This image was taken looking out across Plymouth Sound (UK) during Storm Eunice in February 2022. The area was the focus of new research which analysed existing records on two years of combined sewer overflows into Plymouth Sound, alongside same-day and long-term meteorological and satellite data. Credit: University of Plymouth.

Researchers have used sewage and weather data and satellite monitoring to highlight a potential hidden source of microplastic pollution.

A combination of sewage overflows and coastal winds could be sending billions of airborne microplastic particles into the world’s coastal towns and cities, a new study suggests.

Scientists analysed existing records on two years of combined sewer overflows into Plymouth Sound, UK, alongside same-day and long-term meteorological and satellite data to assess how often conditions for aerosolisation (the transfer of particles from water to air) occurred.

They found that on 178 days within the two-year period, sewage spills from land to sea coincided with winds of at least 6.5 metres per second (23.4km/h) pushing back to shore and towards the city of Plymouth.

Detrimental effects

This, they say, could have resulted in microplastics and nanoplastics known to be discharged through sewage spills being lifted from the sea – specifically, according to the meteorological data, this could have happened during almost 1,600 hours (10%) of the period studied.

Once there, the airborne particles could have been breathed in by local residents, with an increasing and emerging body of research suggesting microplastics can have a range of detrimental effects on human health.

By examining satellite data, the scientists also found river plumes coincident with sewage spills detectable up to around 10km offshore, with a significant degradation in coastal water clarity during late autumn and early winter over the past decade. These months coincided with peak spill months.

The study was conducted by experts in marine science, human health and big data from the University of Plymouth and Plymouth Marine Laboratory.

It draws together existing research which has highlighted the presence of microplastics in sewage overspills, and the role of the wind in picking up and transporting sea spray and sea foam into the air and onto land.

Potential health risks

The researchers say that with thousands of cities in the UK and worldwide still using combined sewer systems, comprising sewerage from treatment works and storm runoff, their findings suggest coastal spills – when combined with onshore aerosolising winds – may serve as a plausible and previously overlooked source of airborne microplastics.

Dr Lauren Biermann, lecturer in marine science at the University of Plymouth and the study’s lead author, said: “Increasingly, I have been reading separate studies about incredibly high concentrations of microplastics and nanoplastics in sewage spills, how winds are stripping microplastics and nanoplastics from the ocean surface into the air, and the negative impacts of ingested or inhaled microplastics and nanoplastics on human health.

“Our study is the first to make the connection between water pollution and air quality, and raises the question about potential health risks.”

Based on their theoretical findings, the research team has called for further investigation into any links between sewage spills, air quality and any potential risks to human health.

They have also recommended future scientific studies integrate air quality monitoring with assessments of coastal water quality so as to better understand potential exposure pathways.

Dr David Moffat, artificial intelligence and data scientist lead at Plymouth Marine Laboratory and co-author on the study, said: “There has always been a gap between the amount of microplastics we believed were being deposited in the oceans, and the concentrations that were observed by ship-based measurements.

“We think we have finally worked out why, and the impacts on human health are concerning.”

Professor Clive Sabel, professor of big data and spatial science at the University of Plymouth and co-author on the study, added: “The health implications of this work are important. Inhaled microplastics can cross into our blood streams and from there can accumulate in organs such as our brains and livers.

“We need legislation to force our UK water supply companies to remove microplastics from our wastewater systems.”

The study is published in Scientific Reports.