Study On Sorption-desorption And Transportation Of Typical Antibiotics In Soils

Antibiotic residues, kind of emerging pollutants, are increasingly attractive by people. Other pollutants like heavy metals are also able to enter into the soils. Thus the polluted soil is always regarded as a typical combined pollution system. Recently, as a soil amendment, biochar pyrolyzed from biomass wastes has been broadly applied in different fields including agriculture, geosciences and environment. In case of soil amended with biochar, to a certain extent, biochar would affect the geochemical behavior of antibiotics in soils. Therefore, it is necessary to explore the sorption and migration characteristics of antibiotics in soils with or without biochar. Herein, we focused on typical antibiotics such as oxytetracycline（OTC）, sulfamethoxazole（SMX）, sulfamethazine（SMZ） and sulfadiazine（SD） in soils. The influencing factors of soil pH, Cu²⁺ concentrations, ionic strength, dissolved humic acid and the presence of biochar were discussed in this thesis. The results were showed as the follows.1. We conducted the batch experiements of sorption and desorption of OTC in three cinnamon soils in Beijing. The effects of solution pH, ionic strength, coexistence copper and additive biochar were studied. It showed that adsorption isotherms and kinetics of OTC on three cinnamon soils in Beijing were well fitted with Freundlich equation and Elovich equation, respectively. During the sorption process, it indicated that adsorption was a spontaneous endothermic reaction, and the reaction was a physical adsorption. Desorption experiments revealed that the hysteresis was positive. Elevated temperature, coexistence copper and additive biochar promoted the adsorption of OTC on three cinnamon soils. Whereas, both solution pH and ionic strength reduced the capacity of OTC adsorbed on cinnamon soils.2. Comparative experiments were designed to study sorption, desorption and transport of three sulfonamides in soils amended with biochar. The effects of solution pH, coexistence copper and humus acid（HA） were also studied. It showed the complexation of Cu²⁺ with containing-oxygen functional groups of biochar inhibited adsorption of SMZ and SD on the soil, and the cation(Cu²⁺) could reduce hydrophobicity by neutralizing the charge of SMX and thus enhanced SMX adsorption on the soil. The low solution pH accelerated the sorption of three sulfonamide antibiotics. Competitive effect of humic acid inhibited adsorption of SMZ and SD on the soil, while the formation of hydrogen bonds promoted SMX adsorbed on the soil.3. Column and desorption experiments demonstrated that the mobility of non-ionic antibiotic（OTC） in the soil was slower and that of ionic antibiotics（SMX, SMZ and SD） was faster. Biochar was an effective adsorbent in soils for controlling the migration behavior of ionic antibiotics.The above results help us understand the environmental geochemical behavior of antibiotic residues and evaluate the potential of biochar for antibiotics behavior in soils. The present study aslo provides scientific basis and theoretical support for environmental risk assessment of antibiotics in northern China and the selection of treatment technology in soils.