title: Degradation of 2,4-D in soils by Fe₃O₄ nanoparticles combined with stimulating indigenous microbes.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Resources and Environment, Anhui Agricultural University, Hefei 230036, China.
authors.forename: Guodong
authors.initials: G
authors.lastname: Fang
authors.forename: Youbin
authors.initials: Y
authors.lastname: Si
authors.forename: Chao
authors.initials: C
authors.lastname: Tian
authors.forename: Gangya
authors.initials: G
authors.lastname: Zhang
authors.forename: Dongmei
authors.initials: D
authors.lastname: Zhou
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D000135:Acid Phosphatase / Q000378:metabolism; D000681:Amylases / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D055598:Chemical Phenomena; D052918:Environmental Restoration and Remediation / Q000379:methods*; D005656:Fungal Proteins / Q000378:metabolism; D005658:Fungi / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development; D006207:Half-Life; D006540:Herbicides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D058185:Magnetite Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D014510:Urease / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D005656:Fungal Proteins; D006540:Herbicides; D058185:Magnetite Nanoparticles; D012987:Soil; D012989:Soil Pollutants; D015084:2,4-Dichlorophenoxyacetic Acid; D002374:Catalase; D000135:Acid Phosphatase; D000681:Amylases; D014510:Urease