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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Nouryon, a leading supplier of organic peroxides and a developer of organic peroxide solutions, has formally announced the completion of capacity expansion of its organic peroxides manufacturing facility in Ningbo, China.

The company's production capacity for Perkadox 14 and Trigonox 101 organic peroxide products, which are crucial components for altering polymer characteristics and crosslinking rubbers and thermoplastics, has increased to 6,000 tonnes each as a result of this capacity expansion. Furthermore, by improving the qualities of recycled polypropylene (R-PP), these solutions can also allow consumers to employ recycled polymers in applications that were previously exclusive to virgin plastics.

Alain Rynwalt, Senior Vice President – Performance Materials, Nouryon, said, “Nouryon is a world leader in essential ingredients for the polymer industry and this expansion highlights our dedication to supporting our customers’ growth across the entire polymer cycle. Customer interest in improving the properties of recycled polypropylene continues to rise, in line with increased consumer awareness and more stringent regulations.”

Sobers Sethi, Senior Vice President – Emerging Markets and China, Nouryon, said, “Asia Pacific is a key region for Nouryon and our most recent expansion in China strengthens our supply position even more in this growing region. Our customers rely on our existing network of manufacturing facilities and innovative technologies, and we are pleased to build more capacity to meet growing customer demand around the world.”

Trinseo, a speciality materials solutions provider, has signed agreements to supply its polycarbonate technology license as well as all proprietary polycarbonate production equipment in Stade, Germany to Deepak Chem Tech Ltd, a wholly owned subsidiary of Deepak Nitrite Limited, a diversified chemical intermediates company based in Vadodara, Gujarat, India.

The combined deals are worth USD 52.5 million. Subject to significant milestones, the business anticipates receiving around USD 9 million by the end of 2024 and an additional USD 21 million in the first part of 2025. The firm has made the decision to leave Stade, Germany, with this disposal of the production assets.

Frank Bozich, President and Chief Executive Officer, Trinseo, said, “While Trinseo recently announced its decision to exit virgin polycarbonate production, our polycarbonate technology is highly valued and the manufacturing equipment in Stade, Germany, can be utilised in India by Deepak. These are the initial steps of a strategic, collaborative partnership with Deepak, as we explore additional opportunities to leverage our technology portfolio and expand in higher-growth areas such as India.”

China's butadiene exports have experienced significant growth in recent years, particularly in 2021 and 2024. According to Sublime China Information (SCI), this surge is primarily driven by supply constraints in key regions, including the US and Southeast Asia.

Export Volume and Price Trends

In 2021, China's butadiene exports reached a historic high due to a supply gap in the US market. According to SCI, this trend continued in 2024 as reduced deep-sea cargo shipments and production challenges in Southeast Asia further tightened global supplies. From January to September 2024, China's total butadiene exports surged by 111 percent year-over-year to approximately 120.8 kilo tonnes.

The average export price of butadiene has fluctuated over the past five years. In 2023, weak demand in South Korea and competition from deep-sea cargoes led to a significant decline in export prices. However, in 2024, supply shortages from key regions drove prices to a five-year high. As of September 2024, the average export price reached USD 1,391 per metric ton, a 35 percent month-over-month increase, added SCI.

Export Destinations and Regional Dynamics

The majority of China's butadiene exports are directed to South Korea and Taiwan. In 2024, South Korea accounted for 74 percent of total exports, a significant increase from the previous year. This surge was driven by factors such as limited domestic supply and increased demand for spot butadiene.

While China's butadiene exports have been strong, the long-term potential for significant growth in deep-sea exports remains limited due to established supply chains and regional demand dynamics. Most of China's exports are currently concentrated in Northeast Asia, with limited opportunities for expansion into other regions.

Future Outlook

SCI added that 2025 China's butadiene supply is expected to be relatively sufficient, and export volumes may increase further. However, the sustained growth of exports will depend on various factors, including downstream demand in key markets, the availability of deep-sea cargoes, and the development of new production capacities in other regions.

Despite these uncertainties, China's butadiene industry is well-positioned to capitalize on global supply-demand imbalances and continue to play a significant role in the global market.

Cabot Corporation, a global speciality chemicals and performance materials company, has announced through an official statement that it will raise prices globally for carbon black products sold by its speciality carbons business. The price rise will be global and will come into effect for all shipments on or after 1 December 2024, or as contracts allow.

The company claims that the price rise is necessary owing to the impact of inflation on labour, maintenance and other production activities, as well as supply chain-related expenditures. The price increase will vary depending on the product and region.

The statement further elaborates that these price adjustments will help the company remain a dependable, long-term provider of high-quality products and services to its consumers. Cabot also underlined its commitment to guaranteeing supply security and the best service standards for its clients, as well as providing technological and process improvements and moving forward with its environmental goals.