Kent A. Orlandini

Pu(V) as the stable form of oxidized plutonium in natural waters

Abstract This work presents analytical evidence supporting the proposition that Pu(V) is the sole or predominant form of oxidized plutonium in natural waters. Two independent methods, the selective adsorption of Pu(VI) by silica gel, and the somewhat less selective coprecipitation of Pu(V) with calcium carbonate, were developed to separate Pu(V) from Pu(VI). Measurements of ambient plutonium in several natural waters by these methods found only Pu(V). In laboratory tracer studies, Pu(VI) was shown to be highly unstable in dilute bicarbonate solution and in Lake Michigan water, reducing in first-order fashion to Pu(V).

Sources of the transuranic elements plutonium and neptunium in arctic marine sediments

Abstract We report here thermal ionization mass spectrometry measurements of 239 Pu , 240 Pu , 241 Pu , 242 Pu , and 237 Np isolated from oceanic, estuarine, and riverine sediments from the Arctic Ocean Basin. 238 Pu/ 239+240 Pu activity ratios are also reported for alpha spectrometric analyses undertaken on a subset of these samples. Our results indicate that the Pu in sediments on the Alaskan shelf and slope, as well as that in the deep basins (Amerasian and Eurasian) of the Arctic Ocean, has its origin in stratospheric and tropospheric fallout. Sediments from the Ob and Yenisei Rivers show isotopic Pu signatures that are distinctly different from those of northern-hemisphere stratospheric fallout and indicate the presence of weapons-grade Pu originating from nuclear fuel reprocessing wastes generated at Russian facilities within these river catchments. Consequently, sediments of the Eurasian Arctic Ocean, particularly those in the Barents and Kara Seas, probably contain a mixture of Pu from stratospheric fallout, tropospheric fallout, and fuel-reprocessing wastes of riverine origin. In particular, the 241 Pu/ 239 Pu ratios observed in these sediments are inconsistent with significant contributions of Pu to the arctic sediments studied from western European reprocessing facilities, principally Sellafield in the UK. Several other potential sources of Pu to arctic sediments can also be excluded as significant based upon the transuranic isotope ratios presented.

Isotopic Pu, U, and Np signatures in soils from Semipalatinsk-21, Kazakh Republic and the Southern Urals, Russia

Mass spectrometry measurements of Pu, U and Np isolated from soils contaminated by the 1957 accident at the Mayak nuclear complex in the Southern Ural mountains (‘Kyshtym accident’) and from soils collected at and near the Former Soviet Union (FSU) test site at Semipalatinsk-21 are reported. The results provide a coherent isotopic data set suggesting (1) that Pu recovered from irradiated uranium fuels processed at Mayak formed the source material for Pu devices tested at Semipalatinsk-21; (2) that 237Np in the breached Mayak storage tank resulted, principally, from enrichment of this radionuclide in waste streams during the processing of low burn-up uranium fuels to recover both Pu and U and (3) the presence of 236U at both sites may be useful in tracing inputs of this, and other transuranic radionuclides, to nearby river systems that flow to the Arctic Ocean.

Uptake of natural and anthropogenic actinides in vegetable crops grown on a contaminated lake bed

Abstract Activity concentrations and plant/soil concentration ratios (CRs) of 239,240 Pu, 241 Am, 244 Cm, 232 Th, and 238 U were determined for three vegetable crops grown on an exposed, contaminated lake bed of a former reactor cooling reservoir in South Carolina, USA. The crops included greens and tubers of turnips ( Brassica rapa var. white-globe), bush beans ( Phaseolus vulgaris ), and husks and kernels of sweet corn ( Zea mays var. silver queen). Although all plots were fertilized, some received K 2 SO 4 , while others received no K 2 SO 4 . The K 2 SO 4 fertilizer treatment generally lowered activity concentrations for 241 Am, 244 Cm, 232 Th and 238 U, but differences were statistically significant for 241 Am and 244 Cm only. Highly significant differences occurred in activity concentrations among actinides and among crops. In general, turnip greens exhibited the highest uptake for each of the actinides measured, while corn kernels had the least. For turnip greens, geometric mean CRs ranged from 2.3×10 -3 for 239,240 Pu to 5.3×10 -2 for 241 Am (no K 2 SO 4 fertilizer). For corn kernels, geometric mean CRs ranged from 2.1×10 -5 for 239,240 Pu and 232 Th to 1.5×10 -3 for 244 Cm (no K fertilizer). In general, CRs across all crops for the actinides were in the order: 244 Cm> 241 Am> 238 U> 232 Th > 239,240 Pu. Lifetime health risks from consuming crops contaminated with anthropogenic actinides were similar to the risks from naturally occurring actinides in the same crops (total ∼2×10 -6 ); however, these risks were only ∼0.3% of the risk from consuming the same crops contaminated with 137 Cs.

Laboratory and field studies of the relative mobility of 239,240Pu and 241Am from lake sediments under oxic and anoxic conditions

Abstract Laboratory extraction experiments and field observations were employed to determine the relative mobility of 239,240pu and 241Am from lake sediments under aerobic and anaerobic conditions. Laboratory investigations show that under aerobic conditions 241Am is more readily extracted from Lake Michigan sediments than is 239,240Pu. Under anaerobic conditions, the extractability of plutonium and americium does not increase significantly relative to aerobic conditions. Field studies indicate that neither element is recycled from the sediment to the overlying water column during anaerobic conditions attendant with thermal stratification. The adsorption of these elements onto sediments does not appear to be correlated with extractable iron, manganese, and organic compounds such as humic and fulvic acids.

The distributions of 239,240Pu, 238Pu, 241Am and 137Cs among chemically-defined components of sediments, settling particulates and net plankton of Lake Michigan

Abstract The application of selective extraction techniques to samples of consolidated sediments, surficial sediment floc and suspended particulate material collected in sediment traps from Lake Michigan shows that 239,240Pu, 238Pu and 241Am are removed primarily with the hydrous oxide coatings while 137Cs is strongly associated with the mineral fraction. Low concentrations of plutonium and americium are found associated with isolated humic acid fractions. The selective extraction of plutonium from net plankton samples results in the observation of a different distribution of plutonium among phases than that observed for sedimentary material, but, in all cases, the major fraction of the plutonium is found in the same extractant as with sediment samples. Attempts to displace 137Cs from the mineral fraction by several techniques indicate that the adsorption of 137Cs is not readily reversible.

Measuring low concentrations of 234Th in water and sediment

Th/ 238 U disequilibria have been used extensively in studies of particle dynamics and the fate and transport of particle- reactive matter in marine environments. Similar work in low salinity, estuarine, and freshwater systems has not occurred primarily because the lower concentrations of both parent and daughter nuclides that are typical of these systems often render established methods for the analysis of 234 Th inadequate. The application of this radionuclide tracer technique to these systems, however, has great potential. To this end, we present a method for measuring low activities of 234 Th in relatively small samples (<200 l) using low background gas-flow proportional counters, a 229 Th yield monitor, and empirical corrections for the interferences from real and apparent betas that are emitted by other thorium isotopes and their progeny. For samples with low 234 Th/ 228 Th activity ratios, we improve upon current beta counting methodologies that rely on immediate sample counting, weak beta absorption, or multiple beta counts so that, using the analytical approach outlined here, it should be possible to measure 234 Th activities (i) as low as 1.5 dpm/total sample, (ii) up to 2 weeks after radiochemical purification of thorium, and (iii) with only one sample count for alpha and beta activity. D 2002 Elsevier Science B.V. All rights reserved.

Chemical characterization of size-fractionated humic and fulvic materials in aqueous samples

Abstract Humic and fulvic acids have been shown to be potentially important transport agents for inorganic and organic contaminants, including radionuclides, in surface and groundwaters. In this work, the possibility of characterizing humic and fulvic materials in the colloidal and macromolecular size ranges (i.e., between 3000 molecular weight (1 nm) and 0.45 μm) after size fractionation and collection with hollow-fiber ultrafilters has been investigated. Three surface waters have been examined as test cases. Using ultrafiltration, sized samples of humic and fulvic acids were chemically characterized with 13 C-nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) using diffuse reflectance, and pyrolysis/gas chromatography (GC). These test cases demonstrate that sufficient material can be obtained by ultrafiltration with minimal or no alteration to the materials. In addition, inorganic analyses performed on the size fractions show that ultrafiltration can also allow the binding capacity of the humic materials in each fraction to be measured. Substantial variability among the different humic and fulvic fractions demonstrates the importance of sizing submicron materials in attempts to understand the mechanisms of pollutant transport by natural humic materials.

Oxidation states of plutonium in carbonate-rich natural waters

Abstract Adsorption of actinide elements to calcium carbonate in waters of moderate to high carbonate concentration has been shown to be dependent on the oxidation state. This property has been exploited for distinguishing the (III) and (IV) oxidation states of plutonium. Ambient plutonium in Mono Lake, California, a natural high-carbonate water, appeared to be entirely in the (IV) oxidation state. Tracer experiments in carbonate media and in Mono Lake water, in the presence of atmospheric oxygen, confirmed that Pu(III) is rapidly oxidized under these conditions.

Measurements of 7Be and 210Pb in rain, snow, and hail

Abstract Measurements of the levels of 7Be and 210Pb are reported for rain, snow, and hail samples taken at Argonne, Illinois, and Socorro, New Mexico. These natural radioisotopes are indicators of the sources of the aerosols contributing materials to the precipitation samples. The data presented indicate that the more soluble 7Be is enriched in the precipitation samples with respect to 210Pb, as compared to the ratios of these radioisotopes found in aerosol samples. Use of the 210Po/210Pb activity ratios as an internal clock indicated that the aerosols contributing to the precipitation ranged in age from 10 to 47 days. Levels of 7Be ranged from 11 to 55 pCi L−1 for the samples, with the highest levels in a stratus precipitation event and in a thunderstorm with the lowest wet deposition rate. These results are discussed with regard to the potential for use of these radioisotopes in the determination of stratospheric-tropospheric mixing and in their geochemical usage as indicators of sedimentation rates.