Periodically, a vehicle’s tires reach a state of considerable wear and necessitate replacement. The salient question then arises: what becomes of the abraded tire material?
Regrettably, this dissipated tire matter frequently finds its way into aquatic ecosystems, where minuscule microplastic fragments originating from the tires’ synthetic rubber matrix serve as vectors for numerous chemical compounds. These substances can subsequently transfer to fish, crustaceans, and potentially even the human consumers of these organisms.
We are engaged in the scientific pursuit of both analytical and environmental chemistry, dedicating our research to devising methodologies for the extraction of these microplastics—and the associated toxicological agents they transport—prior to their ingress into water bodies and the attendant aquatic biota.
Microplastics: A Magnified Environmental Challenge
An immense volume of plastic detritus, measured in millions of metric tons, is introduced annually into the global oceanic systems. Analysis has revealed that, in contemporary times, tire particulate matter contributes approximately 45% of the total microplastic load observed in both terrestrial and aquatic environments.
As vehicular tires traverse roadways, they continuously shed microscopic plastic particles. Subsequent precipitation events facilitate the migration of these tire wear residues into drainage channels, ultimately leading them into streams, lakes, rivers, and oceans.
During their transit, aquatic organisms such as fish, crabs, and oysters frequently ingest these tire wear particles, mistaking them for sustenance. With each ingestion event, these creatures also assimilate highly deleterious chemical substances capable of adversely impacting both the organisms themselves and any predators that consume them.
Certain fish species, for instance, rainbow trout, brook trout, and coho salmon, are experiencing mortality attributable to toxic compounds demonstrably linked to tire wear particulates.
A 2020 investigation documented that a substantial proportion, exceeding 50% of the coho salmon returning to their spawning grounds in Washington state succumbed before reproduction could occur. This attrition was largely ascribed to 6PPD-Q, a metabolite derived from 6PPD, an additive incorporated into tire formulations to enhance their durability and retard degradation.
However, the deleterious consequences of tire wear particles extend beyond aquatic biota. Both human populations and the broader animal kingdom are potentially exposed to airborne tire wear particles, particularly individuals residing in proxmity to major transportation arteries.
In a notable study conducted in China, the same constituent, 6PPD-Q, was detected within the urine samples of both children and adult subjects. While the precise physiological effects of this chemical on the human organism are still under investigation, recent findings suggest that exposure could precipitate damage to several vital human organs, including the liver, lungs, and kidneys.
Our empirical observations in Oxford, Mississippi, revealed the presence of over 30,000 individual tire wear particles within a mere 24-liter sample of stormwater runoff collected from road surfaces and parking areas following a duo of precipitation events. It is posited that in locales characterized by substantial vehicular traffic, such concentrations could demonstrably escalate.
The Interstate Technology and Regulatory Council, an entity comprising a coalition of state governments, issued a recommendation in 2023 advocating for the identification and implementation of substitutive compounds for 6PPD in tire manufacturing to mitigate environmental 6PPD-Q contamination. Notwithstanding these recommendations, tire producers assert that a viable substitute has not yet been developed.
Strategies for Community Harm Reduction
Within the academic confines of the University of Mississippi, our ongoing research endeavors are focused on developing ecologically sound methods for the remediation of tire wear particles from watercourses, utilizing readily accessible and economically viable organic materials derived from agricultural byproducts.
The fundamental principle guiding this initiative is straightforward: to intercept and sequester tire wear particles before they can infiltrate natural water systems.
In a recent experimental undertaking, we evaluated the efficacy of pine wood chips and biochar—a form of charcoal produced through the thermal decomposition of rice husks under oxygen-restricted conditions, a process termed pyrolysis. Our findings indicated that these materials possessed the capacity to extract approximately 90% of tire wear particles from stormwater runoff at our designated experimental sites in Oxford.
Biochar is a well-established medium for the removal of waterborne contaminants, owing to its intrinsic characteristics, including a vast surface area coupled with a porous structure, abundant reactive chemical binding sites, inherent stability, formidable adsorptive capabilities, and cost-effectiveness.
Wood chips, due to their rich endowment of natural organic compounds, have likewise demonstrated efficacy in adsorbing pollutants. Alternative research endeavors have explored the utilization of sand for the filtration of microplastics; however, its efficiency in particle removal was found to be comparatively lower than that of biochar.
We devised a biofiltration apparatus employing biochar and wood chips encased within a filter sock, subsequently deploying it at the effluence point of a drainage conduit. Following this, stormwater runoff samples were procured for analysis, with tire wear particle concentrations meticulously quantified both prior to and subsequent to the placement and operation of the biofilters across a two-month interval encompassing two rain events. The findings indicated a marked reduction in tire wear particle concentrations post-biofilter implementation.
The distinctive elongated and irregular morphology of tire wear particles facilitates their entrapment and entanglement within the porous matrix of these biomaterials during storm surges. Even the most minute tire wear fragments were effectively captured within the complex interstitial spaces presented by these filtering media.
Future Deployment of Biomass Filtration Systems
We are confident that this innovative methodology possesses substantial potential for scalable application in ameliorating tire wear particle pollution and other contaminants during meteorological phenomena involving precipitation.
Given that both biochar and wood chips can be sustainably sourced from agricultural waste streams, they represent relatively low-cost and readily accessible resources for local communities.
Longitudinal monitoring studies will be imperative, particularly within environments characterized by high traffic volumes, to comprehensively ascertain the efficacy and scalability of this approach. Furthermore, the provenance of the filtering material warrants careful consideration. Concerns have been raised regarding the potential for raw agricultural residues, which have not undergone pyrolysis, to leach organic pollutants.
Consistent with the operational principles of most filtration systems, the biofilters would necessitate periodic replacement. The spent filters, having accumulated contaminants and undergone degradation, would require appropriate disposal protocols.
The pervasive issue of plastic waste poses a significant threat to ecological integrity, the human food supply, and potentially human health. We advocate for biofilters derived from plant biomass as a viable, cost-effective, and environmentally responsible resolution.
