Determination And Microbiodegradation Of Unsymmetrical Dimethylhydrazine And Its Degradation Produets In Soil

Unsymmetrical dimethylhydrazine(UDMH)is an important liquid propellant,which is widely used in launch vehicle,missile and spacecraft.UDMH,a kind of high toxic substances,has carcinogenic,teratogenic and mutagenic effects and genetic toxicity.The leaking accidents of UDMH which can cause serious soil contamination happened frequently in the process of storage and usage,which bring huge security risk to human health and ecosystems.In order to explore the soil treatment method,the analysis and biolodegradation of UDMH and its degradation products in soil are systematically studied.The study results provide theoretical basis for in site bioremediation of UDMH in soil in the future.The main research contents and results are shown as follows:(1)Seven degradation products of UDMH were analyzed by solid phase micro extraction-gas chromatography mass spectrometry(SPME-GC/MS).The physical and chemical parameters of the 7 compounds were calculated based on the QSAR model.Among all 7 products,N-nitrosodimethylamine(NDMA)was selected as a persistence compound by analyzing the biodegradability,the half-life of the water retention period in water and the half lives in different environmental media combining with the environmental durability judgment standard.Formaldehyde dimethylhydrazone(FADMH)was selected as a compound with environmental toxicity by analyzing the harm of chemical compounds to aquatic organisms.Thus,ND MA and FADMH were chosen as the main monitoring objects of UDMH degradation transformation products.(2)An analytical method was developed for the determination of UDMH in soil samples by GC/MS with the pretreatment of alkaline distillation and ultrasoni c catalytic derivatization.The UDMH soil samples were pretreated by alkali distillation/ultrasonic catalytic derivatization,for the first time.The method solved the problem of the UDMH standard sample could not be prepared in the soil by using the water sealing.The ultrasonic catalytic derivatization conditions were optimized and the effect of alkali distillation on the transformation from FADMH converted into UDMH was discussed.In comparison with the methods of Spectrophotometry and Soxhlet extractionn-Ultrasonic catalytic derivatization,this method developed had lower detection limit,and was more accurate.(3)An analytical method was developed for the determination of NDMA in soil samples by GC/MS with Soxhlet extraction.The influential factors including GC/MS conditions of the injection mode,the programmed temperature and the Soxhlet extraction condition of extraction time had been made optimized.In comparison with the method of ultrasonic-assisted extraction(UAE),Soxhlet extraction can provid e higher extraction efficiency(82%),whereas the UAE could only reach 68%.The analytical method for FADMH in soil was established in the first time,based on the HS-SPME-GC/MS.The influential factors including SPME fibers,desorption time,extraction temperature and p H value had been optimized.This method showed some advantages such as simple,rapid and sensitive,which overcomed the defects of the unstable and easily decomposed property of FADMH.(4)The biodegrading strains of UDMH were isolated and indetified.Eleven UDMH-degrading bacteria strains P1~P11 were isolated from the activated sludge.And 5 strains P1,P2,P4,P6 and P10,whose 72 h degrading ratio of UDMH was more than 70% were filtered out.The identification results of the 5 strains bacte ria were Enterobacter asburiae sp.,Bacillus tequilensis sp.,Comamonas testosterone sp.,Pseudomonas putida sp.and Enterobacter cloacae sp.,respectively.The strain P4 had the best biodegradation effect.The degradation characteristics of strain P4 in so lution were studid,and the highest degrading rate of P4 reached 88.8% under the optimum conditions.The removal effect of the intermediate produ cts was also investigated.Experiments were carried out comparing degradation capacity of UDMH with P4 and M12,and the important influence factors of two strains of bacteria in solution were discussed.(5)The laboratory studies were carried out using the strain P4 to degrade the UDMH in soil.The P4 was inoculated into UDMH contaminated soil samples,then the degradating rates of UDMH in soil under different condictions were investigated.The results indicated that the biodegrading capacity of P4 bacteria could effectively enhanced in soil with nutrient solution.The influential factors including indigenous microorganism,extra carbon source and initial UDMH concentration were investigated.Indigenous microorganisms could improve the degradation rate of UDMH to a certain extent,and P4 relied on extra carbon source to biodegrade UDMH in soil.P4 bacteria had tolerance capacity to UDMH in the concentration of 600 mg/kg,and it could overcome the toxicity of UDMH at a high level.Contracting P4 with M12,the latter could not degrade UDMH in soil although it could degrade UDMH as the sole carbon source in the solution.According to the qualitative and quantitative analysis of UDMH degradation products,we found that P4 bacteria could not only reduce the concentration of UDMH,but also the intermediate products.Based on the determination result,the synchronous degradat ion theory was proposed,and the degradation pathway was discussed.(6)The microbial community and diversity in UDMH contaminated soil were studied by denaturing gradient gel electrophoresis(DGGE),and the effects of UDMH on soil microbial community and diversity were judged from the genetic level.The results showed that UDMH could increase the number of bacteria and diversity during the first 3d,then gradually decreased,and after 15 d the system would recover to the beginning.P4 bacteria as an external strain inoculated in the soil might disturb the growth of indigenous microorganisms.The diversity and abundance of soil bacterial communities were fluctuated with the addition of P4.Bacterial diversity index and abundance were decreased;however,evenness of community structure was increased after 35 d.This indicates that microbial community diversity decreased when strain P4 was added into soil after a period of time,while the common species and rare strains of the gap has gradually become smaller.