Occurrence of Traffic-Derived Microplastics in Different Matrices in the Road Environment
Doctoral thesis, 2022

The prevalence of microplastic contamination has raised concerns about the potential risk and impact on the global environment. Traffic-derived microplastics, i.e., tire wear particles (TWP), polymer-modified bitumen, and road markings contribute to the emissions, and TWP are assumed to be one of the largest sources of microplastic emissions. Due to analytical difficulties, there is still a knowledge gap regarding transport routes, environmental concentrations, and toxicity. This thesis aims to investigate the occurrence of traffic-derived microplastics in several traffic environments and thereby increase the understanding of the particles.

Samples were collected on the road surface (Paper I‒IV), in the stormwater (Paper I, II, and IV), in the air (Paper IV), and in material collected by a street sweeper (Paper I‒II). In addition to environmental samples, a road-simulator was used to generate TWP in a controlled environment enabling comparison between tire types and brands resulting in a deeper understanding of the characteristics and physicochemical properties of TWP (Paper V). Different sample preparation steps such as optimised density separation, solvent cleaning, and size fractionation have been assessed, and several analytical methods light microscopy, SEM/EDX, FTIR, and pyr-GC/MS have been evaluated and used for the analysis of traffic-derived particles. Further, a novel method, automated SEM/EDX single particle analysis coupled to a machine learning classifier, has been developed for the analysis of TWP and other traffic-derived particles (Paper III, implemented in Paper IV). The automated SEM/EDX determined the size, shape, surface texture, and elemental composition of the different particles, and was able to categorize the particles into several subclasses: TWP, bitumen, road markings, metals, organics, and minerals. The estimated absolute masses showed that the fine fraction (2‒20 µm) corresponds to more than 50w% of the TWP and bitumen wear particles independently of the sample matrix indicating that TWP can both affect the PM10 concentrations and be transported long distances through water and air (Paper IV). Further, it was concluded that the stormwater system is an important transport route for traffic-derived particles, especially since the road runoff in Sweden is not commonly treated prior to release to recipients. Street sweeping as a potential measure to prevent the spreading of TWP was evaluated in Paper I‒II. Even though the street sweeper collects considerable amounts of material containing high concentrations of TWP, metals, and organic pollutants, no clear reduction was detected neither on the road surface nor in the stormwater. Besides traffic-derived microplastics, Paper II analysed metals and organic pollutants. The results showed concentrations of metals, PAH, phthalates, and aliphatic hydrocarbons exceeding the national guidelines.

The result from this thesis contributes to an increased knowledge about the properties and composition of TWP as well as the occurrence of traffic-derived microplastics in different environments. The results can be used as validation against theoretical emissions and transport models. The results have also highlighted the importance of including fine particles (<20 µm) in forthcoming works.

non-exhaust particles

tire wear particles

road dust

automated SEM/EDX

environmental samples

optimized sample preparation

organic pollutants

street sweeping

traffic-derived microplastics

road simulator

HC3, Password to zoom: 933464
Opponent: Ph.D. Stephan Wagner, Hochschule Fresenius, University of Applied Sciences, Germany


Ida Järlskog

Chalmers, Architecture and Civil Engineering, Geology and Geotechnics

Occurrence of tire and bitumen wear microplastics on urban streets and in sweepsand and washwater

Science of the Total Environment,; Vol. 729(2020)

Journal article

Tire and road wear particles (TRWP) - variable physicochemical properties and wear characteristics influenced by tire formulation and road surface, V. Wilkinson, T., Järlskog, I., Aristéia de-Lima, J., Mattsson, K., Gustafsson, M., Andersson-Sköld, Y and Hassellöv, M

Trafiken, den största utsläppskällan till mikroplast

När vi kör bil slits både asfalt och däck och bildar små slitagepartiklar. Det årliga däckslitaget i Sverige beräknas vara ca. 11 000 ton. Efter att partiklarna bildats kan de antingen stanna i vägmiljön eller virvla upp i luften och försämra vår luftkvalitet. När det sedan regnar sköljs en del av partiklarna ner i dagvattenbrunnar och diken. Där kan de antingen fastna eller transporteras vidare till vattendrag, sjöar och hav. Däckpartiklar är den enskilt största källan till mikroplastutsläpp i naturen, dessutom bryts partiklarna ned långsamt i naturen och så länge vi fortsätter köra bil med gummidäck kommer problemet med däckslitagepartklar att kvarstå.

I den här avhandlingen har prover samlats in i labb (vägsimulator), från flera olika trafikmiljöer samt från en gatusopningsmaskin. Resultaten visar att vägdamm och dagvatten från urbana och rurala miljöer innehåller stora mängder däckpartiklar. Materialet från sopmaskinen innehöll förutom mycket däckpartiklar, höga koncentrationer av metaller och organiska miljögifter vilket indikerar att det materialet bör hanteras som miljöfarligt avfall. Resultaten visar också att däckpartiklarnas storlek, form och egenskaper varierar, men att de flesta är mycket små (<20 µm). Avhandlingen bidrar till en ökad kunskap om förekomsten av däckpartiklar, och resultaten kan b.la. användas som indata till transport- och riskmodeller, och som jämförelse med andra studier.

Traffic, the largest source of microplastic emissions

When you drive a vehicle, both tires and road pavement are worn and generate wear particles. The annual release of tire wear particles, TWP, in Sweden is assumed to be 11 000 tons. After generation, the particles are either deposited at the road surface or transported into the environment directly through the air. Runoff transports deposited TWP into the stormwater system or to the ditches where the TWP either sediment or are further transported to surface waters and finally into the oceans. TWP is the largest source of microplastic emissions, the particles degrade slowly in the environment, and as long as the traffic continues and rubber tires are in use, the problem with TWP emissions will remain.

In this thesis, samples have been collected in the lab (road simulator), from several traffic environments, and from a street sweeper. The results indicate that samples from urban and rural environments contain large amounts of TWP. The street sweeping material contains besides a substantial quantity of TWP, high concentrations of metals and organic pollutants, indicating that the material should be handled as hazardous waste. The results show that the size, shape, and properties of TWP varies and that the majority of the TWP is very fine (<20 µm). This thesis contributes to an increased knowledge about the occurrence of TWP and the results can be used as input data to transport models and risk assessments, and for comparison with other studies.

Load and measures to reduce the load of traffic related persistent organic pollutants (POP) and micro/nanoplastics

The Swedish National Road and Transport Research Institute (VTI), 2019-01-01 -- 2021-12-31.

Formas (2017-00720), 2019-01-01 -- 2021-12-31.

Driving Forces

Sustainable development

Areas of Advance


Subject Categories

Infrastructure Engineering

Earth and Related Environmental Sciences

Environmental Sciences



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5141



HC3, Password to zoom: 933464


Opponent: Ph.D. Stephan Wagner, Hochschule Fresenius, University of Applied Sciences, Germany

More information

Latest update