Which UK city tops list for cocaine traces in Europe-wide sewage study?
Bristol has registered the highest concentration of cocaine traces in a Europe-wide study of sewage.
Researchers examined wastewater in dozens of cities around the continent to explore drug-taking habits.
In order to assess cocaine levels, experts tested samples for benzoylecgonine (BE), which is produced when the body breaks down the class A substance.
The average daily concentration of benzoylecgonine in Bristol's wastewater was 969.2mg per 1,000 people in 2018.
This was up from 754.7mg in the previous year.
Amsterdam recorded the second highest figure in 2018, with 932.4mg, followed by Zurich (856.0mg), Antwerp Zuid (771.8mg) and Barcelona (733.2mg).
Bristol was the only UK city participating in last year's research.
London's wastewater, which has previously topped the cocaine chart, was not included.
A report on the research, published by the European Monitoring Centre for Drugs and Drug Addiction, said: "The BE loads observed in wastewater indicate that cocaine use remains highest in western and southern European cities, in particular in cities in Belgium, the Netherlands, Spain and the United Kingdom.
"Very low levels were found in the majority of the eastern European cities studied, but the most recent data show signs of increases."
The paper suggested a range of factors could be influencing an increase in cocaine residues detected in several cities.
"While it may indicate that more people are consuming cocaine, it may mean that there is greater use of cocaine by the same people," the report said.
"Alternatively, it may simply reflect the increased purity of cocaine in Europe, leading to increased metabolite detection in wastewater.
"This increase could also be explained by a combination of these three causes."
The project analysed wastewater in 73 cities in 20 European countries, covering a total population of around 46 million, in March last year.
As well as cocaine, wastewater was examined for traces of amphetamine, MDMA and methamphetamine.
The 2018 findings pointed to increases in MDMA, or ecstasy, traces and amphetamine residues in several locations.
Methamphetamine, which has historically been concentrated in the Czech Republic and Slovakia, now also appears to be present in Cyprus, the east of Germany, Spain and northern Europe, according to the report.
The analysis also indicated that use of MDMA and cocaine rose sharply at weekends in most cities.