Shiraz University Iran Agricultural Research 1013-9885 45 2 2026 07 01 Evaluating the efficiency of assisted treatments in the phytoremediation of multi metal-contaminated soil using Response Surface Methodology optimization approach 27 35 8796 10.22099/iar.2026.55708.1741 EN Ava Mohrazi Department of Soil Science, School of Agriculture, Shiraz university, Shiraz, I. R. Iran Reza Ghasemi-Fasaei Department of Soil Science, School of Agriculture, Shiraz university, Shiraz, I. R. Iran Journal Article 2026 02 19 Phytoremediation is a green, economic, and efficient tool for remediating soils contaminated with heavy metals. The present experiment was conducted to investigate the effect of growth regulator (GR) treatments (gibberellic acid (GA₃) and indole acetic acid (IAA)), biological treatments (<em>Thiobacillus</em> and <em>Bacillus subtilis</em>), and chemical treatments (nitrilotriacetic acid (NTA) and ethylene glycol tetraacetic acid (EGTA)) on the phytoremediation efficiency of zinc (Zn), cadmium (Cd), and nickel (Ni) using response surface methodology (RSM). The optimal chelate, bacterial strain, and GR for maximizing the translocation factor (TF) of Cd were NTA, <em>Thiobacillus</em>, and GA3, respectively. For the phytoremediation of Zn, the optimal combination was NTA, <em>Thiobacillus</em>, and IAA. For Ni, the highest TF was achieved without chelate, while using <em>Thiobacillus</em> and GA₃. Based on the TF values, the mechanisms governing metal uptake and translocation in maize appear to differ among metals and treatments. For example, the application of NTA increased the TF of Zn to above 1, indicating enhanced phytoextraction, whereas EGTA promoted Zn retention in the roots, reflecting phytostabilization. In the case of Cd, GA₃ enhanced metal accumulation in the shoots. Regarding Zn, IAA was more effective in promoting shoot accumulation. These findings demonstrate that individual metals exhibit distinct responses even within the same plant and under identical experimental conditions, highlighting the need for metal-specific assisted treatments to optimize phytoremediation. https://iar.shirazu.ac.ir/article_8796_f371303e1caf3502d4747f4e82203b48.pdf