Combined sewer overflow contribution to pharmaceutical pollution: a case study in northern Spain

The use of combined sewer systems is associated with frequent overflow events and discharges of untreated wastewater containing micropollutants, including APIs. The aim of this study was to evaluate the impact of weather-related factors on the presence of pharmaceuticals and illicit substances and assess the related environmental risk. To address this goal, three sites in the surroundings of the city of Vitoria-Gasteiz were sampled in April (dry week) and November (wet week): Betoño Pond in the Salburua Wetlands, and Zadorra River before and after receiving the Crispijana wastewater treatment plant’s (WWTP) effluent. An environmental risk assessment was performed by measuring the hazard quotient. This is the first time when an enantioselective risk assessment has been performed for environmentally relevant concentrations of illicit drugs measured in a wetland of an international importance. A total of 33 out of 102 substances were detected in at least one of the samples and a minimum of 6 APIs in all sample sites. Post-WWTP samples taken in autumn (wet week) presented the highest cumulative concentration (7739 ng L-1). Risk quotients of 12 APIs in the most contaminated site (SP3) in the rainy weather sampling period reached values > 1: diclofenac (3.12) and eprosartan (1.59).