Tires, an everyday item that billions of people use across the world, are often under-recognized to be a massive contributor to global pollution. They can be compared to erasers, which are made of very similar components physically and mechanically. Like erasers, tires are made of rubber that wears under pressure against a rougher surface. Tires wear against asphalt in the same way erasers shave down when rubbed against paper. However, they are a much larger problem as there are billions of driven miles that wear them down. On top of that, the shavings are ground into microscopic “tire and road wear particles” (TRWP) that mix with road dust. They become mechanically bonded into particles that can either become airborne or directly enter water systems. Erasers, on the other hand, simply rub against paper and produce shavings that are less complex, as they are designed for a smaller use compared to tires. Although eraser shavings do produce micro-rubber and vinyl particles, the overall volume is incomparable to the amount of shavings tires produce. Approximately 3 billion new tires are produced and used each year.
Tires release approximately 6 million tons of wear particles into the environment annually. That is comparable to the weight of around 1 million elephants. About an average of 0.8 kg of TRWP is emitted per person every year.
The substances that specifically make up tires include rubber (made of natural rubber and synthetic variants), 6PPD, heavy metals (zinc,lead, cadmium, and copper), polycyclic aromatic hydrocarbons (PAHs), and other petroleum-based organic compounds, and fillers (carbon black and silica).
Simply using rubber would be problematic because of degradation, so tires also have 6PPD, a highly effective antioxidant and antiozonant. 6PPD is specifically designed to prevent rubber degradation and protect tires. They interact with ozone and oxygen before it damages the rubber. The reason this does not make tires invincible is that once the 6PPD near the outer layer of rubber has completely reacted, the tire will crack. On top of that, 6PPD may protect against chemical degradation, but cannot prevent physical wear, similar to the eraser. 6PPD also has a byproduct called 6PPD-quinone(6PPD-Q) that has been proven to be highly toxic to aquatic life. Studies also indicate that both 6PPD and 6PPD-Q can cause oxidative stress, cellular and DNA damage, and a negative effect on organs in humans.
Heavy metals are added for a similar reason: to increase the lifespan of the tire. PAHs are a byproduct during the manufacturing process. Many other substances that make up fillers for increasing durability are released to the environment as tires wear out.
Another important issue to consider replacing gas vehicles with electric ones may not be the perfect solution. Electric vehicles are heavier due to heavier batteries. This means that tires will break down faster compared to gas vehicles. Overall, it is consistently proven that tire pollution must raise more concern as it is a huge contributing factor to the global pollution crisis.
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