Fe Removal by Pistia stratiotes Under Mixed-Metal Conditions: Evaluating Ionic Competition During Phytoremediation

Abstract

Heavy metal contamination in industrial wastewater generally occurs as mixtures of several metals, whereas phytoremediation studies have predominantly evaluated metal removal under single-metal conditions. Consequently, the influence of coexisting metals on Fe removal remains insufficiently understood. This study investigated the effect of mixed-metal systems on Fe removal by Pistia stratiotes and examined the potential occurrence of ionic interactions during phytoremediation. Batch experiments were conducted for six days using single-metal (Fe) and mixed-metal (Fe–Mn–Co) systems. Fe concentrations were determined by ICP–OES, root morphology and elemental composition were characterized by SEM–EDX, and the data were evaluated using Kruskal–Wallis and Spearman's rank correlation analyses. P. stratiotes maintained Fe removal efficiencies exceeding 99% in all treatments. SEM–EDX analysis confirmed the accumulation of Fe, Mn, and Co in the roots, while the porous root morphology provided potential sites for metal adsorption. Statistical analysis indicated that the addition of Mn and Co did not significantly affect Fe removal efficiency (p = 0.321), whereas Spearman's rank analysis revealed a weak and non-significant negative correlation between the number of coexisting metals and Fe removal efficiency (r = −0.293, p = 0.482). These findings suggest that the concentrations of Mn and Co investigated were insufficient to substantially interfere with Fe removal because P. stratiotes maintained effective metal homeostasis through regulated uptake and intracellular detoxification. This study contributes to a better understanding of phytoremediation performance under multi-metal conditions and provides relevant information for the application of aquatic plants in industrial wastewater treatment.