Graduate Student, University of Cincinnati
The isolation of long-lived radioisotopes in a complex, urban matrix.
Detonation of a nuclear device in an urban area will generate debris comparable to the composition, particle size, and concentration created by the collapse of the World Trade Center (WTC) buildings. New pathway analyses are needed to accommodate the dispersion, resuspension, and inhalation of a contaminated debris that is intrinsically different from previous incidents at nuclear power plant incidents, including the Chernobyl and Fukushima, as well as dispersion from atmospheric testing. Dust from WTC is a mixture of concrete and gypsum, materials with an abundance of calcium, like soils from the Marshall Islands. Thus, because of the similar abundancies of interferences, Marshall Island soil can be regarded as an analog for urban rubble. Therefore, this soil is useful for developing robust analytical methods for calcium-rich samples. Marshall Island soil also presents a unique opportunity to evaluate terrestrial to marine pathways, especially for strontium-90. Residual, post detonation, radioactive contamination in the Marshall Islands is related to trace amounts of uranium and plutonium and long-lived fission products specifically, cesium-137 and strontium-90. Cesium-137 and strontium-90 are chemical congeners of potassium and calcium and increase risk to human health by depositing in soft tissue and bone, respectively. Studies conducted by Lawrence Livermore National Laboratory show that cesium-137 contamination in Marshall Islands soil, water, and plants decreases by half in 8–10 years. Furthermore, an understanding of the cycling of cesium-137 in coral atoll ecosystems, and proposed remedial measures to help reduce doses from locally grown food products has been developed. However, much less is understood about the fate of strontium-90. With the possibility for resuspension causing redistribution in an urban environment, understanding the behavior of strontium-90 in this unique matrix is significant for assessment of the health risks from inhalation. The WTC incident demonstrates that direct inhalation of dispersed and resuspended particles, rather than dietary intake, represents the greatest risk to human health. At Livermore, there is a large, well-documented archive of environmental samples. These samples can be used to evaluate terrestrial-aquatic environmental transport and cycling of strontium-90 to establish a technical basis for assessing risk to the population following a nuclear detonation in an urban, calcium-rich environment.
Abstract: The United States conducted a series of nuclear tests from 1946 to 1958 at Bikini, a coral atoll, in the Marshall Islands (MI). The aquatic and terrestrial environments of the atoll are still contaminated with several long-lived radionuclides that were generated during testing. The four major radionuclides found in terrestrial plants and soils are cesium-137, strontium-90, plutonium-239+240 and americium-241. Cesium-137 in the coral soils is more available for uptake by plants than 137Cs associated with continental soils of North America or Europe. Soil-to-plant 137Cs median concentration ratios (CR) (kBq·kg-1 dry weight plant/kBq·kg-1 dry weight soil) for tropical fruits and vegetables range between 0.8 and 36, much larger than the range of 0.005 to 0.5 reported for vegetation in temperate zones. Conversely, 90Sr median CRs range from 0.006 to 1.0 at the atoll versus a range from 0.02 to 3.0 for continental silica-based soils. Thus, the relative uptake of 137Cs and 90Sr by plants in carbonate soils is reversed from that observed in silica-based soils. The CRs for 239+240Pu and 241Am are very similar to those observed in continental soils. Values range from 10-6 to 10-4 for both 239+240Pu and 241Am. No significant difference is observed between the two in coral soil. The uptake of 137Cs by plants is enhanced because of the absence of mineral binding sites and the low concentration of potassium in the coral soil. Cesium-137 is bound to the organic fraction of the soil, whereas 90Sr, 239+240Pu and 241Am are primarily bound to soil particles. Assessment of plant uptake for 137Cs and 90Sr into locally grown food crops was a major contributing factor in: (1) reliably predicting the radiological dose for returning residents and (2) developing a strategy to limit the availability and uptake of 137Cs into locally grown food crops.
Pub.: 01 Feb '00, Pinned: 01 Jul '17
Abstract: Radiostrontium is concentrated in the shells of mollusks and other animals due to the isomorphic substitution of strontium for calcium in the calcium carbonate shell matrix. Radiochemical separation of strontium from such matrices is difficult because of the chemical similarity between strontium and calcium. This paper describes a technique using a commerically-available, solid-phase extractant to separate Sr-89 and Sr-90 from high concentrations of Ca2+. The extractant removes Sr(NO3)2 from acidic nitrate media, and strontium activities are determined via conventional β-counting techniques. This method has been used to process mollusk shells collected from contaminated reactor cooling ponds at the Savannah River Site and Chernobyl Nuclear Power Plant.
Pub.: 01 Jul '95, Pinned: 01 Jul '17
Abstract: A series of Kd tracer batch experiments were conducted to assess the absorptive-desorption properties of Biochar as a potential agent to selectively sequester labile soil Cs or otherwise help reduce the uptake of Cs isotopes into plants. A parallel experiment was conducted for strontium. Fine-grained fractionated Woodlands tree Biochar was found to have a relatively high affinity for Cs ions (Kd > 100) relative to coral soil (Kd < 10) collected from the Marshall Islands. The Biochar material also contains an abundance of K (and Mg). These findings support a hypothesis that the addition of Biochar as a soil amendment may provide a simple yet effective method for reducing soil-to-plant transfer of Cs isotopes in contaminated environments.
Pub.: 19 Oct '15, Pinned: 01 Jul '17