El rol de las partículas sólidas en la persistencia de bacterias en aguas recreativas y sus implicancias en la salud pública: un estudio preliminar

Abstract

Microbiological pollution of recreational aquatic environments is a global concern since 80% of water-borne diseases are caused by microorganisms that reach the water through feces, organic and inorganic particles and other residues excreted by infected people. The assessment of microbial water quality is carried out through monitoring campaigns where fecal indicator bacteria are measured, according to legislation. Despite the advances made in detection and control methods, water-borne outbreaks are still reported. It is then possible that other environmental factors are influencing on the persistence of microorganisms in water. One of the main causes of persistence is the presence of solid particles. Microorganisms can be found and eventually transported in water as planktonic cells or attached to particles. During low flow rate events, some particles can sediment with microorganisms adsorbed, removing them from the water column and thus increasing their persistence. The resuspension process due to recreational activities or natural turbulence causes the return of these solid particles with the microorganisms attached and their probable desorption, becoming a health risk for users. The aim of this work was to evaluate if the presence of solid particles in different environmental matrices with recreational uses exerts some effect on the persistence of two indicator bacteria. Sedimentation-resuspension tests were carried out in the laboratory using four water matrices prepared with recreational ambient waters: two with low and two with high turbidity values. Known concentrations of Escherichia coli and Enterococcus faecalis were spiked on each matrix and homogenized. Samples were taken from the surface over time to evaluate their disappearance during sedimentation process. Turbidity decrease over time was also measured. When colony count was below the detection limit, a resuspension was performed, and bacteria were quantified again. A first-order decay model was applied from which different kinetic parameters were obtained. Although a greater persistence of Escherichia coli compared to Enterococcus faecalis was observed in the presence of solid particles, which was evidenced in the reappearance of culturable bacteria after resuspension of matrices with high turbidity, the decay constant rates was similar for matrices for both low and high turbidity. This would indicate that other water characteristics rather than turbidity may be influencing on their persistence. Finally, the determination of kinetic parameters is of quite importance due to their potential inclusion into risk assessment and water quality models, allowing a better analysis of the situation.