Stoichiometric insights into heavy metal phytoremediation by two aquatic macrophytes: Comparative evaluation of <i>Pontederia crassipes</i> and <i>Actinoscirpus grossus</i>

Aquatic macrophytes are increasingly explored for their potential in remediating wetlands contaminated with heavy metals (potentially toxic elements: PTEs), yet the biochemical determinants of their adsorption efficiency remain poorly understood. Present study investigates the phytoremediation potential of Actinoscirpus grossus and Pontederia crassipes by linking organ-specific distributions of total organic carbon (TOC) and total nitrogen (TN) with PTEs uptake. The sediment and plant samples were collected from polluted aquatic environments, followed by elemental analysis using WD-XRF and inductively coupled plasma mass spectrometry (ICP-MS). Plant organs (roots, stems, leaves, and flowers) were analyzed for TOC and TN using high-temperature combustion methods. Statistical analysis, including paired t-test, Wilcoxon’s signed-rank test, and Pearson’s correlation, were used to compare species differences and method agreement. Roots acted as the primary accumulation sites, accounting for approximately 20–30% higher concentrations of Zn, Cu, Pb, and Cd compared to aerial tissues. The Pontederia crassipes favored phytostabilization, particularly for Pb and Cu, whereas Actinoscirpus grossus showed enhanced uptake of Cr, Ni, and Co, indicating stronger phytoextraction potential. Actinoscirpus grossus also exhibited consistently higher TOC and TN across plant organs, suggesting greater metabolic flexibility and biosorption capacity. The C/N ratio demonstrated clear organ-level differentiation, with highest values in flowers (≈21–28) and lowest in roots (≈7–10), reflecting structural versus metabolic allocation strategies. Bland–Altman’s analysis confirmed good agreement between TOC and TN estimation approaches. Overall findings suggest that stoichiometric balance (TOC-TN) is closely associated with PTE uptake behavior, and that combining species with complementary functional traits can enhance the efficiency of phytoremediation systems in contaminated aquatic environments.