Free phase radon in the Earth's subsurface: Occurrence, sources, transport pathways, and insights

氡是一种放射性元素，以溶解和游离气体的形式存在。它是第六大致癌原因(和仅次于吸烟的第二大肺癌致病原因)，但人类的感官无法察觉。氡普遍存在于室内空气、浅层土壤和地下水中，但其来源尚不清楚(S)。尽管浅层土壤和家庭中的氡通常被归因于浅层(不到100米深)的富铀土壤和岩石，但这一点尚未在研究中得到证实。了解导致氡普遍存在但在空间上不均匀分布的主要地下来源(S)和传输路径将有助于减轻其对公共健康的重大影响。虽然我们对地下氡的主要来源(S)和迁移途径知之甚少，但我们有一些重要的线索。在火山、洞穴、地下矿山和一些地质断层释放的游离气体中，氡通常以相对较高的浓度(与二氧化碳一起)共生。在大陆的空气中，氡的浓度高于海洋，这与大陆来源一致。这项研究将评估在地球大陆地壳或地幔的重要深度(即&gt；1公里)广泛产生氡的可能性，并在浮力的作用下通过广泛的路径网络作为游离气体输送到地下。这一概念在概念上具有挑战性，因为放射性衰变会导致氡浓度每3.82天下降一半，因此从深处的迁移必须是快速的。尽管几乎没有进行现场研究，但长期以来一直有报道称，自由相气体通过裂缝和孔洞的传输速度高达每天数十公里，因此这是可能的。我将与10名受训人员(5名理科学士、3名理学硕士、1名博士生和1名博士后)一起对地下气泡发出的深层气源和相关流体(包括充气的泉水和池塘、井、间歇泉和地质断层)进行采样。将结合一系列其他参数对氡进行分析，以深入了解氡和其他流体的来源(S)和深度(S)，以及相对地下停留时间。这项工作将提供对氡源和途径的洞察，以支持政府和工业降低氡的致癌风险，特别是在家庭中。这项研究还将提供对地源碳排放到大气中的洞察(全球范围内限制很差，除了火山排放)。第三，这项工作将深入了解地球次表层的自由相气体传输路径和速度，我们对这些路径和速度知之甚少，但需要对设施(例如泄漏的油井、天然气储存点和碳捕获和储存点)进行适当的监测和测量，以便加拿大人能够有效地排放温室气体。

Radon is a radioactive element that occurs in dissolved and free phase gas forms. It is the 6th leading cause of cancer (and 2nd leading cause of lung cancer after smoking), but imperceptible to the human senses. Radon is ubiquitous and highly variable in indoor air, shallow soil, and groundwater, but its source(s) are not clear. Although radon in shallow soil and homes is most often attributed to shallow (less than 100 metres or so depth) uranium-rich soil and rocks, this has not been borne out in research studies. An understanding the major subsurface source(s) and transport pathways that are are responsible for radon's ubiquitous but spatially heterogeneous occurrence would help mitigate its significant public health impacts. Although we know very little about the main source(s) and transport pathways of subsurface radon, we have some important clues. Radon often co-occurs at relatively high concentrations (along with carbon dioxide) in free phase gas emissions from volcanoes, caves, underground mines, and some geologic faults. Its concentrations are higher in air over the continents than the oceans, consistent with a continental source.  This research will evaluate the possibility that Rn is widely produced at significant depths (i.e., > 1 km) in the earth's continental crust or mantle, and transported to the subsurface under buoyancy as free phase gas through a widespread pathway network. This notion is conceptually challenging because radioactive decay causes Rn concentrations to decrease by one-half every 3.82 days, so the transport from depth has to be rapid.  Although little field research has been conducted, free phase gas transport through fractures and pores has long been reported, with rates up to tens of kilometers per day, however, so this is possible.    I will work with ten trainees (five BSc, three MSc, and one PhD student and one PostDoc) to sample deep sources of gases and associated fluids (including gassy springs and ponds, wells, geysers, and geologic faults) where gas bubbles issue from the subsurface. Radon will be analysed alongside a suite of other parameters to provide insight into the source(s) and depth(s) from which radon and other fluids originated, and also relative subsurface residence times. This work will providing insight into radon sources and pathways to support governments and industry to mitigate  cancer risk from radon, especially in homes.  This research will also provide insight into geogenic carbon emissions to the atmosphere (which are poorly constrained globally, except for volcanic emissions).  Thirdly, this work will  provide insight into free phase gas transport pathways and velocities in the earth's subsurface about which we know relatively little, but is needed for appropriate monitoring and measurement around facilities (e.g. leaking petroleum wells, gas storage sites, and carbon capture and storage sites) so Canadians can greenhouse gas emissions effectively.