Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, CAS, Nanjing, Jiangsu Province, 210008, China; State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu Province, 210023, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, CAS, Nanjing, Jiangsu Province, 210008, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
Water Res. 2019 Nov 15;165:114997. doi: 10.1016/j.watres.2019.114997. Epub 2019 Aug 21.
Smectite clays are widely found in subsurface soils and waters. Although they strongly sequester tetracyclines (TCs), little is known about their reactions with these antibiotics under dark anoxic conditions. This study investigated the interactions between TCs and Fe-bearing smectite clays and the influences of environmental factors. Fe-bearing smectite clays were shown to significantly induce the transformation of TCs, including tautomerization, dechlorination, and dehydration. Moreover, the adsorbed TCs reduced the structural Fe(III) in clay particles to structural Fe(II) through electron transfer. The transformation of TCs was more readily induced by smectite clays with a higher rather than a lower Fe content. Tetrahedral Fe(III), and distorted cis- or trans-octahedral Fe(III), were more reactive as an electron acceptor than cis-octahedral Fe(III), as observed on the Mössbauer and FTIR spectra. A lower pH facilitated the adsorption of TCs through dimethyl-amino, amide, and conjugated -OH functional groups and induced a higher rate of TCs transformation. The transformation of chlortetracycline (CTC) was faster than that of oxytetracycline or tetracycline (TTC) due to -Cl substitution. The major transformation CTC products included keto-CTC, epi-CTC, iso-CTC, anhydro-CTC and TTC. Mixtures of these transformed products were found to have a higher acute toxicity than their parent compounds to Photobacterium phosphoreum T3. Our study revealed several previously overlooked interactions between TCs and clay particles that could cause these antibiotics to become unstable in the subsurface environment, with negative effects on the soil-borne microbial community.
蒙脱石黏土广泛存在于地下土壤和地下水中。尽管它们强烈螯合四环素（TCs），但对于它们在黑暗缺氧条件下与这些抗生素的反应知之甚少。本研究调查了 TCs 与含 Fe 蒙脱石黏土之间的相互作用及其环境因素的影响。结果表明，含 Fe 蒙脱石黏土显著诱导 TCs 的转化，包括互变异构、脱氯和脱水。此外，吸附的 TCs 通过电子转移将粘土颗粒中的结构 Fe(III)还原为结构 Fe(II)。具有较高而非较低 Fe 含量的蒙脱石黏土更容易诱导 TCs 的转化。四方 Fe(III)和扭曲的顺式或反式八面体 Fe(III)比顺式八面体 Fe(III)更易作为电子受体，这可以从 Mössbauer 和 FTIR 光谱中观察到。较低的 pH 值通过二甲氨基、酰胺和共轭 -OH 官能团促进 TCs 的吸附，并诱导更高的 TCs 转化速率。由于 -Cl 取代，金霉素（CTC）的转化速度快于土霉素或四环素（TTC）。CTC 的主要转化产物包括酮基 CTC、表 CTC、异 CTC、脱水 CTC 和 TTC。发现这些转化产物的混合物对 Photobacterium phosphoreum T3 的急性毒性高于其母体化合物。我们的研究揭示了 TCs 和粘土颗粒之间一些以前被忽视的相互作用，这些相互作用可能导致这些抗生素在地下环境中变得不稳定，对土壤传播的微生物群落产生负面影响。
