Degradation of 2,4-D in soils by Fe3O 4 nanoparticles combined with stimulating indigenous microbes

PURPOSE: Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in soils by Fe3O4 nanoparticles combined with soil indigenous microbes was investigated, and the effects of Fe3O4 nanoparticles on soil microbial populations and enzyme activities were also studied. METHODS: The soils contaminated with 2,4-D were treated with Fe3O4 nanoparticles. The microbial populations and enzyme activities were analyzed by dilution plate method and chemical assay, respectively, and the concentration of 2,4-D in soil was determined by high-performance liquid chromatography (HPLC). RESULTS: The results indicated that Fe3O4 nanoparticles combined with soil indigenous microbes led to a higher degradation efficiency of 2,4-D than the treatments with Fe3O4 nanoparticles or indigenous microbes alone. The degradation of 2,4-D in soils followed the pseudo first-order kinetic. The half-lives of 2,4-D degradation (DT50) of the combined treatments were 0.9, 1.9 and 3.1 days in a Red soil, Vertisol and Alfisol, respectively, which implied that the DT50 of the combination treatments were significantly shorter than that of the treatments Fe3O4 nanoparticles or indigenous microbes alone. The effects of Fe3O4 nanoparticles on soil microbial populations and enzyme activities were also investigated and compared with the α-Fe2O3 nanoparticles. The results suggested that the α-Fe2O3 nanoparticles had only comparatively small effects on degradation of 2,4-D in soils, while the Fe3O4 nanoparticles not only degraded 2,4-D in soils but also increased the soil microbial populations and enzyme activities; the maximum increase in enzyme activities were 67.8% (amylase), 53.8% (acid phosphatase), 26.5% (catalase) and 38.0% (urease), compared with the untreated soil. Moreover, the introduction of Fe3O4 nanoparticles at the different dosage resulted in a variable degradation efficiency of 2,4-D in soil. CONCLUSION: The method of combining Fe3O4 nanoparticles with indigenous soil microbes may offer great benefits for the application of nanotechnology in remediation of herbicide contaminated soil.