抗生素磺胺嘧啶和磺胺甲恶唑在土壤中的淋溶行为研究

农业生产中畜禽粪污还田会将残留的抗生素带入农田土壤，并能通过淋溶作用迁移至深层土壤最终进入地下水. 该研究采用模拟土壤柱淋溶试验方法，研究了2种磺胺类抗生素——磺胺嘧啶(sulfadiazine，SDZ)和磺胺甲恶唑(sulfamethoxazole，SMX)在农田土壤中的淋溶行为，以及表层土抗生素含量、淋溶液pH和有机质对各土柱剖面SDZ和SMX残留水平的影响. 结果表明:①不同表层土抗生素含量下，SDZ和SMX在供试土壤中均呈向下迁移的趋势，但淋溶结束后上层土壤中二者含量明显高于下层，土柱各层抗生素的含量随表层土抗生素含量的增加而增加. ②淋溶液pH为3.00和5.00时，各层土壤中SDZ和SMX的含量均高于淋溶液pH为7.00时. 淋溶液pH较高时两种磺胺类抗生素多以阴离子形态存在，会与带负电荷的土壤颗粒产生静电斥力而易于向下迁移；随着淋溶液pH的降低，两种磺胺类抗生素阴离子形态占比减少，上层土壤中保留的抗生素含量变高，向下迁移的能力减弱. ③粪便添加组上层土壤中SDZ和SMX的含量明显高于未添加组，抗生素向下迁移的能力减弱，这与有机质的添加使得上层土柱吸附能力增强有关. 通过模型模拟，SDZ和SMX的地下水污染指数分别为3.50和4.45，均大于2.8，表明在供试土壤中这2种磺胺类抗生素的淋溶迁移性较强. 研究显示，淋溶试验结果与模型模拟结果一致，表明SDZ和SMX对地下水存在潜在污染风险. 

Leaching Behavior of Antibiotics Sulfadiazine and Sulfamethoxazole in Soil

In agricultural production, livestock manure and urine applied as fertilizers bring the residual antibiotics into the farmland soil, which can migrate to the deeper soil through leaching and eventually into the groundwater. In this study, the soil column method was used to investigate the leaching behavior of two sulfonamide antibiotics: sulfadiazine (SDZ) and sulfamethoxazole (SMX) under multiple conditions including different antibiotic content in topsoil, leachates with different pH values, and different doses of manure in columns. The results showed that SDZ and SMX had similar downward migration under different antibiotic content in topsoil. The antibiotics remained higher in the upper soil than in the deeper soil, and the residues in every layer of soil columns increased when antibiotic content in topsoil was higher. When the pH values of leachate were 3.00 and 5.00, the concentrations of SDZ and SMX in each layer of soil were higher than those at pH 7.00. It was possibly because at high pH, the two sulfonamide antibiotics existed as anions and generated electrostatic repulsion with negatively charged soil particles. On the contrary, when the pH value decreased, the two sulfonamide antibiotics were less negatively charged, the migration capacity of antibiotics was weakened and the concentration of antibiotics retained in the upper soil increased. When cattle manure was added as organic matter, the contents of SDZ and SMX in the upper soil were significantly higher than those of the non-addition group, reflecting their ability to migrate downward was impaired. This was mainly the result of the altered physicochemical properties (e.g., the enhanced absorption) of the surface soil by organic matter. Moreover, the groundwater ubiquity scores (GUS) of SDZ and SMX were calculated as 3.50 and 4.45, indicating that both of them had strong leachability (>2.8) in soil. Based on the consistent results between model calculation and the experiment, the target sulfonamide antibiotics pose potential risks to groundwater, which is worthy of further investigation.