Chemicals released from car tyres as they wear down are washing into rivers, estuaries and the sea and they could be disrupting life at the base of the marine food web, according to a new study .
Researchers from the University of Portsmouth found that just four days of exposure to three common tyre-derived chemicals significantly slowed the growth of tiny marine algae known as diatoms - single-celled plants that produce oxygen and support entire ocean ecosystems.
The study focused on a species called Phaeodactylum tricornutum, a diatom that like others, is responsible for converting sunlight and carbon dioxide into energy that is used by animals - a process that helps sustain fish, crustaceans and other marine life.
The findings raise concerns about how urban road runoff could be impacting the oceans, especially in densely populated areas where concentrations of tyre chemicals are already high.
The research team examined three chemicals that are widely used in tyre manufacturing or formed as byproducts as tyres degrade: mercaptobenzothiazole (MBT), diphenylguanidine (DPG), and 6PPD-quinone. All three are known to enter the environment via stormwater and urban runoff, but until now, their specific effects on marine plant life have been poorly understood.
The results showed all three chemicals suppressed diatom growth, with DPG and MBT proving especially harmful even at very low concentrations, levels already recorded in waterways in countries including Canada, China and Australia. 6PPD-quinone, which has previously been implicated in mass die-offs of coho salmon, was less acutely toxic to diatoms but still raised concerns. It required higher concentrations to cause damage, but because it's widespread and persistent, the researchers warned it could accumulate in marine environments over time.
Our findings highlight the urgent need to better understand how these widespread pollutants affect marine life. This almost omnipresent and long-overlooked form of pollution impacts not only coastal ecosystems, but aquatic environments more broadly, and must be brought to the forefront of environmental regulation.
Dr Fran Cabada-Blanco, Institute of Marine Sciences, University of Portsmouth
Though tiny and often overlooked, diatoms play an outsized role in global ecology. They produce a significant portion of the world's oxygen - comparable to that of land forests - and form the foundation of the marine food chain. Any reduction in their numbers could have knock-on effects for other species, including commercially important fish.
Dr Fran Cabada-Blanco from the University's Institute of Marine Sciences explained: "Diatoms play a disproportionately important role in coastal food webs and the global carbon cycle. Our findings highlight the urgent need to better understand how these widespread pollutants affect marine life. This almost omnipresent and long-overlooked form of pollution impacts not only coastal ecosystems, but aquatic environments more broadly, and must be brought to the forefront of environmental regulation."
The researchers say that while vehicle exhaust emissions are regulated, the tiny particles and chemicals released as tyres wear down often escape attention, despite being one of the largest sources of micro-pollution in urban environments. Rainfall can quickly transport these pollutants from roads to rivers and coastal waters, exposing marine life to complex chemical cocktails.
Something as ordinary as driving a car can contribute to pollution that reaches far beyond the road, all the way to the sea floor, and to the microscopic organisms that help keep our planet breathing.
Henry Obanya, Institute of Marine Sciences and member of the Revolution Plastics Institute at the University of Portsmouth
"This is a real warning sign," said Henry Obanya, also from the Institute of Marine Sciences and member of the Revolution Plastics Institute at the University of Portsmouth. "We need to start treating tyre pollution with the same urgency we apply to other plastic or oil pollution. These substances don't just vanish - they travel through drainage systems and end up in habitats that are already under pressure."
There are also concerns that the problem could grow with the global shift to electric vehicles. While these vehicles cut tailpipe emissions, they tend to be heavier, potentially accelerating tyre wear and increasing the release of these compounds unless tyre formulations change.
The authors of the study are calling for tighter regulation of tyre ingredients , improved monitoring of road runoff, and investment in the development of safer, less harmful alternatives. They also urge further research to examine the long-term and combined effects of tyre-related chemicals on marine life, particularly under real-world conditions where multiple stressors often interact.
Henry Obanya concluded: "Something as ordinary as driving a car can contribute to pollution that reaches far beyond the road, all the way to the sea floor, and to the microscopic organisms that help keep our planet breathing."
