Enhancing Soil Remediation: Integrated Mycobacterium and Barley (Hordeum Vulgare) Systems for Petroleum Hydrocarbons and Heavy Metals Restoration in Soils Near Shiraz Oil Refinery

Abstract

Industrial activities, particularly oil refining, release significant pollutants like TPH, PAHs, and heavy metals into the environment,  necessitating sustainable remediation strategies. Therefore, in this study we evaluated the synergistic potential of bioremediation  using Mycobacterium and phytoremediation with barley to remediate contaminated soils in Shiraz oil refinery, Iran. 36 soil samples were analyzed to isolate bioremediating mycobacteria using turbidometric, chromatographic, biochemical, and molecular assays.  Greenhouse experiments used soil spiked with PAHs (100–200 mg/kg)and heavy metals (As, Hg, Cd, Pb, Cr; 3–400 mg/kg) at low, medium, and high levels. Five phytoremediation(P),bioremediation(B), combined treatments include phytoremediation control, and bioremediation(MB), and sterile control, were assessed over 90 days, analyzing soil properties, contaminant levels, plant growth, TF, and BAF.13 Mycobacterium isolates (36.11%)representing nine species were identified. Key species such as M. gilvum and M. 
smegmatis achieved >60% degradation of both PAHs and heavy metals, while M. austroafricanum and M. vaccae showed superior PAH degradation (65–80%),with M. vaccae also achieving 75% heavy metal reduction. The MB treatment significantly outperformed the others, achieving 78–86% PAH degradation and 58–68% heavy metal removal (p< 0.001). Soil quality indicators improved notably: microbial biomass increased by 35%, pH rose from 5.8 to 6.8, organic matter increased from 2.0% to3.5%, and EC decreased from 1.5  to 1.0 dS/m. Barley biomass increased by 25%(roots)and 20% (shoots), with TF and BAF values ranging from 0.25 0.55. This study  demonstrates that integrated bioremediation using barley and Mycobacteria offers a sustainable strategy for restoring petroleum and heavy metal contaminated soils in industrial areas.