Onsite wastewater treatment systems are a major source of pharmaceutical products in surface water of peri-urban/rural areas

Most of the published studies on pharmaceutical products (PhPs) focus on their occurrence in the influent/effluent at wastewater treatment plants (WWTPs) in urban areas with high population density. In peri-urban/rural areas not collected to any WWTP, despite the lack of sewage collection, and often (poor) on-site treatment, data on PhPs occurrence in surface water bodies is scarce. In this study, we investigated the impact of onsite wastewater treatment systems on the occurrence of six PhPs, along with hydrological and hydrochemical data, in the drainage network of a peri-urban/rural area in Italy. Our results, along with data from other studies, show onsite treatment systems are a major source of PhPs. In the drainage water 76% of the analyses positively quantified the presence of PhPs, with carbamazepine and clarithromycin always quantifiable, even in scarcely inhabited areas, at generally higher concentrations of PhPs than those reported in previous studies. As a result, onsite treatment systems may cause ubiquitous, even if at low concentrations, PhPs occurrence in the aquatic systems. In order to allow data comparison, studies reporting PhPs environmental concentration values should clearly detail the urban /environmental setting (population density, presence of WWTPs) and the hydrological/hydrochemical conditions. Furthermore, the joint use of hydrochemical parameters and PhPs data may provide useful proxies for the occurrence of PhPs or to identify nitrate sources of urban origin. Discharge, T, EC and ORP values may help understanding relevance of mixing and, then, the importance of dilution processes in reducing PhPs concentration. The occurrence of PhPs in surface water has to be duly considered in order to protect the aquatic ecosystems and groundwater, and the use of such water for safe irrigation purposes. Further treatment trains based on the concept of nature-based solutions (i.e, vegetated channels, artificial wetlands) could constitute a valuable solution exploiting the soil–water-plant continuum around main residential areas in order to enhance degradation processes.