Combined sewer overflows attributable to wet weather season contributing 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 active pharmaceutical ingredients (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 quotients for each compound, in addition to individual chemical enantiomers of amphetamine and 3,4-methylenedioxymethamphetamine. 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 in the rainy weather sampling period reached values >1: diclofenac (3.12) and eprosartan (1.59).