Microplastics – tiny pieces of broken-down plastic, have spread to virtually every ecosystem on the planet from the tops of our tallest mountains to the depths of our deepest oceans. While banning microbeads in cosmetics and introducing restrictions around plastic bag use may help us to feel like we are making a difference, one of the largest sources of microplastic pollution consistently ignored by the public debate is caused by driving your car.
When measured by volume of emission, tyre, brake and road wear from vehicles is the second largest contributor to microplastic pollution worldwide.
The tyres on your car are made from a complex blend of different materials and chemicals including several types of plastic in addition to their rubber base. As vehicles are driven, the friction, pressure and heat caused from the tyres rubbing against the road and the brakes rubbing against the wheels results in tiny pieces of plastic material known as microplastics to be shed on to the road surface and accumulate as a dust.
The plastic in this dust can easily be picked up and blown around through the air. A recent study in Germany analysed more than 500 small particles pulled from the air around three busy highways and found that 89 per cent of them came from vehicle tyres, vehicle brakes and the roads. These tiny particles are categorised by size and a UK study showed that brake, tyre and road surface wear made up 60 per cent of air pollution emissions for particles 2.5 micrometres in diameter, and 73 per cent of the particles that were 10 micrometres in diameter. Air pollution measurements involve counting these very fine-sized particles which can post a threat as they can be drawn deep into the lungs or trapped in the nose, mouth or throat.
If not blown into the air, rain washes the tyre-created road dust into drains and eventually oceans where it can be eaten by filter feeders such as mussels as well as fish, eventually entering the human food chain.
The consequences of breathing in and eating these microplastics are still unclear with some research proposing that once inside our bodies microplastics could release toxic substances causing oxidative stress or increase cancer risk. What is known is that each year the average person consumes more than 74,000 particles of plastic – the equivalent of one credit card's worth per week.
While moves are being made to help to switch New Zealand to electric or hybrid vehicles to help to reduce air pollution, no legislation is currently in place to reduce these tyre-emitted microplastics referred to as non-exhaust emissions.
The simplest and most efficient way to reduce tyre microplastic pollution with our current vehicle fleet is to reduce the overall volume of traffic on our roads through increasing public transport use and to lower the speed where traffic is free-flowing, such as on motorways. Adapting driver behaviour by reducing the amount of braking needed through increasing following distances and reducing high-speed cornering are also other simple strategies that can help in the short term.
Long term industry practices may also need to change, with the possible resurgence of natural rubber tree sourced latex as a tyre material, however, this could lead to other environmental challenges as rubber plantations require large volumes of water and expansion can lead to deforestation.
As we make our way through plastic-free July with increased awareness around the visible plastic packaging in our consumer products, let's not forget the sources of the plastics that are smaller than the eye can see but big when it comes to volume of microplastic pollution.