By combining chemical analysis with ecotoxicological testing, the study found high concentrations of polycyclic aromatic hydrocarbons (PAHs) and leachable metals, particularly in smaller particle sizes. The finest fractions released greater amounts of bioavailable contaminants and showed stronger toxicity to soil organisms, plants, and aquatic bacteria, highlighting potential environmental and health concerns.
The rapid growth of the global automotive industry has generated millions of tons of waste tires annually. Because tires are highly durable and resistant to biodegradation, disposal remains a major environmental challenge. Recycling tires into rubber granulate offers a practical alternative to stockpiling or incineration and has become common in artificial turf systems, playground surfaces, running tracks, and noise barriers. Yet recycled tire rubber contains aromatic oils rich in PAHs—persistent organic pollutants known for their toxicity and carcinogenicity. Previous studies have detected high PAH levels in rubber surfaces, but few investigations have integrated chemical measurements with biological toxicity testing across different particle sizes. Moreover, total contaminant concentrations do not necessarily reflect ecological risk; the bioavailable fraction is what determines biological uptake and toxicity. Due to these uncertainties, a systematic, size-resolved evaluation was urgently needed.
A study (DOI: 10.48130/ebp-0025-0016) published in Environmental and Biogeochemical Processes on 29 December 2025 by Patryk Oleszczuk’s team, Maria Curie-Skłodowska University, highlights that particle size critically determines the environmental risk of recycled tire rubber granulate by controlling contaminant content, bioavailability, and ecological toxicity.
To evaluate chemical contamination and ecological risk, the researchers first quantified total concentrations of 16 priority PAHs (Σ16 PAHs), measured freely dissolved (bioavailable) PAHs (Cfree), calculated partition coefficients (Kd), analyzed potentially toxic elements (PTEs) in leachates, and conducted both liquid- and solid-phase ecotoxicological assays using bacteria ( Aliivibrio fischeri ), plants ( Lepidium sativum ), and soil invertebrates ( Folsomia candida ). Chemical analysis showed that Σ16 PAHs ranged from 49 to 107.6 mg/kg, with the highest levels in the smallest granulate fraction (<1.5 mm), which contained more than twice the PAHs of the largest fraction. Four-ring PAHs dominated (51.5–65.0%), particularly pyrene (29–42%), phenanthrene (11–16%), and fluoranthene (10–14%). Measurement of Cfree revealed elevated bioavailable PAHs (445–543 ng/L), again highest in the smallest particles, with 3-ring PAHs dominating the dissolved fraction (49–63%), indicating greater leaching potential of lighter compounds. Kd values confirmed strong contaminant affinity to the granulate matrix, especially in fine particles, and aligned with coal tar partitioning behavior. Metal analysis demonstrated substantial leaching of Zn (13–103 mg/L), Cu, and Cr, with concentrations exceeding drinking water limits and decreasing as particle size increased. Ecotoxicological tests corresponded closely with chemical findings: aqueous extracts caused complete inhibition of bacterial luminescence and up to 57% plant root inhibition, while solid-phase exposure resulted in 29.8–65.9% root growth inhibition and severe impacts on F. candida, including up to 70% mortality and 100% reproductive inhibition in the finest fraction. Across all assays, toxicity consistently declined with increasing particle size, demonstrating that finer granulate poses a disproportionately greater environmental hazard due to higher contaminant content and enhanced bioavailability.
In conclusion, this study demonstrates that recycled tire rubber granulate—particularly fine particle fractions—can act as a sustained source of bioavailable PAHs and metals in environments where human contact is frequent. Although the material exhibits strong contaminant-binding capacity, environmental aging and weathering may intensify pollutant release over time. These findings underscore the need for risk assessments that incorporate bioavailability and ecotoxicological evidence, and for size-specific regulatory standards to better protect soil ecosystems and public health.
##
References
DOI
Original Source URL
https://doi.org/10.48130/ebp-0025-0016
About Environmental and Biogeochemical Processes
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
Experimental study
Not applicable
Toxicity and polycyclic aromatic hydrocarbons bioavailability in recycled tire rubber granulate of varying particle sizes
29-Dec-2025
The authors declare that they have no competing interests