The distribution of plutonium-214 in rodents.

Plutonium-214 citrate solution at pH 6-5 was injected intravenously or intra-peritoneally into hamsters and rats at a dose of 50 MBq kg-1 (1-35 mCi kg-1). The animals were killed 1 day or 1 week later, and tissues were removed for autoradiography and radiochemical analysis. Plutonium-241 was distributed in rats in the same way as plutonium-239, and is a suitable isotope for high-resolution tissue-section autoradiography. Plutonium deposits in cells consisted of a nuclear and a cytoplasmic component. In the hamster kidney cells, the amount associated with the nucleus was about 55 per cent of the total cellular plutonium at 24 hours after injection. Six days later, it was only about 30 per cent. Plutonium deposits were also characterized in hepatocytes, in the interstitial cells of the testes, in the cells of ovarian follicles, in chondrocytes and in bone cells, including osteoblasts and osteocytes. In bone there appeared to be both an extracellular and intracellular deposit. No evidence was found of substantial incorporation of plutonium into the mineral phase of bone.     

The uptake and redistribution of 241pu within the gonads.

Male and female hamsters and a female rabbit were injected with 241Pu citrate. The hamsters were killed serially at 15 min, 2 hours, 1 day and 10 days after injection, and the rabbit 1 week after injection. The gonads were examined for 241Pu by tissue-section autoradiography. Soon after injection the plutonium was concentrated by the contents of atretic Graafian follicles and by thecal rings in the ovary, but was found to be dispersed throughout the testes. It is suggested that the disperse distribution in the testes which is only seen soon after injection may be an artefact of tissue processing. One day after injection, plutonium was accumulated by macrophages in both the follicles of the ovary and in the interstitial tissue of the testes. Macrophages containing plutonium later migrated away from the aretic ovarian follicles towards the ovarian medulla. This pattern of distribution and redistribution in the ovary is regarded as likely to lower the effective dose from a-emitting plutonium isotopes to the viable oocytes. No migration of macrophages was seen in the testes. Histochemical staining methods revealed the presence of acid protoglycans, including chondroitin sulphate, and glycoproteins at the sites of plutonium concentration in the ovary. These molecules are regarded as likely receptor sites for plutonium. In the testes no acidic carbohydrates were found, and it is suggested that the initial binding site for plutonium may be a compound lipid. This was deduced from the apparent inability of the interstitial tissue of the testes to bind plutonium in situ.     

The absorption of ingested neptunium, plutonium and americium in newborn hamsters

Hamsters aged 1, 4, 7, 22 and 30 days were given oral doses of either plutonium-239 citrate or americium-241 nitrate. The values of gastrointestinal absorption obtained were 3.5, 1.4, 0.04, 0.007 and 0.003 per cent, respectively, for plutonium and 4.5, 1.7, 0.5, 0.006 and 0.02 per cent, respectively, for americium, compared with values in adults of 0.01 per cent for plutonium and 0.05 per cent for americium. The absorption of neptunium was measured in hamsters aged 2 and 4 days and values of 2.3 and 1.7 per cent, respectively, were obtained for 239Np as the nitrate and 5.5 and 2.1 per cent, respectively, for 239Np as the bicarbonate compared with the values in adults of 0.02 per cent for both chemical forms. Thus, the absorption of plutonium, americium and neptunium at 1-2 days of age was about 100 times greater than in adults. The results for plutonium and americium show that absorption decreased rapidly with age over the suckling period. The values of absorption obtained at the time of weaning at 22 days were lower than in adults.     

Factors affecting the mobility of plutonium-238 dioxide in the rat.

A major factor influencing the movement of plutonium-238 from the lungs to blood after the intubation of oxide suspensions is the presense of 0.001 micrometer diameter particles. In a polydisperse suspension of particles this fraction increases with time, due it is thought, to fragmentation of larger particles induced by alpha decay. The rate of this process could account for the greater transportability in vivo of plutonium-238 relative to plutonium-239 when the oxides are inhaled. In blood, 0.001 micrometer diameter plutonium-238 oxide particles undergo a rapid reaction to form a low molecular weight species before plutonium is complexed with transferrin and citrate ions. The filtration of this species through the kidneys may explain the observed enhanced urinary excretion of plutonium relative to administered plutonium citrate. The mechanism of urinary excretion and relationship between cumulative urinary excretion and body content for plutonium-238 is similar to that previously observed for plutonium-239, even though different methods of preparation of the oxides were used.     

Role of biocomponents of the bile and excreta in the elimination of plutonium and americium from the body

A study was made of the role of biocomponents of bile, urine and feces in the elimination of plutonium and americium from the organism. Plutonium 239 and americium 241 were separated in bile due to higher tropism of plutonium to low molecular weight ligands, and of americium, to a protein-containing fraction. The status of plutonium excreted in feces was the same as the physicochemical status of americium. Plutonium 239 and americium 241 eliminated in urine were in a completely ultrafiltered state.     

The relationship of bone marrow type and microvasculature to the microdistribution and local dosimetry of plutonium in the adult skeleton

Most plutonium-induced bone tumors in beagles arise in trabecular bone sites surrounded by hematopoietic tissue. The microvasculature and the relative incorporation of 241Pu (a low energy beta emitter) on trabecular bone surfaces from red and fatty marrow sites were studied in the adult beagle. The vascular volume, as determined by India ink perfusion, was about 16% in the red marrow and about 2% in the fatty marrow. The red marrow has large vascular sinusoids with a discontinuous endothelial lining whereas fatty marrow has a closed capillary bed. Plutonium concentrations on bone surfaces of red marrow sites are about 0.43 pCi/cm2/nCi/kg of injected dosage, a factor of eight greater than at fatty marrow sites (0.053 pCi/cm2/nCi/kg). The differences in the bone marrow microvasculature between red and fatty marrow help to explain differences in plutonium incorporation and local bone physiology in these skeletal sites. These observations may relate to the nonuniform distribution of plutonium-induced osteosarcomas observed in adult, long-lived mammals.     

Association of plutonium with lysosomal, lipofuscin-like granules in Chinese hamster hepatocytes: evidence from electron microscopic and biochemical studies with 241Pu and 239Pu

This electron-microscopic-autoradiographic study was undertaken to identify the cell organelles, which bind plutonium in Chinese hamster hepatocytes at different times after injection. Female Chinese hamsters were injected intraperitoneally with 241Pu and sacrificed at time intervals of between 4 days and 35 weeks. The Chinese hamster was chosen as the experimental animal as it is a species in which there is virtually no elimination of plutonium from the liver. From the 4th day onwards beta-tracks were found over globular electron-dense structures, which were randomly distributed in the cytoplasm of the hepatocytes and strongly resembled lipofuscin bodies. Comparison of the results with those from biochemical experiments showed good agreement between the morphological and biochemical observations. At early times after injection 241Pu was also found in the hepatocyte nuclei. All the evidence suggests that in this species plutonium in hepatocytes becomes bound to lipofuscin-accumulating lysosomes, which cannot be excreted.     

The distribution of intratracheally administered plutonium-239 throughout the skeletal bones]

The data are presented on distribution of the intratracheally administered plutonium-239 within the skeleton bones. Plutonium was found to be distributed non-uniformly within the skeleton: it was concentrated mainly in the bones where the trabecular fraction of the bone tissue was most manifest. The results obtained were supported by the correlation analysis.     

The induction of liver tumors by 239Pu citrate or 239PuO2 particles in the Chinese hamster

The influence of radiation dose distribution on the frequency of 239Pu-induced liver tumors was evaluated in the Chinese hamster. Different concentrations of 239Pu citrate 239PuO2 particles of known sizes were injected intravenously via the jugular vein. About 60% of the injected 239Pu citrate was deposited in the liver and 40% in the bone. The 239Pu citrate was rather uniformly distributed throughout the liver parenchyma. Injected plutonium oxide particles were taken up by the reticuloendothelial system with 90% of the body burden deposited in the liver. The 239PuO2 particles were localized in the Kupffer cells and produced nonuniform dose distributions that were dependent on particle size. There was an activity- and dose-dependent increase in the incidence of total liver parenchymal cell tumors following injection with either plutonium particles or citrate. For animals that received 14.0-, 2.7-, 0.3-, and 0.04-Gy dose to liver from 239Pu citrate the cumulative tumor incidence was 39, 32, 5, and 0%, respectively. Animals that were injected with the 0.24 micron 239PuO2 particles had doses of 42.0, 7.2, and 0.8 Gy to the liver and tumor incidences of 34, 26, and 5%, respectively. Plutonium citrate also produced hemangiosarcomas of the liver and tumors in bone and bone marrow. The latent period for liver tumor appearance in animals exposed to 239Pu citrate or 239PuO2 particles increased as the injected activity decreased. For animals injected with a similar total activity (7.4 Bq/g), the lifetime cumulative liver tumor incidence was similar for animals exposed to either 239Pu citrate (32%) or 239PuO2 (26%). There was little effect of particle size on liver tumor incidence. These data indicate that, in Chinese hamster liver, local radiation dose distribution is less important in altering tumor incidence than injected activity or average dose. However, the more uniform irradiation from 239Pu citrate administration was more effective in cancer production than the nonuniform irradiation from 239PuO2 particles.     

The reactions of 1.0 nanometre diameter plutonium-238 dioxide particles with rat lung fluid.

The reactions of 1.0 nm particles of plutonium-238 dioxide with rat lung fluid have been studied both in vivo and in vitro. In both cases two products have been identified, (i) plutonium-labelled pulmonary surfactant and (ii) a heterogeneous plutonium-labelled material isolated by column chromatography. The formation of plutonium-labelled pulmonary surfactant results in the rapid translocation of plutonium from lungs to blood and in a high urinary excretion relative to administered plutonium citrate.     

The gastrointestinal absorption of organically bound forms of plutonium in fed and fasted hamsters

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.     

Plutonium in the tissues of foetal, neonatal and suckling mice after Pu-administration to their dams.

Twelve-week-old female (C3H x 101)F1 mice were injected intravenously with an ultrafiltered solution of 239Pu in per cent trisodium citrate, and mated to uninjected PCT males. The plutonium content was examined radiochemically and autoradiographically in placentae and foetuses on the 12th and 18th days of gestation, and in neonates during the 24 hours after birth and also at 18 days postnatally. Plutonium was distributed in most tissues of the late foetus and the suckling as it is in adult mice. However, on both the 12th and 18th days of gestation the concentration in the yolk-sac splanchnopleure was much higher than in any other foetal tissue. The amount of 239Pu in 18-day-old sucklings was between two and seven times as great as in 1-day-old neonates because of ingestion of milk from the lactating dams. In the first litter following administration of the radionuclide to the dam, about 0.02 per cent of the plutonium injected was transferred to an individual offspring by the time of birth, and a further 0.08 per cent by the time of weaning.     

The effect of pure LICAM(C) on the retention of plutonium-238 in mice and rats

Studies with pure LICAM(C) and with its methyl esters showed that all the substances caused increased renal retention of plutonium-238 in the kidneys of mice and rats but were equally effective in reducing plutonium retention in bone and liver.     

A comparison of the distribution of 239-Pu and calcein in the illium of the female CBA mouse

Conclusions As a model for the behaviour of plutonium in bone, calcein data must be treated with some care. It does not label the same surfaces as plutonium which results in different distribution patterns at later times. However, it might be that if in man or a long lived animal, labelling occured over a period of weeks, so that most surfaces become labelled, the resultant distribution pattern at late times would more nearly model plutonium behaviour. The single biggest difference between the behaviour of the two substances is the build up of plutonium in the bone marrow, an effect seen only slightly with calcein. The other differences noted was the redeposition of plutonium, as a consequence of recycling of the radionuclide, maintaining a concentration of plutonium on endosteal surface.     

The specificity of the deposition of intratracheally administered plutonium in different skeletal bones with a change in iron homeostasis]

A study was made of the distribution of plutonium-239 injected intratracheally within different bones of the skeleton, the iron status in the blood being changed. The iron preparation caused a 2.5-3-fold decrease in the plutonium loading onto cancellous bone tissue that displayed, in ordinary conditions, a higher tropism to the radionuclide than a cortical highly mineralized bone did.     

Effects of plutonium-239 on haemopoiesis. I. Quantitative and qualitative changes in CFU-S in different regions of the mouse femur and vertebrae

Mice were injected with plutonium-239 (960 Bq/mouse) and, over a period of four months, the response of haemopoietic tissue and the self-renewal capacity of its stem cells was monitored. Cellularity, CFU-S concentration and self-renewal capacity were measured in five different regions of bone and marrow--axial and marginal marrow of the femoral shaft, femur shaft, proximal and distal ends of the femur shaft and vertebrae. Cellularities were little affected by plutonium but CFU-S were reduced in all regions, most severely in the bone shaft and marginal marrow due to the initial deposition of plutonium on the bone surface, by four days. The reduction in axial CFU-S, however, was due probably to a relatively long plasma half-life resulting from the tendency of plutonium to combine with plasma proteins. The capacity of CFU-S for self-renewal was reduced and remained low in all zones. Thus, although the highly self-renewing axial CFU-S were depleted, and remained so, due probably to a longer term redistribution of plutonium throughout the marrow, additional proliferation of the more mature CFU-S in the other zones kept their self-renewal low while replenishing their numbers and maintaining a normal cell output.     

In vitro and in vivo assessment of plutonium speciation and decorporation in blood and target retention tissues after a systemic contamination followed by an early treatment with DTPA

This study identifies the main sources of systemic plutonium decorporated in the rat after DTPA i.v. at the dose recommended for humans (30 mumol kg(-1)). For this purpose, standard biokinetic approaches are combined to plasma ultrafiltration for separation of plutonium complexes according to their molecular weight. In vitro studies show that at the recommended DTPA dose, less than 5% of the plasma plutonium of contaminated rats can be displaced from high-molecular-weight ligands. After i.v. administration of Pu-DTPA, early ultrafiltrability of plutonium in plasma decreases with total DTPA dose, which is associated with an increase in plutonium bone retention. This demonstrates the instability of Pu-DTPA complexes, injected in vivo, below the minimal Ca-DTPA dose of 30 mumol kg(-1). Plutonium biokinetics is compared in rats contaminated by plutonium-citrate i.v. and treated or not with DTPA after 1 h. No significant decrease in plasma plutonium is observed for the first hour after treatment, and the fraction of low-molecular-weight plutonium in plasma is nearly constant [5.4% compared with 90% in Pu-DTPA i.v. (30 mumol kg(-1)) and 0.7% in controls]. Thus plutonium decorporation by DTPA is a slow process that mainly involves retention compartments other than the blood. Plutonium-ligand complexes formed during plutonium deposition in the retention organs appear to be the main source of decorporated plutonium.     

Determination of the plutonium-239 content of the body

In order to increase the informativeness of the indirect dosimetric estimates of plutonium-239 body levels complex makers are widely used to enhance natural excretion of the radionuclide in urine, the ratio between 239Pu levels in urine and skeleton being measured. However, as the onset of chelate application is postponed its efficacy, with respect to the skeleton, sharply decreases making it impossible to obtain reliable information concerning plutonium 239 levels in bone tissues at later times.     

Risk of cerebrovascular disease incidence in the cohort of Mayak production association workers first employed during 1948-1958

Incidence of cerebrovascular diseases (CVD) has been studied in a cohort of 12210 workers first employed at one of the main plants (reactors, radiochemical or plutonium) of the Mayak nuclear facility during 1948-1958 and followed up to the end of 2000. Information on external gamma doses is available for virtually all (99.9%) of these workers; the mean (+/- one standard deviation) total gamma dose was 0.91 +/- 0.95 Gy (99% percentile 3.9 Gy) for men and 0.65 +/- 0.75 Gy (99% percentile 2.99 Gy) for women. Plutonium body burden was measured only for 30.0% of workers. Amongst those monitored, the mean (+/- standard deviation) cumulative liver dose from plutonium alpha exposure was 0.40 +/- 1.15 Gy (99% percentile 5.88 Gy) for men and 0.81 +/- 4.60 Gy (99% percentile 15.95 Gy) for women 4418 cases (first diagnosis) of CVD were identified in the studied cohort. A statistically significant increasing trend in CVD incidence with total external gamma dose was revealed after adjustment for non-radiation factors and internal exposure from incorporated plutonium-239. Excess relative risk per Gy was 0.464 (95% confidence interval 0.360-0.567). Incidence of CVD was statistically significantly higher for the workers chronically exposed to external gamma rays at a dose above 1.0 Gy A statistically significant increasing trend in CVD incidence with internal liver dose from plutonium alpha exposure was observed after adjustment for non-radiation factors and external exposure. ERR per Gy was 0.155 (95% confidence interval 0.075-0.235). CVD incidence was statistically significantly higher among workers with a plutonium liver dose above 0.1 Gy, although the trend estimates differed between workers at different plants. The incidence risk estimates for external radiation are generally compatible with estimates from the study of Chernobyl clean-up workers, although the incidence data point to higher risk estimates compared to those from the Japanese A-bomb survivors.     

Immunohistochemical localization of osteogenetic protein (OP-1) and its receptors in rabbit articular cartilage.

We assessed the distribution and relative immunohistochemical staining intensity of the bone morphogenetic protein-7, osteogenic protein-1 (OP-1), in its pro- and mature forms, and four of its receptors, type I (ALK-2, ALK-3, and ALK-6) and type II in normal adolescent New Zealand White rabbit articular cartilage. Expression of the protein and its receptors was also examined in cartilage from joints that had been previously subjected to cartilage matrix degradation. Pro-OP-1 was moderately expressed in chondrocytes of the superficial, middle, and deep cartilage zones and in the osteocytes. The expression of mature OP-1 was similar, with the exception of less staining in the superficial zone of cartilage. Expression of these two forms of OP-1 was enhanced in the middle and deep cartilage zones after catabolic challenge. The type I receptor, ALK-6, displayed the strongest staining of the receptors in both cartilage and bone, whereas ALK-2 displayed the weakest staining. No differences were observed in the receptor staining levels after catabolic challenge. This study shows that OP-1 and its receptors have been identified in rabbit articular cartilage and bone, suggesting a possible role for this pathway in cartilage and bone homeostasis.