Sulfidated Nanoscale Zero-Valent Iron (S-nZVI) Facilitates Remediation and Safe Crop Production in Cr(VI) and Microplastics Co-contaminated Soil

Emerging Cr(VI)-microplastics (MPs) co-contamination in agricultural soil poses an increasing environmental and food safety risk, primarily due to their joint toxic effects on the soil–plant system (e.g., the “Trojan horse” effect). To address this issue, sulfidated nanoscale zerovalent iron (S-nZVI) is utilized as a remediation agent. S-nZVI possesses a metallic iron core that rapidly reduces Cr(VI) to Cr(III), while the surface layer contains high-density sites for attracting and absorbing MPs, resulting in larger aggregates and lowering their mobility and solubility in soil. Results show that the application of S-nZVI at 0.5 wt % achieves a Cr(VI) removal efficiency of over 98.74% for total Cr(VI) concentrations, as well as facilitates the transformation of 40% of Cr into the favorable Oxidizable and Residual fractions. Exemplified by lettuce planting, the pot experiment proves the greater toxicity of Cr(VI)-MPs co-contamination than individual contaminations, evidenced by the decreased plant biomass and elevated ROS levels. Conversely, lettuce grown in remediated soil keeps a well-developed growth, with Cr levels of 0.03–0.05 mg/g dry weight, and MPs not entering the body, reaching safe levels. In contaminated soils worldwide, these findings provide new insights into the application of nanoscale zerovalent iron technology for remediation and crop safety.