Degradation Mechanism Of Soil Atrazine By Magnetic Biochar Coupled Degrading Bacteria Pellets

In China,atrazine herbicide is mainly used to prevent weeds in corn fields.However,due to its own characteristics,atrazine can remain and accumulate in soil for a long time.This phenomenon has resulted in a serious decline in the yield of the later crop(soya bean),so the problem of atrazine pollution in farmland needs to be addressed urgently.Atrazine degrading bacteria DNS32 can efficiently degrade atrazine,however,various adverse factors in the environment can reduce the microbial activity and decrease the removal efficiency of atrazine.Therefore,magnetic biochar and DNS32 were embedded and immobilized with sodium alginate to form magnetic biological pellets(DMBC-P)in this study,which were applied to the remediation of atrazine contaminated soil.Furthermore,its ability to remove atrazine and the mechanism of alleviating atrazine stress on soybean seedlings were explored.The recovery performance and reusability of DMBC-P were also discussed.In this study,the synthesis parameters of DMBC-P were optimized by adjusting the concentrations of sodium alginate and calcium chloride based on the removal capacity of atrazine and the mechanical strength of pellets.The internal structure of DMBC-P was analyzed by means of SEM,FT-IR,XRD,and VSM.The removal properties of atrazine by DMBC-P under different factors were also discussed.The results showed that DMBC-P had the strongest atrazine removal ability when the concentration of sodium alginate and calcium chloride was 2%.When the dosage of DMBC-P was 2%,the temperature was 30 ~oC,and the p H was 7.3,the removal efficiency of atrazine could reach 100.00%.Besides,DMBC-P also showed an excellent atrazine removal performance under the condition of p H were 3.3-7.3,temperatures were 10-50 ~oC,and atrazine concentrations were 30-140 mg/L.Additionally,DMBC-P was further applied to the remediation of atrazine polluted soil in farmland,and the effect of DMBC-P on the removal of atrazine and soil environment was explored.The results manifested that the application of 0.5%DMBC-P could completely remove 22 mg/kg atrazine from soil within 4 d under the condition of moisture content of60%and soil p H of 7.36,and DMBC-P also had an excellent atrazine removal ability under different soil moisture content and soil p H.According to the determination of soil physical and chemical properties,DMBC-P could increase the contents of organic matter,available phosphorus,and available potassium in soil.Meanwhile,the activities of catalase,urease,sucrase,and neutral phosphatase increased significantly compared with the CK treatment.Furthermore,after three rounds of repeated regeneration experiments,DMBC-P still had an efficient removal performance of atrazine,and could also be effectively recovered in extremely dry and waterlogged environments.Pot experiment results showed that the physiological indexes of soybean seedlings after the remediation of DMBC-P were significantly higher than CK treatment,and the contents of four photosynthetic pigments were increased.The activity of antioxidant enzymes in plants decreased significantly,and the contents of malondialdehyde and proline decreased,while soluble protein content increased.In addition,the remediation mechanism of DMBC-P on atrazine contaminated soil was as follows:firstly,MBC embedded in the soil adsorbed free atrazine through pore filling,hydrogen bonding,andπ-πstacking,and then DNS32 was used to gradually degrade the adsorbed atrazine through a series of hydrolytic enzymes,and finally produced non-toxic cyanuric acid.DMBC-P remediation could improve the richness and diversity of microbial community in contaminated soil.Besides,the relative abundance of Proteobacteria in DMBC-P was significantly increased.The relative abundance of Oxalacidobacteriaceae,Myxococcus,Pseudomonas,Sphingosinomonas,and Rhizobiaceae increased significantly.Therefore,the application of DMBC-P can respond to the changes of soil microecological characteristics by changing soil microbial structure and abundance,so as to recover soil function.In conclusion,the application of DMBC-P can effectively remove atrazine from contaminated soil and be effectively recovered,alleviating the stress effect of atrazine on the growth of soybean seedlings,which provide a new strategy for the remediation of atrazine polluted soil in farmland.