## 3 Results
### Degradation Intermediates  
If UDMH was spilled into the environment, the oxidative transformation would form a wide range of oxidation intermediates simply because of its strong reducing properties [36]. Recent studies showed that UDMH would transform a number of compounds such as dimethylamine (DMA), 1,1,4,4-tetramethyltetrazene (TMT), formaldehyde dimethylhydrazone (FADMH), \(N\)-nitrosodimethylamine (NDMA), 1-methyl-1H-1,2,4-triazole (MTA), and others [1]. Those compounds both constitute transformation products, which are formed directly from UDMH, as well as compounds that are formed in various consecutive processes [37]. Among all the transformation products, NDMA is a particularly harmful nitrosamine and potential carcinogen classified by the U.S. Environmental Protection Agency (EPA). Current concerns with NDMA in ground water began more than a decade ago when the compound was detected at various military and aerospace facilities that previously handled liquid propellants containing UDMH [38]. Studies conducted on the containment systems indicate that NDMA is not being effectively removed from the extracted groundwater. Concentrations of NDMA in the Rocky Mountain Arsenal groundwater, which was used to produce rocket fuel for the U.S. military, generally range from 0.87 to 2.7 \(\mu\)g\(\cdot\) L\({}^{-1}\)[39]. The degradation intermediates of UDMH biodegraded in aerobic activated sludge had been studied by the SPME-GC/MS analytic method in 2005. DMA, FADMH, TMT, DMF (\(N\),\(N\)-dimethylformamide), acetaldehyde dimethylhydrazone, and MTA were found [28]. However, the SPME-GC/MS method could not detect low concentration NDMA in an aqueous solution. This problem was resolved by adopting the GC/MS method [29]. UDMH and its degradation intermediates could bind tightly to the soil absorbing complex. When soil substances were introduced into an aqueous solution, absorption of a significant portion of the dissolved substances proceeds quickly, which is indicative of the high absorption capacity of the substance in question [40]. The standard UV spectrophotometer method could not detect UDMH in the soil by dissolving and filtering if the concentration of UDMH was not high enough. So the pretreatment method of alkali distillation was used to extract UDMH from the soil [41]. Chemical analysis of the UDMH degradation intermediates revealed some differences between aqueous MSM and the soil samples (Figure 4). In the aqueous MSM, M12 could effectively biodegradable both UDMH and NDMA. The same also happened in the soil for P4. In particular, the NDMA concentration of the biodegradation sample was far lower than that of the control, which showed that the bacteria M12 and P4 were involved in the degradation of NDMA at the same time. Figure 4: The final concentrations of UDMH and \(N\)-nitrosodimethylamine (NDMA) (**a**) in aqueous MSM and (**b**) in SS. The qualitative analysis results of the degradation intermediates in the aqueous MSM and soil are shown in the total ion chromatograms (TIC) (Figure 5). Table 2 lists seven kinds of final compound identified by the NIST MS library match; any compounds that were not clearly identified (probability match <85%) are not listed. Whether in the aqueous solution or in the SS, the kinds of main final intermediates of the control did not have a visible difference. FADMH, NDMA, TMT, and MTA were detected in all the TICs. The concentration of these compounds biodegraded was also far lower than those of the controls. Although other compounds such as DMA, tetramethylhydrazine, and acetaldehyde dimethylhydrazone could not be detected in the TICs of biodegradation in the SS and aqueous solution, their characteristic ion peaks were clearly found in the extract ion chromatograms. For the control sample, it was mainly oxidized by the air, and the exogenous bacteria did not change the course of natural oxidation of UDMH, but the exogenous bacteria could degrade UDMH and other intermediate products at the same time.