Combating water pollution is at the forefront of our work here at Final Straw Foundation. With only a tiny 16% of the UK’s surface waters currently being classed as being in good ecological status, it’s important to consider all aspects of why our waters are in such dire conditions. Often, air pollution from exhausts is the only thing considered when talking about pollution from vehicles. However, road runoff has significant ecological and health impacts and is often overlooked and under-researched. Evidence suggests that particulate emissions from tyres may be up to 2000 times more significant than that from exhausts. Join us in exploring what makes up road runoff pollution, and its effects.
There are multiple ways in which runoff is composed. One of which is the wear and tear of tyres and brake pads, as well as the weathering of the road surface, all which create particulate matter. Fuel combustion byproducts, released from the exhaust and leakage of automotive fluids such as engine oil and brake fluid, are also contributors to road runoff pollution. Road runoff will vary considerably depending on rainfall, population density and traffic. Areas such as tunnels and sedimentation ponds are susceptible to high levels of pollutants due to their topography.
Micro and nano plastics (MNPs) are a growing concern when it comes to highway runoff, with plastic particles originating from tyre wear, brake pads, erosion of paint from road markings, and roadside litter. Microplastics are characterised as being plastic particles smaller than 5mm, and nanoplastics are particles smaller than 1𑇕m. Plastic particles from tyre wear contribute anywhere from 5-10% of all plastic emissions into the Earth’s oceans.
Studies into the effects of MNP exposure on human health are still in their early stages, but some concerning findings are coming to light. For example, recent studies have found that nanoplastic particles are capable of passing through the placenta from mother to foetus. There has also been association made between maternal exposure to MNPs and subsequent autism diagnosis in male offspring.
Bioaccumulation is also a concern when it comes to MNPs. Bioaccumulation of plastic particles occurs when the ingestion of particles by an organism is greater than the excretion of said particles. The effects of bioaccumulation are magnified as you move up the food chain, with organisms ingesting plastic particles from their food, as well as from their surrounding environment.
MNPs are an ecological concern as well as a health one, with tyre wear particles having a negative effect on the growth of marine phytoplankton. Phytoplankton are a group of incredibly important species, especially in the regulation of our climate, as they are vital to carbon capture in the ocean via photosynthesis. They are also at the very bottom of the food chain in the marine environment, meaning lots of species depend on their survival. The colour of the tyre wear particles coming from our roads and making their way into the oceans is also a concern. It has been found that, in seven species of sea turtle, blue and black were the colour of the most frequently ingested microplastics.
Tyre wear particle pollution in the marine environment is exacerbated by overflows of stormwater and untreated sewage into our waterways and oceans, a method used by water companies as a way to prevent flooding after heavy rainfall. A study by Final Straw Foundation and the University of Brighton has found an up to 110% increase in plastic tyre wear particles in Langstone and Chichester harbours in post storm water samples compared to the same site pre storm overflow.
Heavy metals are also a concern when it comes to road runoff. They originate from tyres, brake pads and engines as well as settling on the road surface from exhaust fumes and leaching from asphalt and concrete from the road surfaces themselves. Exposure to heavy metals in humans have been linked to increased risk of cancer, cardiovascular disease and infertility. Heavy metals are known to accumulate in the environment. This is particularly prevalent in estuarine, aquatic and marine environments where they persist in sediments, and are equally as toxic to other organisms as they are to humans.
Another type of pollutant that is present in road runoff are permanent organic pollutants (POP). Organic pollutants can be categorised as pollutants that contain naturally occurring substances, but are synthetic. One prominent type of POP are poly aromatic hydrocarbons (PAHs). These compounds mainly come from incomplete fuel combustion and into the environment from exhausts, but can also be traced back to asphalt and engine oil. These compounds are hydrophobic so bind with sediment and end up buried in marine and aquatic ecosystems. However, dredging and other disturbances to the seabed such as storms remobilise PAHs. Therefore, the impact of PAH pollution is felt years down the line. The presence of PAHs in sediments poses a risk to filter and deposit feeders, and the organisms above them in the food chain (including humans). PAHs are extremely toxic to life, causing cancers and disruption of endocrine systems. The Environment Agency’s most recent data from 2010 shows 656 Kg of PAHs being emitted into the UKs aquatic environment. With an increase of 37% cars on the road since 2010, the rate of PAH pollution now may be higher.
So what can we do about it? Highway runoff is exacerbated by more cars on the road, so taking public transport and lift sharing can be a great way to reduce your impact. Highway runoff is an under researched and fairly unknown issue, and therefore regulation and legislation around the matter is in its early days. The Tyre Collective is an amazing start up company that has developed technology to capture tyre wear particles. The particles then have the ability to be upcycled into new products such as shoe soles and soundproofing materials. Although in their infancy, we will be keeping a close eye on The Tyre Collective’s progress, and sharing information on how road users can get involved, so watch this space!
Sources:
https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1374835/full
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