Risk assessment of antibiotics in surface waters: applying SWAT and GREAT-ER in a modelling cascade

Among the emerging pollutants that may negatively affect river ecosystems, pharmaceuticals are of major concern. Their presence was detected in several rivers around the world. Their management requires tools and plans of measures to reduce the ecotoxicological risk. The aims of the present paper were (i) to set a modelling approach for evaluating the fate of pharmaceuticals in surface waters in Mediterranean rivers, and (ii) to assess the ecotoxicological risk associated with the presence of azithromycin (AZ). At this aim, a modelling cascade application was implemented in the Canale D’Aiedda basin (S, Italy), an intermittent river. The outputs of the Soil and Water Assessment Tool were used as input in the Geography-referenced Regional Exposure Assessment Tool for European Rivers Hydraulic. The models were calibrated by using field measurements. Both the Predicted Environmental Concentrations (PEC) of AZ and the ecotoxicological risk were assessed for the dry and wet seasons. The results of monitoring and modelling showed that the dilution effect does not play an important role, meanwhile, seasonal changes in AZ domestic consumption greatly affected the concentrations in surface waters. In-stream attenuation of AZ in the water column of a near-natural river reach was higher than that recorded in the channelized reaches. In winter, most of the river network showed a high degree of ecotoxicological risk associated with the presence of AZ.