Remediation Of Thiamethoxam Contaminated Water And Soil By White-rot Fungi

Thiamethoxam belongs to the second generation of neonicotinoids pesticides.It is one of the most widely used pesticides in the world,with a wide application range,high water solubility and long half-life.Although most pesticides are not directly applied to water bodies,they are easily enter into the water environment through surface runoff,leaching,dry and wet settlement,soil infiltration and other ways during application because of their high solubility in water,and then causing water pollution.The pollution problems of environmental agricultural products caused by excessive usage of pesticides should not be ignored.White-rot fungus is a kind of fungus that can decompose wood into white spongy lumps.It has been found that white rot fungi can degrade organochlorine,organophosphorus,carbamate and pyrethroid pesticides effectively.This thesis mainly investigated the remediation effects of white-rot fungi to thiamethoxam polluted water and soil.On the basis of the remediation effects,the functional enzymes behavior of the white-rot fungi,the degradation pathway of neonicotinoids pesticides and the main degradation products as well as their biological toxicity during the remediation process were analyzed.The community structure and diversity of the indigenous microbial were investigated to reveal the molecular response mechanism of microbial communities to the white-rot fungi remediation mechanism and cause of the effect of the response of the microbial community and soil environment level,to understand the white-rot fungi repair new nicotine pesticide thiamethoxam during the process of contaminated soil.The main research work and achievements of this paper are as follows:The first part is to investigate the degradation and physiological responses of white-rot fungi to thiamethoxam.Firstly,Phanerochaete chrysosporium,a model species of white-rot fungi,was cultured and applied to the treatment of thiamethoxam contaminated water.The effects of photolysis,hydrolysis and initial thiamethoxam concentration on the removal efficiency were investigated.Moreover,the trends of cell activity,protein content and enzyme activity were monitored.The results showed that:(1)The effects of photocatalysis and hydrolysis on thiamethoxam degradation in water can be ignored as compared with its biodegradation by white-rot fungus.There were only 0.72% and 1.01% for photocatalysis and hydrolysis at the sixth day,respectively.(2)White-rot fungi can effectively degrade thiamethoxam in water.On the 25 th day,the degradation rates of thiamethoxam in 5 mg/L and 10 mg/L by white-rot fungi reached 100% and 98.15%.(3)In the process of repairing thiamethoxam polluted water by white-rot fungi,thiamethoxam can cause chronic damage and even death of cells,thus reducing the protein content,cell activity,CAT,POD enzyme activity of thiamethoxam.The second part is the structure analysis and toxicity analysis of the products of thiamethoxam under the degradation of white rot fungus.The products of thiamethoxam degradation by white rot fungi were determined by LC-MS,and the growth of Escherichia coli,Microcystis aeruginosa,cabbage seeds and rape seeds were monitored by adding thiamethoxam products.It was found that:(2)Thiamethoxam had no significant effect on the growth of escherichia coli,while thiamethoxam products of 10 mg/L and 20 mg/L had obvious promoting effect on the growth of Escherichia coli.Thiamethoxam solution had a significant inhibitory effect on the growth of Microcystis aeruginosa,while thiamethoxam products of the same concentration had no inhibitory effect on the growth of microcystis aeruginosa.(3)Thiamethoxam had no significant effect on the growth of seed bud length of rapeseed,while thiamethoxam product of the same concentration could significantly promote the growth of seed bud length of rapeseed.By the 5th day,20 mg/L thiamethoxam degradation product promoted the growth of seed bud length by 33.46%.Thiamethoxam solution significantly inhibited the growth of rapeseed seeds,and the seed bud length of cabbage grown in thiamethoxam solution of 5 mg/L was only 83%of that of the control group.The addition of thiamethoxam degradation products of 20mg/L increased the bud length by 76% compared with the control group.In the third part,the effect of inoculation form of white-rot fungi on the remediation of thiamethoxam contaminated soil was studied.The second generation high-throughput sequencing technology was used to analyze the effect of white-rot fungi on soil microbial community during the remediation of thiamethoxam contaminated soil.The results showed that:(1)The native soil microorganisms can effectively degrade thiamethoxam in soil,the degradation rate of thiamethoxam in the soil treated with different forms of white-rot fungi and i native soil microorganisms was different.Among them,when inoculated with spore suspension of white-rot fungus,the degradation effect of thiamethoxam in soil reached 96.69% on the 25 th day.(2)Immobilized white-rot fungi,free white-rot fungi and spores suspension of white-rot fungi can enrich the diversity of soil fungus community.Soil inoculation with immobilized white-rot fungi,free white-rot fungi,spores suspension of white-rot fungi and spores strengthened by white-rot fungi can enrich the diversity of soil bacterial community.(3)Inoculation of different forms of white rot fungi can cause changes in the relative abundance of native fungi in soil and inhibit the growth of microorganisms in ascomycetes in soil.Inoculation of white rot fungi in soil can also change the proportion of dominant bacteria in soil.This paper confirmed the feasibility of white-rot fungi to repair the water and soil pollution caused by the new nicotine pesticide thiamethoxam.The way of degradation of thiamethoxam by white-rot fungus and the toxicity of the product were also clarified.It was found that the best inoculating form of white-rot fungi for remediation of thiamethoxam contaminated soil,the response mechanism of microbial community in the process of white-rot fungus restoration was revealed.The results of this study are helpful to provide theoretical basis and scientific support for the development of white rot fungus technology for the effective application of neonicotinoids pesticides in water and soil pollution,it provides a new way for the effective control of neonicotinoids pesticides pollution.