Consumption of illicit drugs and benzodiazepines in six Spanish cities during different periods of the COVID-19 pandemic

Wastewater-based epidemiology (WBE) can provide objective and real time information about the use of addictive substances. A national study was conducted by measuring the most consumed illicit drugs, other drugs whose consumption is not so widespread but has increased significantly in recent years, and benzodiazepines in untreated wastewater from seven wastewater treatment plants (WWTPs) in six Spanish cities. Raw composite wastewater samples were collected from December 2020 to December 2021, a period in which the Spanish and regional governments adopted different restriction measures to contain the spread of the COVID-19 pandemic. Samples were analyzed using a validated analytical methodology for the simultaneous determination of 18 substances, based on solid-phase extraction and liquid-chromatography tandem mass spectrometry. Except for heroin, fentanyl, 6-acetylmorphine and alprazolam, all the compounds were found in at least one city and 9 out of 18 compounds were found in all the samples. In general, the consumption of illicit drugs was particularly high in one of the cities monitored in December 2020, when the restrictions were more severe, especially for cannabis and cocaine with values up to 46 and 6.9 g/day/1000 inhabitants (g/day/1000 inh), respectively. The consumption of MDMA, methamphetamine and mephedrone was notably higher in June 2021, after the end of the state of alarm, in the biggest population investigated in this study. Regarding the use of benzodiazepines, the highest mass loads corresponded to lorazepam. This study demonstrates that WBE is suitable for complementing epidemiological studies about the prevalence of illicit drugs and benzodiazepines during the COVID-19 pandemic restrictions.