Trace analysis and occurrence of anhydroerythromycin and tylosin in influent and effluent wastewater by liquid chromatography combined with electrospray tandem mass spectrometry

Two wastewater treatment plants (WWTPs) of northern Colorado were monitored for anhydroerythromycin and tylosin. An analytical method has been developed and validated for the trace determination and confirmation of these compounds in the raw influent and final effluent water matrices. This method was used to evaluate the occurrence and fate of these compounds in WWTPs. The method uses solid-phase extraction and liquid chromatography–tandem mass spectrometry with positive electrospray ionization. Detection and quantification was performed using selected reaction monitoring, and a method detection limit of between 0.01 and 0.06 μg/L was obtained. Unequivocal confirmation analysis of analyte identity according to the criteria (based on the use of identification points) of the 2002/657/EC European Commission Decision was possible with satisfactory results. Average recoveries for the two compounds ranged from 89.2±9.7% for raw influent to 93.7±6.9% for effluent wastewaters. The within-run precision of the assay was found to be always less than 14.1% for the two analytes. The overall precision was always less than 13.7%. The relative uncertainty of the present assay was also evaluated and the combined relative uncertainty ranged from 6.4 to 15.5% over three days of the validation study. These compounds were partially removed in the WWTPs with a removal efficiency of >50%. The measured concentrations in raw influents and effluents ranged from 0.09–0.35 and 0.04–0.12 μg/L for anhydroerythromycin to 0.06–0.18 and ND–0.06 μg/L for tylosin, respectively. The results indicate that WWTP effluents are relevant point sources for residues of these compounds in the aquatic environment. These occurrence results were compared with those in WWTP wastewaters of other countries.