Tyre wear particles in the North Atlantic air have been re-emitted by the ocean

Air sampled during a research cruise along the Norwegian coast was found to contain microplastics including tyre wear particles, polyethylene terephthalate (a member of the polyester family used in clothing and containers for liquids and foods), polystyrene, polypropylene, and polyurethane.

Atmospheric transport and dispersion models suggest they had been introduced into the marine atmosphere equally from sea and land-based emissions, meaning we might have to now consider the ocean to be a source of microplastic, rather than a sink for them. 

The study was undertaken by a team of German and Norwegian researchers led by Dr Barbara Scholz-Böttcher of the University of Oldenburg.

Marine air was actively sampled using a vacuum pump positioned 12m above the bow of the ship to avoid cross-contamination with particles emanating from the ship itself.

The above graph shows the composition of microplastics across the seven sampling periods. The grey block shows the quantity of CTT  (car tyre tread) and the black shows TTT (truck tyre tread). In T1 and T3, tyre particles represented 94% and 87% of the total microplastics concentration in the respective samples,.

The researchers measured concentrations of up to 37.5 nanograms (one nanogram = one-billionth of a gram) of microplastics per m³ of air. 

Isabel Goßmann, a doctoral candidate at the University of Oldenburg’s Institute for Chemistry and Biology of the Marine Environment (ICBM) and first author of the paper said: ‘These pollutants are ubiquitous. We find them even in remote polar regions,’

The researchers observed that large parts of the air masses that influenced T1 and T3 did not pass over any landmasses, raising the question of where the tyre wear particles have come from. Studies are emerging that suggest sea spray as a potential secondary source for microplastics in the marine atmosphere, with breaking waves causing bubbles of trapped air to rise and burst.

Microplastics find their way from land into seawater via rivers and the atmosphere – particles are washed out of the atmosphere by rain as well as ship traffic. An earlier study, also led by Scholz-Böttcher demonstrated that in the open North Sea, the paint and coatings used on ships is the main source of microplastics. 

Photo: Alvise Vianello