The Induction by 239Pu of Myeloid Leukaemia and Osteosarcoma in Female CBA Mice

Summary

Plutonium-239 was injected into 12-week-old female CBA/H mice in the range 1·85–18·5 kBq kg^?1 either as a single injection or as 16 injections spaced at 3·5 day intervals over eight weeks. There was a highly significant increase in the yield of fully developed osteosarcomas with increased amounts of ²³⁹Pu for both modes of injection. Osteosarcomas too small to be diagnosed radiographically were also seen in many bones and small but significant yields of myeloid leukaemia were seen in animals given plutonium. Although more myeloid leukaemia was seen in the mice given plutonium in divided amounts than in those given the plutonium in a single injection it could not be shown that multiple injection significantly affected the yield of either late effect.     

The Incorporation of Plutonium by the Embryo and Fetus of Rats and Guinea-pigs

Summary

The transfer of ²³⁸Pu from the maternal circulation to the developing embryo and fetus was studied in rats and guinea-pigs to provide data for the development of dosimetric models for the human embryo and fetus. Following administration at different stages of gestation, measurements were made after 3 days in the rat and 7 days in guinea-pigs. The amount transferred was greater after administration at later stages of gestation, up to a maximum of about 0·8–0·9% of the injected activity per fetoplacental unit (FPU) and about 0·2% per fetus in both species. In advanced gestation the yolk sac, the initial site of haemopoietic stem cells, contained up to 80% of the total activity in the FPU in rats, compared with about 25% for the guinea-pig; retention in placental trophoblast was greater in the guinea-pig. The concentrations of ²³⁸Pu in the yolk sac were generally about two to three orders of magnitude greater than fetal concentrations and of the same order as in maternal liver and bone. In both species, concentrations in the embryo and fetus were greatest after injection early in gestation, reached their lowest around mid-organogenesis and increased again in later gestation. The fetus:mother whole-body concentration ratios in late gestation were about 0·1 and 0·05 in rats and guinea-pigs, respectively. Measurements were also made of the ²³⁸Pu retention in neonates at birth. In guinea-pigs the liver accounted for about 6–9% of retained activity; similar values for femora indicated skeletal retention of about 60–80%. For administration at each stage of gestation, and particularly at early stages, transfer of ²³⁸Pu to the fetus continued throughout gestation but concentrations decreased due to fetal growth.     

Alpha-particle Irradiation of Haemopoietic Tissue in Pre- and Postnatal Mice

Summary

Pregnant mice (at 13 days gestation) and age-matched controls were injected with 30 kBq ²³⁹Pu/kg and the distribution of plutonium in maternal and foetal tissues measured. Approximately 2% of the activity injected into the mother reached each foetus in 24 h, 95% of which was contained in membranes and placenta. The concentration of plutonium in foetal liver was 3 times the average foetal body concentration; both liver and body concentrations in the foetus increased by the end of gestation. Each pup accumulated only 0.01% extra injected activity after 9 days lactation and, as the resulting concentrations in the neonatal skeletion were low, we conclude that the greatest haemopoietic risk to the offspring from mid-term contamination in utero is in the foetal liver (which received an average dose of 10–14 mGy between the time of mid-term contamination and birth). By the end of gestation about one-quarter of the original activity was transferred to foetal tissues from the maternal liver and skeleton. No significant changes in maternal distribution were detected as a result of lactation. The results of this study are discussed, along with a compilation of previously published data.     

Distribution of 239Pu in the Skeleton of the Tree Shrew (Tupaia Belangeri) between 15 and 50 Months after Injection

Summary

The macroscopic and microscopic distribution of intramuscularly injected, essentially monomeric, ²³⁹Pu was studied in the skeleton of the adult tree shrew (Tupaia belangeri). Data for the period between 15 and 50 months after injection are presented and compared with the data from earlier time points. Between 83 and 500 days after injection the nuclide content and the wet weight of the skeleton decreased to a constant level at about 55 per cent of the maximum values. The microscopic distribution has been analysed in distal femora, proximal humerus, proximal tibia and lumbar vertebra over the whole observation time; additionally at some selected time points proximal femur, femur shaft, distal humerus and distal tibia were analysed. The initial endosteal surface activity ranged from 3·8 to 5·3 Bq/cm² and decreased to a minimum at about 1000 days after injection and increased thereafter. A similar behaviour was found for the dose rate near bone surfaces which was initially about 0·075 Gy/day on endosteal surfaces. In the deep bone and the deep marrow the dose rate was negligible, about 0·008 Gy/day and 0·001 Gy/day, respectively. The average cumulative dose 1500 days after injection was about 67 Gy on the endosteum, six times greater than the cumulative dose calculated from the mean concentration of plutonium in the whole skeleton. All values are normalized to an injected activity of 37 kBq/kg body weight. The tupaia data are discussed in relation to the available data from monkeys, dogs and rats.     

Uptake and Clearance of Plutonium-238 from Liver Cells Transplanted into Fat Pads of F344 Rats

Summary

This research is directed toward understanding the role of liver cells and the liver environment in plutonium biokinetics. Animals injected with liver cells and control animals received a single intraperitoneal injection of 37 kBq (1 µCi) ²³⁸Pu citrate and were serially sacrificed 1, 5, 10, 15, 30, 60 or 70 days later. Uptake, retention and distribution of Pu in intact liver and in liver cells growing in fat pads were determined. From these measurements, it was observed that the cells of the intact liver took up about twice as much ²³⁸Pu as liver cells transplanted into the fat pads of the same animal. The retention half-life was 8·3 days for the total activity in the liver, 20 days using tracks/cell measurements in the liver and 16 days for the tracks/cell measurements in the liver cells translocated to fat pads. When the data on tracks/cell were standardized relative to the amount of Pu present at 5 days after the injection, there was no significant difference between the retention of Pu in liver cells from intact animals and liver cells transplanted into the fat pads. About 20 per cent of the 5-day Pu liver burden in both liver cells and liver cells transplanted into fat pads was retained at 70 days. The smaller retention and clearance for liver cells in different environments indicate that uptake and clearance of Pu from the body is dependent, to a major extent, upon hepatocyte function.     

The Gastrointestinal Absorption of Organically Bound Forms of Plutonium in Fed and Fasted Hamsters

Summary

Values of about 0·005–0·01 per cent were obtained for the absorption in fed hamsters of plutonium ingested as Pu⁴⁺ citrate, isocitrate, phytate and malate complexes and Pu³⁺ ascorbate compared with about 0·003–0·004 per cent for Pu⁴⁺ nitrate. Replacing drinking water with tea did not affect the result for Pu⁴⁺ nitrate. Fasting hamsters for 8 h before the administration of plutonium citrate increased absorption to 0·1–0·2 per cent. An extra period of fasting for 4 h after administration did not lead to a further increase in absorption. Similar values were also obtained when plutonium citrate was administered after a 24 h fast, followed either by immediate access to food or a further 4 h fast. In hamsters fasted for 24 h before administration of either Pu³⁺ ascorbate or Pu⁴⁺ nitrate, about 6–7 per cent of the ingested plutonium was retained in the gastrointestinal tract after one week. At three weeks after ingestion of Pu³⁺ ascorbate, gastrointestinal retention had fallen 100-fold without an increase in absorption.     

Efficacy and Toxicity of NN′N″N‴-tetra(2,3,4-trihydroxybenzoyl)-spermine for Decorporation of 239Pu from Mice

Summary

Male SAS/4 mice were injected i.v. with 6·6 kBq ²³⁹Pu-citrate. After 1 or 24 h a single i.p. injection of 15 or 30 μmol kg^?1 or repeated (three or four) daily injections of 30 μmol kg^?1 of tetra-THB-spermine were given, and at 4 or 7 days Pu retention was measured in liver, kidneys and femur. Besides tetra-THB-spermine, equimolar doses of tetra-DHB-spermine were injected for comparison, or equimolar doses of diethylene triamine-pentaacetic acid (DPTA) as a reference compound. Histological changes in kidneys and liver were examined after i.p. injections of 30 μmol kg^?1 or at 2–13 times higher doses of tetra-THB-spermine. The results show that: (1) Introduction of an additional hydroxy group into the aromatic moieties of tetra-DHB-spermine results in increased hydrophilicity, lower toxicity and a lower renal retention of Pu. (2) Tetra-THB-spermine and tetra-DHB-spermine are similarly effective in removing plutonium from liver and bone. Their efficacies in removing Pu from bone are approximately similar to those of DTPA but for whole-body removal they are generally inferior. (3) Multiple (30 μmol kg^?1) of tetra-THB-spermine were no more effective than a single injection at mobilizing Pu from the liver. (4) Four injections of tetra-THB-spermine induced cloudy swelling and fatty degeneration in epithelial cells of the proximal convoluted tubules. At levels of 400 μmol kg^?1 tetra-THB-spermine produced severe degenerative glomerular lesions, foci of liver necrosis and thromboses of the portal vein branch.     

Alpha-particle irradiation of haemopoietic tissue in pre- and postnatal mice. 1: Distribution of plutonium-239 after mid-term contamination.

Pregnant mice (at 13 days gestation) and age-matched controls were injected with 30 kBq 239Pu/kg and the distribution of plutonium in maternal and foetal tissues measured. Approximately 2% of the activity injected into the mother reached each foetus in 24 h, 95% of which was contained in membranes and placenta. The concentration of plutonium in foetal liver was 3 times the average foetal body concentration; both liver and body concentrations in the foetus increased by the end of gestation. Each pup accumulated only 0.01% extra injected activity after 9 days lactation and, as the resulting concentrations in the neonatal skeleton were low, we conclude that the greatest haemopoietic risk to the offspring from mid-term contamination in utero is in the foetal liver (which received an average dose of 10-14 mGy between the time of mid-term contamination and birth). By the end of gestation about one-quarter of the original activity was transferred to foetal tissues from the maternal liver and skeleton. No significant changes in maternal distribution were detected as a result of lactation. The results of this study are discussed, along with a compilation of previously published data.     

Remeasurement of 241Pu half life by gamma-ray spectrometry

The half life of ²⁴¹Pu has been remeasured to be 14.355 y with an estimated standard deviation of 0.040 y (a mean tropical year of 365.242 d) by a new method based on high-resolution γ-ray spectrometry. During 10 y, 156 sets of normalized spectral full-energy peak-area ratios (proportional to ²⁴¹Pu/²³⁹Pu mass ratios) from 13 plutonium samples were obtained by γ-ray spectrometry. The ²⁴¹Pu half-life value was extracted by an appropriate statistical analysis of the measured ratios. In the method used, the measured ratios are essentially independent of plutonium sample properties, of counting geometry, and of detector efficiency as well as of pile-up and deadtime. The much longer-lived ²³⁹Pu served as a monitor by which differences in detection efficiency between ²⁴¹Pu/²³⁹Pu γ-ray pairs were normalized, and by which implicit corrections for electronic counting losses were made.     

Retrospective estimation of Plutonium-239 doses from transfer to the fetus for Mayak PA workers

Abstract

Purpose: The estimation of plutonium fetal transfer and the calculation of individual in utero and postnatal doses for the Mayak Production Association (PA) offspring cohort.

Materials and methods: The model developed by the International Commission on Radiological Protection (ICRP) for the transfer of plutonium to the fetus following maternal intakes before and during pregnancy has been adjusted for application to analysis of the fetal transfer of ²³⁹Pu for Mayak workers. Improved estimates of fetal to maternal concentration ratios (C_F:C_M) have been obtained based on a correlation observed between adult offsprings’ measured daily urine ²³⁹Pu activity and estimates of their mothers’ systemic activity at conception. Data on ²³⁹Pu activity in daily urine samples were collected from 13 selected adults whose mothers worked at the Mayak PA facility during the period from 1948–1953, before and/or during pregnancy.

Results: A comparison of measured and modeled excretion data enabled a mean value of 0.18 ± 0.02 (n = 21) to be inferred for the Pu C_F:C_M ratio, with a coefficient of variation of 60%.

Conclusions: Point estimates of the individual in utero and postnatal absorbed doses for the red bone marrow and liver were in the range 2…13 mGy in 95% of the cases for the cohort of 1936 offspring.     

Radioprotective Effect of an Acute Non-specific Inflammation in Mice

Summary

Protection against 8·7 Gy whole-body γ-irradiation (lethal in 100 per cent of mice by 30 days) was observed in 90 per cent of mice bearing a one-day-old granuloma induced by polyacrylamide beads. When the inflammatory reaction was induced sooner or later a lower or null protection was obtained. A dose-effect relationship between the volume of injected beads and resulting radioprotection was established. The radioprotective effect depends only on the acute non-specific inflammation since hydrocortisone acetate injected into mice before the beads abolished this protection. This inflammatory pattern led to a dose reduction factor of 1·36 ± 0·08 (P < 0·05) for LD 50/30. A 90 per cent survival was observed in mice bearing a one-day-old granuloma when they were injected 1 h before 10 Gy with the granuloma acellular eluate (P < 0·02 compared to a 50 per cent survival observed with polyacrylamide beads alone). Substances with a molecular weight higher than 300 000 are involved in the synergistic radioprotective effect of the granuloma-eluate association.     

First-generation offspring of male mice exposed to 239Pu-citrate show no evidence of leukaemia or life shortening

The aim was to test whether male mice injected with ²³⁹Pu citrate transmit induced mutations that lead to specific causes of death, decrease longevity or both. Male CBA/Ca mice injected with ²³⁹Pu citrate solutions at nominal activities of 6 and 60 Bq g^?–?1 were mated to females (same strain) 54?–?68 days later. Absorbed doses to the testes were estimated to be approximately 0.3 and 4.0?cGy. Control males were injected with carrier only. Longevity was evaluated. All 1807 progeny were given detailed necropsies. Haematological analysis was used in an attempt to identify leukaemia. Male progeny from both treated groups lived significantly longer than those from the control, and there was no difference in longevity between the two treatments. No evidence was found of the induction of leukaemia or of any of the numerous probable causes of death. Although numerous significant differences were found in the many comparisons made between the three groups, there was no clear indication that any harmful effects were associated with paternal preconceptional plutonium exposure. This was in spite of the initial body burden (higher dose) being approximately 2800 times the maximum body burden allowed for workers when this study was initiated.     

Determination of plutonium in feces and urine

A method was developed for the determination of plutonium (²³⁹Pu, ²³⁸Pu, etc.) in feces and urine excreted by persons for 24 h. Plutonium is successively separated from inorganic macrocomponents present in samples and from other α emitters by the help of coprecipitation with BiPO₄, LaF₃ and extraction with TTA. After separation, the electrodeposition of plutonium on stainless-steel discs can be carried out. The chemical yields of separation of plutonium are about 80%.     

Stem Cells in Bone and Bone Marrow after Contamination with Bone-seeking Radionuclides

Summary

The effects of time, mass and oxidation state on plutonium gastrointestinal absorption and tooth adsorption were studied during and after chronic ingestion of plutonium-238 (IV) or (VI) (1·55–15·60 kBq/ml) in 6·5 mm bicarbonate medium by fed rats via drinking water for 8 days to 3 months. Animals were killed during the ingestion to follow the kinetics of whole-body storage and clearance of plutonium. At 1·55 kBq/ml the amount of plutonium retained in the skeleton increased continuously during the 85 days of ingestion and reached a plateau thereafter. This plutonium retention was therefore dependent on the total mass administered but not proportional to this mass, as the fraction of administered plutonium retained decreased during the first 22 days of ingestion and then stabilized. This is reflected by the gastrointestinal transfer (f₁), which had risen to (3·80 ± 0·82) × 10^?5 on Day 3 of ingestion and then decreased to a stabilized value of (1·07 ± 0·06) × 10^?5 from Day 30 to the end of the ingestion period. In the liver, the amount of plutonium retained reached a plateau, which lasted from Day 30 to the end of ingestion. The kidneys and spleen were also found to be retention sites. By Day 3 of ingestion, for a mass ingested of 5 × 10^?7 g/kg of body mass, the maximum mean value of f₁ we found was smaller than the 10^?4 recommended by ICRP Report 30. The oxidation state had no effect on f₁. Large plutonium deposition was observed on the teeth. For both oxidation states (IV) and (VI), about 0·10% of the administered dose was deposited on the teeth after 3 days of ingestion, whatever the plutonium concentration administered. However, whereas the amount of plutonium (IV) deposited did not change throughout the ingestion period, tooth deposition of plutonium (VI) decreased.     

Spatial distributions of 137Cs and 239+240Pu in surface seawater within the Exclusive Economic Zone of East Coast Peninsular Malaysia

The studies of ¹³⁷Cs and ^239+240Pu distributions in surface seawater at South China Sea within the Exclusive Economic Zone (EEZ) of Peninsular Malaysia were carried out in June 2008. The analysis results will serve as additional information to the expanded baseline data for Malaysia’s marine environment. Thirty locations from extended study area were identified in the EEZ from which large volumes of surface seawater samples were collected. Different co-precipitation techniques were employed to concentrate cesium and plutonium separately. A known amount of ¹³⁴Cs and ²⁴²Pu tracers were used as yield determinant. The precipitate slurry was collected and oven dried at 60 ^oC for 1–2 days. Cesium precipitate was fine-ground and counted using gamma-ray spectrometry system at 661.62 keV, while plutonium was separated from other radionuclides using anion exchange, electrodeposited and counted using alpha spectrometry. The activity concentrations of ¹³⁷Cs and ^239+240Pu were in the range of 3.40–5.89 Bq/m³ and 2.3–7.9 mBq/m³, respectively. The ^239+240Pu/¹³⁷Cs ratios indicate that there are no new inputs of these radionuclides into the area.     

Biochemical Binding and Distribution of Protactinium-233 in the Rat

Summary

Following intravenous injection into male Sprague–Dawley rats ²³³Pa, like other elements, deposits predominantly in the skeleton (ca. 70–80 per cent), but unlike Pu and Am the liver deposition of ²³³Pa is low, about 2–3 per cent between 1 and 7 days. About 99 per cent of the injected ²³³Pa is lost from the plasma compartment in 3 days, a clearance comparable to that of Pu but much slower than that of Np, Am or Cm. On entering the liver cell cytosol ²³³Pa is bound rapidly to an unidentified protein of molecular mass 200 kDa and to a protein of 80 kDa, which is probably transferrin. Within a few hours the metal migrates to bind to a protein of > 400 kDa which has been tentatively identified as ferritin. Some ²³³Pa remains bound to small ligands until virtually all the intracellular ²³³Pa has been deposited in the lysosomes, or to a lesser extent in some other, as yet, unidentified organelles.     

The Effect of Dietary Phosphorus on the Metabolism of Calcium and Strontium in the Rat

Summary

An investigation has been made of the way in which changes in dietary phosphorus within the physiological range influence the comparative metabolism of calcium and strontium in the rat. Radioactive calcium and strontium were used as tracers.

The absorption of both calcium and strontium after oral administration was dependent on the phosphorus level in the diet, but not to the same degree. The skeletal ratio ⁸⁵Sr/⁴⁷Ca decreased by some 40 per cent as the dietary phosphorus was increased from 0·5 to 1·3 g per cent.

After intraperitoneal injection of radioactive calcium and strontium, the skeletal retention of ⁸⁵Sr was about 25 per cent more on a diet containing 1·3 per cent phosphorus than on a diet containing 0·5 per cent phosphorus. Skeletal retention of calcium varied little.

It is concluded that renal discrimination against strontium as well as intestinal absorption of calcium and strontium were affected by the phosphorus content of the diet, but in opposite directions.     

The Effect of 238Pu α-particles on the Mouse Fibroblast Cell Line C3H 10T1/2: Characterization of Source and RBE for Cell Survival

Summary

Considerable interest has been aroused in recent years by reports that the transforming and carcinogenic effectiveness of low doses of high LET radiations can be increased by reducing the dose rate, especially for transformation of 10T1/2 cells in vitro by fission-spectrum neutrons. We report on conditions which have been established for irradiation of 10T1/2 cells with high LET monoenergetic α-particles (energy of 3·2 MeV, LET of 124 keV μm^?1) from ²³⁸Pu. The α-particle irradiator allows convenient irradiation of multiple dishes of cells at selectable high or low dose rates and temperatures. The survival curves of irradiated cells showed that the mean lethal dose of α-particles was 0·6 Gy and corresponded to an RBE, at high dose rates, of 7·9 at 80 per cent survival and 4·6 at 5 per cent survival, relative to ⁶⁰Co γ-rays. The mean areas of the 10T1/2 nuclei, perpendicular to the incident α-particles, was measured as 201 μm², from which it follows that, on average, only one in six of the α-particle traversals through a cell nucleus is lethal. Under the well-characterized conditions of these experiments the event frequency of α-particle traversals through cell nuclei is 9·8 Gy^?1.     

Alpha-irradiation of haemopoietic tissue in pre- and postnatal mice: 2. Effects of mid-term contamination with 239Pu in utero.

The distribution of 239Pu in various tissues of foetal and postnatal offspring of pregnant mice, injected i.v. at 13 days gestation with 30 kBq 239Pu/kg (in some cases with 10 or 100 kBq/kg), together with the numbers of haemopoietic progenitors in the bone marrow, spleen and liver, were measured through to 1 year post-partum. The quality of the haemopoietic microenvironment in these mice was also measured using the renal-capsule implant method. The largest radiation dose received by any haemopoietic organ was that in the liver, amounting to 10-14 mGy, as reported previously. In spite of normal numbers of haemopoietic spleen colony-forming cells (CFC-S) in the liver and seeding, at birth, into the bone marrow where the level of plutonium was minimal, a long-term deficit in their number rapidly developed. The development of the stromal microenvironment, however, was also deficient, suggesting that the dose of alpha-irradiation to the foetal liver was sufficient to cause sublethal damage in those cells destined to become the precursors of the supportive haemopoietic microenvironment in bone marrow and spleen. The results of this study suggest that although the placenta affords significant shielding to the tissues of the developing foetus from maternal contamination, the long-term effects on haemopoiesis are comparable to those in mice contaminated as adults. This further implies that the developing haemopoietic tissues are exquisitely sensitive to 239Pu contamination.