The Degradation And Translocation Characteristics Of Thiamethoxam In Tidal Flat Environment And The Regulation Mechanism Of Biochar

In recent years,the pollution of neonicotinoid pesticides in the tidal flat environment has strengenthened great environmental risks to the tidal flat ecosystem.How to eliminate the neonicotinoid pesticides efficiently and conveniently has become a research hotspot.Biochar can remain organic pollutants in the soil and reduce the migration of pollutants.Therefore,it can be used as a repairing material for degrading pesticide pollution in soil,and biochar can also be used as a soil conditioner.The research on biochar which affects the accumulation of pesticides in plants mainly focuses on the description of phenomena,and the lack of internal mechanisms.In this paper,the neonicotinoid pesticide thiamethoxam?THI?and its metabolite clothianidin?CLO?were used to study the digestion dynamics of thiamethoxam in the coastal soil and its representative vegetables?Chinese chives?and the rules related with absorption and accumulation.Three kinds of biomass materials,such as wood,Tamarix chinensis and reed,were selected to obtain biochar by slow pyrolysis.The physical and chemical properties of biochar were characterized by elemental analysis,scanning electron microscopy and Fourier transform infrared spectroscopy?FTIR?.The obtained biochar explored the efficacy and regularity of biochar on the adsorption and degradation of THI and CLO in soil and plants,and analyzed the mechanism that biochar influences action of thiamethoxam in the soil-root system-plant system from the perspectives of soil properties,soil adsorption,rhizosphere soil microbial community structure and function.The research results provide a comprehensive evaluation of the feasibility of biochar technology for soil pesticide pollution remediation,and the establishment of biochar control technology for soil nicotine pesticide pollution.There are theoretical value and practical significance in restoring contaminated soil ecological service functions and ensuring agricultural product safety.The main research results are as follows:?1?To study the fate characteristics of neonicotinoids thiamethoxam in Qingdao coastal vegetable garden soil.The results showed that the half-life of thiamethoxam in soil was 72.6 days,and the cumulative amount of thiamethoxam was 5.29 mg·kg^-11 after 42 days of incubation in soil with an initial concentration of 6.91 mg·kg^-1.Soil sterilizing treatment will delay the degradation of thiamethoxam,and its degradation half-life in soil will be extended to 191.2 days.Meanwhile,at 42 days,the cumulative amount of thiamethoxam in amaranth plants will accumulate to 5.71 mg·kg^-1.The migration ratio is 82.6%.?2?Biochar characterization results show that there are differences in the basic properties of biochar from different sources.The ash content and pH of terrestrial biochar?wood?are higher than that of tidal biochar?tamarix chinensis and reed?.Compared with shoal biochar,terrestrial biochar has a higher carbon content of 83.26%,a lower nitrogen content of 0.17%,H/C?0.038?are smaller than tidal biochar.H/C is an index for evaluating the aromaticity of biochar.The smaller the H/C ratio,the higher the degree of aromatization of biochar.Therefore,terrestrial biochar is more aromatic.Wood biochar has the largest specific surface area,it's 219.144 m²·g^-1.Biochars obtained from biomass from different sources have similar functional groups but different functional groups have different contents.?3?Adsorption experiments of three biochars on THI and CLO showed that the pseudo-second-kinetic model better described the adsorption process of THI and CLO on three biochars,and R² _adjis between 0.93-0.99.The Langmuir model has a good fitting efficiency on the adsorption isotherms of THI and CLO on three biochars,R ²_adj>0.99.?4?Biochar can change the fate behavior of THI and its metabolite CLO in the soil-root-plant system.1.5%wood biochar was added to the soil with an initial concentration of THI of 6 mg·kg^-1.At42nd days,the accumulation of THI by chives was reduced by 22.8%,and the accumulation of CLO was reduced by 37.6%.THI in soil.The half-life increased from 106 days to 135.9 days.The results showed that the addition of biochar increases the adsorption capacity of THI and CLO on soil,thereby reducing their bioavailability.At the same time,the application of biochar changed the microbial community structure and abundance of soil,and the microbial taxa related to THI biodegradation,such as the decrease of the proportion of Firmicutes,the increase of Chloroflexi gate ratio,the decrease of Bacilli scale,etc.