Tyres shed microplastics; those particles build up on our roads in large volumes; they get carried into rivers when it rains heavily: simple facts that should hardly be a surprise to anyone who has ever replaced a worn-out tyre.

So why are tyre microplastics barely recognised as a source of persistent and pervasive pollution in the water environment? How can something so blindingly obvious have become such a blind spot for pollution control?

Is our love affair with the automobile so strong that we blank it out? Probably. Has this microscopic pollution become invisible to the public conscience?  Certainly. Is this a case of one public body ill-equipped to regulate another? Highly likely…

Mounting Evidence

We may ponder these conundrums, but, meanwhile, evidence that the pollution exists and is grave, is mounting. For sure, greater public and Government awareness is vital to drive research to build up the evidence: We urgently need peer-reviewed evidence of how tyre microplastics cause pollution, their pathways through the environment and their effects on ecosystems, aquatic and plant life – even on human beings.

But, when it comes to actually cleaning up, tyre microplastics have become a big fat elephant in the room.  There may be more questions than answers at the moment, but two things are already certain: Firstly, that the pollution is happening now, and secondly, that we know how to prevent it.

Proven Technologies

There is plenty of knowledge and many technologies are available to protect our sensitive water environments.  SDS’s Aqua-SwirlTM vortex separator and Aqua-XchangeTM engineered filter media are among a well-proven and extensive toolbox of sustainable drainage solutions that can be designed, and combined, to suit the circumstances.  We can stop this pollution before it happens.

The University of Plymouth’s report, published in May and commissioned by the Department for Environment, Food and Rural Affairs (DEFRA), is the first to provide empirical evidence that plastic particles from tyres in road runoff could be contaminating up to 100 million square metres of the UK’s river network and 50 million square metres of estuarine and coastal waters.

It has followed on from other modelling studies, most notably the Eunomia report: Reducing Household Contributions to Marine Plastic Pollution, commissioned by Friends of the Earth (FoE) and published in November 2018. Applying UK traffic statistics to tyre wear data, the study calculates 68,000 tonnes of microplastics are released from tyre abrasion in the UK every year with 7,000 – 19,000 tonnes entering surface waters annually.  Those estimates could well prove to be conservative, but do we really need to wait for a more accurate measurement?

Ample Evidence

There is ample evidence that aquatic species and birds ingest microplastics and it’s not just the plastics that are damaging.  The polluting particles emitted by tyres, brakes and exhaust fumes include copper, zinc and Polycyclic Aromatic Hydrocarbons (PAHs), particularly benzo[a]pyrene which is classed as a ‘Substance of Very High Concern’ under the European REACH regulations.

When it rains these mutagenic, carcinogenic, bio-accumulative chemicals are discharged via highway drainage outfalls. They bind to sediment that also silts and chokes the rivers, and some metals dissolve in the surface water.

We also know where some of the worst pollution is likely to be. There are more than one million discharges of highway runoff across the UK. Highways England, through its Highways Agency Water Risk Assessment Tool (HAWRAT) tool, has identified 2,500 high-risk pollution locations as part of its ongoing Priority Outfall Programme.  While some have been fixed, many more are not currently being actioned.

The University of Plymouth team suggests that measures are needed to capture tyre particles at the roadside, and this fits well with the concept of Sustainable Drainage Systems (SuDS) to control pollution at source.  These highway outfalls are neither too difficult, costly, nor complex to tackle. We can intercept tyre microplastics before they pollute our water environments.

Sustainable Drainage Devices

Indeed, the Highways England Design Manual for Roads & Bridges and the CIRIA SuDS Manual C753 both detail manufactured devices and sustainable drainage components that can reduce this pollution.

Filter drains retain suspended solids in the spaces between the stones. Innovative new engineered media can be added to filter drains to capture dissolved heavy metals. Sedimentation devices such as vortex separators, oil water separators, SuDS ponds and basins will capture and retain tyre particles. Unlike the simple sumps widely installed in roads across the country, they will prevent the sediment from being washed out when it rains.  The solution depends on the site; especially at high risk locations, a management train of treatment devices is advisable to keep persistent bio-accumulative chemicals out of the environment.

New smart sensing and remote monitoring technologies are also being developed that can measure the deposited sediment in gully pots and vortex separators so that maintenance is targeted and costs minimised.

Further research will build our knowledge of tyre microplastics’ pollutions. SuDS device manufacturers, including SDS, will gladly work with Defra to further develop the available and new technologies.  But, in the meantime, our aquatic wildlife cannot afford to wait.  It must be protected now, or some species might have disappeared by the time anyone gets around to fixing the pollution.

Tyre microplastics are just one element of a toxic cocktail of silts, sediments, hydrocarbons and metals routinely entering our water environment.  Isn’t it time to stop ignoring the obvious and commit to protecting the quality of our waters?

As part of a green recovery in the months and years ahead, let’s commit to developing an effective sustainable drainage infrastructure for our motorways and heavy-traffic highways and protect our aquatic and roadside environments before it is too late.

Jo Bradley, SDS Limited

Written by Jo Bradley
Stormwater Shepherds, UK Director of Operations