Indole-3-Acetic Acid and Humic Acid Increase the Bio-Degradation of Diesel Oil in Soil Polluted with Pb and Cd

Introduction: Soil remediation is one of the most important fields in environmental studies. This study was conducted to investigate the effect of indole-3-acetic acid (IAA) and humic acid (HA) on increasing the bio-degradation of diesel oil in soil polluted with (lead) Pb and cadmium (Cd). Materials and Methods: Treatments included foliar application of IAA (0 (control) and 30 ppm) and soil application of HA (0 (control) and 200 mg/kg soil) in the soil contaminated with Cd (0 (control), 10 and 15 mg/kg soil), Pb (0 (control) and 1600 mg/kg soil), and diesel oil (0 (control), and 8% (W/W)). The sunflower was planted in all soil samples. The plants were harvested after 70 days and Pb and Cd concentrations of plants were measured using Atomic Absorption Spectroscopy. Results: Foliar application of IAA at the rate of 30 mg/l significantly increased the Cd and Pb phytoremediation by 14.8% and 13.4%, respectively. For HA application, it was increased by 11.3% and 10.2%, respectively.  A significant increase was found in degradation percentage of diesel oil in soil by 12.6%, when the soil was treated with 200 mg HA/kg soil. Conclusion: It can be concluded that application of organic amendments such as IAA or HA can be a suitable way for increasing plant growth and increasing plant phytoremediation efficiency, especially in the soil contaminated with diesel oil. However, the phytoremediation efficiency is dependent on the plant physiology and the type of soil pollution that should be considered.