Enhancing Phytoremediation of Heavy Metal-Contaminated Aridic Soil Using Olive Mill Wastewater, Sulfur, and Chelating Agents

Soil contamination with heavy metals (HMs) poses a significant environmental threat. Phytoremediation, a sustainable and eco-friendly emerging bioremediation approach, utilizes plants to remove, immobilize, or stabilize soil contaminants. This study examines the interactive effects of sulfur (S), ethylenediaminetetraacetic acid (EDTA), and olive mill wastewater (OMW) on HM uptake and the growth of maize (Zea mays L.) and mustard (Brassica juncea). Mustard exhibited superior dry matter (DM) yield (2.4 g/pot with 5% OMW), nutrient uptake, and tolerance to metal toxicity. The translocation factor (TF) and bioaccumulation factor (BF) for maize and mustard plants vary significantly with different treatments. For maize, the S 2T/ha treatment achieved the highest TF and BF for cadmium (Cd), while 5% OMW led to maximum chromium (Cr) and manganese (Mn) uptake. In mustard, 5% OMW treatment resulted in the greatest bioconcentration factor (BCF) for cadmium (Cd), lead (Pb), and zinc (Zn), whereas sulfur application yielded the highest TF for Cd. The 5% OMW treatment overall enhanced HM uptake most significantly. Lower sulfur application rate (1 ton/hectare) increased the availability Cd and Pb, boosting plant growth and nutrient uptake. For instance, 1 ton/hectare of sulfur elevated Cd availability to 24.102 mg·kg−1 in maize and 58.705 mg·kg−1 in mustard. EDTA treatments further improved metal bioavailability, increasing Cd levels in maize (10.09 mg·kg−1) and mustard (7.78 mg·kg−1). Mustard’s superior tolerance and nutrient efficiency identify it as a promising candidate for phytoremediation of HM-contaminated soils in arid regions. Innovative treatments with sulfur, EDTA, and olive mill wastewater significantly enhance soil decontamination and plant growth.