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.

中文翻译：

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低流沉积物厌氧微观世界中乙草胺降解：来自生物地球化学数据、转化产物和同位素分析的见解


厌氧低流区陡峭的氧化还原梯度和多样化的微生物群落为除草剂的降解创造了复杂的途径，通常与各种末端电子接受过程 （TEAP） 有关。确定各种 TEAP 下的降解途径及其控制因素，对于理解低流区水净化机制具有重要意义。然而，目前对该领域除草剂的研究仍然不足。乙草胺是水生环境中常见的除草剂，是本研究的目标污染物。采用生物地球化学数据、转化产物检查和化合物特异性同位素分析 （CSIA） 阐明了低流沉积物厌氧微观世界中各种 TEAP 下乙草胺的降解机制。结果表明，乙草胺在还原硫物质（ε _bulk,C = -16.4 ± 0.4‰）（如 HS ^– 和 S _n ^2– ）的非生物还原过程中的碳同位素分馏显著大于厌氧生物降解过程中观察到的碳同位素分馏（ε _bulk,C = -3.7 ± 0.4‰）。这表明 CSIA 在识别厌氧环境中乙草胺的生物/非生物降解途径方面的效用。CSIA 和转化产物检查表明，在 Fe（III） 还原条件下的生物降解和 SO ₄ ^2– 还原条件下还原硫物种的非生物还原是厌氧低流沉积物中乙草胺降解的主要途径。 TEAP 控制不同流下沉积物中乙草胺降解的能力和机制，与末端电子受体 （Fe（III） 和 SO ₄ ^2– ）、Fe（III） 还原菌 （Geobacter 和 Anaerolinea）、SO ₄ ^2– 还原菌 （Bacteroidetes_vadinHA17） 和色氨酸样物质高度相关。这项研究为低流区除草剂降解的机制提供了重要的见解。