Interactions between the antibiotic tetracycline and humic acid: Examination of the binding sites, and effects of complexation on the oxidation of tetracycline

Bo Yang; Chengjin Wang; Xin Cheng; Yongli Zhang; Wei Li; Jingquan Wang; Zixin Tian; Wenhai Chu; Gregory V Korshin; Hongguang Guo

doi:10.1016/j.watres.2021.117379

Interactions between the antibiotic tetracycline and humic acid: Examination of the binding sites, and effects of complexation on the oxidation of tetracycline

Water Res. 2021 Sep 1:202:117379. doi: 10.1016/j.watres.2021.117379. Epub 2021 Jun 22.

Authors

Bo Yang¹, Chengjin Wang², Xin Cheng¹, Yongli Zhang¹, Wei Li¹, Jingquan Wang¹, Zixin Tian¹, Wenhai Chu³, Gregory V Korshin⁴, Hongguang Guo⁵

Affiliations

¹ MOE Key Laboratory of Deep Earth Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, China.
² Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada.
³ State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China.
⁴ Department of Civil & Environmental Engineering, University of Washington, Box 352700, Seattle, WA, United States.
⁵ MOE Key Laboratory of Deep Earth Science and Engineering, College of Architecture and Environment, Sichuan University, Chengdu 610065, China. Electronic address: hgguo@scu.edu.cn.

PMID: 34246001
DOI: 10.1016/j.watres.2021.117379

Abstract

The binding between dissolved organic matter (DOM) and micro-pollutants (MPs) results in significant impacts on their migration, transformation and degradation. However, the role of the DOM/MP binding on their oxidative transformation remains poorly studied. The binding of MPs by DOM, in combination with DOM's roles as a photosensitizer and/or a competitor for free radicals, needs to be considered in the context of understanding the DOM's impacts on the oxidative degradation of MPs. This study aims to explore this aspect of DOM/MP interactions based on the quantitation of humic acid (HA) and tetracycline (TET) complexation and its role in TET removal. This study also compared the degradation of free TET versus that bound in HA-TET complexes in different oxidation processes. Fourier transform infrared (FTIR) data show that the carboxyl and phenolic hydroxyl groups in HA are the main binding sites of TET, while nuclear magnetic resonance (NMR) analysis shows the binding of TET engages its -N(CH₃)₂ groups, and two-dimensional correlation spectroscopy (2D-COS) data show that the carboxyl groups in DOM are sensitive than phenolic groups in the binding of TET. The difference between the degradation rates (Δk_obs) of the free and bound TET decreased with the increase of ionic strength using sodium nitrate, but increased with the introduction of Ca²⁺ and Mg²⁺ due to the formation of TET-Ca²⁺/Mg²⁺ complexes. Quenching experiments showed that the free radicals (•OH and •SO₄^-), PMS oxidant and UV light were the main contributors to the TET degradation in UV/PS, UV/PMS and UV/H₂O₂ processes, respectively. In-situ fluorescence time scanning and differential absorbance spectra showed that free TET was preferentially oxidized over the bound TET in all the tested treatments except UV/PS. These results provide new insights into the role of DOM/MP complexation in the degradation of MPs in natural and engineered systems.

Keywords: Binding interactions; Bound tetracycline; Chemical transformation; Humic acid.

MeSH terms

Anti-Bacterial Agents*
Binding Sites
Humic Substances* / analysis
Hydrogen Peroxide
Tetracycline

Substances

Anti-Bacterial Agents
Humic Substances
Hydrogen Peroxide
Tetracycline