Enhanced Biodegradation Of DDT And DDE In The Soil And Its Effect On The Microbial Community Structure Diversity Of The Soil

DDT （1,1,1-trichloro-2,2-bi （4-chlorophenyl） ethane） belongs to the one of the22persistent organic pollutes, high DDT levels in the soil were still being observed recently inChina in the soil, and its residue and the risk was still an issue of great contention, DDT wasclassed the first product directory with the high pollutes and high environment risk. It was theimportant thing that speedy removal the residue of DDTs in the soil for protection the safetyof agricultural products and health of the people. The effective way of removal of DDTs fromthe contaminated soils was bioremediation using the microorganism degrading. Many DDT-degrading bacteria were isolated from the sewage and sewage sludge from the pecticidefactory, it was discovered by the research of metabolite that the p,p’-DDT was degraded intop,p’-DDE by the bacterial KK and p,p’-DDE was not further degraded, but p,p’-DDE wasdegraded furthermore by the other bacteria named with DXZ9, by the preliminary research,the degrading rates of p,p’-DDT and p,p’-DDE by the DXZ9were55.0%and39.88%respectively in the medium. Basing on the research foundation, the DXZ9was chosen andfurther researched. The contents of the thesis included three aspects, the degradingmechanism of p, p’-DDT and p, p’-DDE in the medium was researched firstly; and secondly,the biodegradation of p, p’-DDT and p, p’-DDE in the soil was researched by the DXZ9in theexperiment culture; in the end, the combined biodegradation of p, p’-DDT and p,p’-DDE inthe soil was researched by the DXZ9and the ryegrass in the pot.1. The step of a proposed pathway for the biodegradation of DDT by DXZ9was confirmed.The degradation products were extracted by the different polar organic solvents, the twodifferent polar organic solvents were used, one was benzene, the other was hexane and ethylacetate, from this study we can reasonably infer that p,p’-DDT firstly degraded into p,p’-DDEand p,p’-DDD, and then translated into9-Methylidenefluorene, and in the end degraded into1,2-benzenedicarboxylic Acid,2-benzenedicarboxic Acid， Dodecanoic Acid and2,6-bis（1,1-dimethylethyl）-4-methyl-phenol。2. The residual methods of the ten organochlorine pesticides in the soil were established.The column was OV-1701（Australia） capillary column （30m length,0.25mm i.d., and0.25μm film thicknesses）. The oven temperature was programmed from an initial temperature of150℃（1.0min hold）, and to240℃at a rate of4C/min, maintained at240℃for5min, and then to270℃at a rate of1.5℃/min, maintained at270℃for5min; Injector temperatureswere maintained at250℃, Detector temperatures （ECD） were maintained at300℃; the flowpressure of make up and the carrier gas was both80kpa. The chromatograms of tenorganochlorine pesticides in the soil were separated very well without the interference fromthe impurity peak. The chromatograms of the soil samples were separated very well not onlyin the high addition level but also in the low addition level, it was indicated that the detectioncondition and pretreatment method were suitable for the ten organochlorine pesticides, at thiscondition, minimum detection quantity of the ten organochlorine pesticides was10-12¹0-13g,minimal detectable concentration of the methed was10-2¹0-3mg·kg^-1, the method is sensitiveenough to detect the presence of the low level residue of the pesticides in the soil. Recoveriesrate of the four DDT isomers and六六六isomers pesticides in the soil tested were90.90%-104.4%, and the coefficient variation （CV） was less8.93%, and it could fulfill therequirements of the high standard of the pesticides residue.3. The biodegradation of p, p’-DDT and p, p’-DDE in the soil was researched by the DXZ9in the indoor experiment, it was explicit that DDT was degraded by the DXZ9in the soil; thedegradation half-life of DDTs was reduced through inoculating strains. Double chamberdegradation model was used in the degradation dynamics of DDTs, by the model, thedegradation half-life of p,p’-DDT, p,p’-DDE and DDTs was420d、1203d and532d in thesoil without the inoculation DXZ9treatment respectively, the degradation half-life of DDTswas reduced in the soil with the inoculation DXZ9treatment, its was42.5d,642d and221drespectively. Comparing the two modes, it was obvious that the treatment with the DXZ9could reduce the half-lives of pesticides in the soil. The residual concentrations of p, p’-DDTwere1.38mg·kg^-1and2.06mg·kg^-1in the soil with the two different treatments, the degradedrate were55.3%and33.3%. The residual concentrations of p,p’-DDE were1.19mg·kg^-1and1.43mg·kg^-1in the soil with the two different treatments, the degraded rate were37.0%and24.3%. The residual concentrations of DDTs were2.67mg·kg^-1and3.60mg·kg^-1in the soilwith the two different treatments, the degraded rate were45.2%and29.3%.4. The colonization of DXZ9was confirmed by denaturing gradient gel electrophoresis（DGGE） in the pot. On the basis of the monitoring predominant bacterium using denaturinggradient gel electrophoresis （DGGE）, the colonization of DXZ9was evaluated by the band ofDGGE during the combination with ryegrass and the microorganism, DXZ9was predominantwithin the30d in the soil, the band was more distinct than the band of the210d, it is evident that DXZ9was predominant bacterium on the preliminary period of experiment, as time wenton, the dominance of DXZ9began to wear off gradually.5. It was explicit that the combined remediation was the best method by the pot experiment,and the contribution of the DXZ9was more than the ryegrass, the degradation half-life ofDDTs in the soil was reduced significantly through the combined remediation with theryegrass and the microorganism. The result showed that the residual concentration of p, p’-DDT p, p’-DDE and DDTs was significant difference in the soils with different treatments.There was the same trend that the degraded speed was very quickly in the earlier stage slowlyin the later stage, evaluating the degrading effect according to the degrading rate, thetreatment of S+G+D+B was the best method, the degrading rate of DDTs was the highest, thedegrading rate of p, p’-DDT, p, p’-DDE and DDTs were80.7%,54.5%and69%respectively.The treatment of S+D+B was better method, the degrading rate of p, p’-DDT, p, p’-DDE andDDTs were77.1%,52.4%and65.5%respectively. The treatment of S+G+D was bettermethod, the degrading rate of p, p’-DDT, p, p’-DDE and DDTs were72.2%,48.4%and60.8%respectively. The last one was the treatment with S+D, which was degraded by the indigenousmicroorganism, the concentration of p,p’-DDT, p,p’-DDE and DDTs varied very little in thetreatment with S+D during the210d experimental period, the degrading rate of p,p’-DDT,p,p’-DDE and DDTs were30.0%,30.9%and28.8%respectively. The degradation half-life ofp,p’-DDT was48.0d,58.5d,75.5d and1055d in the soil with S+G+D+B, S+D+B, S+G+Dand S+D treatment; The degradation half-life of p,p’-DDE was162.5d,229d,235d and745din the soil with the same four treatments, and the degradation half-life of DDTs was71.8d,86.5d,114.8d and1095d in the soil. Comparing the degradation half-lives of pesticides in thesoil with different treatments, we could conclude that the residual concentration of pesticidewas reduced significantly by the combination of bioremediation and phytoremediation.6. It is thus obvious that the gene toxicity of the polluted soil was reduced significantly bythe phytoremediation and microbial remediation. The gene toxicity of the metabolites of thep,p’-DDT and p,p’-DDE in the soil, which was evaluated by the coelomocytes comet olivetails moment of the earthworm （Eisenia foetida）, the gene toxicity was the maximum in thesoil with S+D treatment, the gene toxicity was minimum in the soil with S+G+D+Btreatment, the gene toxicity of treatment with S+G+D was more than treatment with S+D+B,so it could be concluded that the gene toxicity was reduced significantly by the inculcationDXZ9and cultivating ryegrass. On the210d, the gene toxicity of pollutes in the soil wasreduced58.1%、52%and36.9%comparing the treatments S+G+D+B, S+D+B, S+G+D withS+D. 7. It was explicit that the effect of the microbial community structure diversity of the soilwas less during the combination with ryegrass and the microorganism. During thecombination with ryegrass and the microorganism, under the action of the bacterial strain,ryegrass and pesticide, the microorganism amount and the activity of soil enzyme wereaffected with different degrees in the soil, and as time went on, the effect was tapering off. Inthe period of210d experiment, the bacteria amount in the soil changed very much, there wassignificant difference between the treatment with inoculated strains and treatment withoutinoculated strains, there was significance at1%level on the5d and10d. The bacteriacommunity structure was different in the different treatments during the combination withryegrass and the microorganism by DGGE, but as time went on, the effect was tapering off.