Survival of bacterial indicator organisms and enteric viruses in the Mediterranean coastal waters off Tel-Aviv

Abstract

Field and laboratory studies were initiated on the die-away kinetics of coliforms and enteric viruses in coastal waters off Tel-Aviv. Samples were taken from the sewage boil located approx. 880 m out to sea and from three main Tel-Aviv beaches designated as sampling stations, ranging 3 km to the north and 2 km to the south. Routine bacteriological tests were made from these stations; in addition, approx. 50% of the samples were also examined for enteroviral content and occasionally, samples were taken from most of the other Tel-Aviv beaches for comparison of bacterial and viral content. The concentrations of total coliforms, fecal coliforms and fecal streptococci were correlated with the concentrations of enteroviruses. In general, the data suggests that the number of enteric bacteria in the sea was reduced relatively more rapidly than that of the enteroviruses, while fecal streptococci displayed a die-away rate similar to that of enteroviruses. The percentage of samples positive for enteroviruses was found to be lower during the summer months of the year than in the remaining months. The concentration of coliforms was also significantly lower during the summer months. This suggests that the decreased microbial level is associated with increased summertime daylight and solar radiation which affect the micro-organisms' die-away rate. About 76% of the positive enteroviral samples were found at beaches with a fecal coliform bacterial level considered safe for bathing beaches.