Green Solutions for Heavy Metal Pollution in the Aquatic Environment of the Nile Islands: Cues from some Submerged and Emergent Macrophytes

Abstract

The study evaluates the phytoremediation potential of five wild macrophytes ‒Setaria geminata (Forssk.) Veldkamp, Ceratophyllum demersum L., Myriophyllum spicatum L., Persicaria senegalensis (Meisn.) Soják, and Ludwigia adscendens subsp. diffusa (Forssk.) P.H. Raven‒ for iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) on the shore of two islands in Luxor governorate, Egypt: Armant (sites 1 and 2) and Aqalata (site 3). The study aimed to assess how site, season, and species influence heavy metal accumulation in plant organs, chlorophyll content, and antioxidant compounds; to evaluate phytoremediation efficiency using bioaccumulation factors; and to explore the relationship between heavy metals concentrations in shoots and the behavior of chlorophyll and antioxidants. Heavy metal concentrations in water at all three sites fell within the safe irrigation limits. However, Cu and Mn levels in sediments exceeded global freshwater recommendations during summer. Fe and Mn levels in submerged species (C. demersum and M. spicatum) and emergent species'belowground tissues (S. geminata, P. senegalensis, and L. adscendens) surpassed the permissable limits in most seasons. In contrast, Zn levels in all studied species remained within the acceptable limits, while Cu levels in S. geminata and P. senegalensis roots exceeded the permissible limits during spring and summer, respectively. The bioaccumulation factors (BAFs) for submerged species exceeded one for all metals, whereas emergent species showed BAFs greater than one only for Mn. Translocation factors (TFs) for all metals were less than one, except for Zn in P. senegalensis and L. adscendens. Chlorophyll pigments in S. geminata, M. spicatum and L. adscendens negatively correlated with most heavy metals in shoots, while a positive correlation was observed in C. demersum. Also, heavy metals in shoots negatively correlated with total phenolics and flavonoids, carotenoids and phenolics, and phenolics in C. demersum, M. spicatum and S. geminate, respectively. In contrast, L. adscendens exhibited a positive correlation between most of these elements and antioxidant compounds. The differential relationships between the studied heavy metals in shoots and chlorophyll/antioxidant compounds suggest species-specific energy allocation strategies. Our results highlight the potential of these species for phytoremediation in contaminated aquatic ecosystems, and indicate that submerged species are suitable for hyperaccumulation, while emergent macrophytes function as accumulators for Mn and excluders for Fe, Cu, and Zn.