| Sulfonamide antibiotics is a kind of synthetic antibiotics widely used in livestock and poultry breeding.However,antibiotics ingested by livestock and poultry are usually not fully absorbed,and about 30～90%of them are excreted through excreta in the form of raw drugs and metabolites,posing risks to the ecological environment and human health.This paper selected the frequent and high detection rate of sulfadiazine（SDZ）and sulfamethoxazole（SMX）these two kinds of typical SAs as the research object,in north central university surrounding soil for different profile,of the tested soil by dynamic laser method to measure the solubility of two kinds of antibiotics in soil leachate,and associated with the experience Apelblat equation of the solubility data,The solubility of SDZ and SMX was obtained.Based on solid phase extraction and high performance liquid chromatography,the leaching behavior of SDZ and SMX in different sections of soil was studied by soil column leaching method,and the effects of different initial concentration and different leaching time on the leaching behavior of SDZ and SMX in soil column were analyzed.The relationship between solubility and leachate migration ability was studied.The possible degradation products of SDZ in soil were predicted according to the charge/mass ratio（m/z）by LC-MS.The main results of this paper are as follows:（1）The solubility of SDZ and SMX in soil leachate at 278.15～313.15 K was measured by laser dynamic method in pure water and in neutral,acidic and alkaline leachate solution for1～9 days.The solubility data were fitted by Apelblat empirical equation and the dissolution law was analyzed.The results show that the solubility values calculated by Apelblat model are in good agreement with the experimental values,and the model can be used to predict the solubility data at other temperature points in the system.The solubility of SDZ and SMX in water was measured by laser dynamic method in the temperature range of 278.15～313.15K.It was found that the solubility of SDZ and SMX in water was very low.By comparison,it was found that the solubility of SDZ and SMX in soil leachate was higher than that in water at the same temperature,which was related to the chemical structure of SAs.It was also proved that there were substances promoting The migration of SAs in the soil,which indicated that SDZ and SMX had strong migration ability in the soil,and posed potential harm to deep soil and groundwater.By comparing the solubility data of SDZ and SMX,it was found that the solubility of SDZ and SMX in soil leachate increased with the increase of temperature,indicating that the dissolution process was endothermic.The solubility of SDZ and SMZ in leachate after leaching with neutral solution is generally higher than that in leachate after leaching with acid and alkaline solution,which indicates that SDZ and SMX are easier to infiltrate with neutral solution in soil environment.The solubility of SMX is higher than that of SDZ at the same temperature,indicating that the solubility of SMX in soil leachate is better than that of SDZ.The solubility of SDZ and SMX in soil leachate provided data support for the study of the relationship between the solubility of SAs and leachate migration.（2）The leach mobility of SDZ and SMX antibiotics was analyzed by Groundwater Ubiquity Score（GUS）.The results showed that the GUS value of SDZ and SMX antibiotics was higher than 2.80,which indicated high leach mobility,and the GUS value of SMX was higher than that of SDZ.The results showed that SMX migrated to deep soil more easily than SDZ through rain erosion,leaching and infiltration.In addition,soil column leaching experiments also confirmed this point,and SMX showed superior downward migration ability than SDZ in soil regardless of different initial contamination concentrations or different leaching time.The higher the initial pollution concentration,the higher the residual concentration of SDZ and SMX in soil leachate,indicating that the residual concentration of SAs in soil leachate is proportional to the initial concentration.This laid a foundation for the correlation study of the solubility and leaching mobility of SAs in soil.（3）By fitting the solubility and residual concentration of SDZ and SMX in soil leachate for 1～9 days,it was found that the residual concentration of SDZ in soil leachate had a great correlation with the solubility at low concentration,while the residual concentration of SDZ in soil leachate had a certain correlation with the solubility at high concentration.The results showed that the solubility of SDZ affected the leaching and transport ability of SDZ in soil to a certain extent.However,no matter the initial concentration was 2mg·kg-1or 5mg·kg-1,there was no obvious correlation between the residual concentration of SMX in soil leachate and solubility,indicating that solubility had no effect on the leachate migration ability of SMX in soil.（4）The degradation pathway of SDZ in soil under natural environment was simulated.The results showed that 12 kinds of degradation products,such as sulfamic acid derivatives,were generated through the process of S-C fracture,C-N fracture and S-N hydrolysis,indicating that SDZ could easily react with substances contained in soil to form new substances.In the degradation process of SDZ,the toxicity of some intermediates generated,such as catechol,4,6-dimethyl-2-hydroxypyrimidine,decreased.There are also some intermediates that are more toxic than SDZ,such as dimethyl pyrithanil and sulfamethacyl.We need to carry out further research on SDZ intermediates to control relevant influencing factors in pollution control or contaminated soil treatment,reduce the generation of toxic substances,and protect soil and groundwater. |
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