Five-year monitoring of 19 illicit and legal substances of abuse at the inlet of a wastewater treatment plant in Barcelona (NE Spain) and estimation of drug consumption patterns and trends

Illicit and legal drugs of abuse, including alcohol, continue to be in the focus of many governmental national and international studies due to the important consequences of their consumption at both individual and social level. Estimation of drug use at the community level from the concentrations of the drugs themselves or their major metabolites measured in wastewater has become an increasingly accepted and extended tool, complementary to the methods traditionally used for this purpose. The present work describes the application of this approach, generally known as wastewater epidemiology, to investigate the latest drug consumption patterns and trends in the European city of Barcelona. To this end, a total of 19 selected drugs of abuse and metabolites were monitored at the inlet of one of the main wastewater treatment plants of Barcelona every day during one week in March between 2011 and 2015. Analysis of the selected drugs and metabolites in the wastewater samples was performed by means of two methodologies based on liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the concentrations obtained were translated into consumption data. In agreement with official records, alcohol, followed by cannabis, cocaine, amphetamine-like compounds, and methadone were the most consumed drugs. Alcohol, cannabis, and cocaine consumption were on average 18mL(14g)/day/inhabitant (>15), 38g/day/1000 inhabitants aging 15-64, and 2.4g/day/1000 inhabitants aging 15-64, respectively. As for drug use trends, consumption increased over the 5years monitored for all drugs, but for heroin and diazepam. Weekly profiles characterized by higher consumption over the weekend as compared to weekdays were observed only for alcohol, cocaine, and MDMA. Extrapolation of the data obtained for the area under study to the national Spanish territory yields consumption figures of 142t of illicit drugs per year and >2500 million euro turnover per year in the black market.