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, H 2 O 2, and O 2 – ), 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.