Hydrogen Peroxide Detection in Groundwater at Rifle, Colorado

We here present evidence for the unrecognized and light-independent generation of H2O2 in groundwater of an alluvial aquifer adjacent to the Colorado River near Rifle, CO. In situ detection using a sensitive chemiluminescent method suggests H2O2 concentrations ranging from lower than the detection limit (< 1 nM) to 54 nM along the vertical profiles obtained at various locations across the aquifer. Our results suggest dark formation of H2O2 is more likely to occur in transitional redox environments where reduced elements (e.g., reduced metals and NOM) meet oxygen, such as oxic-anoxic interfaces. Due to its transient nature, the widespread presence of H2O2 in groundwater suggests the existence of a balance between H2O2 sources and sinks, which potentially involves a cascade of various biogeochemically important processes that could have significant impacts on metal/nutrient cycling in groundwater-dependent ecosystems, such as wetlands and springs. More importantly, our results demonstrate that reactive oxygen species are not only widespread in oceanic and atmospheric systems, but also in the subsurface domain, possibly the least understood component of biogeochemical cycles.

本研究提供证据表明，在科罗拉多州里弗尔附近毗邻科罗拉多河的冲积含水层地下水中，存在此前未被认知的、不依赖光照的过氧化氢（H₂O₂）生成过程。采用灵敏化学发光法开展的原位检测结果显示，在该含水层不同点位获取的垂直剖面中，过氧化氢浓度范围从低于检测限（<1纳摩尔）至54纳摩尔不等。本研究结果表明，过氧化氢的暗生成过程更易发生在还原态物质（例如还原态金属与天然有机质（Natural Organic Matter, NOM））与氧气接触的过渡氧化还原环境中，例如氧-缺氧界面。鉴于过氧化氢具有瞬时性的特性，其在地下水中的广泛分布表明过氧化氢的源与汇之间存在动态平衡，这一过程可能涉及一系列具有重要生物地球化学意义的级联反应，进而对依赖地下水的生态系统（如湿地与泉水）中的金属/养分循环产生显著影响。更为重要的是，本研究结果证实，活性氧（Reactive Oxygen Species, ROS）不仅广泛存在于海洋与大气系统中，同样也分布于地下领域——这一区域或许是生物地球化学循环中认知程度最低的组成部分。