What type of pollution do car tires cause?
–BL, San Francisco, California
Tire wear pollution recently emerged after a group of Native American tribes in the Pacific Northwest asked the U.S. Environmental Protection Agency (EPA) to investigate a possible link between tire pollution and declines in wild coho salmon populations. It became news. The tribes blame 6PPD, a chemical that has been used for more than 60 years to make car tires more durable.
It is also widely used in other rubber products such as footwear, artificial turf, playgrounds, etc. 6PPD can make rubber stronger, but when it reacts with ozone pollution in the air it can produce a byproduct called 6PPD-quinone. Stormwater runoff containing 6PPD-quinone inevitably flows into streams and other water bodies during rains, exposing aquatic organisms to it. Concentrations of 6PPD-quinone in rainwater in the Pacific Northwest were found to be lethal to coho salmon after just a few hours of exposure.
6PPD is not the only bad thing that comes out of tires. Another is microplastics, which are also used to strengthen the rubber in tires, but are associated with a wide range of toxic effects that can travel up the food chain and onto our plates. Another big effect of tire wear is the release of pollutants into the air. When tires roll on the road, they create friction, which creates small particles and compounds that can become airborne. These pollutants can include fine particulate matter (PM2.5), volatile organic compounds (VOCs), and polycyclic aromatic hydrocarbons (PAHs).
Particulate matter from tire wear is a pollutant of particular concern because it can be inhaled by humans and animals, causing respiratory illnesses and other problems. Particulate matter also contributes to the formation of smog and haze, which can reduce air quality in urban areas. VOCs and PAHs released from tire wear can react with other pollutants in the atmosphere to produce ground-level ozone, a major component of smog. Ground-level ozone is harmful to human health and can cause respiratory problems, especially in vulnerable populations such as children and the elderly.
Tire wear pollutes water as well as salmon habitat. When it rains, water washes tire particles down storm drains and eventually into rivers, lakes, and the ocean. Runoff can contain not only microplastics, but also various chemicals used in tire manufacturing and chemicals produced during tire wear. These chemicals can contain heavy metals such as zinc and cadmium, which can have toxic effects on aquatic life and disrupt ecosystems. Additionally, leaching of chemicals from tires into water bodies can lead to long-term pollution of the aquatic environment.
Tire manufacturers are working to develop more durable and environmentally friendly tire materials that emit fewer pollutants. In other words, tires with low rolling resistance improve fuel efficiency and help reduce both tire wear and the pollution that comes with it. On the other hand, we can all help by maintaining our cars regularly and making sure our tire pressures are at recommended levels. Getting out of the car completely and walking, cycling or using public transport is also a great way to reduce car dependence and all the environmental harm it causes.