A STUDY THAT examines drug residue in the wastewater of 70 European cities has found that the highest amounts of cocaine residue were in Bristol, Amsterdam and Zurich.

Cocaine use remains highest in western and southern European cities, in particular in cities in Belgium, the Netherlands, Spain and the United Kingdom. Ireland did not partake in the study.

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 (or ecstasy) and methamphetamine.

The below graph shows the top 10 cities for high cocaine traces found, measured per person on a daily basis. 

Emcdda Emcdda

In the large majority of countries with multiple study locations, cocaine and MDMA loads were higher in large cities compared to smaller locations. No such differences could be detected for amphetamine and methamphetamine.

“MDMA loads were consistently found in the wastewater of cities in Belgium and the Netherlands,” the study states.

It also notes that “wastewater MDMA loads” were higher in 2018 than in 2011 in some cities, “with sharp increases” in some cities, including Antwerp and Amsterdam.

One part of the study notes:

“Similarly, studies based on self-reported drug use and those using wastewater data both point towards the same weekly variations in use, with stimulants such as amphetamine and cocaine being primarily used at weekend music events and in celebratory contexts.”

Wastewater-based studies is a new scientific development that has a potential for close to real-time, population-level trends in illicit drug use. Limitations to this methodology include limited “information on prevalence and frequency of use, main classes of users and purity of the drugs”.

Fourteen countries took part in the study: Austria, Belgium, Cyprus, Czech Republic, Germany, Finland, France, Italy, Lithuania, Netherlands, Portugal, Spain, Slovakia and
Slovenia.