A novel liquid-phase passivator for cadmium immobilization in acidic and alkaline soils: Chemical and microbial mechanisms for reducing cadmium accumulation in wheat

Cadmium (Cd) contamination in agricultural soils severely threatens global food safety and human health. Conventional solid-phase passivators for Cd remediation face limitations in pH adaptability, complex preparation, and field-scale application. This study introduces a novel strategy using liquid-phase 3-mercaptopropyltrimethoxysilane (L-MPTMS) as a passivator for in situ Cd immobilization in wheat systems. Through soil incubation and pot experiments across six geographically diverse acidic and alkaline soils (pH 5.20–7.64), L-MPTMS (0.025–0.2 % wt) significantly reduced Cd bioavailability (9.01–65.6 %) and Cd accumulation in wheat roots (11.3–70.2 %) and shoots (11.7–67.6 %), while enhancing manganese (Mn) uptake in roots (14.3–40.9 %) and boosting wheat biomass by 5.83–16.9 %. Mechanistic analyses (FTIR, XPS, and DFT) revealed that L-MPTMS immobilized Cd primarily via strong complexation between Cd 2+ and mercapto (-SH) groups, forming stable monodentate (Cd S) and bidentate (S-Cd-S) complexes. Furthermore, L-MPTMS optimized the soil bacterial community structure, enriching Cd-immobilizing bacteria (e.g., Devosia ) and plant growth-promoting rhizobacteria (e.g., Bradyrhizobium ), while enhancing metabolic functions and improving soil ecological health without compromising wheat growth. Crucially, field validation demonstrated dose-dependent reductions in wheat grain Cd (42.5–56.2 %), with 0.2 % L-MPTMS achieving grain Cd levels compliant with China's food safety standards (0.10 mg kg −1 ). This study establishes L-MPTMS as a highly effective and practical liquid-phase passivation strategy for in situ Cd immobilization in wheat systems across variable soil pH. Its unique integration of chemisorption, micronutrient bioavailability modulation, and beneficial microbiome regulation significantly reduced Cd transfer within the soil-plant continuum, ensuring food safety production and enhancing soil ecological health in Cd-contaminated agroecosystems. • L-MPTMS was applied as a liquid-phase passivator to inhibit Cd accumulation in wheat. • L-MPTMS passivated Cd by forming Cd S and S-Cd-S complex structures. • L-MPTMS decreased the availability of Cd by 9.01–65.6 % in acidic and alkaline soils. • L-MPTMS promoted the abundance of Cd-immobilizing bacteria and plant growth-promoting rhizobacteria. • L-MPTMS elevated Mn accumulation in root and reduced Cd accumulation in wheat grains.