Remediation of Cd-polluted soil, improving Brassica napus L. growth and soil health with Hardystonite synthesized with zeolite, limestone, and green Zinc oxide nanoparticles

Acidic laterite may exhibit high cadmium (Cd) bioavailability and thus can cause potential environmental and human health hazards. We investigated the soil addition of zeolite (Ze), limestone (LS), and green synthesized zinc oxide nanoparticles (G-ZNPs) as sole soil additives, their mixture (LZ-Zn) and synthesized hardystonite {(S-Hyd), produced by calcination of all three additives}, to reduce Cd uptake and mitigate oxidative stress in Brassica napus L. (B. napus). Synthesis of hardystonite (S-Hyd) was confirmed by SEM, EDS, FTIR, and XRD and showed superior results than other additives for improving various parameters of plants and soil. Porous structure, larger surface area, alkaline properties, different functional groups (-OH, CO32−, Zn–O), and mineral crystals (cristobalite, calcite, zincite, and hardystonite) in S-Hyd facilitated Cd adsorption, reducing DTPA-Cd by 50%, compared to sole Cd polluted soil. S-Hyd enhanced soil enzymes and notably reduced Cd concentrations in plant roots and shoots by 59% and 78%, respectively, thereby decreasing the expression of Cd transport-related genes in plants. Interestingly, S-Hyd enhanced antioxidative defense, bioactive compounds, and photosynthetic pigments while lowering oxidative stress at molecular and physiological levels of plants. Economic comparison revealed that using S-Hyd was 87.0% more cost-effective than naturally occurring hardystonite (Hyd) to remediate Cd-polluted soil.