Interactions of tetracycline and dissolved organic matter from freshwater lakes

Abstract

采用荧光滴定法研究四环素（tetracycline，TC）与太湖溶解性有机质（dissolved organic matter，DOM）和玄武湖DOM的相互作用.三维荧光光谱结合平行因子分析显示，2个湖泊的DOM含有3个荧光组分：类富里酸组分C1、类色氨酸组分C2和类络氨酸组分C3.其中C2的荧光强度远高于C1和C3，是DOM的主要荧光组成.3个荧光组分与TC发生了不同程度的静态猝灭，特别当TC浓度为45.5 μmol/L时，类蛋白组分的荧光强度完全被猝灭（100%），并且猝灭作用改变了DOM分子的微环境极性.同步荧光光谱联合二维相关图谱进一步表明类色氨酸组分优先和TC发生猝灭作用，其次为类络氨酸组分和类富里酸组分.Ryan-Weber方程适于拟合DOM与TC的猝灭过程，2个湖泊的DOM中3个荧光组分的络合常数lgK值范围为5.05~5.85，大小顺序为C2 > C3 > C1.因此，类蛋白组分为主的DOM对TC的络合作用大于类腐殖组分为主的DOM，影响抗生素在湖泊水体中的生物有效性和生态毒性.;Interactions of tetracycline (TC) with dissolved organic matter (DOM) collected from Lake Taihu and Lake Xuanwu were investigated through fluorescence quenching. Three fluorescent DOM components, fulvic-(C1), tryptophan-(C2), and tyrosine-like (C3) component, were identified in DOM via excitation emission matrix spectra with parallel factor analysis (EEM-PARAFAC). Results from fluorescence quenching titration showed that the fluorescence of 3 components was quenched at different degree by TC through static quenching. When the TC concentration increased to 45.5 μmol/L, the whole florescence of C2 and C3 were almost quenched, while 20% of C1 fluorescence was inaccessible. The quenching also induced conformational changes in DOM molecules. Synchronous fluorescence spectra combined with two dimensional correlation spectroscopy (2D-COS) further revealed that the complexation firstly occurred for tryptophan-like substance, followed by tyrosine-and fulvic-like substance. The associated complexing constants (lgK) of 3 components with TC were in the range of 5.05-5.85, followed the order of C2 > C3 > C1. The strong binding ability of protein-like substances confirmed their prominent role in the TC-DOM complexation. These results highlight the significant impact of DOM on the bioavailability and ecotoxicity of antibiotics in freshwater lakes.