Exploring a Source to Sea approach for plastic pollution policy integration in the European Union: the case of tyre wear particles

Despite decades of regulatory efforts to limit marine pollution, levels of pollution are still high. Of particular concern in recent years is (micro)plastic pollution. Sources of microplastics are either intentionally added to products, such as cosmetic and personal care products, or released unintentionally, such as wear from textile, tyres and the breakdown of larger plastic items. Marine microplastic pollution is by nature transboundary which therefore requires collaborative and concerted efforts both within and between countries. Microplastic pollution has a strong land-sea interaction as much pollution enters the sea from land, via air and waterways. Addressing microplastics pollution thus requires a multifaceted governance approach that encompasses land-based manufacturing and trading sectors, transportation and urban planning, as well as consumer behaviour and waste(water) management systems. These fluid characteristics of microplastic pollution challenges conventional ways of assessing and understanding governance efforts to combat marine pollution. Given the vastness of the governance challenge of combatting pollution across land, water and sea and the multitude of pollution sources, the assessment of governance efforts requires a scope that extends from land to sea. In addition, to understand why marine pollution governance is failing, attention should be paid to actor interactions and power dynamics that explain the limited scope and effectiveness of existing governance efforts. Within the Horizon Europe project SOSZeroPol2030[1], we developed a source-to-sea governance assessment framework for fluid marine pollutants, such as microplastics. This framework covers potential sources and the source-to-sea pathways of/for marine pollution. Sources can be at the different life cycle stages of production, use, and end-of-life of materials and products as well as at their end-of-pipe release. The governance assessment framework takes as a unit of analysis a governance arrangement. A governance arrangement is the temporary stabilisation of the organisation and substance of a policy domain within which actors take and implement decisions. The concept allows to analyse how actors interact, subject to rules, discourses, and power dynamics. By identifying governance dynamics at and between different life cycle stages, we better understand how the architecture and power dynamics of governance evolve along the whole source-to-sea trajectory that pollutants take. We will illustrate the use of this framework with a case study of how the EU is governing a particular type of microplastics: Tyre Wear Particles (TWPs). The European Union adopted its European Green Deal (EGD) in December 2019 aiming to make the EU the first climate-neutral continent. Implementation of the EGD is done through a set of strategies and action plans, one of which is the Zero Pollution Action Plan. The EGD zero pollution target is to reduce microplastics released into the environment by 30% by 2030. We will focus on the regulatory developments and governance dynamics of governance arrangements for respectively the production , use and end-of-life of tyres, as well as end-of-pipe TWP emissions. [1] ‘Source to Seas – Zero Pollution 2030’ (SOS-ZEROPOL2030) is funded by the European Union’s Horizon Europe programme under grant agreement No. 101060213

The presence of microplastics, including tire wear particles, has been documented in various environmental systems, including soils. Despite a lot of research of the effects of microplastics and tire wear particles on individual soil organisms, an evaluation of their overall impact on soil ecosystems is still missing. Thus, it is not possible to assess their complete effects. Life cycle assessment can be used as a tool to fill this gap, however, effect factors which enable quantifying the toxic pressure on soil ecosystems in relation with the pollutant concentration are limited for microplastics and are not available for tire wear particles. As a first step to address this gap, we conducted a hazard assessment and developed a probabilistic species sensitivity distribution (pSSD) for microplastics and tire wear particles, from which the effect factors were derived. The mean hazard concentration at which 20 % of the species were exposed to a concentration above EC10eq was found to be 0.22 g/kg for microplastics and 0.25 g/kg for tire wear particles. The calculated effect factors, which define the change in the potentially affected fraction (PAF) of species, were 0.90 and 1.24 PAF kg/g for microplastics and tire wear particles, respectively. This indicates that tire particles may have a slightly greater effect than microplastics on soil systems. However, it should be noted that studies reporting only highest no observed concentrations (HONEC) were included in the tire wear particle database, while they were excluded from the microplastics database as enough data were available. When comparing their impact on ecosystems, microplastics and tire wear particles appear to exert less toxic pressure on soil ecosystems than on aquatic ecosystems per unit of microplastics and ecosystem volume. Our results enhance understanding of the toxic impact of microplastics and tire wear particles on soil systems and support their integration into life cycle assessment through effect factors which can be combined with fate and exposure factors to obtain the ultimate characterization factors used in life cycle assessment.

Tire and road wear particles (TRWPs) were collected from road dust and thermogravimetric analysis (TGA) was performed to measure the content of tire wear particles (TWPs) in the TRWPs. The TGA thermograms of TRWPs showed two weight loss steps associated with polymer decomposition including weight loss after 480℃ which may be due to road wear particles. Different samples gave different TGA thermograms because the types and contents of the road wear particles attached to the TWPs should be different from each other, and each TWP might have different composition. The TGA results of the model asphalt pavement wear particles, with (volatile organics + polymers + carbon black) : ash = 33.5 : 66.5, was applied to the TRWP results, and the TWP contents of TRWPs were found to be 50-65%. The zinc oxide content in the rubber compound was negligible.

With the implementation of strict emission regulations and the use of cleaner fuels, there has been a considerable reduction in exhaust emissions. However, the relative contribution of tire wear particles (TWPs) to particulate matters is expected to gradually increase. This study conducted laboratory wear experiments on tires equipped on domestically popular vehicle models, testing the factors and particle size distribution of TWPs. The results showed that the content of tire wear particle emission was mainly ultrafine particles, accounting for 94.80% of particles ranging from 6 nm to 10 μm. There were at least two concentration peaks for each test condition and sample, at 10~13 nm and 23~41 nm, respectively. The mass of TWP emission was mainly composed of fine particles and coarse particles, with concentration peaks at 0.5 μm and 1.3–2.5 μm, respectively. Both the number and mass of TWPs exhibited a bimodal distribution, with significant differences in emission intensity among different tire samples. However, there was a good exponential relationship between PM10 mass emissions from tire wear and tire camber angle. The orthogonal experimental results showed that the slip angle showed the greatest impact on TWP emission, followed by speed and load, with the smallest impact from inclination angle.

Tires, bitumen, and road markings are important sources of traffic-derived carbonaceous wear particles and microplastic (MP) pollution. In this study, we further developed a machine-learning algorithm coupled to an automated scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) analytical approach to classify and quantify the relative number of the following subclasses contained in environmental road dust: tire wear particles (TWP), bitumen wear particles (BiWP), road markings, reflecting glass beads, metallics, minerals, and biogenic/organics. The method is non-destructive, rapid, repeatable, and enables information about the size, shape, and elemental composition of particles 2–125 µm. The results showed that the method enabled differentiation between TWP and BiWP for particles > 20 µm with satisfying results. Furthermore, the relative number concentration of the subclasses was similar in both analyzed size fractions (2–20 µm and 20–125 µm), with minerals as the most dominant subclass (2–20 µm x̄ = 78%, 20–125 µm x̄ = 74%) followed by tire and bitumen wear particles, TBiWP, (2–20 µm x̄ = 19%, 20–125 µm x̄ = 22%). Road marking wear, glass beads, and metal wear contributed to x̄ = 1%, x̄ = 0.1%, and x̄ = 1% in the 2–20-µm fraction and to x̄ = 0.5%, x̄ = 0.2%, and x̄ = 0.4% in the 20–125-µm fraction. The present results show that road dust appreciably consists of TWP and BiWP within both the coarse and the fine size fraction. The study delivers quantitative evidence of the importance of tires, bitumen, road marking, and glass beads besides minerals and metals to wear particles and MP pollution in traffic environments based on environmental (real-world) samples

Adsorption and desorption behaviors of antibiotics by tire wear particles and polyethylene microplastics with or without aging processes

Automated identification and quantification of tire wear particles (TWP) in airborne dust: SEM/EDX single particle analysis coupled to a machine learning classifier

Aging increases the particulate- and leachate-induced toxicity of tire wear particles to microalgae

Rapid generation of aged tire-wear particles using dry-, wet-, and cryo-milling for ecotoxicity testing

Surface reactivity heterogeneity-driven redox activation of tire wear particles enhances nitrate removal in activated sludge: Unraveling photoelectrochemical-extracellular polymeric substances synergy.

In recent years, microplastics (MPs), a new type of pollutant, have been widely dispersed in aquatic ecosystems. Compared with typical MPs (PVC, PP, PE, and PS), tire wear particles (TWP) exhibit significant differences in composition, additives, and characteristics. In this study, the adsorption and desorption of organic pollutants were compared between the typical MPs and TWP. With TWP and polyvinyl chloride (PVC) particles as adsorbents, oxytetracycline (OTC) and sulfamethoxazole (SMZ) as adsorbates, the adsorption and desorption of organic pollutants by TWP and PVC particles before and after aging were studied. Correctly understanding the behavior of MPs in an aquatic environment is of great significance. The results indicated that during the UV aging process, both TWP and PVC exhibited cracks, pits, and bulges on the particle surface, increased specific surface areas, increased strength of oxygen-containing functional groups, and enhanced hydrophilicity. The adsorption modes of TWP and PVC before and after aging were in two stages:surface adsorption and liquid film diffusion. TWP has a better fit for the Freundlich model, belonging to multi-layer adsorption, while PVC has a better fit for the Langmuir model, belonging to monolayer adsorption. The carrier effect of TWP on antibiotics was better than that of PVC, with the adsorption capacity of OTC on virgin TWP and PVC reaching 5.14 mg·g-1 and 1.38 mg·g-1, respectively. Additionally, the adsorption capacity of OTC on the aged TWP and PVC reached 5.82 mg·g-1 and 2.13 mg·g-1, respectively, which was better than with the virgin samples. The desorption capacity of aged TWP and PVC for antibiotics was better than the virgin materials, while the desorption rate was lower. In the same desorption solution, the desorption effect of TWP on antibiotics before and after ageing was better than that of PVC. The desorption effect of TWP and PVC on antibiotics in a simulated intestinal fluid environment was significantly better than that in an ultra-pure water environment.

Investigation on the adsorption and desorption behaviors of heavy metals by tire wear particles with or without UV ageing processes

Tire wear particles (TWP) originating from tire abrasion on roads are a major source of microplastics to the environment. Together with associated pollutants like polycyclic aromatic hydrocarbons and trace metals, TWP are emitted to roadside soils in the immediate vicinity of road networks. Our study aimed at quantifying TWP number and mass concentrations and investigating particle features in low-traffic roadside soils using a novel particle-based analytical approach. On the example of fifteen Swiss cantonal roadside soils, with average daily traffic volumes of 2,290 vehicles per day− 1, we sampled composite samples from distances of 1, 2, 5 and 10 m to the roadside. TWP were extracted via density separation and wet-chemical sample purification. TWP analysis was performed using microscope images and trainable Weka segmentation image analysis. Furthermore, associated road pollutants like polycyclic aromatic hydrocarbons, benzop[a]pyrene and trace metals were analysed using TQ GC-MS/MS and ICP-MS. We found average concentrations of 111,000 TWP per kg soil dry weight (TWP kg− 1) highest values reaching 615,000 TWP kg− 1 and mean TWP masses of 52.7 ± 83.2 mg TWP kg− 1. TWP had a minimal Feret diameter of 62.8 ± 45.6 μm on average and showed mean circularity values of 0.7 ± 0.2, resulting in elliptic particle morphology. TWP concentrations and sizes decreased with increasing distance from the road. Positive relationships were found between TWP numbers and polycyclic aromatic hydrocarbons, benzop[a]pyrene and zinc concentrations in roadside soils. However, a moderate relationship to speed limits was identified. We were able to demonstrate that even in low-traffic areas, roadside soils act as an environmental sink for high concentrations of TWPs and associated pollutants and that spatial distribution and the spread of TWP to soils strongly dependent on the distance to the road.

The difference between tire wear particles and polyethylene microplastics in stormwater filtration systems: Perspectives from aging process, conventional pollutants removal and microbial communities

Sulfate radical-based advanced oxidation process effects on tire wear particles aging and ecotoxicity