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因具有广谱、价廉和高效等优点,四环素(Tetracycline,TC)被广泛地应用于水产养殖和畜牧业[1]. 动物对TC的吸收利用率较低,超过75%的TC以活性物质形式排出体外,进而通过不同途径进入水环境,导致不同程度的水体污染问题[2]. TC在我国地表水中被广泛检出,其检出浓度为2.32 ng·L−1—100.75 μg·L−1[3 − 5]. 尽管浓度较低,但长期接触低剂量的抗生素,会破坏微生物生态,导致抗性基因的富集[6].
鉴于TC在水中赋存浓度极低且具有较大的溶解度,致使常规净水处理工艺(混凝、沉淀、过滤)难以将其有效去除[7]. 作为水处理中常见的氧化剂,KMnO4具有性质稳定、使用简单、成本低等优点[8],且处理过程中产生的水合MnO2,有利于氧化和吸附反应的进行[9]. 因此,KMnO4被广泛应用于降解包含TC在内的新污染物[10]. TC(解离常数为pKa1=3.3、pKa2=7.68和pKa3=9.3)为典型的酸碱两性化合物,随着溶液pH的升高,TC先后主要以TC+(pH<3.3)、TC0(3.3<pH<7.68)、TC−(7.68<pH<9.3)和TC2-(pH>9.3)形态存在. 有研究表明,KMnO4与TC反应遵循二级反应动力学,具有pH依赖性,pH为6—9时,kapp从10.12 mol·L−1·s−1增长到38.43 mol·L−1·s−1. 溶液pH增加,TC分子静电势负性加强,增强了化学结合能,是导致速率变化的主要原因[10]. 此外,不同的TC赋存形态会改变其分子表面的电子分布密度,可能会导致生成不同的降解产物,进而影响溶液的综合生物毒性,然而,相关研究尚未见报道.
为探究KMnO4对TC四种形态的氧化效率及机理,本研究系统探究了不同pH(2、6、9、11)条件下TC的降解动力学、矿化度、降解产物及路径,并选用表征急性毒性的费氏弧菌、湖泊水库中常见的斜生栅藻和传统好氧工艺中的活性污泥等受试生物,综合评估了降解产物的生物毒性. 此外,还采用ECOSAR软件对不同氧化产物单体的理论毒性进行评估,以期能够更好地揭示其在水环境中的转化和归宿.
溶液pH对高锰酸钾降解四环素动力学、产物和生物毒性的影响
Effect of solution pH on kinetics, product and biotoxicity of tetracycline degradation by potassium permanganate
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摘要: 四环素(TC)是一种典型的酸碱两性化合物,其在水中的赋存形态受溶液pH影响. 为探究TC降解路径和溶液毒性是否会随pH产生规律性变化,本研究考察了KMnO4氧化过程中,溶液pH(2、6、9和11)对TC降解动力学、降解产物和溶液毒性的影响规律及机制. 结果表明,TC在KMnO4体系中的反应符合二级反应动力学模型,速率常数(kapp)为7.92 mol·L−1·s−1(pH=6)—37.74 mol·L−1·s−1(pH=11);使用超高效液相色谱-串联质谱法(UPLC-MS/MS)对经KMnO4处理后TC的降解产物进行定性分析,共有6种降解产物被检出,溶液pH为2、6、9和11时,分别有3、3、3和5种降解产物,表现出显著的pH依赖性. 采用费氏弧菌、活性污泥细菌和斜生栅藻对氧化处理后的TC溶液进行毒性评价,发现部分降解产物具有比母体更强的生物毒性,ECOSAR模拟毒性数值也能佐证.
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关键词:
- 四环素 /
- 超高效液相色谱-串联质谱法(UPLC-MS/MS) /
- 化学氧化 /
- 降解产物 /
- 生物毒性.
Abstract: Tetracycline (TC) is an acid-base amphoteric compound that undergoes changes in its species within aqueous solutions due to solution pH. This study aimed to investigate the relationship between solution pH and the degradation pathways, solution toxicity, and degradation kinetics of TC during KMnO4 oxidation, as well as the underlying mechanism. The results indicated that the reaction of TC in the KMnO4 system followed a second-order rate law. The pH-dependent rate constants (kapp) ranged from 7.92 mol·L−1·s−1 (at pH 6) to 37.74 mol·L−1·s−1 (at pH 11). Using the ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS) method, qualitative analysis revealed a total of six degradation products. The number of degradation products identified varied with pH, with three, three, three, and five degradation products observed at pH 2, 6, 9, and 11, respectively. The degradation products exhibited significant pH dependence. The toxicity of the oxidized TC solution was assessed using Vibrio fischeri, activated sludge bacteria, and Scenedesmus obliquus. The study discovered that some of the degradation products exhibited higher toxicity than TC itself, which was further supported by simulated toxicity values obtained from ECOSAR. -
表 1 TC及其降解产物的保留时间、分子式、MS质谱信息及分子结构
Table 1. Retention time, molecular formula, MS mass spectrum information and molecular structure of TC and its degradation products
pH 名称
Name保留时间/min
Retention time质荷比m/z 分子式
Molecular formula可能结构
Proposed structure理论值
Theoretical测量值
Measured2、6、11 P362 9.052 362.13 362.52 C20H18O5 2、6、9、11 P419 9.263 419.1 419.07 C19H18N2O9 2、9、11 P301 11.904 302.08 301.36 C16H14O6 6、11 P413 13.418 413.16 413.54 C22H24N2O6 9 P437 11.202 437.15 437.46 C20H24N2O9 11 P475 9.547 476.14 475.49 C22H24N2O10 -
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