Henan Joint International Research Laboratory of Environmental Pollution Control Materials, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, 475004, China.
Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Nankai University, Tianjin, 300350, China; Department of Hydrology, University of Bayreuth, Bayreuth D, 95440, Germany.
Ecotoxicol Environ Saf. 2020 Aug;199:110754. doi: 10.1016/j.ecoenv.2020.110754. Epub 2020 May 20.
Antibiotics, a highly prevalent class of environmental organic pollutants, are becoming a matter of global concern. Clay minerals that are ubiquitous in subsurface environments may play an important role in the fate and transport of antibiotics. Taking ciprofloxacin (CIP) as a model antibiotic, this work explored the role of clay colloids (kaolinite and montmorillonite) on the adsorption and transport of CIP under different chemical solution conditions. The adsorption isotherms showed that montmorillonite colloids had a larger CIP sorption capacity than kaolinite colloids. The results of transport experiments indicated that montmorillonite colloids could promote CIP transport in saturated sand columns, but the addition of kaolinite colloids affected CIP mobility to a much smaller extent. The much stronger transport-enhancement effect of montmorillonite colloids was due to CIP adsorbed strongly to the colloids and desorption hysteresis of colloid-adsorbed CIP, likely stemming from the intercalation of this antibiotic in the interlayer of montmorillonite. Interestingly, transport of clay colloids increased with the increasing pH from 5.0 to 9.0; however, CIP transport decreased with the increasing pH in the presence of clay colloids. The observations were likely attributable to pH-dependent ciprofloxacin adsorption/desorption to clay minerals. Increasing the concentrations of NaCl and CaCl generally decreased the contaminant-mobilizing ability of montmorillonite colloids, mainly by increasing the aggregation of colloids and thus, decreasing the transport of colloid-adsorbed CIP. Moreover, under the test conditions (1 mM NaCl and pH 7.0), the presence of CIP inhibited the transport of clay colloids due to the increase in aggregate size of clay colloids with the addition of CIP. Overall, these findings suggest that clay colloids with high adsorption abilities for antibiotics in the subsurface environment may act as a carrier for certain antibiotic compounds.
抗生素是一类在环境中广泛存在的有机污染物，已成为全球关注的焦点。在地下环境中普遍存在的粘土矿物可能在抗生素的归宿和迁移中起着重要作用。以环丙沙星（CIP）为模型抗生素，本研究探讨了粘土胶体（高岭石和蒙脱石）在不同化学溶液条件下对 CIP 的吸附和迁移的作用。吸附等温线表明，蒙脱石胶体对 CIP 的吸附容量大于高岭石胶体。运移实验结果表明，蒙脱石胶体可促进 CIP 在饱和砂柱中的运移，但添加高岭石胶体对 CIP 迁移的影响要小得多。蒙脱石胶体的运移增强作用更强，是由于 CIP 强烈吸附到胶体上，以及胶体吸附的 CIP 的解吸滞后，这可能源于这种抗生素在蒙脱石层间的插层作用。有趣的是，随着 pH 值从 5.0 增加到 9.0，胶体的运移增加；然而，在存在粘土胶体的情况下，CIP 的运移随着 pH 值的增加而降低。这种观察结果可能归因于 pH 值对粘土矿物上的环丙沙星吸附/解吸的依赖性。增加 NaCl 和 CaCl2 的浓度通常会降低蒙脱石胶体的污染物迁移能力，主要是通过增加胶体的聚集，从而减少胶体吸附的 CIP 的运移。此外，在测试条件（1 mM NaCl 和 pH 7.0）下，由于添加 CIP 导致粘土胶体的团聚体尺寸增大，CIP 的存在抑制了胶体的运移。总的来说，这些发现表明，在地下环境中对抗生素具有高吸附能力的粘土胶体可能作为某些抗生素化合物的载体。
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