Particles from tunnel cleaning water look like this: Aquateam COWI has used FlowCAM analyses to show that the black particles are most likely from car tyres and asphalt, while the transparent ones are other plastic from road markings etc.

Car tyres are among the culprits when it comes to microplastics – but how dangerous are they really?


Microplastics from tyres account for around 28 per cent of the microplastic pollution in our seas. In a research project for the Norwegian Retailers' Environment Fund, Aquateam COWI is now investigating what impact the black microplastic actually has.

In recent years, a lot of the media coverage relating to microplastics has been concerned with whales and seabirds with their stomachs full of plastic. The alarms have sounded and the challenges are real, but this is not microplastic.

There has been much less talk of the microscopic black particles floating around in our seas: the results of long-term wear to car tyres, which are gradually worn down by contact with the road – and then flow out into the sea with rainwater and cleaning water.

In 2017, Dutch researchers estimated that tyres could account for around 10 per cent of all microplastics in our seas. Another report from the same year, from the International Union for Conservation of Nature, upped the figure to 28 per cent. There may also be local variations: the Norwegian Institute of Marine Research estimated in 2018 that almost 80 per cent of the particles in Oslo Fjord could come from tyres and road dust.

The black peril

In 2018, Aquateam COWI applied for research funding from the Norwegian Retailers' Environment Fund to investigate the microscopic black particles more closely. They got the funding, and have since discovered a number of new issues associated with the black microplastic, explains the lead researcher in Aquateam COWI, Eilen Arctander Vik.

Sample preparation: cleaning water from tunnels and surface water from the roadway is sedimented and filtered through several processes. A lot of particles have to be separated out to leave the microplastic particles.


“We chose one of the main culprits to take a closer look at how big the problem is and what the impact might be. There was no analytical method for measuring microplastics from car tyres, so it suddenly turned into quite a difficult exercise. And it is fundamentally challenging because of the nature of the material. Tyres are made of rubber, but are there also microplastics in them?”

They were originally made from rubber trees, and felling of forests to produce the rubber had a significant impact on the environment in the early years. Synthetic rubber was made on an industrial scale from the 1930s. Today’s tyres are a good mix of synthetic and natural rubber. They also have radial reinforcement made of rayon, polyamide, polyester, steel and sometimes glass.

Separating chemicals and particles

One of the things the researchers are working on is to differentiate between the effects of the microplastic itself and of the other substances contained in the plastic.

“In normal environmental risk assessments, we generally look at the chemicals that are emitted. In this study we are looking at particles. These particles contain many different chemicals, but it is not certain that these particular substances constitute the risk. For the moment, this is an area where we do not have a complete overview,” says Arctander Vik.

The riddle of microplastic

But microplastic is a demanding material to work with.

“It is small and there is not much of it. That is the reality out in the natural world. We have seen whales and seabirds that have ingested seaborne plastic, but they have taken decades to accumulate these materials. But microplastics are another story. In the northern hemisphere we do not discard as much plastic as in southern areas, so the concentrations are smaller here. That makes it hard to separate out the microplastic particles.”

A long way to go: pinning down the environmental impact of microplastic is no simple matter. First, the researchers have to agree on a standardised method of measuring microplastics, says the lead researcher in Aquateam COWI, Eilen Arctander Vik.


A graphic example comes from one of the tunnels they have examined thus far. This work was carried out in collaboration with Nye Veier (‘New Roads’), NIBIO and Aalborg University in connection with studies conducted by Nye Veier to check the effectiveness of the new cleaning system in the tunnel. The recipient is sensitive, and a detailed monitoring programme is under way.

“Among other things, we spent four hours filtering 3,000 litres of water flushed out of Bamble tunnel, and still we collected almost no microplastic particles. We are talking about very low concentrations of extremely small particles, so you need a lot of sample material or analytical methods that can detect very small particles, down to 1 micron,” says Arctander Vik.

Growing demand for microplastic research

Microplastics have been high on the agenda in the media and with the authorities in recent years. Arctander Vik is also seeing increased interest in Aquateam COWI’s expertise within the field. The researchers’ microplastics portfolio is growing.

The first projects involving analyses of microplastics were initiated with funding from the Norwegian Retailers' Environment Fund, and led to collaboration with Aalborg University (AAU) and Nye Veier. Nine months later, a research project kicked off to study microplastic from roads, in collaboration with the Norwegian Public Roads Administration. Last out of the blocks is a 3-year R&D project for which Aquateam COWI has received a grant from the Research Council of Norway, together with NTNU, AAU and Nye Veier. This will examine surface water from roads and tunnel cleaning water in several of Nye Veier’s new and existing facilities, and the plan is to develop new cleaning methods. COWI is also working on a project to analyse microplastics in house dust and microplastic levels in Norwegian rivers.

Looking for an answer to the riddle of microplastics

Both the R&D project for the Norwegian Public Roads Administration and the Research Council project will be working on risk assessment methods for microplastics, an area where there is now extensive research going on in the EU.

“There is a lot of interest in this type of research right now. As things stand, it is very expensive to get microplastic analyses that you can rely on. These are restricted to a few experts and laboratories that have the equipment to measure these small concentrations, and these can easily turn into bottlenecks in the research process.”

These samples from the tunnel cleaning water may look clean, but they contain many tiny microplastic particles.


She expects this to change soon.

“In a few years we are likely to have much simpler and more practical methods of analysing, and we will get new scales so we don’t have to ‘cry wolf’ every time microplastics are mentioned. That will allow us to be more specific in warning about the genuine environmental risks, so we can scale the problem properly,” says Arctander Vik.

Uncertain implications for health

We currently know little about the impact of microplastics and how much of a health risk they pose to people and to our ecosystems. Science Advice for Policy by European Academics (SAEA) points to experiments showing that high concentrations of microplastics can cause physical damage to the environment and to humans, but no place in ‘the real world’ currently has such high concentrations.

In any event, Eilen Arctander Vik thinks they have a good deal still to do on the method side before they can determine the possible health implications of microplastics.

“First you have to be able to measure the concentrations, then you have to find the thresholds for what is acceptable. Only when you have the first in place can you establish these thresholds. We have been working to a standard which uses what we are able to measure and is based on the available literature. We still have a way to go to arrive at an internationally agreed way of measuring microplastic concentrations,” she says.

In their work for the Norwegian Retailers' Environment Fund, the researchers examined microplastic levels in cleaning water from tunnels. The picture is from the first washing of the Bamble tunnel. 


When this is in place, the real work can start: identifying the health risks that microplastics could carry.

“The EU has come up with some suggested ways of assessing the health risk, but the uncertainty levels are very high. In Asia there are areas with high microplastic concentrations in the marine environment, and it is said that some parts of Asia are now at levels where they can demonstrate negative effects on health from microplastics. In North American and other waters, on the other hand, the levels are significantly below this.”

About the project

  • The Norwegian Retailers' Environment Fund is working to reduce plastic waste, increase recycling and cut the use of plastic bags.
  • The plastic bag levy is used to finance research to help realise this vision.
  • Among other things, Aquateam COWI has used the research funding from the Norwegian Retailers' Environment Fund to:
    - Publish a research article discussing various cleaning techniques for tunnel water,  with the emphasis on removing particles and heavy metals
    - Develop an internal microplastic analysis method based on instrumentation that takes pictures of the samples (fluid imaging).
    - Establish a collaborative research effort with NORCE and Aalborg University to develop analytical methods suitable for surface water from roads and tunnel cleaning water.
    - Apply for and win research funding from the Research Council of Norway (for a 3-year project) together with Nye Veier, focusing in cleaning tyre particles from surface water from roads and from tunnel cleaning water.
    - Enhance methods for collecting, preparing and analysing these types of sample.

Get in contact

Eilen Arctander Vik
Aquateam COWI, Norway

Tel: +47 950 42 783