Mass-balance-model-based evaluation of sewage treatment plant contribution to residual pharmaceuticals in environmental waters

In this study, a total of 52 pharmaceuticals in the influent and effluent of two sewage treatment plants (STPs) and in the receiving waters were quantified with an analytical method using on-line solid phase extraction coupled to liquid chromatograph-tandem mass spectrometry. 36 out of the 52 pharmaceuticals were detected in the influent and effluent of the STPs at quantifiable levels; influent and effluent concentrations ranged 1 ng L⁻¹ to 30 μg L⁻¹ and 3 ng L⁻¹ to 3 μg L⁻¹, respectively. They were also detected from the receiving waters (both tributaries and main river); their concentrations ranged from 1 to 310 ng L⁻¹. A simple mass balance model was applied for the pharmaceutical data measured for the STPs, tributaries, and the main river to demonstrate the contribution of the STPs to the pollution of the streams and the main river. The average ratio of the model estimations and the measured concentrations was calculated 97% for the downstream of the STPs, while that for the main river was 89%. This modeling result clearly demonstrates that many pharmaceuticals flowing into an STP are not degraded and discharged to a nearby river, affecting the whole water body, and that the STP is the only source of the pollutants. While their discharge into STPs should be avoided. In addition, development of new technologies capable of completely degrading them is desirable.