Effects Of Soil Fauna (Nematodes And Earthworms) On The Removal Of Polycyclic Aromatic Hydrocarbons (PAHs)from Contaminated Soil

With the rapid development of industry and agriculture, there are amounts of organic contaminants enter into the soil, which seriously affect the soil environmental quality and ecological function. Especially the POPs, PAHs and PCBs, of which there are different levels of output in soil in our country. As the PAHs toxicity and its amounts in soil seriously inhibit the crops growth, it reduces the quality of agricultural product. Moreover, it is also harmful to human health through the food chain enrichment transmission function. The PAHs pollution problem becomes the most serious environmental problems. The development of bioremediation research is conducive to the remediation of organic contaminated soil.Many researches have focused on the effects of soil fauna (nematodes and earthworms) on the bioremediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil because soil fauna were closely related to soil microorganisms and played key roles in bioremediating the contaminated soils. However, the inherent mechanisms of soil fauna in the bioremediation of the PAHs contaminated soils were still unclear. Therefore, we conducted a series of experiments to investigate the effects of soil fauna (nematodes and earthworms) on the bioremediation of PAHs contaminated soils. Our studies were mainly concentrated on:(1) Effects of bacterial-feeding nematodes and bacteria(Pseudomonas Putida) interactions, in the presence of glucose or not, on the degradation of phenanthrene in gnotobiotic system;(2) Effects of bacterial-feeding nematodes on phenanthrene removal from the contaminated soil;(3) Effects of earthworms and ryegrass interaction on the removal of fluoranthene from contaminated soil;(4) Effects of earthworm mucus on ryegrass growth and the removal of fluoranthene from hydroponic system.The main results were shown as following:(1) A gnotobiotic culture experiment was constructed to study the effects of bacterial-feeding nematodes and bacteria(Pseudomonas Putida) interactions on phenanthrene removal from the gnotobiotic system. Bacterial-feeding nematodes could promote the removal of phenanthrene from gnotobiotic system. Compared with the treatments of control and bacteria inoculated only, the inoculation of bacterial-feeding nematodes significantly accelerated the phenanthrene removal from gnotobiotic system (P <0.05). Bacterial-feeding nematodes also could promote the catechol2,3-dioxygenase (C23O) and catalase (CAT) activity.(2) The effect of adding carbon (glucose) and bacterial-feeding nematodes on the phenanthrene removal was investigated in a gnotobiotic system. Compared with control, the removal of phenanthrene was increased by25.6%and36.6%in the presence of carbon (glucose) and bacterial-feeding nematodes, respectively. Nematodes could also significantly increase the bacterial abundance and the catechol2,3-dioxygenase (C23O) activity, especially when the glucose present. These results implied that nematodes might promote the removal of phenanthrene from medium via stimulating bacteria performance and catechol2,3-dioxygenase (C23O) activity.(3) A soil microcosm incubation experiment was constructed to study the effect of bacteria-feeding nematodes, which feed phenanthrene-degrading bacteria (Pseudomonas Putida), on phenanthrene removal from the unsterilied soil. Compared with control, the inoculation of bacteria-feeding nematodes could increase the soil enzyme activities (Catalase and Hydrolysis rate of fluorescein diacetate)(P<0.05). But inoculation of bacteria-feeding nematodes could not significantly increase the removal of phenanthrene from contaminated soils. It was contributed to the complex environment in soil.(4) The effects of earthworms and ryegrass interaction on the removal of fluoranthene from contaminated soil were investigated in a70-day microcosm experiment. During the incubation time, the changes of fluoranthene in soil among all four treatments were fitted with the first-order kinetic model. The half-life (T1/2) of the fluoranthene in soil with earthworms and ryegrass together was the smallest among all treatments and36.3%smaller than that of control. Earthworms significantly increased microbial biomass and polyphenol oxidase activity (POD) in the presence of ryegrass at the final sampling (P<0.01). Microbial biomass and polyphenol oxidase activity (POD) were significantly (P<0.05) and negatively related to the residual fluoranthene concentration, respectively. The results implied that earthworms might promote the removal of fluoranthene from soil via stimulating microbial biomass and POD activity.(5) A hydroponic culture study was carried out to study the effects of earthworm mucus on ryegrass growth and the removal of fluoranthene from hydroponic system. Results indicated that compared with treatments with only amending earthworm mucus or growing ryegrass, the interaction between earthworm mucus and ryegrass was more significantly on the removal of fluoranthene, especially on the12th day. Earthworm mucus significantly increased ryegrass root growth and superoxide dismutase (SOD) activity (P<0.05). The earthworm mucus also promoted the concentration and translocation factor (TF) of fluoranthene in plant.In conclusion, these results demonstrated:1) Bacteria-feeding nematodes promoted the removal of phenanthrene from the contaminated gnotobiotic culture;2) Adding the carbon (glucose) could promote the stimulation effects of the bacteria-feeding nematodes on the bacteria abundance and C23O activity, and be helpful on the removal of phenanthrene from the gnotobiotic system;3) In the presence of earthworm, the fluoranthene removal from contaminated soil were closely related to the increase of soil microbial biomass and polyphenol oxidizes (POD) activity;4) Earthworm mucus significantly increased the bacterial growth and reproduction, and ryegrass root growth and superoxide dismutase (SOD) activity. Earthworm mucus also promoted the concentration and translocation factor (TF) of fluoranthene in plant.