Tracing the History of Nuclear Releases:  Determination of ¹²⁹I in Tree Rings

Abstract

Concentrations of the long-lived radioisotope 1291 were measured in dated tree rings in order to determine whether the distribution of this isotope reflects the history of nuclear deposition. 129I concentrations and 129I/127I ratios were analyzed in tree rings and bark samples from four trees at West Valley, NY, and from one tree at Rochester, NY. West Valley was the site of short-lived nuclear fuel reprocessing activities (1966-1972), while Rochester, located 115 km to the northeast, provided a regional control site for the study. The selected trees reflect different modes of fluid and nutrient transport in trees, with three species of ring-porous trees (elm, oak, and locust), one semidiffuse (cherry), and one diffuse-porous tree (maple). The results show that 1291 levels in ring-porous trees, in which xylem or hydrologic tissue is localized in the outermost growth ring, are generally well correlated with the expected 1291 deposition pattern for the region. In contrast, tree rings of the more common semidiffuse to diffuse-porous wood, where xylem is disseminated throughout the trunk, show a less well developed 129I signal, probably due to the transport of iodine ions across annual rings. Iodine concentrations in the tree rings range from 0.04 to 2 mg/kg, 129I/127I ratios from 6 x 10(-10) to 3.8 x 10(-6). Tree bark and the outermost rings show significantly higher 129I concentrations than the wood of the trunk. The 129I/127I ratios for bark are very similar to values obtained for surface soil and water at the two localities, while inner rings have ratios similar to those in deeper layers of the soil, reflecting different pathways for 129I uptake and the differences in ambient 1291 levels between the atmosphere and deep soil. Although ring porous trees preserve the depositional pattern of nuclear releases, rings older than or close to the onset of the nuclear age have 129I/127I ratios significantly above the preanthropogenic level, suggesting that even in these trees some redistribution of 129I occurs throughout the trunk. Our results indicate that growth rings from ring-porous wood are useful in time-series analyses of regional 129I deposition, yielding reliable information on relative changes in 129I concentrations but requiring caution in the reconstruction of absolute ambient concentrations during any given time.

Iodine toxicity in a plant-solution system with and without humic acid

“…The environmental fate of iodine (I) has been of historic interest because radioactive isotopes, especially 129 I, may be released into the environment as a byproduct of the nuclear power industry (Rao et al, 2002). More recently, iodine is noted for its effectiveness as a general biocide in water sanitation for manned spacecraft, as well as in the health care, livestock, dairy, and poultry industries.…”

Some considerations in the reconstruction of lead levels using laser ablation: lessons from the design stage of dendrochemistry study, St.John's, Canada

“…1 Elms found in two public parks in downtown St. John's represent ring-porous wood ( Table 1). Species with this kind of structure are commonly used in dendrochemical studies because water transport usually involves the outermost annual rings only, which increases the temporal resolution of the dendrochemical record (Ault et al, 1970;Cutter and Guyette, 1993;Eklund, 1995;Rao et al, 2002;Prapaipong et al, 2008 andWu et al, 2010). Perhaps related to this characteristic is the relatively high Pb accumulation noted in the ring-porous wood of oak and ash (Kardell and Larson, 1978).…”

Analysis of ¹²⁹I and its Application as Environmental Tracer

“…7 shows 129 I recorders in tree rings of three species, of them locust and oak samples were collected from West Valley, and another tree rings of elm from Rochester, the background area in USA. A high 129 I/ 127 I level was observed in tree rings of oak and locust, this corresponds to the air emission of 129 I from a reprocessing plant located in West Valley (USA) [62]. Corals live in shallow waters, generally within 100 meters depth.…”

“…I from the seawater in the North Sea, Irish Sea and Norwegian Sea is another source of 129 I in the ice core, but this might be not the major source due to a relatively long distance (>600 km) from Swiss Alpines to the marine sources and high altitude of the sampling site. Tree rings are also specimen used to retrieve the 129 I level in the environment if the cross section migration is small [62,63]. However, because the tree can absorb iodine from both atmosphere directly through leaves and the soil through root, a special correction might be needed to retrieve the 129 I level in the atmosphere using the 129 I concentration in the tree ring.…”

“…In addition, the selection of the tree species is also critical, since the fixation of iodine in the specific year layer and cross section migration of absorbed iodine will seriously interfere with the application of 129 I for reconstruction of atmospheric 129 I level. It has been suggested that elm, oak, and locust are three optimal species for this application [62]. Fig.…”