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Influence of aging processes on the toxicity of tire wear microplastic

Sefine Oksal Kilinc, Jana Maria Kraft, Maria Hermesmeyer, Eduardo Cerull

 The plastic pollution rises worldwide with increasing plastic production. Especially microplastic (MP) particles (size range 5 mm to 1 µm) are a major point of concern, since they are found to harm marine and terrestrial flora and fauna and ecosystem parameters. The concerns about MP comprise two main topics. One is the MP’s absorption of hydrophobic toxins from the surrounding environment. This could lead to a bioaccumulation of such substances in organisms by ingestion of MP particles. The other major concern is the leaching of different chemicals from MP into the environment. Most of plastics ingredients are not chemically bound into the polymer structure and can leach out into the surrounding medium.  The biggest source for MP in Germany is tire abrasion. Once released into the environment different aging processes can alter the characteristics of MP. In this work, the impact of tire wear MP in the environment was investigated starting from aging processes found in the nature to the effect of tire MP leachate on the model organism C. elegans.  To mimic aging processes, the tire wear samples were oxidized and/or irradiated with UV. The changes in the surface structure were determined by the measurement of functional groups. The results showed a significant enrichment of carboxyl functional groups on the surface of UV and ozone aged particles in comparison to pristine MP. Oxidation increases the concentration of functional groups on the polymer surface and could therefore enlarge the capability and reactivity of the particles with other substances.  The ecotoxicological tests with the nematode C. elegans were conducted according to the ISO 10872:2010. Ten juvenile worms were exposed to the leachates from aged tire wear MP particles. The body size of worms exposed to the leachate were significantly larger than of worms developing in buffer. On the other hand, the number of offspring decreased after leachate exposure. These results could be a first hint for a change in life strategy of the worms to survive a hostile environment.