Excessive Tire Degradation Identified as a Significant Contributor to Pollution in Waterways.
Researchers from Australia have uncovered that tire degradation constitutes a significant source of contamination in urban waterways, generating particulate matter, including microplastics. However, they have also identified effective methods to mitigate this form of pollution, which poses risks to both the environment and human health.
Many individuals might naturally assume, given the extensive recent research focus, that vehicle exhaust is the primary source of pollution. However, it is actually demonstrated that tire wear and tear generate a greater quantity of particle pollution by mass.
According to a briefing paper from February 2023 prepared by a team of experts at Imperial College London, tire wear in urban areas could present an environmental risk up to four times greater than other microplastics.
Tire Wear Particles (TWPs) as a Source of Microplastics in Waterways
The release of particulate matter from tire wear is a significant source of microplastics in water bodies, as it gets transported through road runoff during rainfall. In a recent investigation, scientists from Australia’s Griffith University examined the quantity and types of tire wear particles (TWPs) present in stormwater runoff within urban areas and explored strategies to mitigate this issue.
Lead author of the study, Shima Ziajahromi, emphasized, “Microplastic pollution in our waterways is an emerging environmental concern due to its persistence and accumulation in aquatic organisms and ecosystems. Stormwater runoff, which carries a mix of sediment, chemical, organic, and physical contaminants, serves as a crucial pathway for microplastics washed off from urban environments during rain and entering local aquatic habitats.”
The Disintegration of Tires and the Proliferation of Tire Wear Particles (TWPs)
As tires undergo wear and tear, they emit various particles that range in size from visible rubber fragments to tiny microparticles. On a global scale, approximately 6.6 million tons (or 6 million tonnes) of Tire Wear Particles (TWPs) are released annually. Tire waste does not naturally decompose and accumulates in the environment, where it can interact with other contaminants and biological organisms.
In 2020, the researchers collected 25 stormwater samples from parking lots and road locations across Queensland during 11 separate storm events. To minimize the potential for contamination during the sampling process, the sample containers remained sealed at all times, and no plastic materials were employed for sample collection. A control sample in the field (an open glass jar) was also used to monitor the possible presence of airborne microplastics that could contaminate the samples.
Microplastic Examination and Characterization
The suspected microplastics were visually examined using a stereo microscope and quantified. Furthermore, the researchers categorized the suspected microplastics based on their physical characteristics, such as fiber, fragment, and bead, as well as their color.
The majority (85%) of the suspected microplastics in the stormwater samples were identified as plastic polymers, meaning they were microplastics. The quantity of microplastics in the samples varied from 3.8 to 59 particles per liter, with TWPs alone accounting for 2.5 to 58 particles per liter of the total microplastics. The researchers assert that their findings underscore the substantial contribution of stormwater runoff to the presence of microplastics in water bodies.
Wetlands and retention ponds have been proposed as solutions for reducing the release of microplastics into water bodies. Sediment samples gathered by the researchers from the inlet and outlet of a constructed stormwater wetland contained between 1,450 and 4,740 particles per kilogram (2.2 pounds) of sediment. More microplastics were observed in the sediment at the inlet, indicating the wetland’s capacity to extract them from stormwater.
Shima Ziajahromi explained, “Microplastics that enter constructed wetlands within stormwater drainage systems settle in the sediment and form a biofilm, leading to their gradual accumulation, effectively removing them from stormwater runoff.”
In addition to constructed wetlands, the researchers evaluated the effectiveness of a stormwater treatment device designed to eliminate contaminants from stormwater.
Efficiency of a Stormwater Capture Device Designed by Fred Leusch
Fred Leusch, one of the study’s co-authors, described the device as “a bag made of 0.2-millimeter mesh, which can be retrofitted to stormwater drains.” Although originally designed to capture larger pollutants, sediment, litter, and oil and grease, it significantly reduced microplastics in the sediment, thereby preventing their release into stormwater runoff.
Both approaches, according to the researchers, offer viable methods for mitigating the buildup of microplastics in our water bodies.
Ziajahromi summarized, “Our findings demonstrate that both constructed wetlands and the stormwater capture device are strategies that could potentially be employed to prevent or at least reduce the quantity of microplastics and tire wear particles transported from stormwater into our waterways.”
Health Concerns Associated with Tire Wear Particles (TWPs)
The impact of TWPs on human well-being is a subject of growing apprehension. In the tire manufacturing process, various chemicals are combined to create durable rubber, which is then molded into tires. These components encompass polyaromatic hydrocarbons (PAHs), benzothiazoles, isoprene, and heavy metals such as zinc and lead. Research has demonstrated that ambient microparticles, including TWPs, have adverse effects on cardiopulmonary, developmental, reproductive, and cancer-related health outcomes.
Similar to the recent study, the aforementioned research from Imperial College underscores the importance of giving priority to addressing the potential detrimental effects of TWPs on both human health and the environment, rather than solely concentrating on reducing fuel emissions.
Mary Ryan, a co-author of the paper, emphasized, “Electric vehicles represent a critical step in decarbonizing transportation, but we must take a comprehensive view. Some concerns revolve around the increased weight of electric vehicles, which could lead to greater tire wear. This is precisely why Imperial College is advocating for a holistic, integrated approach to sustainability challenges.”
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