Soil Responses to Nano-enhanced Bioremediation Techniques: Comparative Analysis of Bio-based Vermicompost, Fe3O4 Nanoparticles, and Their Novel Synergistic Effects against Phthalate Contamination

Phthalate esters' toxicity, bioaccumulation, and food safety challenges have drawn increased attention to their effects on soil health. This study aimed to improve the agricultural soil health under Di(2-ethylhexyl) phthalate (DEHP) stress by comparing vermicompost, vermicompost assisted by Fe ₃ O ₄ NPs, and Fe ₃ O ₄ nano-enhanced remediating techniques. The randomized complete block design (RCBD) was set to evaluate soil responses. There was a significant difference between the final removal efficiencies (RE, %) of all three amended groups with the control (P-value < 0.0001) and compared to each other (P-value < 0.0001; R ²  = 0.99). After 42 days, the removal efficiency was significantly higher in the mixed amended soil with vermicompost and Fe ₃ O ₄ NPs (RE = 94.58%) compared to the soil assisted by Fe ₃ O ₄ NPs (RE = 80.90%) and vermicompost (RE = 69.34%) (P-value < 0.05). The final C:N ratio in the vermicompost-consisted treatments was in the range of 10.24–13.16. The ultimate rate of nutrient decomposition in the S ₁ VN treatment (DEHP concentration = 10 mg.kg ^− 1 (dw. soil), Fe ₃ O ₄ NPs dose = 1.2 gr.kg ^− 1 (media)) with synergistic efficiency followed this order: AP (81.25%) > SOM (43.64%) > TC (36.33%) > TN (32.09%) > EK (26.76%). The five dominant DEHP-degradation bacteria in S ₁ VN were found to be Bacillus licheniformis , Bacillus subtilis , Pseudomonas stutzeri , Microbacterium hibisci , and Bacillus aerius . Following the DEHP breakdown, the Bacillus and Pseudomonas taxa demonstrated the function of phosphate-solubilizing bacteria (PSB) in phosphorus availability. These findings suggest the use of Fe ₃ O ₄ NPs-enhanced vermicompost as an ecofriendly remediation strategy for supporting soil health, nutrients, and microbial population.