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, 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 6.5metres per second (23.4km/h) pushing back to shore and towards the city of Plymouth.
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, published in the journal Scientific Reports, 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.
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.
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