Microbiological risk assessment in a coastal marine environment through the use of mathematical models

Most of human pathologies related to the use of marine waters for bathing purposes are caused by the presence of pathogens discharged in the aquatic environment during faecal contamination episodes. The assessment of seawater microbiological quality is conventionally performed through the search of indicator microorganisms. The use of criteria relying exclusively on the analytical evaluation of seawater quality, however, not always provides enough information about the exposure risk for human health. To better assess the sanitary risk related to the use of possibly contaminated seawaters, it is important to integrate "in situ" data with the use of mathematical models, which allow us to estimate and forecast the accumulation and the dynamics of spread and transport of potentially infectious microorganisms in relation with meteo-marine conditions. This study aimed at assessing the potential risk for human health related to pathogens in the Santa Marinella beach (Rome, Italy) during the bathing season. The coastline morphology and the presence of submerged and emerged barriers, with consequent separation of the waters nearest to the coastline from the offshore ones, reduce the possibility of water recirculation in that area. During August 2011, samples of water and sediment were drawn along the shoreline in front of Santa Marinella, and examined to measure faecal coliforms, faecal streptococci, Salmonella spp., spores of sulphite-reducing clostridia, mycetes. The collected dataset has been fed as the initial condition in a numerical model using wind speed and direction and wave measurements to evaluate the half life of bacterial load. The study pointed out the significant effects played by meteo-marine events on the diffusion of potentially pathogenic microorganisms along the shoreline, providing useful information for the set up of measures for public health protection in the Santa Marinella area.