Foliar application of surfactant-stabilized nanoscale zero-valent iron inhibits fluoranthene accumulation and alleviates phytotoxicity in tomato

To inhibit the uptake and accumulation of fluoranthene (Flu) in tomatoes cultivated in Flu-contaminated soil, foliar application of nanoscale zero-valent iron (nZVI) was employed. The dispersion stability of nZVI was optimized by screening surfactant types (IGEPAL ® CA-720, HPCD, APG, Brij-35) and concentrations (0.1–1 g/L), followed by evaluating the inhibitory effects of nZVI at varying concentrations (0.1–1 g/L) on Flu accumulation, growth, and physiological parameters in tomatoes. The results showed that 0.5 g/L IGEPAL ® CA-720 was the optimal dispersant, which reduced the average particle size of nZVI to 150 nm, with a Zeta potential of −26.8 mV and a 24 h total iron retention rate of 92%. On this basis, spraying 0.5 g/L nZVI (Tn3 treatment) exhibited the best inhibitory effect. A surfactant-only control (Ts: Flu-contaminated soil +0.5 g/L IGEPAL ® CA-720) was added to distinguish component effects. Compared with the sole Flu contaminated treatment (T), this control only slightly reduced Flu accumulation, by 8.2% in shoots and 6.2% in roots, and alleviated growth inhibition, with an 11.4% increase in plant height and an 11.3% increase in shoot fresh weight. In contrast, Tn3 treatment significantly outperformed Ts. Compared with the T treatment, the Flu contents in shoots and roots of tomatoes in Tn3 treatment decreased by 62.4 and 30.7%, respectively, while the bioconcentration factor (BCF) and translocation factor (TF) decreased by 38.9 and 46.1%, respectively. Meanwhile, Tn3 treatment significantly alleviated the inhibition of Flu stress on tomato growth: plant height and biomass increased by 36.4 and 61.3% compared with T treatment, recovering to 85.7 and 79.8% of those in the uncontaminated treatment (CK). The activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and the content of malondialdehyde (MDA) in Tn3 treatment significantly decreased by 31.2–35.1 and 41.2% compared with T treatment. This study demonstrates that foliar application of 0.5 g/L nZVI dispersed with 0.5 g/L IGEPAL ® CA-720 effectively inhibits Flu accumulation and mitigates stress damage in tomatoes, providing a practical strategy for crop safety in contaminated soils.