Estimation of legal and illegal drugs consumption in Valencia City (Spain): 10 years of monitoring

Wastewater-based epidemiology (WBE) approach provides objective, quantitative, near real-time profiles of illicit drug consumption by monitoring the concentration of unchanged parent drugs or their metabolites entering the municipal sewage system. Valencia is the third most populous city in Spain (an important country for the use and transit of several of these drugs). Estimations of consumption over long periods of time will help get better understanding of spatial and temporal trends in the use of licit and illicit drugs. Accordingly, applying the "best practice" protocol, 16 drugs of abuse and metabolites were monitored in this study, and 8 were daily measured during one-two weeks between 2011 and 2020 at the inlet of three wastewater treatment plants of Valencia City. Analysis of the selected compounds was performed by liquid chromatography-triple quadrupole mass spectrometry, and the concentrations obtained were used to back-calculate the consumption data. Cannabis, tobacco, and cocaine were the most consumed drugs whereas opioids were less used. Cannabis and cocaine consumption are on average 2.7-23.4 and 1.1-2.3 g/day/1000inh, respectively, and their use tended to increase since 2018. Weekly profiles were characterized by higher consumption of cocaine, ecstasy, and heroin during weekends compared to weekdays. Similarly, during "Las Fallas" (main local festivity), increased use of cocaine and amphetamine-type stimulants, mainly MDMA, was measured. WBE proved to be an objective and useful methodology to get more insight on temporal drugs of abuse consumption, and the changes derived from local festivities.