Department of Earth Science, Department of Geography, Dartmouth College, Hanover, NH 03755, USA.
Proc Natl Acad Sci U S A. 2012 Mar 13;109(11):4064-9. doi: 10.1073/pnas.1118665109. Epub 2012 Feb 29.
Isotopes of iodine play significant environmental roles, including a limiting micronutrient ((127)I), an acute radiotoxin ((131)I), and a geochemical tracer ((129)I). But the cycling of iodine through terrestrial ecosystems is poorly understood, due to its complex environmental chemistry and low natural abundance. To better understand iodine transport and fate in a terrestrial ecosystem, we traced fallout (131)iodine throughout a small temperate catchment following contamination by the 11 March 2011 failure of the Fukushima Daiichi nuclear power facility. We find that radioiodine fallout is actively and efficiently scavenged by the soil system, where it is continuously focused to surface soils over a period of weeks following deposition. Mobilization of historic (pre-Fukushima) (137)cesium observed concurrently in these soils suggests that the focusing of iodine to surface soils may be biologically mediated. Atmospherically deposited iodine is subsequently redistributed from the soil system via fluvial processes in a manner analogous to that of the particle-reactive tracer (7)beryllium, a consequence of the radionuclides' shared sorption affinity for fine, particulate organic matter. These processes of surficial redistribution create iodine hotspots in the terrestrial environment where fine, particulate organic matter accumulates, and in this manner regulate the delivery of iodine nutrients and toxins alike from small catchments to larger river systems, lakes and estuaries.
碘同位素在环境中扮演着重要的角色，包括一种限制微量元素（127I）、一种急性放射性毒素（131I）和一种地球化学示踪剂（129I）。但是，由于碘的复杂环境化学性质和低天然丰度，其在陆地生态系统中的循环过程仍知之甚少。为了更好地了解陆地生态系统中碘的迁移和归宿，我们在福岛第一核电站 2011 年 3 月 11 日事故后，对一个小温带集水区中的放射性碘沉降物进行了追踪。我们发现，放射性碘沉降物被土壤系统积极有效地吸收，在沉积后数周内，其不断向表层土壤集中。同时，在这些土壤中观察到的历史（福岛之前）（137）铯的迁移表明，碘向表层土壤的集中可能是生物介导的。随后，通过河流过程，大气中沉积的碘被重新分配到土壤系统中，这与颗粒反应示踪剂（7）铍的方式类似，这是由于这些放射性核素对细颗粒有机物具有共同的吸附亲和力。这些表层再分配过程在陆地环境中形成了碘热点，细颗粒有机物在此积累，从而调节了从小集水区到大的河流系统、湖泊和河口的碘营养物质和毒素的输送。
