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Forever: Iodine-129 “a growing radiological risk” — 15.7 million year half-life — Almost undetectable — Traveled along with iodine-131 from Fukushima — Concentrates in hotspots

Published: April 3rd, 2012 at 8:31 am ET
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I-129 there forever
hotspots

Title: Dartmouth scientists track radioactive iodine from Japan nuclear reactor meltdown
Source: Dartmouth College
Date: April 2, 2012

[...] The radioisotope iodine-131, a significant constituent of the fallout, is a by-product of nuclear fission, highly radioactive, acutely toxic and presents a health risk upon its release to the environment. It does have a relatively short half-life, which is both a blessing and a curse, Landis notes. “It releases a lot of radioactivity, which makes it dangerous, but it’s gone very quickly so there is no long term exposure risk,” he says. Its high radioactivity, however, makes it very detectable by the gamma-ray spectroscopy instruments used by the Dartmouth team in its analyses.

This is not the case with another isotope, iodine-129, released concurrently with iodine-131. It is not as radioactive, which makes it much harder to measure, but it is much longer lasting [15.7 million year half-life] and, as it concentrates in certain areas over time, it may become more hazardous. “Due to its long half-life and continued release from ongoing nuclear energy production, [iodine-129] is perpetually accumulating in the environment and poses a growing radiological risk,” the authors point out.

The production rate of these two isotopes in a nuclear reactor occurs at a fixed ratio of 3 parts iodine-131 to one part iodine-129. The two substances travel together, so the presence of the easily detectable isotope also signals the presence of the longer-lived one. “If you have a recent event like Fukushima, you are going to have both present. The iodine-131 is going to decay away pretty quickly over the course of weeks, but the iodine-129 is there forever, essentially,” Landis says. However, he explains, “Once the iodine-131 decays, you lose your ability to track the migration of either isotope.”

Thus, the group’s research turned toward the development of an innovative alternative approach to measuring and tracking the iodine. What became an important off-shoot of their work was the methodology of using the benign radioisotope, beryllium-7, as the tracking indicator. It’s an easily detected natural radionuclide, and is routinely used by the Dartmouth researchers in their environmental analyses.

The Dartmouth researchers have shown that beryllium-7 follows the same transport paths as the iodine isotopes. By ascertaining the ratio of association of the beryllium to the iodine, tracing the beryllium-7 as it moves through the environment then allowed the researchers to track the parallel transport of iodine, and to demonstrate the accumulation of iodine fallout in stream sediments.

Title: Surficial redistribution of fallout 131iodine in a small temperate catchment
Source: National Academy of Sciences
Authors: Joshua D. Landisa, Nathan T. Hamma, Carl E. Renshawa, W. Brian Dadea, Francis J. Magilliganb, and John D. Gartnera
Date: March 13, 2012

Abstract

Isotopes of iodine play significant environmental roles, including a limiting micronutrient (127I), an acute radiotoxin (131I), and a geochemical tracer (129I). 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 131iodine 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) 137cesium 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 7beryllium, 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.

Published: April 3rd, 2012 at 8:31 am ET
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April 3rd, 2012 | Category: Fukushima Daiichi
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20 comments to Forever: Iodine-129 “a growing radiological risk” — 15.7 million year half-life — Almost undetectable — Traveled along with iodine-131 from Fukushima — Concentrates in hotspots

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