Benzimidazoles in wastewater: Analytical method development, monitoring and degradation by photolysis and ozonation.

Pharmaceutical residues are constantly released into natural waters, mainly from wastewater treatment plants (WWTPs) whose processes are unable to completely eliminate them. Among these drugs, the occurrence of benzimidazoles, a class of antiparasitics for human and veterinary use, has been reported in WWTP effluents and surface waters. In this study, an SPE-UHPLC-MS/MS method was developed and optimized for extraction and quantitation of benzimidazoles in influents and effluents of a local WWTP and in hospital wastewater. The extraction procedure was optimized using response surface methodology (Box-Behnken design) and the optimal parameters were as follows: 2.0 mL of loading solvent consisting of a mixture of water:methanol (95:5, v/v) and temperature at 43 °C. In hospital wastewater, albendazole (ABZ) and its principal metabolite ricobendazole (RBZ) were the main benzimidazole-related contaminants and were found at concentrations of up to 3810 and 3894 ng L, respectively. The WWTP system was able to remove from 46% to 95% of the ABZ quantified in the influent, discharging an effluent with 16-441 ng L of ABZ. The concentrations of other benzimidazoles and metabolites in the WWTP effluents remained below 350 ng L. WWTP effluents fortified with 50 μg L of ABZ required 26.7 mg L to remove ABZ and RBZ. After ozonation, the COD and BOD of the effluents were reduced by 27%. Photolysis by UVA radiation was not effective to remove ABZ and FBZ from the effluent samples.