Tire Wear Particles Inhibit Tomato Growth and Disrupt Rhizosphere Microbial Function

Tire wear particles (TWPs), a widespread source of microplastic pollution, may pose ecological risks to terrestrial agroecosystems due to their persistence and chemical additives. However, their mechanisms in soil–plant systems remain poorly understood. A 30 day pot experiment investigated the effects of TWPs (100, 150, and 200 μm; 0.1 and 1%, w/w) on tomato (Solanum lycopersicum) growth, oxidative stress (MDA, H2O2, and O2–), soil enzymes (dehydrogenase, urease, and sucrase), and microbial communities. The smallest (100 μm) TWPs induced the strongest phytotoxicity (up to 55% biomass reduction, impaired photosynthesis, and elevated oxidative markers). High-dose (1%, w/w) 100 μm TWPs reduced soil nutrients and suppressed key enzyme activities. They also enriched stress-tolerant microbes (Actinobacteriota and Bacteroidota) while decreasing beneficial decomposers (Mortierella), disrupting microbial networks, and reducing modularity. Our findings highlight the particle-size-dependent toxicity of TWPs, which could adversely affect crop productivity and undermine soil ecosystem stability.