The impact of phosphorus on the migration of cadmium in vetiver-submerged media contaminated with cadmium combined sulfamethoxazole

A greenhouse pot experiment simulated submerged conditions with gradient phosphorus additions. The study measured vetiver biomass and Cadmium (Cd) speciation in roots, stems, leaves, and submerged soil under single Cd and Cadmium-Sulfamethoxazole (Cd-SMX) composite pollution. Dynamic changes in Cd speciation and translocation coefficients were analyzed, and vetiver growth parameters were calculated using logistic regression. 1. The addition of 400 mg·L−1 phosphorus significantly promoted the biomass growth of vetiver stems and leaves and increased the proportion of phosphate-bound Cd (CdHAc) in roots, stems, and leaves. This treatment also notably enhanced the translocation of pectate-bound Cd (CdNaCl) and CdHAc to stems and leaves. 2. Cd2+ entering wetland water partially remains free and dissolved, while some bind with phosphate (PO₄3−) to form Cd2+-PO43− complexes or associates with soil at the water-sediment interface. Under redox conditions, it mainly migrates into vetiver roots as acid-soluble Cd (CdHOAc). Within the roots, part of Cd2+ binds with phytochelatins, accumulating as oxalate Cd (CdHCl) and residual Cd (CdResidual); the rest translocates to shoots as CdHAc, further accumulating as CdHCl and CdResidual to reduce toxicity. This study reveals that under Cd–SMX stress, vetiver enhances shoot biomass via phosphorus uptake and promotes Cd translocation as CdHAc from roots to shoots.