A new perspective on wastewater phytoremediation: pH-driven cadmium removal by Atriplex halimus L

Phytoremediation using halophytes provides a sustainable, low-cost method for removing heavy metals from saline-contaminated water. However, the influence of pH on cadmium (Cd) uptake is unclear. This study investigates the combined effects of pH and salinity on Cd uptake and phytoremediation efficiency in the halophyte Atriplex halimus L. A hydroponic experiment was conducted with three pH levels (5.5, 7.0, and 8.5) and two irrigation types (tap and saline water at 20 dS m-1), using 40 µg Cd L-1. Results showed that saline irrigation enhanced plant growth, root development, and Cd accumulation, especially under acidic conditions. The highest Cd removal (39.1%), shoot Cd uptake (10.53 μg plant-1), bioconcentration factor (4.88), and translocation factor (1.18) were observed under saline-acidic conditions, indicating enhanced Cd uptake and efficient translocation to shoots. In contrast, alkaline pH reduced Cd uptake, likely due to decreased exudation of low molecular weight organic acids (citrate, malate, oxalate). Physiological responses, including increased proline and reduced chlorophyll, reflected stress induced by Cd and salinity effects. These findings highlight the importance of pH and root exudates in enhancing halophyte-based phytoremediation and support the use of A. halimus in treating saline wastewater and reclaiming marginal water resources.