Impact of tire particles and tire leachate contaminants on plant physiology and soil health: Case study in mung bean and tomato

Tire particles and their associated leachates represent emerging microplastic pollution of growing concern. The accumulation of tire-derived pollutants beside road agricultural systems remains poorly characterized, yet species-specific responses to these pollutants also remain poorly understood. This study investigated the differential impacts of tire particles and tire leachate on germination, plant growth, photosynthetic function, and oxidative stress response in two ecologically important crops. Mung bean (Vigna radiata) and tomato (Solanum lycopersicum) were exposed to tire particles (0.1, 1, and 10 g/kg) and tire leachate (10 %, 20 % and 30 %) in soil medium under controlled greenhouse conditions. The tomato plant exhibited superior resistance, mounting a robust, induced superoxide dismutase (SOD) response that successfully mitigated systemic stress and maintained growth. Tire leachate exposure in mung beans causes high Molondialdegyde (MDA) accumulation and significant chlorophyll degradation. This damage coincided with the signifying failure of the antioxidant defense system. Tire-leachate significantly alters soil dynamics, increasing available nitrogen in mung bean soil while causing phosphorus immobilization in tomato soil, demonstrating complex tire-derived contaminant soil-plant interactions. Principal components analysis (PCA) shows a distinct metabolic fingerprint for each treatment, inducing fundamental biochemical reorganization in both species. This study demonstrates that tire contamination effects are highly species-dependent, with mung bean roots being sensitive and inhibition, while tomato growth remained stable, despite clear internal stress. The findings highlight that the highly bioavailable leachate fraction poses the most acute threat to plant health and underscore the critical need for species-specific risk assessment for tire-derived contamination.