This study describes an investigation on the occurrence of 27 pharmaceutical compounds, belonging to different classes, in the effluent from two wastewater treatment plants (WWTPs) and their receiving water bodies in the sensitive area of the Po Valley (northern Italy). These canals were monitored upstream and downstream of the effluent discharge points in order to evaluate the effluent impact on the quality of surface waters, commonly used for irrigation. An environmental risk assessment was also conducted by calculating the risk quotient, i.e. the ratio between measured concentration and predicted no effect concentration. Collected data show that, although average values of the selected compounds were in general higher in the effluent than in the surface waters, some compounds not detected in the WWTP effluent were detected in the receiving water (upstream as well as downstream), indicating that sources other than treated effluents are present as contaminations during extraction and analysis have to be excluded. The most critical compounds for the environment were found to be the antibiotics sulfamethoxazole, clarithromycin and azithromycin. The study shows that the potential toxicological effects of persistent micropollutants can be mitigated to some extent by a high dilution capacity, i.e. a high average flow rate in the receiving water body with respect to the effluent.
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