Wastewater Analysis and Correlation with Demographic Indicators in the Province of Valencia

Abstract While wastewater-based epidemiology (WBE) is well-established in metropolitan areas, its application in rural settings remains largely unexplored. This study addresses this gap by evaluating the consumption patterns of 47 psychoactive biomarkers across 17 municipalities in Valencia, Spain. We demonstrate that monthly grab sampling over 24 months effectively captures long-term trends, overcoming technical constraints in rural infrastructures. Using SPE-LC-MS/MS, we detected high concentrations of cocaine, cannabis, and benzodiazepines, with significant correlations between parent drugs and metabolites confirming their human origin. A key novelty is the analysis of chemical data alongside socioeconomic indicators. Results show that while cocaine consumption is ubiquitous, cannabis and ketamine loads are driven by urban density and younger demographics. Conversely, therapeutic pharmaceuticals predominate in rural areas with higher aging and dependency indexes. These findings validate WBE as a sensitive tool for monitoring public health across the rural-urban divide, providing essential data for targeted social and health interventions in underserved populations.