Urban sewer sediments as a potential matrix for retrospective wastewater-based epidemiology

Wastewater-based epidemiology (WBE) provides near real-time insight into population exposure to chemicals and microbial targets but lacks retrospective depth because monitoring depends on the initiation of sampling. Here, we demonstrate that sediments accumulated in settling basins constitute multi-year, time-integrated archives of wastewater composition that can extend WBE into the past. Four sediment cores collected in 2024 from a large combined-sewer desilting basin in Paris, undisturbed since 2020, were analyzed across stratigraphic layers corresponding to discrete depositional events. A total of 44 targeted pharmaceuticals, illicit drugs, and lifestyle markers were quantified, with concentrations ranging from tens of ng g −1 to several µg g −1 . Stable WBE microbial targets were consistently detected, whereas SARS-CoV-2 was not detected. Reorganization of layers by depositional age revealed reproducible multi-year patterns and consistent parent/metabolite relationships. Contaminant preservation was strongly modulated by sediment geochemistry and compound properties, with organic matter and mineral phases jointly controlling partitioning and favoring retention of neutral and cationic molecules. Despite discontinuous, event-driven accumulation and pronounced matrix heterogeneity, recurring stratigraphic structures across independent cores demonstrate that sediments provide a semi-quantitative record of wastewater composition over discrete time windows. These findings establish urban sewer sediments as complementary, retrospective observatories of public health.