Recently, models on the fate of tyre wear particles (TWPs) have estimated that 18% of TWP emissions are transported from roads to freshwater bodies and approximately 2% are led out to estuaries and then marine habitats. What then happens to the remaining 16% of TWP emissions left in the freshwater compartment is not yet clear

 

The presence of tyre wear particles (TWP) in the aquatic environment is considered an emerging contaminant, and one that has gained increasing interest during the past few years. Although the presence of TWPs in the environment is given greater attention these days, TWPs have probably been present since the dawn of the pneumatic car tyre production in the late 19th century. The first scientific report of tyre dust identification along a roadside was published in 1961. Different perspectives have since been applied to this field of research and almost decade by decade shifted foci from degradation patterns to heavy metal release, to impacts of scrap tyres on the aquatic environment and leaching of chemicals from tyres. More recently, research within this field has been directed towards repurposing scenarios using crumb rubber in turf fields and playground material. Finally, in the 2010s, micronised tyre rubber has become grouped with other polymer debris and hence become part of the polymer landscape usually referred to as ‘microplastics.’ TWPs are considered to represent the majority of microplastics (or polymer debris) in the environment, and the newest calculation on the wear of tyres is estimated at 0.81 kg per person per year.

Now, looking at TWPs through the lens of microplastic pollution, research and information from the microplastics field are very well applicable to TWPs in many instances. With this new perspective of TWPs, increasing awareness of possible adverse effects in the environment follows - how do TWPs distribute in the different environmental compartments (soil, air, sediment, water and biota (living organisms)) and how do TWPs behave when exposed to different abiotic factors in these environmental compartments. For example, UV-radiation or pH, temperature and salinity differences could affect TWPs, but to what degree? A recent paper on this very subject concluded that particularly temperature and mechanical stress could influence the toxicity of TWPs. The focus of tyre production and function have seemingly always been directed towards maximising the three hallmarks: grip, wear and rolling resistance, and rightfully so, but somewhere along the road we forgot to consider where tyre abrasion actually disappears to. Luckily, some scientists already thought of this and today we can begin to lay the foundation to our collected TWP knowledge, based on the available scientific literature.

 

From roads to water

Research shows that the minority of TWPs end up in the airborne fraction (0.1-10%) and recently TRWPs have been assessed to contribute a low risk to human health in the particulate matter (PM) PM2.5 and PM10 range. So, where to find the remaining 90.0-99.9% of tyre debris emissions? Early research on particulate distribution showed a decreasing concentration of TWPs with increasing distance from the road. From there, TWPs are expected to wash off during rainfalls, transporting them to different environmental compartments. Recently, models on the fate of TWPs have estimated that 18% of TWP emissions are transported from roads to freshwater bodies and approximately 2% are led out to estuaries and then marine habitats. What then happens to the remaining 16% of TWP emissions left in the freshwater compartment is not yet clear and more research is needed to answer this question.

Aquatic organisms living in the water column or the sediment can interact with TWPs in their natural habitats during this particle transportation through freshwater to the marine environment. Although there are no scientific references on field observations of TWP ingestion by aquatic biota yet, few recent observations of this behaviour under controlled laboratory settings have been reported. In 2009 the first observation of the water flea, Daphnia magna, ingesting TWPs was described in the scientific literature and only two years ago the first photos were published showing ingestion of TWPs in the benthic amphipod Gammarus pulex following sediment exposure. Shortly thereafter photos of TWP ingestion in the amphipod Hyalella azteca and opossum shrimps from the mysidae family followed after water-only exposures, and most recently freshwater and marine fish species have been documented ingesting TWPs under laboratory conditions.

The recent focus on particulate effects of TWPs on biota is still in its infancy and the latest development in this field investigates the possible effects of both the particulate fraction and the leachate fraction. The leachate fraction is the suite of chemicals that leach out from TWPs to the surrounding water. Previously, tyre toxicity investigations in the aquatic environment revolved solely around the leachate fraction, which has been the primary focus over the last 30 years. Among the first papers the effect of whole tyre leachate was investigated showing worn tyre leachate to exhibit greater toxicity than leachate from a pristine tyre to rainbow trout. Furthermore, decreasing toxicity was observed with increasing salinity indicating that salinity either influences the leachability of toxic constituents or that an interaction of salts and toxic chemicals is present. Exposure of shredded tyre chips to different bacteria likewise showed a correlation between decreasing toxicity and increasing salinity, concluding that tyre leachate is likely to be a greater threat to freshwater habitats than to estuarine or marine habitats.

Toxicity pattern

Further testing of TWPs and leachate on a freshwater species recently showed a dissimilar toxicity pattern when comparing acute toxicity responses of TWPs or leachate. Here, the amphipod H. azteca was exposed to either TWPs in freshwater or the leachate fraction alone, i.e. with no particulates present. This showed that leachate was more toxic in lower concentrations, presumably because dissolved chemicals are more bioavailable. Although, at higher concentrations, the particle fraction of TWPs became more toxic. This phenomenon very well describes the complexity and discrepancies when working with TWPs in the aquatic environment. It is not just a question of determining toxicity of a single chemical under controlled settings, but rather investigating a mixture of many chemicals in changing ambient environments. This complex matrix of polymer and chemicals can be more or less bound to the particle, which in itself might have adverse effects. However, the particle could also function as a vessel, containing chemicals and making them more or less bioavailable depending on the surrounding environment. Discovering exactly which chemicals leach out under different exposure scenarios, and most importantly, what of that is actually bioavailable to aquatic living species is the more interesting question to answer.

Due to the amorphous nature of rubber, end-of-life tyres (ELTs) have been used as leachate collection material and been used to collect polycyclic aromatic hydrocarbons (PAHs) and metals from contaminated waters. This discrepancy between the different TWP uses that in some cases could deem toxic and have adverse effects but at the same time might serve to mitigate other environmental issues is a great conflict of contradictory traits. Now, we need to unravel exactly when these contradictory traits are possibly affecting aquatic environments negatively and when these traits might be used for our advantage.

 

So how do scientists quantify TWPs and chemical constituents or ‘biomarkers’ from TWP leachate in water? The quick answer is that no tried and tested procedure is more right than any other now, we simply do not have conformity or guidelines on how to do this. Especially when looking to find particulates from tyre debris, as this is not usually detected when investigating for other polymer debris e.g. microplastics. Therefore, it is expected that the total amount of microplastics has been underestimated due to the lack of data from TWPs, which make up a large part of the estimated microplastic load worldwide and have not been reported on a regular basis. A multitude of methods have been used to estimate TWP emissions by measuring the concentration of chemicals in samples, with more or less success over the years. The biomarkers that have been used to determine TWP concentration most successfully include quantification of benzothiazoles and zinc. Both chemicals are used as part of the vulcanisation process and are also ubiquitous in nature. They are used for manufacturing of other materials, but specific versions can be attributed mainly to tyre manufacturing and are thus the most reliable compounds to measure.

How this emerging field of tyre ecotoxicology will progress ultimately depends on cooperation between different stakeholders having a common goal to pursue. The one thing that we can probably all agree on, is the need for tyres and other rubber products in our society. How we then fill that need, and what future decisions we make to maximise our understanding of the possible negative implications of TWPs in the aquatic environment is of paramount importance. Our job now is to continue our research within this field and ultimately prevent excess and unnecessary pollution of the water bodies that we all depend on, in a manner that stays true to both the environment and our need for safe and reliable tyres. 

*The author is a PhD student in Environmental Biology at Roskilde University, Department of Natural Science and Environment, Denmark, with funds from Danish Environmental Analysis

 

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Australia has released its first national specification for the use of crumb rubber asphalt on local roads, a move intended to give councils clearer guidance on designing and maintaining light-to-medium-duty networks and to strengthen domestic recycling demand for end-of-life tyres.

The Crumb Rubber Modified Dense Graded Asphalt (CRM DGA) Model Specification for light to medium duty roads was published by the Australian Flexible Pavement Association (AsPA) following collaboration with Tyre Stewardship Australia. The document offers standardised technical requirements for councils, which manage about 75 percent of the national road network — roughly 675,000km of streets and community-level infrastructure.

Existing asphalt standards were largely developed for higher-order state roads, leaving local governments to interpret specifications that did not reflect lower traffic loads or the environmental conditions typical of suburban and regional networks. The new model specification aims to close that gap by setting guidance aligned with the factors that most influence degradation on council roads, such as surface ageing and weather exposure.

The specification promotes the use of crumb rubber modified binders, which can extend pavement life under light-to-medium-duty conditions. Incorporating recycled rubber also aligns with broader circular-economy policies across Australia’s states and municipalities, which are seeking to reduce landfill and illegal dumping while supporting domestic tyre-recycling capacity.

AfPA said the CRM DGA Model Specification V1.0, dated October 2025, is publicly available. It includes requirements for mix design and materials, construction processes such as compaction and temperature control, and performance testing suited to council networks. It also offers practical guidance on integrating reclaimed asphalt pavement content.

Local governments seeking case studies and procurement tools on crumb rubber applications can access Tyre Stewardship Australia’s Crumb Rubber Resource Centre for further technical and project information.

Flexsys has created what it says is the tyre industry’s first practical and scalable alternative to 6PPD, marking a major step toward replacing a chemical used for decades but now under regulatory pressure.

The company said the new antidegradant is the result of several years of research and testing with federal laboratories, independent scientific groups and tyre makers. Early results show the material could match the performance and safety of 6PPD while avoiding the environmental risks linked to 6PPD-quinone, a transformation product identified in 2020.

Flexsys said the new chemistry provides the short- and long-term protection needed to stop tyres cracking or ageing. It is also designed to fit into existing rubber compounds with minimal changes, which could help manufacturers adopt it quickly. The company added that the product meets environmental and regulatory benchmarks, including criteria set by the Washington State Department of Ecology.

Importantly, the new molecule is not part of the “PPD” family, meaning it does not form quinone during use. Flexsys said this would remove the environmental impact associated with 6PPD-quinone. The company is also using many of the same intermediate chemicals already used in 6PPD production. This could allow manufacturers to rely on existing factory assets and speed the shift to the new technology.

“This achievement reflects our unwavering commitment to responsible innovation, built on decades of expertise in tire protection chemistry,” said Carl Brech, Chief Executive Officer of Flexsys. “Our solution is formulated to deliver the performance and reliability that tire makers expect and is designed for future environmental and regulatory standards.”

6PPD has been essential to tyre durability for 50 years. But studies published in 2020 showed that 6PPD-quinone could harm aquatic species, including coho salmon. Regulators and tyre producers have been looking for a safer option since then. Flexsys said its new antidegradant meets this challenge without reducing tyre safety.

“Our team set out to develop a next-generation antidegradant that meets the tire industry’s highest performance standards without compromising tire safety, while also reducing toxicity,” said Neil Smith, Chief Technology and Sustainability Officer. “I could not be more proud of the perseverance and dedication of the Flexsys R&D team. Our group has been highly motivated by both the technical challenges of this project as well as the positive societal impact that this work will ultimately have.”

Flexsys acknowledged support from the Sustainable Polymers Tech Hub in Akron, Ohio, part of the U.S. EDA Tech Hubs programme.

The company is now working on process optimisation to allow large-scale production. It is also in discussions with regulators around the world to secure approvals for commercial use. Testing with tyre makers is continuing.

“Flexsys is helping set the direction of the tire industry for the coming decades with this development,” Brech said. “We will continue to work tirelessly to bring this breakthrough to the market as soon as possible.”

Wacker Chemie AG has strengthened its position in China’s fast-growing market for silicone specialities by opening a new application development centre with joint-venture partner SICO Performance Material in the eastern city of Jining.

The 2,300-square-metre facility brings together several laboratories focused on organofunctional silanes, which are used as high-performance additives in plastics, coatings and adhesives. By locating the centre next to SICO’s production and scale-up lines, Wacker aims to shorten development cycles and move new products into the market more quickly. The companies said investment in the site is in the mid-six-figure euro range.

Tom Koini, who leads Wacker’s silicones division, said the opening marks an important step in its China strategy. “As a provider of innovative silicone specialties and solutions, we can use this development center to achieve a key milestone for our business in China. Our focus is on high-margin specialty silanes, for which demand in China is rising continuously. This investment together with our partner SICO strengthens our presence and commitment to the region,” he said.

Wacker, which took a majority stake in SICO in 2022, is seeking to build a larger share of China’s specialty chemicals market, where demand for hybrid polymers has increased for years. These materials help improve the mechanical and chemical properties of adhesives, sealants, coatings and engineered plastics, all of which are used in sectors such as electric mobility, electronics and power equipment.

At the opening ceremony, SICO General Manager Kevin Qu called the centre an investment in the long term. “We can now pool all of our silane expertise here at our application development centre. This know-how ranges from chemical product properties and supply chain matters through to questions of process engineering and current marketing trends. We will leverage this in-depth knowledge to develop forward-looking innovations for our customers. This marks a new chapter of success in the history of our joint venture,” he said.

The companies said the centre will act as a link between research, technical service and manufacturing teams. Scientists will focus on developing additives, adhesion promoters and stabilisers based on organofunctional silanes and functional silicone fluids.

The Association of Natural Rubber Producing Countries (ANRPC) has released its Monthly NR Statistical Report for October 2025, providing an overview of key developments in the global natural rubber sector.

According to the report, the global natural rubber market in October was characterised by a distinct bearish trend in pricing. This decline can primarily due to a significant surge in production and export activities, which were initially stimulated by the higher prices seen earlier in the year. Meanwhile, overall demand has remained relatively subdued.

Looking ahead to the full year, projections indicate a modest 1.3 percent increase in global production for 2025, a figure that follows a recent downward revision for Indonesia. On the demand side, consumption is anticipated to grow by a slight 0.8 percent, influenced by an upward adjustment to Indonesia's consumption data. Despite the current price pressures, market sentiment shows some mixed signs of improvement, particularly within the tyre trade of certain specific markets.