Acetochlor degradation in anaerobic microcosms with hyporheic sediments: Insights from biogeochemical data, transformation products, and isotope analysis

Yuanzheng Zhang; Bing Wen; Yanyan Ni; Yunping Tong; Benyi Cao; Aiguo Zhou; Jian Xu; Yunde Liu

doi:10.1016/j.watres.2024.123035

Acetochlor degradation in anaerobic microcosms with hyporheic sediments: Insights from biogeochemical data, transformation products, and isotope analysis

Water Res. 2024 Dec 22:274:123035. doi: 10.1016/j.watres.2024.123035. Online ahead of print.

Authors

Yuanzheng Zhang¹, Bing Wen², Yanyan Ni², Yunping Tong², Benyi Cao³, Aiguo Zhou⁴, Jian Xu⁵, Yunde Liu⁶

Affiliations

¹ Hubei Key Laboratory of Yangtze River Basin Environmental Aquatic Science, School of Environmental Studies & State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074, Wuhan, PR China; State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, 210042, Nanjing, PR China.
² State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, 210042, Nanjing, PR China.
³ School of Sustainability, Civil and Environmental Engineering, University of Surrey, Guildford GU2 7XH, UK.
⁴ Hubei Key Laboratory of Yangtze River Basin Environmental Aquatic Science, School of Environmental Studies & State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074, Wuhan, PR China.
⁵ State Environmental Protection Key Laboratory of Soil Environmental Management and Pollution Control, Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of China, 210042, Nanjing, PR China. Electronic address: xujian@nies.org.
⁶ Hubei Key Laboratory of Yangtze River Basin Environmental Aquatic Science, School of Environmental Studies & State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, 430074, Wuhan, PR China. Electronic address: lydcn84@126.com.

PMID: 39754828
DOI: 10.1016/j.watres.2024.123035

Abstract

Steep redox gradients and diverse microbial communities in the anaerobic hyporheic zone create complex pathways for the degradation of herbicides, often linked to various terminal electron-accepting processes (TEAPs). Identifying the degradation pathways and their controlling factors under various TEAPs is of great significance for understanding mechanisms of water purification in the hyporheic zone. However, current research on herbicides in this area remains insufficient. Acetochlor, a commonly detected herbicide in aquatic environments, was the target contaminant in this study. Biogeochemical data, transformation products examination, and compound-specific isotope analysis (CSIA) were used to elucidate the degradation mechanisms of acetochlor under various TEAPs in anaerobic microcosms with hyporheic sediments. Results showed that carbon isotope fractionation of acetochlor during abiotic reduction by reduced sulfur species (ε_bulk,C = -16.4 ± 0.4‰), such as HS^- and S_n^2-, was significantly larger than that observed during anaerobic biodegradation (ε_bulk,C = -3.7 ± 0.4‰). This suggested the utility of CSIA in identifying biotic/abiotic degradation pathways of acetochlor in anaerobic environments. CSIA and transformation products examination revealed that biodegradation under Fe(III) reducing conditions and abiotic reduction by reduced sulfur species under SO₄^2- reducing conditions were the main pathways for acetochlor degradation in anaerobic hyporheic sediments. TEAPs controlled the abilities and mechanisms of acetochlor degradation in different hyporheic sediments, which were highly associated with terminal electron acceptors (Fe(III) and SO₄^2-), Fe(III) reducing bacteria (Geobacter and Anaerolinea), SO₄^2- reducing bacteria (Bacteroidetes_vadinHA17), and tryptophan-like substances. This study provides important insights into the mechanisms of herbicides degradation in the hyporheic zone.

Keywords: Acetochlor; Anaerobic degradation; Compound-specific isotope analysis; Herbicide; Hyporheic sediment; Terminal electron-accepting processes.