Sand as a source of bacteriological pollution in recreational beaches of the Río de la Plata

The southern coastal fringe of the Río de la Plata estuary hosts multiple activities, serving as an economic resource, freshwater supply and recreational center for the largest populations in Argentina. The bacteriological quality of eight beaches was assessed in 78 km of the coast, to measure the presence of two fecal pollution indicators (Escherichia coli and Enterococcus) both in the water and in sand samples. Results indicate that the abundance of microorganisms was generally higher in the sediment than in the water, and in most beaches, they exceeded the recommended guides for the use of recreational waters. Microbial abundances were negatively associated with distance from sewage discharges for both indicators in sand and for Enterococcus in the water, while the abundance of the former in water was also negatively associated with dissolved oxygen. The abundance of E. coli was always higher than Enterococcus, suggesting that it may be a more generalized indicator of fecal contamination in the area.