Occurrence and short-term variability of psychoactive substances in wastewater from a mixed urban catchment in central Chile
Abstract
<title>Abstract</title> <p>Wastewater-based epidemiology (WBE) is increasingly used to assess community-level exposure to psychoactive substances; however, evidence from Latin America remains limited, and uncertainties related to population normalization and short-term variability persist.This study examines the occurrence and short-term variability of selected psychoactive substances in wastewater from a mixed urban catchment in central Chile, providing insight into the interpretation of WBE data under dynamic population conditions. Influent samples were collected during two monitoring campaigns in 2024 and 2025 and analyzed for amphetamine-type stimulants, cocaine and benzoylecgonine, ketamine, phentermine, and fentanyl-related compounds using LC–MS/MS. Population-normalized mass loads and consumption estimates were derived using dynamic normalization based on NH₃–N. Cocaine showed the highest levels among the monitored substances, while ketamine exhibited comparatively high mass loads with marked weekend-associated patterns. Among amphetamine-type stimulants, MDMA was consistently detected but decreased in 2025, whereas amphetamine increased slightly and methamphetamine remained low. Phentermine was detected at relatively high mass loads; however, dose-equivalent estimates suggested that these corresponded to a small fraction of the potentially treated population. Observed patterns were influenced by temporal changes in contributing population, with higher mass loads generally occurring during weekends. These findings underscore the importance of dynamic population normalization when interpreting short-term variability in WBE studies, particularly in mixed or relatively small catchments. While based on a limited dataset, this case study provides evidence of short-term variability patterns that may influence the interpretation of WBE-derived indicators and supports the use of WBE as a complementary approach for environmental monitoring of emerging contaminants.</p>
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