Combined use of passivators and water management strategies for the safe production of water spinach in Cd and Cd-As contaminated farmland

Soil contamination with cadmium (Cd) and arsenic (As) poses serious threats to food safety. While water management and passivators can reduce the bioavailability of Cd and As, the material cost of passivators remains a constraint for large-scale remediation. This study investigated the combined use of water management and industrial by-product-based passivators to mitigate Cd and As accumulation in water spinach ( Ipomoea aquatica ) through field and pot experiments. Field results showed that combining passivators with continuous flooding conditions was the most effective approach, with the FM passivator (ferrous sulfate mineral and manganese slag) performing best. FM application increased shoot biomass by 35.28% and reduced Cd content in stems and leaves by 26.22% and 73.31%, respectively. However, alternating wet and dry conditions increased Cd bioavailability safety risks. Pot experiments confirmed that flooding conditions combined with passivators significantly improved plant growth. FM was the most effective passivators, reducing available As in soil by 40.46%, and decreasing Cd and As in shoots by 38.37% and 56.56–75.59%, respectively—ensuring compliance with Chinese food safety standards (GB 2762-2022). FM also promoted iron plaque formation on root surfaces, serving as a barrier to Cd and As translocation. The health risk index associated with consuming water spinach was reduced from 1.76 to 0.59 following FM treatment. These findings demonstrate that FM combined with flooding conditions offers an efficient, cost-effective strategy for remediating Cd or Cd–As co-contaminated soils. This approach supports safe vegetable production using industrial by-products, addressing both environmental and food security challenges. • FM (ferrous sulfate mineral + manganese slag) enhances iron film formation, reducing Cd-As uptake. • Synergistic use of FM passivator and flooding ensures safe production of water spinach in Cd-As soil. • FM can reduce the health risk index (HI) from eating Cd-As contaminated water spinach. • Industrial by-products (FM) offer a cost-effective remediation strategy for Cd-As farmland.