A new study has found significant levels of cocaine in Welsh wastewater and residue remaining after it has been treated.

University researchers tested water samples at two treatment works and found evidence of cocaine residue at both sites.

It was the first time wastewater testing had been used to examine psychoactive substance use in Wales.  

And they say the sewer samples were highest after Wales had played an international rugby match at the Principality Stadium.

The main substance detected was benzoylecgonine, a compound produced when the body breaks down cocaine.

The Bournemouth University study also found that current treatment methods are unable to remove all of the benzoylecgonine - the metabolite of cocaine - from water ways.

PHD student Bethan Davies, who led the study, said: "Our study highlights how improved monitoring and treatment could address local public health and environmental concerns."

The team monitored wastewater samples before and after treatment from Friday to Monday for two months.

The estimated the average consumption rate of cocaine was 3.88 milligrams per day per one thousand people near one plant and 1.97 milligrams per day per thousand people near the other.

The highest rate was 8.54 milligrams per day per thousand people which was found after a weekend where an autumn international rugby match took place in Cardiff.

They also found that an average of 73 percent of benzoylecgonine was removed during treatment - meaning traces remained in the system.

“Testing for NPS’s can be expensive, especially because they evolve very quickly. So, by knowing what is popular within certainly communities, we can tailor how we test for certain substances in different areas and do not spend time and resources testing for drugs that are not around," added Bethan.

A Welsh Water spokesperson said: “This study, which we supported, looked at levels in wastewater, and should not be confused with drinking water supplies.

“Wastewater is treated to remove a number of chemicals and toxins in line with our regulatory permit.

“Our drinking water is provided from a completely separate system and is highly regulated so the water we provide is of the highest quality.”