Study Of Adsorption And Migration Behavior Of Antibiotics In Soil In A Multiple System

The widespread use of veterinary antibiotics has led to antibiotic contamination and increased environmental risks.In order to understand the effects of sorption-desorption and their migration behaviors in soils where multiple antibiotics co-exist,this study investigated the sorption-desorption behaviors of different soils and their particles to different antibiotics in a multivariate system by batch equilibrium test using Sulfadiazine（SDZ）,Tetracycline（TC）and Norfloxacin（NFX）as the target contaminants with high detection rates in the soil environment.The adsorption-desorption behavior of different antibiotics on different soils and their particles in the multiplex system was investigated by batch equilibrium test;the adsorption mechanism of different antibiotics on soils and their particles in the multiplex system was analyzed by Fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）and specific surface area test（BET）.The results of the study provide theoretical support for a systematic and comprehensive investigation of the environmental behavior and risk assessment of antibiotic complex contamination in soil,with the following main findings.（1）Soil organic matter content and soil particle influence the adsorption-desorption behavior of antibiotics in soil,and the adsorption rate of the two soils with higher organic matter content was greater than that of the two soils with lower organic matter content,but Macroaggregates（MAs）in the two soils with higher organic matter content promoted antibiotic adsorption the most,while clay（Silt and clay,SC）with lower organic matter content weakened antibiotic sequestration in the soil and promoted antibiotic desorption behavior in the soil with the greatest desorption compared to Microaggregates（MIs）with lower organic matter content.The binary and ternary systems weakened the adsorption behavior of antibiotics in soil and the strongest weakening effect was observed in clay,and the binary and ternary systems promoted the desorption behavior of antibiotics in soil with the smallest desorption rate of large agglomerates.The results of isothermal model fitting showed that the adsorption isotherms of these three antibiotics in soil particles all conformed well to the Freundlich model,and the n values were basically greater than 1,which indicated that the process was chemical adsorption,and the adsorption isotherms belonged to the"S"type isotherms.（2）The adsorption-desorption behavior of antibiotics in soil varied depending on the nature of the antibiotics.The order of the magnitude of the adsorption rate of the three antibiotics on the same particle was TC>NFX>SDZ,while the order of the desorption rate was opposite to the adsorption rate;in both binary and ternary systems,antibiotic competition on the same particle promoted the desorption of TC and NFX less,but greatly weakened the adsorption capacity of SDZ,and this weakening capacity was especially significant in the ternary system,indicating that soil particles had a greater affinity for TC and NFX affinity than SDZ.In addition,the HI values of the adsorption hysteresis coefficients of these three antibiotics in the multivariate system were close to 1,indicating that there was almost no hysteresis in their adsorption-desorption processes in soil particles.（3）The FTIR analysis showed that the adsorption of antibiotics on soil particles was accompanied by complexation,hydrogen bonding,hydrophobic interaction,etc.The adsorption mechanism was diversified,and it can be inferred from the SEM results that the surface morphology of the particles did not change significantly after the adsorption of antibiotics,indicating that the antibiotics had no effect on the surface morphology.BET analysis also verified that the larger the specific surface area of the soil,the more adsorption sites,the more favorable antibiotic adsorption.（4）The migration behavior of antibiotics in soil and the vertical migration ability of antibiotics in soil under different drench solutions were investigated by drenching experiments.The results showed that the drenching test with Ca Cl₂solution maintained better stability than the distilled water environment.In a single system,SDZ was the most migratory and TC was less migratory,but its sequestration ability was the strongest in the upper soil layer（0-10 cm）.When multiple antibiotics coexisted in the soil,the changes of antibiotic content in leachate and residual antibiotics in different soil layers under different leaching solutions were similar to the trends obtained in the single system,but their adsorption was lower than that of the single system;NFX and TC reached the maximum adsorption concentration faster than the single system,which was related to the competition of antibiotics for adsorption sites to promote their mobility.The adsorption and desorption behaviors of antibiotics in agricultural soils were consistent with the results obtained from column tests,indicating that the conclusions obtained in this thesis can be applied to agricultural soils and can provide theoretical support for the environmental risk assessment of antibiotic contamination in agricultural soils and remediation treatment.