A study has found microplastics in greater quantities in rural environments than in urban sites.
Scientists at the UK Centre for Ecology & Hydrology (UKCEH) estimated that up to 500 airborne particles of plastic were deposited on a square metre of ground every day in Wytham Woods near Oxford – almost twice as many as in in the city centre.
The researchers believe trees and other vegetation capture airborne microplastic particles from the atmosphere, later depositing them to ground level, and found weather conditions strongly influence movement of particles.
During periods of high atmospheric pressure, which leads to calm, sunny weather, fewer particles were deposited from the air, but in windy conditions, especially from the northeast, particles were deposited in greater numbers. Rainfall reduced the number of particles, but those that were collected were larger.
Previous research has shown that microplastics can remain suspended in the air for weeks, with the smallest particles travelling many thousands of miles. Particles travel on swirling air currents, spreading out as the air moves.
Alexandra Howard, an environmental pollution scientist at UKCEH, who was involved in the new study, said: “These unexpected results challenge the commonly held belief that microplastic pollution is mainly an urban problem.
“Our research highlights that environmental factors influence where particles are deposited, and in what quantities, which will inform future monitoring and management of microplastics pollution.”
Invisible to human eye
The researchers set up sampling units that capture particles falling through the air at three locations in Oxfordshire: Wytham Woods; Summertown, a suburb of Oxford; and the city centre. They took samples every two to three days from May to July 2023 and tested them at the microplastics analysis facility at UKCEH’s site in Wallingford.
The team used a high-resolution FTIR spectroscope, which measures how infrared light is absorbed by materials in a sample, allowing researchers to identify the composition of the materials. Up to 99% of the particles were the smallest size, which are invisible to the human eye.
In Wytham Woods, most of the particles found were polyethylene terephthalate, commonly known as PET, which is used in clothing and food containers.
In Summertown, polyethylene, which is used to make plastic bags, was most commonly found. In Oxford city centre, most particles were of ethylene vinyl alcohol, a polymer widely used in multilayer food packaging, automotive fuel system components and industrial films.
The study was led by Dr Gbotemi Adediran while he worked as an emerging contaminant scientist at UKCEH. He is now a lecturer at the University of Leeds.
Microplastics in the air: Weather and polymer influences on deposition trends across a rural–urban gradient is published in Environmental Pollution.