不同离子强度下SiO_2胶体对磺胺嘧啶土壤吸附迁移行为的影响

Effect of Silica Colloids on Adsorption and Migration of Sulfadiazine in Soil Relative to Ionic Intensity

通过室内批实验和土柱出流实验,以二氧化硅胶体作为外源胶体,定量分析了改变离子强度时胶体对磺胺嘧啶(Sulfadiazine,SDZ)在土壤中吸附、迁移行为的影响。批实验结果表明,离子强度为0.001、0.003 mol L-1时胶体的加入能够抑制SDZ的吸附,而0.005、0.010 mol L-1时胶体的加入对SDZ吸附的影响与SDZ初始浓度有关。Freundlich模型能较好地拟合SDZ在土壤中的吸附情况,R2在0.958~0.997范围内。土柱实验结果表明,不加胶体时,高离子强度会促进SDZ在土壤中的迁移,SDZ在土柱中出流早,相对浓度峰值高且持续时间长;加胶体时,高离子强度下胶体出流量小,抑制SDZ在土壤中的迁移,SDZ的相对浓度峰值降低且更难洗脱,而低离子强度时胶体全部或部分出流,促进SDZ的迁移,SDZ出流早且相对浓度峰值高。总之,吸附迁移实验表明,低离子强度时,胶体的加入促进了SDZ的迁移抑制SDZ的吸附,高离子强度时则相反。该结果有助于全面理解土壤中磺胺类抗生素的运移,指导磺胺类抗生素的风险评估及防治。

【Objective】Colloid is an active component, exsiting extensively in soil, so how it affects adsorption and migration of sulfadiazine in soil is a scientific issue that is worth further exploring.【Method】Taking Neutral Ludox as extraneous colloid, this work quantitatively analyzed effects of ionic intensity（0.001, 0.003, 0.005, 0.010 mol L^-1 Ca Cl2）on the adsorption and migration of sulfadiazine in soil, 6.38±0.03 in p H, where colloid and sulfadiazine coexisted through indoor batch experiments and soil column effluent experiments.【Result】Results showed that the colloid inhibited the adsorption of sulfadiazine in the soil when the ion intensity was 0.001 or 0.003 mol L^-1, but the effect of the colloid inhibiting sulfadiazine adsorption in the soil with ion intensity being 0.005 or 0.010 mol L^-1 Ca Cl2 was effected by the initial concentration of sulfadiazine. Freundlich model could well describe the adsorption process of sulfadiazine in the soil with R^2 being 0.958～0.997. The breakthrough curve of vertical transport of sulfadiazine in the saturated condition was delayed in all conditions mainly due to the existence of different forms of sulfadiazine. Neutral ion form of sulfadiazine was adsorbed on soil organic matter through hydrophobic interaction and sulfadiazine in negative ion form was adsorbed on the soil through bonding action. When concentration of sulfadiazine was 30 mg L^-1, however, in soil higher in ion intensity, the colloid added could inhibit migration of the sulfadiazine due to the dielectric layer was compressed, forming flocculation that absorbed a certain amount of sulfadiazine, while in soil lower in ion intensity, colloid outflowed, entirely or partly, thus impoving sulfadiazine migration. At 0.010 mol L^-1 Ca Cl2 in ionic intensity, the outflow of sulfadiazine from the soil column was advanced, the relative concentration of sulfadiazine peaked higher, and the outflow lasted longer without colloid addition. However, once colloid was added, the relative concentration of sulfadiazine peaked low in value and it was hard for sulfadiazine to outflow. At 0.005 mol L^-1 Ca Cl2 in ion intensity, the outflow of sulfadiazine was earlier and the relative concentration of sulfadiazine peaked higher than that without colloid addition. At 0.001 mol L^-1 Ca Cl2 in ion intensity, relative concentration of sulfadiazine peaked higher than that without colloid addition, and it was more difficult for sulfadiazineto to get eluted.【Conclusion】Generally speaking, in soils with colloid existing and lower in ion strength, the addition of colloidal inhibits the adsorption of sulfadiazine and hence promotes the migration of sulfadiazine, while in soils higher in ion strength, it promotes the adsorption of sulfadiazine and hence inhibits the migration of sulfadiazine. All the findings in this study may be of some guiding significance for controlling the migration of sulfonamides in soil.