Alleviating Pb Toxicity in Rice-Soil Systems by GSNO-Encapsulated Chitosan-Biochar/S-nZVI Composites: Sustained...

Lead (Pb) accumulation in paddy soils promotes its transfer to rice grains, posing persistent risks to food safety and human health. Here, we developed a GSNO-encapsulated chitosan-biochar-supported sulfidized nanoscale zero-valent iron composite (GSNO-CS@S-nZVI/BC) to integrate sustained nitric oxide (NO) delivery with Pb immobilization in rice-soil systems. The novelty of this strategy lies in coupling a biocompatible NO donor with a Pb-reactive CS@S-nZVI/BC matrix to simultaneously alleviate Pb-induced physiological stress in rice and suppress Pb migration from soil to edible grains. In hydroponic experiments, Pb exposure reduced rice fresh weight, dry weight, and chlorophyll levels by 71.2%, 55.6%, and 75.1%, respectively. Compared with Pb treatment alone, GSNO-CS@S-nZVI/BC increased rice dry weight and chlorophyll levels by 68.5% and 260%, respectively, while decreasing Pb concentrations in roots and shoots by 78.2% and 85.8%. In soil pot experiments, GSNO-CS@S-nZVI/BC reduced Pb concentrations in roots, shoots, panicles, and grains by 57.6%, 57.0%, 40.3%, and 64.3%, respectively. It also decreased the grain Pb bioconcentration factor by 80.7%, reduced the soil-to-root Pb translocation factor by 84.41%, and lowered the grain Pb bioconcentration factor to 0.043 ± 0.007. Mechanistically, GSNO-CS@S-nZVI/BC promoted root iron plaque formation by 176.1% and increased Pb adsorption by root iron plaque by 156.9%, while decreasing the oxidizable Pb fraction in soil by 11% and increasing the reducible Pb fraction by 10%. These results indicate that GSNO-CS@S-nZVI/BC mitigates Pb toxicity through sustained NO release, enhanced root iron plaque-mediated Pb sequestration, and soil Pb stabilization. Overall, this nano-enabled amendment provides a promising strategy for reducing Pb transfer from contaminated paddy soils to rice grains and improving the safe utilization of Pb-contaminated farmland.