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Photoaging-induced phytotoxicity of tire wear particles on tomato (Solanum lycopersicum L.): Evidence from oxidative stress, metabolic reprogramming, and microbial shifts
Summary
Tiny bits of tire dust that wash into soil get even more toxic after sitting in the sun, according to a new study on tomato plants. Sun-damaged tire particles leached more heavy metals, stunted tomato growth by up to 77%, and disrupted the helpful soil microbes plants need, raising concerns about how this widespread pollutant, which comes from everyday road traffic, could affect the food we grow. While this study looked at plant health rather than direct human effects, it's a reminder that tire particles are an underexamined source of contamination in the soil where our food comes from.
Tire wear particles (TWPs) undergo intricate photoaging processes that substantially alter their physicochemical properties and enhance their environmental behavior and ecological effects. However, the combined effects of particle size and exposure concentration of photoaged TWPs on plant growth and rhizosphere microbial communities remain inadequately characterized. In this study, a 30-day tomato cultivation experiment was conducted using UV-aged TWPs of two sizes (100 and 200 μm) applied at two concentrations (0.1% and 1%, w/w). The results revealed distinct size- and concentration-dependent phytotoxicity. The highest concentration of 100 μm TWPs (1%, w/w) induced the most pronounced inhibitory effects, reducing shoot biomass by 77.1% and net assimilation rate by 62.1%, while increasing malondialdehyde (MDA) content by 72%. UV photoaging altered TWP surface morphology, chemical composition, and hydrophilicity, promoting the leaching of heavy metals. Furthermore, UV-aged TWPs disrupted soil nutrient cycling and enzyme activities, triggered extensive metabolic reprogramming in tomatoes, particularly in carbon metabolism and TCA cycle, and reduced rhizosphere bacterial and fungal diversity, shifting microbial communities toward more stress-tolerant taxa. Integrated analyses demonstrated that the phytotoxicity of UV-aged TWPs was linked to oxidative stress, metabolic disturbance, impaired soil function, and microbial community shifts. These findings advance the understanding of UV-aged TWP toxicity and underscore the necessity of incorporating particle size and aging status into environmental risk assessments.