Recycled rubber made from used car tires is widely promoted as a sustainable solution for playground surfaces, sports fields, and running tracks. However, new research suggests that this popular material may release harmful chemicals into the environment, particularly when the rubber is broken into fine particles.
In a study published in Environmental and Biogeochemical Processes, researchers examined recycled tire rubber granulate of different particle sizes and found high levels of toxic compounds known as polycyclic aromatic hydrocarbons, or PAHs. These substances are linked to cancer and other health risks and can persist in soil and water for long periods.
The research team analyzed rubber granulate derived from end of life vehicle tires, focusing on three commonly used particle sizes. They measured both the total amount of PAHs in the material and the fraction that is bioavailable, meaning the portion that can dissolve in water and be taken up by living organisms. To understand real world impacts, the scientists combined chemical measurements with biological toxicity tests using plants, soil invertebrates, and aquatic bacteria.
“Our results show that recycled tire rubber contains very high concentrations of PAHs, especially in the smallest particle sizes,” said Patryk Oleszczuk, the study’s corresponding author. “These fine particles are more reactive and release a greater share of toxic compounds into water and soil, increasing the risk to ecosystems and potentially to human health.”
The study found that total PAH concentrations ranged from 49 to 108 milligrams per kilogram, depending on particle size. Smaller granules consistently contained more PAHs than larger ones. Even more concerning, the bioavailable fraction of these chemicals was also highest in fine particles, reaching levels higher than those typically found in many contaminated soils and sediments.
To evaluate toxicity, the researchers exposed springtails, a soil dwelling invertebrate, garden cress plants, and bioluminescent marine bacteria to both solid rubber granulate and its water leachates. All tested organisms showed adverse effects. While larger rubber particles caused less harm, the smallest granules significantly reduced survival, growth, or biological activity across multiple tests.
“Chemical data alone do not tell the whole story,” said Oleszczuk. “By combining chemical analysis with ecotoxicological tests, we were able to demonstrate that the compounds released from rubber granulate are not just present, but biologically active and harmful.”
The study also detected potentially toxic metals such as zinc and copper in water extracts from the rubber granulate. In some cases, metal concentrations exceeded drinking water guidelines, further contributing to the observed toxicity.
Recycled tire rubber is often used in places where people, especially children, come into direct contact with the material. Over time, weathering from sunlight, heat, and moisture can further break down rubber particles, potentially increasing the release of hazardous substances.
“Our findings suggest that the environmental safety of tire derived rubber depends strongly on particle size,” Oleszczuk said. “Fine granulates pose a disproportionate risk and should be carefully regulated, particularly in public spaces like playgrounds and sports facilities.”
The authors emphasize that recycling tires remains an important environmental goal, but caution that not all recycled materials are inherently safe. They call for the development of size specific regulations, long term monitoring, and safer alternatives to ensure that recycled rubber can be used without unintended harm to ecosystems or public health.
“This study highlights the need to rethink how recycled materials are evaluated and applied,” Oleszczuk said. “Sustainability should not come at the expense of environmental or human safety.”
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