Occurrence, transport, and fate of mental health biomarkers in aquatic environments

Mental health is a key part of public health, increasing depression, and stress-related problems have created a need for timely monitoring. Wastewater-based epidemiology (WBE) provides a noninvasive way to track population-level signals of psychotropic drug use through wastewater. This review systematically summarizes the transport and fate characteristics of 12 representative mental-health-related biomarkers throughout the entire pathway from human excretion to receiving waters. The results show that most biomarkers have parent-compound excretion fractions below 5%, whereas existing WBE studies still mainly target parent compounds; their half-lives during sewer transport mostly exceed 10 h; after entering wastewater treatment plants, more than half of the pharmaceuticals show attenuation rates below 30%; and in receiving environments, their occurrence is dominated by water-phase signals, followed by riverbed sediments and other particulate matrices, with a small fraction being taken up by biota. Overall, the attenuation of these biomarkers during 12 h of sewer transport is slightly lower than that during the WWTPs, while their behavior becomes more complex after entering receiving waters. Therefore, this review considers paired monitoring of VEN–ODV, as well as CTP, DZP, and OXA, to be relatively suitable as candidate biomarkers. Sampling locations should preferably be selected at sewer nodes with short transport distances or at untreated influent points of wastewater treatment plants to reduce signal changes. Of course, biomarker selection may also be affected by practical factors such as local prescribing practices and research objectives. This review establishes a whole-process framework to provide a theoretical basis for application of WBE.