Photoaged Tire Wear Particles Leading to the Oxidative Damage on Earthworms (Eisenia fetida) by Disrupting the Antioxidant Defense System: The Definitive Role of Environmental Free Radicals

Tire wear particles (TWPs) have caused
increasing concerns
due
to their detrimental effects on the soil ecosystem. However, the role
of weathering in altering the toxicity of TWP to soil organisms is
poorly understood. In this study, the toxicity of original and photoaged
TWP was compared using earthworms (Eisenia fetida) as soil model organisms. The obtained results indicated that photoaging
of TWP resulted in an increase of environmentally persistent free
radicals (EPFRs) from 3.69 × 1017 to 5.20 × 1017 spin/g. Meanwhile, photoaged TWP induced the changes of
toxic endpoint in E. fetide, i.e.,
the increase of the weight loss and death ratio from 0.0425 to 0.0756
g/worm and 23.3 to 50% compared to original TWP under a 10% concentration,
respectively. Analyses of transcriptomics, antioxidant enzyme activity,
and histopathology demonstrated that the enhanced toxicity was mainly
due to oxidative damage, which was induced by disruption in the antioxidant
defense system. Free-radical quenching and correlation analysis further
suggested that the excessive production of ex vivo reactive oxygen
species, induced by EPFRs, led to the exhaustion of the antioxidant
defense system. Overall, this work provides new insights into the
potential hazard of the weathered TWP in a soil environment and has
significant implications for the recycling and proper disposal of
spent tire particles.