Street cleaning action to eliminate microplastics – but also a source

The situation is complex, according to the VTI research report. Street cleaning collects coarser fractions of microplastics but has problems picking up the finer ones. At the same time, evidence suggests that the plastic brooms themselves contribute to the release of microplastics into the environment.

"Street sweeping – A source to, or measure against, microplastic emissions?" This is the title of the VTI report prepared by senior researcher Mats Gustafsson, research assistant Maria Polukarova, senior researcher Göran Blomqvist, researcher Ida Järlskog and Professor Yvonne Andersson-Sköld.

The study focuses on the success of street cleaning in reducing emissions of tyre wear particles in the form of microplastics. The researchers also examined street cleaning itself, as plastic brooms are often used for this.

Microplastics are now considered to be a global environmental problem. Road traffic is one of the biggest sources of emissions, with microplastics mainly coming from tyre wear. These microplastics then spread to soil, air and water.

“Many studies indicate that microplastics have adverse effects on aquatic organisms, for example, but the results are scattered and more studies on effects are needed. Plastics and tyre particles contain a large number of potentially toxic substances that should not be dispersed into the environment,” says Mats Gustafsson.

The study suggests that cleaning machines may be effective in picking up microplastics, but also that they can be a source. This research was conducted in close cooperation with the municipality of Karlstad, which also carried out the spring sweeping operations analysed by the researchers regarding the uptake and spread of microplastics. The cleaning was done using a machine with vacuum suction and a mechanical sweeper, what is known as an “elevator”.

VTI used a special sampler for taking samples of the dust on the road surface, the Wet Dust Sampler II (WDSII), developed at VTI. This method involves pressure washing a small, circular surface with distilled water, which is then transferred to a sample bottle using compressed air. The samples were then analysed to identify microplastic content.

Both type of cleaning machines reduced the volume of rubber-related polymers on the road surface, but the machines mainly picked up the coarser material, leaving the finer material on the road. Electron microscope analysis of the dust samples showed that mineral particles dominated, but that the second most common particles were tyre and bitumen particles.

According to the Karlstad experiments, the amount of a polypropylene, used in sweeper brooms on the road was greater after sweeping than before during the spring sweeping operation. This suggests that intensive and repeated cleaning with plastic brushes can result in net emissions of certain microplastics. If the wear of brushes in Karlstad is scaled up to apply to all Swedish municipalities, this would correspond to about 20 tonnes of plastic per year. Mats Gustafsson is not surprised.

“We know that the broom bristles wear, so finding plastics that can be linked to this wear is not unexpected; but it would be good if we could also show that most of it is collected by the machines themselves.”

The study also included a survey comprising a questionnaire completed by five municipalities. The survey showed that there is little awareness of the link between street cleaning and microplastics; which was expected, since this issue is relatively new. There are plans to continue this study.

“We would like to work with municipalities and machinery companies to help develop more effective cleaning methods and strategies. There are very few similar studies, so ours has been a pilot study in this field. Hence we have also learned a lot about how we can improve our own sampling operations and analyses, which we hope to be able to refine in future projects.”

Researchers at VTI have also looked at the presence of microplastics in snow, the results of which are presented in another report.

Text: Gunilla Rech

Translation: CBG

Street sweeping: a source to, or measure against, microplastic emissions? External link. (2023, Digitala Vetenskapliga Arkivet, DiVA External link.

Microplastics in snow in urban traffic environments (2023, Digitala Vetenskapliga Arkivet, DiVA) External link.