Chlorinated ethenes (CEs) are legacy contaminants whose chemical footprint is expected to persist in aquifers around the world for many decades to come. These organohalides have been reported in river systems with concerning prevalence and are thought to be significant chemical stressors in urban water ecosystems. The aquifer-river interface (known as the hyporheic zone) is a critical pathway for CE discharge to surface water bodies in groundwater baseflow. This pore water system may represent a natural bioreactor where anoxic and oxic biotransformation process act in synergy to reduce or even eliminate contaminant fluxes to surface water. Here, we critically review current process understanding of anaerobic CE respiration in the competitive framework of hyporheic zone biogeochemical cycling fuelled by in-situ fermentation of natural organic matter. We conceptualise anoxic-oxic interface development for metabolic and co-metabolic mineralisation by a range of aerobic bacteria with a focus on vinyl chloride degradation pathways. The superimposition of microbial metabolic processes occurring in sediment biofilms and bulk solute transport delivering reactants produces a scale dependence in contaminant transformation rates. Process interpretation is often confounded by the natural geological heterogeneity typical of most riverbed environments. We discuss insights from recent field experience of CE plumes discharging to surface water and present a range of practical monitoring technologies which address this inherent complexity at different spatial scales. Future research must address key dynamics which link supply of limiting reactants, residence times and microbial ecophysiology to better understand the natural attenuation capacity of hyporheic systems.

中文翻译：

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漂流带中氯化乙烯的自然衰减：关键生物地球化学过程和原位转化潜力的综述

氯化乙烯（CEs）是传统污染物，其化学足迹预计将在未来数十年内持续存在于世界各地的含水层中。这些有机卤化物已在河流系统中被报道，并具有普遍性，被认为是城市水生态系统中的重要化学应激源。含水层-河流界面（称为低渗带）是CE排放到地下水基流中地表水体的关键途径。该孔隙水系统可以代表天然的生物反应器，其中缺氧和有氧生物转化过程协同作用，以减少甚至消除污染物通向地表水的通量。这里，我们在自然有机物原位发酵推动的流变区生物地球化学循环的竞争框架中，严格审查了当前对厌氧性CE呼吸的过程理解。我们将一系列需氧细菌的代谢和协同代谢矿化的缺氧-缺氧界面开发概念化，重点放在氯乙烯降解途径上。沉积物生物膜中发生的微生物代谢过程与输送反应物的大量溶质迁移的叠加产生了污染物转化率的规模依赖性。过程解释常常与大多数河床环境中典型的自然地质异质性混淆。我们讨论了从CE羽流排放到地表水的最新现场经验中得出的见解，并提出了一系列实用的监测技术，这些技术可以解决不同空间尺度下这种固有的复杂性。未来的研究必须解决关键动力学问题，这些动力学问题将限制反应物的供应，停留时间和微生物生态生理联系在一起，以更好地了解流变系统的自然衰减能力。