Study On Phytoremediation Efficiency Of Beet-grasses Intercropping In The Polycyclic Aromatic Hydrocarbons(PAHs)-Contaminated Soil

Polycyclic aromatic hydrocarbons(PAHs) is one of the widely existed persistent organic polluants(POPs) in the environment. Because of their bioaccumulation, persistent long-distance migration and hydrophobic, more than 90% of the PAHs reside in soil.Therefore, the remediation of PAHs-contamiaated soil has been the subject of intense research.Phytoremediation is a promising approach to soi1 remediation for its environmentally friendly,low investment and low cost compared to other approaches. Compared to single cropping,intercropping has more advantages in plant growth and phytoremeadation of polluted soil.Phenanthrene, Fluoranthene, Pyrene and Benzo(a)pyrene were selectd as the representative of PAHs. Firstly, a rapid method for the determination of the 4 primary PAHs in soil is presented.And then pot experiments were conducted to investigate the mechanisms of the removal and remediation efficiencies of PAHs under intercropping planting models using four plant species, cash crops( beet) and gramineae( ryegrass、sudangrass and vetiver grass)in a greenhouse.(1) Samples were extracted by Qu ECh ERS assisted by sonication with acetonitrile and centrifugation of the extraction, the supernatant was concentrated and filtrated through a 0.20μm filter before analysis by GC-MS. The effects of various operational parameters on the performance of Qu ECh ERS procedure were carefully investigated.The comparison of this method and the conventional Soxhlet extraction(SE) has been carried out. Under the optimized conditions, the four PAHs were separated well, and the limit of detection of the method ranged from 0.27 μg·kg-1to 0.49 μg·kg-1. The proposed method exhibited good relative standard deviation from 2.8% to 8.6%(n=7) and recovery from 81.9% to 116.3%.The Qu ECh ERS extraction efficiency is equivalent to that of SE. The proposed analytical method was applied to determine PAHs levels in soil samples collected from typical sewage irrigation areas in Henan and Beijing. The 4 PAHs were all detected in the samples. This method proved to be rapid, sensitive, environmental protection and so on, and could be more suitable to determine of Phenanthrene, Fluoranthene, Pyrene and Benzo(a) pyrene in soil.(2) The phytoremediation experimental period was 180 days and two harvests. Plants grew normal at initial concentrations of Phenanthrene 101.23±6.63 mg·kg-1 、Fluoranthene99.79±4.21 mg·kg-1,Pyrene 105.41±4.59 mg·kg-1and Benzo(a)pyrene 50.12±7.75 mg·kg-1. All planted treatments had significantly higher PAHs removal efficiency compared with those of unplanted control after phytoremediation. The efficiency of beet-grasses intercropping remediation were better than that of single cropping remediation with a higher removal rate:beet-ryegrass 84.85%, beet-sudangrass 79.96%, beet- vetiver grass 84.11%.The beet could be grown even better that intercropping with remediation plants in contaminated soil.Under the same condition, order of the 4 PAHs degradation rate is Phenanthrene> Fluoranthene>Pyrene>Benzo(a)pyrene.And Benzo(a)pyrene degradation rate was significantly lower than other three kinds of pollutants.(3) In different planting patterns,the PAHs concentration of all plants showed root>shoot. Beet-ryegrass, beet-sudangrass and beet- vetiver grass planting patterns could make PAHs concentration decreased at different degrees when contrasted with those of monoculture treatments.(4) Under the stimulating of the plants, bacteria, fungi and actinomycetes numbers significantly increased. After the first plants harvested, the order of magnitudes of them were5.6~8.6×106CFU·g-1, 13.7~21.3×104CFU·g-1, 6.2~8.5×105CFU·g-1.Increased 2.2~3.4times,4.4~6.3 times,1.2~1.7 times compared with controls, respectively. After the second plants harvested, the microbe number had a higher increase(P<0.05). Overall,microbe number in the intercropping system was significantly higher than it in the single culture. Plants increased the activities of soil polyphenol oxidase and catalase.The two enzyme activity in intercropping system had a higher rate in the range of 4.37%~43.07% than in single-cropping system. Catalase was relatively more sensitive to soil pollution than polyphenol oxidase.