Phytoremediation Potential of Selected Ornamental Woody Species to Heavy Metal Accumulation in Response to Long-Term Irrigation with Treated Wastewater

Arid and semiarid environments of Mediterranean countries suffer from scarcity of water resources, which limits their agriculture productivity. Using treated wastewater (TWW) is considered an alternative strategy for irrigation purposes in such areas. However, TWW contains substantial levels of heavy metals (HMs) and contaminants that pollute the environment and soil. The aim of this study is to evaluate the phytoremediation potential of six selected woody tree species under long-term irrigation with TWW. The concentration, bioaccumulation factor (BFC), translocation factor (TF), and comprehensive bioconcentration index (CBCI) of HMs were measured in the various parts (roots, bark, and leaves) of the studied tree species. The results show a general pattern of mineral accumulation in the roots and low translocation to the areal parts of various species. Cupressus sempervirens, which is a native species in Mediterranean environments, had higher TF values for Fe, Mn, Cu, Cr, Cd, and Pb metals in its areal parts compared to other tree species. The study shows that Ficus nitida has the potential to be a hyperaccumulator for Cd in its bark, with a TF value that exceeds 12. Deciduous trees species (Populus nigra and Robinia pseudoacacia) were found to have high TF values for Ni and Cd toward their areal parts, whereas a higher TF for Cr (1.21) was only found in P. nigra bark. Cupressus sempervirens had, significantly, the highest bark and leaf CBCI values (0.83 and 0.82, respectively), whereas Ficus nitida had the second-highest values in the bark and leaves (0.56 and 0.51, respectively). Therefore, Cupressus sempervirens and Ficus nitida are considered good hyperaccumulators for various HMs, and can be used for phytoremediation activities in polluted areas.