Tire Size And Pollution: Is Bigger Always Better?

Car tyres are a significant source of air, soil, and water pollution. Tyres are made from natural and synthetic rubber, steel, fillers, and heavy metals such as zinc, copper, cadmium, lead, and chlorine. As tyres wear down, they release toxic particles into the environment, including microplastics and heavy metals. These particles contribute to air pollution and can pollute water sources and soil. The increasing weight of cars, including heavier electric vehicles, is causing tyres to wear out faster, leading to more particle pollution. While there is a push to develop more sustainable tyre options, the lack of regulation on tyre wear rates and the chemicals they contain may allow this issue to continue unchecked.

Tire wear and tear

The impact of tire wear and tear on the environment is twofold. Firstly, the release of microplastics and heavy metals from tires has been linked to environmental damage. Tires are among the most common plastic polluters, with an estimated 10-28% of microplastic waste in the world's oceans originating from tires. The degradation of tires into microplastics and the release of heavy metals can have toxic effects on wildlife. For example, a chemical called 6PPD, added to tires to prevent cracking and degradation, has been linked to declines in salmon populations in California.

Secondly, tire wear and tear emit fine particles into the air, which have been linked to heart and lung disease. As tires wear down, they release particulate matter, which can be inhaled and cause respiratory issues. This is a growing concern as the number of cars on the road increases, and heavier electric vehicles put more strain on tires. Unlike car tailpipe emissions, brake and tire emissions are not regulated, suggesting that this source of pollution may continue to grow.

To address the issue of tire wear and tear, several solutions are being explored. One approach is to redesign tires to reduce or eliminate emissions. The Tire Industry Project, formed by major tire manufacturers, aims to develop a holistic approach to mitigate tire pollution. Additionally, researchers are investigating ways to reduce the impact of tire wear particles on the environment, such as making road surfaces less abrasive or more porous to reduce or capture tire wear particles. Proper tire maintenance, including regular tire rotation, inspections, and maintaining correct tire pressure, can also help prolong tire life and reduce wear and tear.

Tire disposal

One common method of tire disposal is recycling. Some counties, like Los Angeles County, offer free tire recycling events where residents can drop off their waste tires to be recycled into rubberized asphalt or slurry for street rehabilitation projects. Commercial recyclers also accept waste tires from tire shops and the public, contributing to a more sustainable approach to tire disposal.

Burning tires in facilities specifically designed for this purpose can be another way to dispose of them while recapturing energy. However, tires contain high levels of potential pollutants, such as zinc and chlorine, so burning them without proper safeguards can lead to toxic emissions. Tire waste can also be incinerated or subjected to pyrolysis, an energy-intensive process that breaks down the tires.

When tires are not recycled or burned, they often end up in landfills. According to a 2018 USTMA report, about 16% of tires are disposed of in landfills, with the number of landfill-disposed tires nearly doubling between 2013 and 2017. This trend is concerning, as tires can take a long time to break down, and their breakdown products can persist in the environment, potentially leaching toxic chemicals into the soil and water.

To address the environmental impact of tire disposal, some tire manufacturers have formed the Tire Industry Project, aiming to redesign tires to reduce or eliminate emissions. Researchers are also exploring ways to reduce the abrasiveness of road surfaces to minimize tire wear and the release of microplastics into the environment.

Toxic tire compounds

Tires are a significant source of air, soil, and water pollution, affecting humans, wildlife, and other organisms. About 3 billion new tires are produced each year, with the market expected to reach 3.4 billion annually by 2030. The problem is not just with rubber, which can be natural or synthetic, but also with the many other ingredients in tires, such as steel, fillers, and heavy metals like copper, cadmium, lead, and zinc. These metals are added to enhance performance, improve durability, and reduce the possibility of fires.

Tire wear and tear produce microplastics, which are a major component of urban runoff, and a source of toxic substances. Tires are among the most common plastic polluters on Earth, with a 2017 study estimating that tires account for as much as 10% of overall microplastic waste in the oceans. Another study by the International Union for Conservation of Nature put that number at 28%.

The breakdown of tires can also form substances that are more toxic than their parent chemicals, such as 6PPD-quinone (6PPD-q), which is formed when 6PPD, a chemical added to tires to prevent cracking and degradation, is exposed to ground-level ozone. 6PPD-q has been linked to the decline of salmon populations in California.

A critical area of research is how long tire waste and its breakdown products persist in the environment. For example, a piece of rubber that settles on the soil can release chemicals over time, which can make their way into water sources.

Another area of concern is the impact of aromatic hydrocarbons, including benzene and naphthalene, which are off-gassed by synthetic rubber or emitted when tires are burned in incinerators. These compounds are toxic to humans, even at low concentrations, and react with sunlight to form ground-level smog, causing respiratory harm.

Tire pollution regulation

Tire pollution is a significant source of air, soil, and water pollution, affecting humans, wildlife, and other organisms. While the rubber rings on car tires may seem harmless, they contain a toxic mix of chemicals, microplastics, and heavy metals. As tires undergo wear and tear, they emit fine particles into the air and leave behind small bits of degraded plastic and rubber that pervade the environment, including oceans.

The lack of direct regulation on tire pollution has allowed this issue to persist and worsen with increasing vehicle usage. However, there is growing recognition of the need for environmental regulation of tires. Regulations should focus on addressing the compounds that partition from tires and disperse in the environment, their mixture effects, and the resulting transformative products.

Several regulatory efforts are being made to address tire pollution. The California Environmental Protection Agency has passed a rule requiring tire manufacturers to declare an alternative to 6PPD, a toxic chemical added to tires, by 2024. This rule has put the chemical composition of tires under regulatory scrutiny, with tire manufacturers now facing similar regulatory scrutiny to car manufacturers. Additionally, 10 of the world's largest tire manufacturers have formed the Tire Industry Project to develop a holistic approach to mitigating tire pollution and redesigning tires to reduce or eliminate emissions.

At the federal level in the United States, the Environmental Protection Agency (EPA) has implemented National Emission Standards for Hazardous Air Pollutants (NESHAP) for rubber tire manufacturing facilities. These standards aim to regulate emissions from the production of tires, but it is unclear if they directly address the environmental impact of tire wear particles during their use on roads.

To effectively regulate tire pollution, future legislation should prioritize transparency in the use of chemicals in tires, mixtures, minimization of emissions, and the capture of particulate pollution. Additionally, there should be a collective approach that transcends legislative areas, as the life cycle of a tire crosses different environmental compartments.

Tire alternatives

While tires are a significant source of air, soil, and water pollution, there are ongoing efforts to develop more sustainable tire alternatives.

One alternative that has gained traction is guayule, a natural rubber sourced from a heat-tolerant desert shrub native to southern parts of Arizona, New Mexico, West Texas, and bordering Mexican states. Bridgestone, a tire company, has been researching and studying guayule production on a commercial scale and plans to sell tires with guayule rubber by 2030. Guayule-based tires have already been tested in IndyCar racing, and the company believes that this alternative rubber has the potential to reduce energy consumption and deliver environmental benefits.

Another interesting plant material that is being explored as a tire alternative is the Russian dandelion, referred to as the TK species. Researchers at the University of Minnesota are also working on a technology to produce automotive tires from trees and grasses using a chemical process to make isoprene, a monomer of natural rubber. Sumitomo Rubber Industries is collaborating with universities in Japan to improve natural rubber yields and develop new strains of natural rubber derived from enzymes in tomatoes.

In addition to plant-based alternatives, silica products made from residual rice husk ash, a byproduct of rice processing, have emerged as an alternative raw material for tires. Goodyear has introduced consumer tires that contain soybean oil and has developed a demonstration tire composed of 90% sustainable materials. Recovered carbon black is another area of exploration, offering the potential to reduce the tire industry's reliance on petrochemicals.

While the development of these alternatives is encouraging, it is important to address the knowledge gap regarding the toxic chemicals, microplastics, and heavy metals present in tires and their environmental impact. Additionally, improving road surfaces to reduce tire wear and implementing better technology to capture tire particle runoff can help mitigate tire pollution.

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