Phytoremediation Potential of Two Hydrophytes Introduced to Egypt: Hydrocotyle umbellata L. and Salvinia auriculata Aubl.

Phytoremediation represents an eco-friendly and cost-effective approach for removing heavy metals from aquatic systems. This study evaluated the phytoremediation potential of Hydrocotyle umbellata L. and Salvinia auriculata Aubl. for copper (Cu), lead (Pb), zinc (Zn), and chromium (Cr) under two hydrological conditions, deep water (DW) and constructed wetlands (CW), in Egypt over a 12-month experimental period. Phytoremediation performance was assessed using rhizofiltration efficiency, translocation factor (TF), and bioaccumulation factor (BAF). Both species demonstrated substantial capacity to remediate the investigated metals, with an overall uptake pattern of Zn > Cu > Cr > Pb. Clear interspecific differences were observed in remediation strategies. Hydrocotyle umbellata exhibited strong rhizofiltration capacity, particularly for Zn and Cu, but limited metal translocation (TF < 1 for most metals), indicating a phytostabilization-dominated strategy. Metals were largely retained in the root system, a recognized tolerance mechanism that reduces toxicity in aerial tissues. In contrast, S. auriculata showed higher rhizofiltration, translocation (TF ≥ 1 for several metals), and bioaccumulation, reflecting a stronger phytoextraction potential, albeit with evidence of metal-induced growth inhibition. Seasonal variation significantly influenced metal removal, with spring showing the highest rhizofiltration and accumulation for most metals, particularly in S. auriculata. Growing H. umbellata in CW enhanced its rhizofiltration efficiency, whereas hydrological conditions had a lesser effect on S. auriculata. Overall, the findings highlight the complementary remediation roles of both species and emphasize the importance of species selection, hydrological setting, and seasonality in optimizing phytoremediation strategies for metal-contaminated waters.