Deriving Correction Factors of Nine Commonly Used Antidepressants by Calibrating Mass Loads in Wastewater against Prescription Volumes in a Well-Defined Study Area

The correction factor (CF) is a crucial parameter in the back-calculation of drug consumption in wastewater-based epidemiology (WBE) studies. In this study, concentrations of 13 antidepressants and six metabolites were measured in wastewater samples for 11 consecutive months at the three largest treatment plants of Changshu, China. The monthly trends of mass loads and prescription volumes of the nine antidepressants widely detected in wastewater were largely parallel, indicating a strong correspondence between prescription and actual consumption during the study period. The correspondence yielded reliable CFs of target substances, among which the CF of norsertraline (14.5) was determined for the first time. The CFs based on excretion rates of venlafaxine and bupropion significantly overestimate consumption of the two drugs (by 76.5 and 82.4%, respectively), whereas the CF based on the excretion rate of N-desmethylcitalopram significantly underestimates its consumption (by 49.3%). The CFs of sertraline (16.4) and milnacipran (19.6) differ dramatically from those (500 and 1.8, respectively) based on excretion rates. The CFs used in previous studies would cause misleading pictures of regional mental health status and compromise the value of WBE. Therefore, the CFs derived here will play important roles in future studies as they yield a much more reliable estimation of consumption of major antidepressants.