Untreated wastewater “routinely released into UK rivers” is creating microplastic hotspots on riverbeds.
That is the conclusion of a study in Greater Manchester, which revealed high concentrations of plastic immediately downstream of treatment works.
The team behind the research concluded: untreated wastewater was the key source of river microplastic.
The water company that operates along the river the scientists studied said it “didn’t fully accept” the findings.
But the scientists, who published their research in the peer-reviewed journal Nature Sustainability, say sewer overflow pipes and outflows from treatment plants can release millions of plastic particles in a day.
Lead researcher Prof Jamie Woodward from the University of Manchester told BBC News that, at the most contaminated site in the River Tame, where the team carried out their research, there were “concentrations over 130,000 microplastic particles per kilogram of sediment on the riverbed”.
“So for every single gram of sediment, there were 130 particles; we have some extraordinarily high levels of contamination.
“It’s clear that wastewater is the key source of microplastics in our rivers.”
While the water company, United Utilities, declined to be interviewed, Jo Harrison, the company’s director of environment said in a statement: “We understand that wastewater will be a contributing factor to microplastics pollution, which is why we are involved in a much wider two-year study beginning this summer to give a more holistic understanding of the sources, pathway and consequences of microplastics in the environment.”
A spokesperson for the Environment Agency, which regulates the activities of the water industry added: “We are working hard to reduce microplastic emissions from wastewater treatment works by aiding water industry research in this area.”
Water companies are permitted to release untreated wastewater when the pipes in their plants are overwhelmed by excess rainwater. But the researchers say that they measured build-ups of plastic during a dry summer period. “That was perhaps the most significant thing from this research,” said Prof Woodward.
“To produce such high levels of contamination, [they] must be releasing wastewater into low flows – so when there isn’t heavy rain.
“It’s almost become routine for many water companies to do this,” he added.
An Environment Agency report published earlier this year revealed that water companies discharged raw sewage into UK rivers 400,000 times in 2020. And a recent study using artificial intelligence to detect “unreported spill events” showed that hundreds more releases were going unrecorded.
Commenting on the recent study, Prof Andrew Johnson, from the UK’s Centre for Ecology and Hydrology (CEH) in Wallingford, said that wastewater from sewer overflows was “likely to be a source of microplastic flushes to rivers”. But, he added, “we should not ignore all sorts of run-off from roads and fields adjacent to rivers”.
Dr Rachel Hurley, at the Norwegian Institute for Water Research, said that the impact of microplastic pollution on river ecosystems was an issue being investigated around the world.
“A lot of wastewater goes untreated globally, she said. “And we know this wastewater concentrates many different types of microplastic in one place.”
“We need to find out what the real reasons for these wastewater discharges are.”