal contamination and hence warn of health risk to swimmers. Although local Health Departments routinely assess the quality of beach water, they do not test the sand. 1bis is surprising since most beachgoers spend more time in contact with sand than water. The present study was part of a two-year project funded by the EPA designed to assess the microbiological quality of beach sand and its possible health risks. Over a ten-month sampling period, water, wet sand, and dry sand samples were collected and the levels of enterococci and fecal coliforms were compared at two South Florida beaches. Levels of fecal indicators were consistently higher in the dry sand relative to the wet sand and were lowest in water. An attempt to source track these indicators using the Biolog identification system suggested that bacteria in sand were from multiple sources. There was, however, some evidence to suggest that gull droppings and land runoff were major inputs to the beach. Surprisingly, offshore sewage outfalls were not found to be a major source in this study. Microspatial sampling of beach sand showed patchy distribution of enterococci. Gull droppings, which provided dense localizations of bacteria, and the subsequent translocation of enterococci through the activity of beachgoers probably accounted for most of the heterogeneity in the dry sand. Enterococci in the wet sand were more evenly distributed presumably due to the normalizing effect of wave action The swash zone, close to the area where water managers collect samples for analysis, had much higher counts of enterococci than 10m offshore. This was due to wave action washing enterococci from the sand into the water column. Research by colleagues showed that enterococci displayed enhanced survival and growth in the sand and suggested that they should be referred to as \u27environmental\u27 enterococci. The delineation between environmental and pathogenic bacteria in the sand was investigated in this study using a molecular approach. Polymerase Chain Reaction (PCR) was shown to be able to detect pathogenic Salmonella in beach sand. However, no clear relationship was apparent between the presence of pathogens on the beach and the numbers of indicator bacteria enumerated by traditional methods. Moreover, results from a health survey conducted at the study beaches showed no obvious health risks associated with exposure to beach sand. It is likely that sand fecal indicator bacteria are predominately \u27environmental\u27 and that when these bacteria are washed into the swash zone, they could lead to unwarranted beach closures. It is recommended that water managers should consider sampling beyond the current testing depth of 3 ft (1 m) to avoid the detection of enterococci from the sand