The European Monitoring Centre for Drugs and Drug Addiction came to its findings by testing levels of illicit substances found in wastewater.
In Portugal, samples were taken in Lisbon, Porto and Almada. In all of the locations, the presence of these substances in the water was higher on the weekends than on weekdays. However, the consumption of cigarettes and alcohol was below the EU average.
The latest findings from the largest European project in the emerging science of wastewater analysis, verified samples in 73 European cities in 20 European countries in March 2018 to explore the drug-taking behaviours of their inhabitants.
The 2018 study points to an increase in the detection of amphetamine, cocaine and MDMA in wastewater samples, compared to the 2017 figures.
From Lisbon to Athens and from Copenhagen to Madrid, the study analysed daily wastewater samples in the catchment areas of wastewater treatment plants over a one-week period. Wastewater from approximately 46 million people was analysed for traces of four illicit drugs: amphetamine, cocaine, MDMA (ecstasy) and methamphetamine.
Wastewater based epidemiology is a rapidly developing scientific discipline with the potential for monitoring close to real-time, population-level trends in illicit drug use. By sampling a known source of wastewater, such as a sewage influent to a wastewater treatment plant, scientists can now estimate the quantity of drugs used in a community by measuring the levels of illicit drugs and their metabolites excreted in urine.
The SCORE group has been conducting annual wastewater monitoring campaigns since 2011.
A total of 33 cities have participated in five or more of the eight campaigns run so far, which allows for time-trend analysis of drug consumption based on wastewater testing.
In cities with wastewater data for 2017 and 2018, the latest figures reveal increases in traces of cocaine, confirming the upward trend reported in 2017. Cocaine residues in wastewater were highest in western and southern European cities, particularly in cities in Belgium, the Netherlands, Spain and the UK.
The analysis points to very low levels of cocaine use in the majority of eastern European cities, but the most recent data shows signs of increases.
The data also shows that most cities reported an increase in amphetamine residues, while data from the previous seven monitoring campaigns showed no major changes in patterns observed. The loads of amphetamine detected in wastewater varied considerably across the study locations, with the highest levels reported in cities in the north and east of Europe. Amphetamine was found at much lower levels in cities in the south of Europe.
The 2018 data point to increased traces of MDMA in most cities, compared with a stabilising trend in 2017. When weekly patterns of drug use were examined, cocaine and MDMA (ecstasy) levels rose sharply at weekends in most cities. Methamphetamine loads were found to be evenly distributed over the week.