Application of direct injection LC–MS/MS for pharmaceutical monitoring in wastewater and reclaimed water from the 14 wastewater treatment plants in Costa Brava (Catalonia, Spain)

In response to increasing global water scarcity, reclaimed water, which is treated wastewater intended for reuse, has become a sustainable alternative for various applications. However, the presence of pharmaceutical residues that persist through conventional treatment processes raises concerns for environmental and human health. In this study, a direct injection liquid chromatography tandem mass spectrometry (DI-LC–MS/MS) method was developed and applied to quantify 75 pharmaceutical compounds in secondary and tertiary effluents from 14 wastewater treatment plants in Costa Brava, Catalonia. Among the compounds analyzed, metformin, tramadol, and azithromycin were the most abundant, with median concentrations above 1000 ng L⁻¹. The method demonstrated acceptable sensitivity, recovery, and matrix effect values for most analytes. Comparison of concentrations in secondary and tertiary effluents showed that tertiary treatment significantly improved removal for only 13 out of 31 evaluated compounds. These findings underscore the limitations of current wastewater treatment technologies and highlight the need for improved strategies to ensure the safety of water reuse.