Monitoring the occurrence of pharmaceuticals in soils irrigated with reclaimed wastewater

The use of reclaimed wastewater for irrigation is foreseen as a possible strategy to mitigate the pressure on water resources in dry regions. However, there is the risk of potential accumulation of contaminants of emerging concern (CECs) in the edaphic environment, their percolation and consequently contamination of aquifers. In the present study, we measured the levels of a wide range of commonly used pharmaceutically active compounds (PhACs) in sewage from a local wastewater treatment plant (WWTP) and in soils irrigated with treated wastewater. Analysis of target compounds showed total concentrations between 73 and 372 μg L⁻¹ in WWTP influents, and from 3 to 41 μg L⁻¹ in effluents. The total concentrations of PhACs detected in surface soil samples were in the range of 2 and 15 ng g⁻¹, with predominance of analgesics and anti-inflammatories (maximum concentration = 10.05 ng g⁻¹), followed by antibiotics and psychiatric drugs (maximum concentration = 5.45 ng g⁻¹ and 3.78 ng g⁻¹, respectively). Both effluent samples and irrigated soils shared similar compositional patterns, with compounds such as hydrochlorothiazide and diclofenac being predominant. Additionally, PhACs were also detected in soil samples at a depth of 150 cm, indicating that these chemical undergo leaching associated with heavy-rain episodes. Their occurrence in soils was affected by temperature too, as maximum concentrations were measured in colder months (up to 14 ng g⁻¹), indicating higher persistence at lower temperatures. Finally, the ecotoxicological risk of PhACs in soil was evaluated by calculating their risk quotients (RQs). The risk was very low as RQ values ranged between <0.01 and 0.07. However, this initial assessment could be improved by future works on toxicity using specific terrestrial organisms.