New research from Plymouth Marine Laboratory (PML) has revealed that particles shed from car tyres – a major but often overlooked source of microplastic pollution – are both eaten by, and stick to the bodies of, small marine animals.

Tyre particles form as a result of abrasion between vehicle tyres and roads. These particles are made from both natural and synthetic rubber and are a type of microplastic. But plastic is not the only problem with this pollutant: tyres contain a cocktail of chemicals, trace metals, volatile organics and antioxidants, designed to increase tyre longevity, reduce road resistance and protect from UV damage.

It is estimated that more than 6 million tonnes of tyre particles are released worldwide into the environment each year.

These tyre particles – smaller than 5mm – are released onto highways, verges and into the air, with rainfall and runoff washing them into rivers and estuaries, where they can settle into sediments or remain suspended in the water.

Studies have found high abundances of tyre particles in intertidal estuaries, making up 73% of detected microplastics.

While tyre particles were first recognised as pollutants in the 1970s, they have received surprisingly little attention until recently.

This new study, led by Plymouth Marine Laboratory (PML) and the University of Exeter, is among the first to look at how these pollutants physically interact with living organisms in estuarine environments.

Researchers exposed Corophium volutator, a small shrimp-like crustacean that plays a critical role in estuarine food webs, to environmentally relevant concentrations of tyre particles.

They found that:

• Adherence: Tyre particles readily stuck to the animals’ appendages, especially their antennae and feeding limbs, making them difficult to remove once attached.
• Ingestion: The animals ingested tyre particles through both of their feeding modes -suspension feeding (drawing in particles from the water) and surface deposit feeding (collecting food particles from sediment). On average, suspension feeders consumed nearly 20 times more tyre particles than surface deposit feeders.
• Egestion: Tyre particles were later found in the animal’s faeces, showing that they can pass through the digestive system and be redistributed in estuarine sediments.

Worryingly, researchers also found that the majority of ingested particles were very small (under 64μm or 0.064mm), around the width of a human hair, raising concerns that they could travel beyond the gut into other tissues, or cause blockages that impair feeding.

Lead author Charlotte Woodhouse, PhD researcher at Plymouth Marine Laboratory (PML) and the University of Exeter, said: 

“Our study shows that tyre particles are not only present in estuarine habitats but are readily ingested by and adhere to ecologically important species. Because Corophium is an important prey item for fish and birds, this raises wider concerns about how tyre particles may move through estuarine food webs.”

“While the long-term impacts of tyre particle ingestion and adherence are not yet fully understood, previous studies suggest risks to growth, reproduction and survival in marine life. This research provides important new evidence of how benthic (seafloor-dwelling) organisms are directly exposed to tyre pollution in estuarine and coastal ecosystems”. 

Full paper: Comparison of the Uptake of Tire Particles via Suspension and Surface Deposit Feeding in the Estuarine Amphipod Corophium volutator.