Precision traceability of trace psychoactive substances under water quality parameter perturbations in a complex...

Wastewater-based drug testing using LC-MS/MS is widely applied to monitor the use of psychoactive substances (PSs), which are chemicals that act on the central nervous system and alter perception, mood, or behaviour. However, due to the spatial distance between sampling and discharge points, as well as the migration and degradation processes of target compounds during sewer transport, measurement deviations may occur. In this study, the relative deviations between directly measured and initial concentrations were found to range from 67.37% to 98.15%, indicating considerable uncertainty in conventional assessment approaches. To address this issue, a laboratory simulation covering the entire wastewater conveyance process was conducted to investigate PS degradation patterns and optimize existing assessment methods. The results showed that under aerobic, anaerobic, and facultative conditions, the removal efficiencies of most target compounds increased over time. In addition, multivariate linear regression models were developed to quantitatively link multiple target compounds with key water quality parameters, including chemical oxygen demand (COD), total nitrogen (TN), and ammonia nitrogen (NH₃-N), with the correlation index R of these models ranging from 0.66 to 0.96. Validation results demonstrated that the relative deviations between estimated and initial concentrations ranged from 12.98% to 29.85%, substantially lower than deviations obtained from direct measurements. This indicates that the established equations provide a more accurate assessment of PS abuse compared to conventional approaches. Nevertheless, factors beyond water quality parameters may also affect the degradation of target compounds in sewage systems, indicating that further investigation is needed to establish more comprehensive models for multi-substance concentration estimation.