Life’s a Beach: Testing the Waters Before you Dive In!

Bathing in the sea at beaches which are not impacted by known point source pollution is a growing concern worldwide. Globally, over 120 million cases of gastrointestinal disease and over 50 million cases of respiratory diseases per year are sourced back to bathing in wastewater-polluted coastal waters. The authors of this paper evaluated the presence of pollution indicator microbes at a bathing beach in South Florida known to be impacted by non-point sources of pollution by taking twelve water samples and eight sand samples and analysing them. EPA (the Environmental Protection Agency) recommend the microbial indicator species Enterococci, as it shows a correlation between its abundance and cases of illness at marine bathing beaches impacted by point source pollution. However, this correlation is not consistant with Enterococci abundance and marine bathing-related illnesses on beaches impacted by non-point source pollution, which lead the authors to question the true extent of how well Enterococci works as an indicator species for predictions of presence of pathogens.

The chosen experimental location was a beach in Miami-Dade County, Florida, where background descriptions state that dogs are allowed on the beach year-round, and that after an extensive search, there are no point sources of pollution. The beach is admission free, and busy in summer months. It is open for the vast majority of the year with the exception of around 4 days a year where it is recommended that bathers do not enter the water due to an increase in pathogens in the water, violating water quality legislations. Water samples were collected in 20 litre sterile containers, and sand samples were collected in the upper 2.5cm and placed into sterile Whirlpak bags; wet sand samples were collected from the intertidal zone, and dry sand samples from above the high tide line. The sand samples were placed in containers filled with 10 litres of phosphate-buffered saline, and this was mixed vigorously. The supernatant from the sand samples along with the seawater samples were then analysed, and the microorganisms were identified and enumerated. Environmental conditions such as weather, temperature, wind speed, water turbidity and the presence or absence of bathers and dogs were also taken into account.

The results of the study revealed that using Enterococci as an indicator showed a variety of results depending on which method was used to enumerate the bacteria. This is important when considering the uses of Enterococci as an indicator species at bathing beaches as differences in enumeration could lead to the unnecessary closure, or the unsafe opening of bathing beaches.Spatial and temporal variations in the area of study also show a difference in enumeration, which could also lead to different management decisions at bathing beaches. Presence of faecal indicator bacteria in the water and the sand samples were predominantly consistent with the Enterococcus results, showing the possibility that the environmental conditions which affect Enterococci also affect the faecal indicator organisms. The pathogens impacting the water is highly intermittent depending on illnesses carried by humans and animals such as dogs contributing to the pollution source entering the beach. Finally, the environmental conditions recorded during water and sand sampling periods show that on the sunnier days where sampling took place, there were less microbes as the UV is known to inactivate them. Sea temperatures and tidal height also played a part in the fluctuation of detection of microbes.

I enjoyed reading this paper as it was interesting to see how beaches which are not directly affected by point source pollution are affected by non-point source pollution from other areas.

Abdelzaher, A. M., Wright, M. E., Ortega,C., Solo-Gabriele, H. M., Miller, M., Elmir, S., Newman, X., Shih, P., Bonilla, J. A., Bonilla, T. D., Palmer, C. J., Scott, T., Lukasik, J., Harwood, V. J., McQuaig, S., Sinigalliano, C., Gidley, M., Plano, L. R. W., Zhu, X., Wang, J. D. & Fleming, L. E. (2010) Presence of Pathogens and Indicator Microbes at a Non-Point Source Subtropical Recreational Marine Beach. Applied and Environmental Microbiology. 76 (3): 724-732.