| Atrazine is one of the most widely used herbicides in corn fields. It has caused seriously environment pollution after years of use. Atrazine is used extensively in Northeast China, where is an important agricultural base. Atrazine is difficult to be degraded by microorganisms for the stable three nitrogen benzene ring structure, so the half-life of atrazine is long in soil, which could cause seriously harm to environment and ecological agriculture. And it even harms people’s health by entering people’s bodies through the biological cycle. The black soil sample was collected from the experimental fields of Heilongjiang Academy of Agricultural Sciences in Northeast China. This paper measured the physical and chemical properties of the soil, studied the migration, adsorption and degradation characteristics of atrazine in soil sample and analyzed the atrazine-degrading bacteria community by PCR-DGGE.Firstly, the adsorption of atrazine in soil was studied. The effect of environmental factors such as temperature, pH, ion concentration on adsorption was investigated, and the adsorption results was analyzed by Freundlich equation and Langmuir equation. The results showed that the Freundlich equation could fit the adsorption isotherm well (R2>0.99), while the R2of Langmuir equation was between0.81-0.93, the Kf=2.98at20℃. The higher the temperature was, the smaller the Kf became, and the smaller the amount of adsorption was. Secondly, the soil sample before and after adsorption is characterized by XRD and FTIR in order to analyse the internal mechanism of the adsorption. The characteristic absorption peaks of3620,3449,1632and1030cm-1in FTIR spectras showed that the black soil belonged to montmorillonite. Combined with the XRD spectras, kaolinite and montmorillonite participate in the adsorption of atrazine. But the amount of adsorption was small. Through adsorption thermodynamic analysis,△G=-3.03kJ/mol,△H=-26.91kJ/mol,△S=-81.52J/(K·mol), this indicated that the adsorption of atrazine in soil was a spontaneous exothermic process. And the entropy is reduced, increasing the temperature was not conducive to the adsorption. The adsorption kinetics experiment results showed that rapid adsorption process completed in8hours and it took70hours to reach adsorption equilibrium. The equilibrium adsorbed amount was24.45mg/kg when liquid concentration was20mg/L. The degradation results showed that illumination could not promote the degradation of atrazine. Both the t1/2under light and dark conditions were9.6d. Add nutrition can promote the degradation of atrazine weakly. The t1/2is8.7d when there was nutrition and the t1/2is9.2d that there was no nutrition. The t1/2of unsterilized group was less than the sterilized groups. This indicated that microbes played a promoting role in the degradation. Degradation kinetics analysis showed that the degradation fits well with first order kinetic equation (R2>0.99). The t1/2of atrazine was between8.7d and10.5d. The degradation products were analyzed by LC-MS. The results showed that the t1/2of atrazine in black soil was very short, only8d. The major degradation products included DIA, HA and DEDIA. DEDIA is stable and degraded little. The microbials in soil were analysed by PCR-DGGE, the number and brightness of bands on electrophoresis indicated that the diversity of the microbial community in soil was rich, the structure of four groups have little difference in microbial community. The phylogenetic tree was constructed after cloning and sequencing. The results showed that two kinds of bacteria could degrade atrazine, which belongs to Pseudomonas, Bacillus. |
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