Nano-enhanced bioremediation of soil co-contaminated with petroleum hydrocarbons and cadmium using Helianthus annuus L. plants
Simultaneously removing petroleum hydrocarbons (PHCs) and heavy metals from soil is a challenging task. This study aimed to evaluate the efficacy of green-synthesized nano zero-valent iron (nZVI) particles and a microbial consortium in combination with sunflower ( Helianthus annuus L.) plants for nano-enhanced bioremediation of soil co-contaminated with PHCs and cadmium (Cd). A pot trial was conducted by growing sunflower plants on soil co-contaminated with 6000 mg kg -1 and 30 mg kg -1 of PHCs and Cd, respectively, and nZVI particles and a microbial consortium were added to the soil for plant growth enhancement and pollutants removal. The results revealed that the co-contaminated soil caused significant phytotoxicity to sunflower plants. However, the co-application of a microbial consortium and nZVI particles considerably alleviated the phytotoxic impacts of Cd and PHCs on sunflower plants, demonstrating up to 72.7% and 83.5% improvements in plant physiology and growth in contaminated soil, respectively compared to the respective unamended control. Furthermore, the combined application of a microbial consortium and nZVI particles caused 59.4% and 58.6% reduction in bioavailable Cd, and 82.7% and 74.7% decrease in PHCs in planted and unplanted treatments, respectively, with respect to their initially applied concentrations. The findings from this study indicate that the integrated application of nZVI particles and a microbial consortium was very effective in improving plant growth, mitigating Cd-accumulation in plants, confirming Cd-immobilization, and removing PHCs from soil, highlighting the potential of nano-enhanced bioremediation as a sustainable solution for the treatment and management of soil co-contaminated with inorganic and organic pollutants.