Tires have a huge environmental impact, from production, to use to discarding them. Tires are made from natural rubber and synthetic rubber, produced from the polymers found in crude oil. The other primary ingredient in tire rubber is carbon black. Carbon black is a fine, soft powder created when crude oil or natural gas is burned with a limited amount of oxygen. Then there are chemicals used in the manufacturing of tires, like sulfur. Specific chemicals, when mixed with rubber and then heated, produce specific tire characteristics such as high friction (but low mileage) for a racing tire or high mileage (but lower friction) for a passenger car tire. Some chemicals keep the rubber flexible while it is being shaped into a tire while other chemicals protect the rubber from the ultraviolet radiation in sunshine. The biggest environmental impacts from production are dust emissions, noise, waste, energy consumption and solvent emissions (VOC emissions).
During use, tires shed tiny pieces of plastic. It is estimated that in Europe alone 500,000 tons of material a year comes from the abrasion of tires and that this wearing down (together with tiny pieces of asphalt abraded from roads) accounts for about 10% of the micro plastics found in the oceans. Reason why it was one of the issues addressed in the European Commission’s Plastics Strategy earlier this year. “Although much of the current research points towards tire particles entering the environment in worryingly large quantities, less is known about exactly where these end up and the damage they may do once there,” said Simon Hann, a researcher for the environmental consultancy Eunomia, who wrote a report on the topic for the Commission. The tire industry didn't agree with that and conducted their own research. By analyzing two river beds in France, it found that less than 5% of tire particles end up in the sea, while the rest are left somewhere along the way (still not a good place for plastics to sit around, if you ask me). One solution would be to treat run-off from roads, something that already is already done by diverting water into roadside ponds.
Even if more research is needed to understand where microplastics come from and how they affect the environment and human health, the EU executive is already looking into how to cut down on microplastics that may be coming from tires. It is also considering regulations for an EU-wide standard for the abrasion rate of tires by putting in place a common testing method and requiring producers to inform consumers about the abrasion rate of tires. In cities, better waste water systems could retain micro plastics and prevent them from ending up in the oceans. But the sludge (the stuff containing the microplastics) that is separated from the water is also used as fertilizer, so then microplastics end up in the environment anyway.
Another solution to reducing abrasion would be to make tires less prone to abrasion but this could have safety issues. If tires would be made of different materials that wear down less, it could be that these would be losing their grip on wet or snowy roads. Another problem according to the tire industry is that only 9 percent of the abrasion rate comes from the design of the tire, with the rest caused by driving behavior and road surface. However, changing the roads´ surfaces is also difficult since roads need to have a certain level of friction to make sure they are safe enough to drive on.
Another source of pollution coming from tires is when they are being discarded. The biggest problem are the chemicals and heavy metals that leach into the environment as the tires break down. Some of these chemicals are carcinogenic and mutagenic (cause cancer and gene mutations). Leaching affects the soil around the old tire and can end up in the groundwater, from which they can be further transported to other locations.
But there is good news. The big tire companies, Bridgestone Group (Bridgestone and Firestone), Michelin, Goodyear, and Continental, have programs that aim to make tires 100% of sustainable materials. For example, Bridgestone has successfully created synthetic rubber made from plant-derived materials as opposed to petroleum products that are used now. Continental, Michelin, and Goodyear are also looking for substitutes for natural rubber, so the environmental impact and logistical expenses of importing natural rubber from subtropical countries can be reduced. Goodyear has experimented with soybean oil as a potential natural ingredient in tires, increasing tread life by 10% and reducing the use of petroleum-based oil by up to 8.5 million gallons per year. Goodyear is also trying to retrieve more raw materials from used tires, a process made difficult due to the vulcanization process that is used to produce tires. If they are successful, the recycling rate of used tires can be significantly increased.
Furthermore, University of Minnesota researchers have patented a new technology in which the chemical process used to make isoprene, the key molecule in car tires, comes from renewable products like trees, grasses or corn. Renewable isoprene is a difficult molecule to generate from microbes, and efforts to make it by an entirely biological process had not been successful. Now this team found a way in which isoprene can be renewably sourced from biomass, a process could have a major impact on the multi-billion dollar automobile tires industry.
Wear and Tear of Tyres: A Stealthy Source of Microplastics in the Environment