Enhanced phytoremediation of Cd- phenanthrene co-contaminated soil through the combined application of electric field and chemical additives.

Electric fields and chemical additives can enhance phytoremediation, but their synergistic mechanisms in cadmium (Cd)-phenanthrene (PHE) co-contaminated soils remain unclear. Here, a greenhouse pot experiment was conducted to investigate the combined effects of a direct‑current electric field and chemical additives (citric acid + ammonium nitrate) on the phytoremediation of Cd-PHE co‑contaminated soil using marigold (Tagetes patula L.). The combined treatment (Phy‑CN‑EK) achieved the highest PHE removal (82.3%) and total shoot Cd uptake (41.443 μg pot-1), and simultaneously increased the relative abundance of potential PHE-degrading functional bacteria such as Pseudomonas and Saccharimonadaceae. The results suggested that the chemical additives accelerated the initial oxidative degradation of PHE, while the electric field subsequently promoted the complete mineralization of its intermediates. For Cd uptake, the chemical additives directly enhanced phytoextraction but indirectly suppressed it via a shift toward Pseudomonas dominance; conversely, the electric field promoted Cd uptake by enhancing plant biomass and facilitating intermediate mineralization, thereby counteracting the microbial-driven suppression. Their integration achieved synergistic enhancement of both PHE degradation and Cd phytoextraction. These findings deepen the understanding of the combined enhancement mechanisms in phytoremediation of Cd-PAH co-contaminated soils and provide a mechanistic basis for future field-scale validation and optimization.