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PubMed1989

The solubility and colloidal behaviour of neptunium (IV).

The solubility and colloidal particle formation of Np(IV) in 10(-1) M Na2S2O4 solution in the pH range 2-10 were studied by sequential filtration with decreasing filter pore size. With the help of spectrophotometry and an extraction technique, the species remaining in the final filtrate were found to be Np(V) at pH less than 6 and Np(IV) at pH greater than 8; particle species were attributed to Np(IV). The solubility data obtained at pH less than 6 were interpreted using the reaction: Np(OH)4(am)----NpO2+ + e- + 2H2O, log K = -6.7 +/- 0.4 At pH greater than 8, the solubility increased rapidly with increasing pH in the presence of air, and this was interpreted as being due to the formation of the negatively charged species Np(CO3)4x - 2x. The formation constants beta 3 and beta 4 were estimated to be similar to those reported for Pu(IV). The size distribution of colloidal Np(IV) was also obtained. Some simple models used to describe the observed size distributions and to estimate the equilibrium size distributions of colloidal Np(IV) were examined.

Colloids↗
PubMed1994

The gastrointestinal absorption of neptunium, plutonium and americium in a primate (C. jacchus).

Mixtures of Np, Pu and Am were administered to primates (C. jacchus) by gastric intubation to measure their fractional gastrointestinal absorption (f1 values). The values obtained were about 2 x 10(-3) and 1 x 10(-3), respectively, for Np and Pu administered as the citrate, and 2 x 10(-3) and 6 x 10(-4), respectively, for Pu and Am in potato. The significance of these values in terms of absorption in humans is discussed.

Americium↗
PubMed2006

Revision and meta-analysis of selected biosphere parameter values for chlorine, iodine, neptunium, radium, radon and uranium.

There is a continual supply of new experimental data that are relevant to the assessment of the potential impacts of nuclear fuel waste disposal. In the biosphere, the traditional assessment models are data intensive, and values are needed for several thousand parameters. This is augmented further when measures of central tendency, statistical dispersion, correlations and truncations are required for each parameter to allow probabilistic risk assessment. Recent reviews proposed values for 10-15 key element-specific parameters relevant to (36)Cl, (129)I, (222)Rn, (226)Ra, (237)Np and (238)U, and some highlights from this data update are summarized here. Several parameters for Np are revised downward by more than 10-fold, as is the fish/water concentration ratio for U. Soil solid/liquid partition coefficients, Kd, are revised downward by 10-770-fold for Ra. Specific parameters are discussed in detail, including degassing of I from soil; sorption of Cl in soil; categorization of plant/soil concentration ratios for U, Ra and Np; Rn transfer from soil to indoor air; Rn degassing from surface water; and the Ca dependence of Ra transfers.

Animals↗
PubMed2002

The distribution and history of nuclear weapons related contamination in sediments from the Ob River, Siberia as determined by isotopic ratios of plutonium and neptunium.

Isotopic ratios of Pu and Np measured in sediment cores from 5 locations in the Ob River drainage basin show clear evidence of input from sources other than global fallout (non-fallout sources). Historical contaminant records obtained by combining isotopic ratio information with chronological information indicate that non-fallout inputs are from several sources that have varied significantly over the past 50 years. Unique isotopic signatures observed in sediments from tributaries that drain areas containing known or suspected sources of non-fallout contamination are used to identify the source of materials in sediments collected at downstream locations. These data can lead to a better understanding of the transport behavior, fate, and relative importance of particle reactive, weapons related contaminants originating from the nuclear facilities Mayak. Tomsk-7, and Semipalitinsk, which lie within the drainage basin. From our work to date, we draw the following conclusions: (1) Persistent non-fallout contamination is observed in the Ob River above its confluence with the Irtysh River, indicating contamination from the Tomsk-7 facility. (2) Non-fallout contamination in the Tobol River above its confluence with the Irtysh River indicates contamination from the Mayak facility. (3) Non-fallout contamination in the Irtysh River above its confluence with the Tobol River indicates contamination from the Semipalitinsk weapons test site. (4) The occurrence of isotopic ratios in Ob Delta sediments that are similar to those observed in source tributaries suggests that contamination from at least two sources has been transported along the length of the river system. (5) Global fallout, a result of high-yield atmospheric weapons tests conducted by the FSU and USA primarily, is the dominant source of Pu and Np to the region; however, there have been brief periods when inputs from non-fallout sources exceeded those from global fallout.

Environmental Monitoring↗
PubMed2005

Neptunium(V) partitioning to uranium(VI) oxide and peroxide solids.

Metaschoepite, [(UO2)8O2(OH)12] x 10H2O, and metastudtite, UO4 x 4H2O, are alteration phases anticipated in a spent nuclear fuel repository following the moist oxidation of UO2 on a geologic time scale. Dissolved concentrations and hence potential mobility of other radionuclides in the fuel, such as the neptunyl cation (NpO2+), will likely be determined by the extent of their partitioning into these U(VI) solids. 237Np is of particular interest due to its potential high mobility and long half-life (2.1 x 10(6) years.) In this study, metaschoepite has been precipitated and subsequently transformed to studtite in the presence of dissolved Np. The metaschoepite and studtite solids that formed initially contained <10 and 6500 ppm Np, respectively. Batch dissolution studies of these solids at pH 6 demonstrate release of Np that exceeds congruent dissolution of U from metastudtite; furthermore, the released Np cation remains in solution. Thus, although the Np partitions into the metastudtite solid initially, it is released to solution over time, indicating that metastudtite is not likely to serve as a host solid for Np incorporation or sorption of the neptunyl cation on long time scales.

Adsorption↗
PubMed1986

Effective chelation therapy after incorporation of neptunium-239 in rats.

It was demonstrated in rats that it is possible to reduce the retention of 239Np in all body tissues by an early combined treatment with small doses of DTPA and DFOA. The content of 239Np can be decreased in soft tissues even if treatment is delayed. Promptly administered LICAM(C) proved more effective than the above chelate combination in reducing 239Np retention in the bones but increased that in the muscles and especially in the kidneys. This side effect of LICAM(C) could be partly prevented by simultaneous treatment with DTPA.

Animals↗
PubMed1987

Effects of the chemical forms and valency states of neptunium on its jejunal transfer in the rat.

The transfer of various Np(IV) and Np(V) chemical forms across the small intestine of rats was measured in instilled and perfused jejunum. Instillation of Np(V) nitrate together with citrate or DTPA resulted in the same absorption of Np as after instillation of Np(V) nitrate alone (3 per cent per hour). Perfusion of Np(V) nitrate with bicarbonate or DTPA resulted in a similar transfer (2 per cent) but added citrate or ascorbate resulted in reduced transfer (0.8 per cent). Addition of phytate reduced Np transfer in both instilled and perfused jejunum (0.4 per cent). Np(IV) transfer was usually the same as, or less than that of, the corresponding Np(V) forms. Np(IV) transfer was similar in perfused and instilled jejunum, increasing from 0.2 per cent in the presence of citrate and phytate, to 1 per cent with EDTA and DTPA. Except for phytate, all the forms of Np(V) tested behaved like Np(V) nitrate after transfer from the intestine or after intravenous injection. By contrast, the behaviour of Np(IV) varied for all the forms tested and, for a given form, varied as a function of the experimental procedure used, i.e. jejunal instillation, perfusion, or intravenous injection. These findings suggest that the intestinal transfer of Np might occur via the intercellular pathway, and that it is controlled by both the molecular weight of the Np compound and its stability constant.

Animals↗