Interaction between organic matter and tetracycline in river sediments in cold regions

In this study, the interaction between river sediments collected from cold regions and typical antibiotics was investigated. The results show that tetracycline addition to the sediment can promote the fluorescence quenching of protein-like, marine humic acid, and humic acid-like substances. The degree of quenching increased with the increase of tetracycline concentration (0-80 μM). The fluorescence quenching degree of protein-like, marine humic acid, and humic acid-like substances is as high as 94.76%, 70.19%, and 77.80%, respectively. In addition, the process belongs to static quenching, and a ground-state complex is formed during the quenching reaction. The number of binding sites of tetracycline and protein-like, marine humic acid, and humic acid-like substances is 1.30, 1.51, and 1.34, respectively. The order of the strength of the formed complex is marine-like humic acid, protein-like, and humic acid-like substrates. The secondary structure of protein-like substrate in the sediment organic matter includes three types: aggregated strands, β-Sheet, and α-helix; and the content ratios are 10.23%, 8.33%, and 81.44%, respectively. When the concentration of tetracycline increased to 80 μM, the content of β-sheet increased significantly, while the content of α-helix decreased significantly. 2D-COS analysis showed that the reaction sequence of organic functional groups and tetracycline in the sediment was phenolic hydroxyl group, fatty group of amino acid structure, nonfluorescent polysaccharide, and protein-like α-helix substrates. After tetracycline interacts with water-extractable organic matters (WEOM), the structure of WEOM becomes compact, and its adsorption capacity on the surface of minerals is significantly reduced, resulting in an increase in the fluidity of tetracycline in the water environment.