Molecular characteristics of leonardite humic acid and the effect of its fractionations on sulfamethoxazole photodegradation

• Published in: Chemosphere (Oxford) Vol. 246; p. 125642
• Main Authors: Zhang, Yiyue, Zhao, Furong, Wang, Fei, Zhang, Yahe, Shi, Quan, Han, Xiaomin, Geng, Huanhuan
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-05-2020
• Subjects: Anti-Bacterial Agents; Chemical Fractionation; Ecosystem; FI-ICR-MS; Humic acids; Humic Substances - analysis; Mass Spectrometry; Minerals - chemistry; Models, Chemical; Molecular weight fractions; Phenols; Photochemical Processes; Photolysis; Solar photodegradation; Sulfamethoxazole; Sulfamethoxazole - chemistry; Sunlight; FI-ICR-MS; Sulfamethoxazole; Molecular weight fractions; Humic acids; Solar photodegradation
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2019.125642

The widespread occurrence of synthetic antibiotic sulfamethoxazole (SMX)— poses a potential risk to aquatic ecosystems where dissolved organic matter (DOM) may affect its photolysis. In this study, the elimination of SMX by solar photolysis was investigated in the presence of leonardite humic acid (LHA) and its fractions. Fourier transform ion cyclotron resonance mass (FT-ICR-MS) spectra showed that LHA has high aromaticity. van Krevelen diagrams demonstrated highly unsaturated and phenolic compounds. The photolytic degradation of SMX was impeded by all DOM, mainly due to the competition of photons and scavenging or quenching of reactive oxygen species (ROS). The evaluation of isolated fractions of LHA suggested that fractions with MW < 3500, 14000–25,000 and > 100,000 had the greatest negative effects on sulfamethoxazole photodegradation; their inhibitory activities could reach up to 56.2%, 52.9% and 50.5%, respectively. The characterization of DOM at the molecular level will provide further insights into the assessment of photolysis for antibiotic elimination in natural waters where DOM exists ubiquitously.
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•FT-ICR-MS spectra showed that LHA has high aromaticity.• •OH, 1O2 and O2•-all make a contribution to SMX photodegradation.•LHA inhibited the photodegradation of SMX profoundly.•Different molecular weight of LHA has significant impact on SMX photolysis.