Crop rotation-based phytoremediation of metal(loid)s in contaminated farmlands: integrative mechanisms, risk boundaries, and implementation strategies

Crop rotation-based phytoremediation offers an agronomically compatible strategy for integrating contaminant removal, soil recovery, exposure control, and continued production in contaminated farmland. Conventional engineering remediation is costly and disruptive, whereas monoculture phytoremediation is limited by low removal efficiency and long treatment periods. This review conceptualizes crop rotation as a full-cycle remediation and risk-management framework linking mobilization, extraction, stabilization, safe production, and contaminated biomass management. Rotation systems are grouped into hyperaccumulator-, energy-crop-, legume/green-manure-, and economic crop-assisted modes according to dominant functions and agronomic endpoints. Evidence indicates that extraction-oriented rotations can increase cumulative metal(loid) removal and gradually reduce soil metal(loid) accumulation, but may enlarge labile pools and uptake risks for subsequent crops. In contrast, stabilization- and production-oriented rotations better reduce metal(loid) accumulation in edible tissues and maintain production, although total soil depletion remains limited. These outcomes are governed by element-specific behavior, soil properties, water management, rhizosphere and microbial processes, legacy effects, and biomass fate. Field implementation remains constrained by low removal fluxes, site heterogeneity, cross-season risks, and contaminated biomass management. Future research should prioritize multi-cycle field validation, standardized indicators, element- and site-specific design, and closed-loop biomass management. Rotation performance should be evaluated over complete cycles using soil, crop-safety, removal-flux, and biomass-pathway indicators.