Zn species mediates PFOA fate and toxicity in an alfalfa-soil system

Agricultural soil contamination by perfluorooctanoic acid (PFOA) is of high concern for alfalfa (Medicago sativa L.) cultivation, a primary feedstock for dairy cattle Zinc-based nanoagrochemicals are increasingly applied to enhance crop performance, yet how zinc speciation (ionic Zn²⁺ versus ZnO nanoparticles, ZnO NPs) modifies PFAS fate and phytotoxicity remains unclear. Here, the partitioning of PFOA and plant responses in an alfalfa-soil system amended with PFOA (1 mg/kg) under co-exposure to Zn²⁺ or ZnO NPs (10-100 mg Zn/kg; molar-equivalent dosing) was quantified. The PFOA levels in roots, shoots, and soil, translocation and bioaccumulation indices studied. Further, the dynamics of oxidative stress responses (CAT, APX, POD, SOD) alongside biomass and pigment endpoints were assessed. Ionic Zn²⁺ consistently amplified plant stress, producing strong reductions in root and shoot biomass and chlorophyll and markedly elevating antioxidant enzyme activities. At lowest Zn dose, the uptake of PFOA in shoots increased up to 5 folds compared to ZnO NPs effect. Overall, ZnO NPs enhanced soil retention of PFOA up to 0.09 mg/kg and reduced overall plant bioconcentration at low-to-moderate doses, partially preserving biomass and chlorophyll; however, intermediate ZnO NP concentrations yielded a pronounced increase in root-to-shoot translocation, consistent with partial dissolution and rhizosphere-mediated transformations. These findings identify zinc speciation as a dominant control on PFOA mobility, soil retention, and phytotoxic outcomes in forage-based agroecosystems and demonstrate that nano-enabled amendments can reduce PFOA bioavailability while introducing concentration-dependent transport pathways that warrant explicit consideration in risk assessment and management.