Does water treatment solve the tire microplastic problem, or complicate it?

Every day, millions of vehicles move across roads worldwide. While exhaust pipe emissions dominate public conversation about vehicle pollution, another form of contamination spreads far more quietly; one that begins the moment a tire touches the road and ends, potentially, in the glass of water on your table. As a Special Research Student at the University of Tokyo and a PhD researcher at Tokyo Metropolitan University, my work dives deep into this hidden issue. Specifically, I explore how tire microplastics and their chemical additives behave during drinking water treatment processes.

What are Tire Microplastics?

When vehicles accelerate, brake, or simply move along roads, small fragments are continuously worn away from tires. These particles are known as Tire Wear Particles (TWP). Unlike conventional plastic litter, tire particles are complex mixtures containing synthetic rubber, heavy metals, antioxidants, and various chemical additives. Recent studies suggest that tire wear particles may contribute significantly to the total microplastic load entering urban waterways. Rainfall runoff can transport these particles from roads into rivers, lakes, and eventually drinking water systems. What makes tire microplastics especially concerning is not only the particles themselves, but also the chemicals they release into water over time.

Chemicals Hidden Inside Tires

Modern tires contain numerous chemical additives designed to improve durability and performance.

In my current research, I investigate several important tire-associated chemicals, including:

·         Benzothiazole (BT)

·         6PPD-related transformation products

·         TMQ antioxidant

·         Diphenyl guanidine (DPG)

·         Heavy metals such as zinc, copper, and iron (Fig. 1).

Fig. 1: This SEM-EDX image is a chemical blueprint revealing the high inorganic complexity of a tire microplastic. Beyond the organic chemicals, the elemental mapping is dominated by key additives and fillers including Zn, S, Si and Al. The image vividly demonstrates that tire microplastics are complex  chemical composites, not just simple plastics. Imagen author: Dilraj.

These chemicals may undergo further transformation under water treatment conditions such as UV exposure and advanced oxidation processes. Some transformation products are suspected to be more toxic than the original compounds. One example that has recently gained global attention is 6PPD-quinone, a transformation product linked to acute toxicity in aquatic organisms, particularly salmon species.

What Happens Under drinking water treatment conditions?

An important part of my research focuses on how tire microplastics change when exposed to UV radiation, oxidation processes and disinfection.

Using analytical techniques such as Py2DGCMS GC-MS, LC-MS/MS, ICP-OES, FTIR, SEM-EDX and Orbitrap mass spectrometry, we can investigate both the physical and chemical transformations occurring during these processes.

What emerges from this work challenges a common assumption: that treatment means elimination. In some cases, degradation produces smaller particles and newly formed transformation products that may actually be more mobile or biologically active than the original compounds. Disinfection processes, like chlorination,  rather than neutralising tire-derived chemical additives, can in some instances convert them into more toxic byproducts. This highlights a critical and often overlooked challenge in environmental science: pollutants can evolve through treatment processes, creating complex mixtures that are difficult to monitor, regulate, and remove. The toxicity of the original compounds is only part of the story, the transformation products formed during water treatment represent an additional and largely unexplored dimension of risk.

Looking Forward: An Overlooked Challenge

My research underscores a major hurdle in environmental science: pollutants evolve. They create complex, shifting chemical mixtures that are incredibly difficult to monitor and regulate using standard water-testing protocols. While the scientific community has rightfully focused heavily on the biological toxicity of tire wear in nature, my work opens a critical new door. It highlights an often overlooked aspect of drinking water security: how the very engineering processes we use to clean our drinking water might accidentally trigger the creation of toxic tire-derived byproducts. By understanding these mechanisms, we can work toward designing smarter, more resilient water treatment systems for the future.

By Dil

PhD at TMU, Japan

Sp-Researcher@UTokyo

dilrajs@g.ecc.u-tokyo.ac.jp