Narayani P. Singh

Plutonium concentration in human tissues: comparison to thorium.

The concentration of 238Pu, and 239,240Pu, and of 228Th, 230Th, and 232Th were measured in 10 sets of human tissues from Washington, DC, and 12 sets from Grand Junction, CO. The tissues were collected at autopsy by qualified pathologists from normal healthy persons most of whom died suddenly. The subjects had acquired plutonium from fallout of global nuclear testing and burnup of a space nuclear generator utilizing 238Pu. The median concentration of 239,240Pu was 0.08 pCi/kg in lung, 0.46 pCi/kg in tracheobronchial lymph nodes, 0.60 pCi/kg in liver, 0.02 pCi/kg in kidney and 0.17 pCi/kg in bone in Washington, DC subjects. Similarly, the concentration of 239,240Pu in Grand Junction subjects was found to be 0.17 pCi/kg in lung, 0.68 pCi/kg in lymph nodes, 0.55 pCi/kg in liver, 0.03 pCi/kg in kidney, 0.22 pCi/kg in bone and 0.08 pCi/kg in spleen. The median concentration in four gonads was 0.02 pCi/kg; the concentration in one thyroid was 0.01 pCi/kg. 238Pu was below the limit of detection in most organs except the liver where it ranged from 0.02 to 0.17 pCi/kg with a median concentration of 0.06 pCi/kg. The organ distribution pattern shows that most of the plutonium was accumulated in bone and liver with 54-60% in bone and 34-43% in liver. Only 3-6% was found in lung including lymph nodes; kidney, spleen, thyroid and gonads together contained around 1%. The analytical results show three major differences between plutonium and thorium concentrations and organ distributions: (1) for plutonium the liver is a major locus for storage (approximately 40% of that found in the total body), whereas little thorium is accumulated in the liver (around 4%); (2) the relative amounts of 230Th and 232Th are much higher in lung and lymph nodes (10-28%) than currently for plutonium (3-6%); (3) the ratio of throium concentrations in lymph nodes to lung is significantly higher than the ratio of plutonium concentration in lymph nodes to lung showing thereby that fallout plutonium is more soluble than natural thorium.

Thorium concentration in human tissues from two U.S. populations.

The concentrations of natural alpha-emitting isotopes of thorium (228Th, 230Th and 232Th) have been determined in 22 sets of human tissue samples obtained at autopsy from Grand Junction, CO and in 10 sets from Washington, DC. Tissues included lung, pulmonary lymph nodes, liver, kidney, bone, a few gonads, spleen and thyroid. Personal data on each individuals age, sex, smoking history and occupation were obtained whenever possible. The concentrations of 228Th, 230Th and 232Th were highest in lymph nodes for both populations with 2.6 and 5.1 pCi/kg of 228Th, 4.60 and 11.10 pCi/kg of 230Th, and 2.8 and 7.8 pCi/kg of 232Th in Washington, DC and Grand Junction, CO, respectively. The order of concentrations of all three isotopes in all other organs for both populations was as follows: (formula; see text) The data suggest that the non-mining residents who lived in the vicinity of uranium mine tailings do not have elevated 230Th concentrations in their lungs, when compared to the residents of Washington, DC who are not exposed to such tailings. However, 230Th concentration in bone of Grand Junction subjects was just significantly higher (at p less than 0.1) than that for Washington, DC subjects after suitable age adjustments. The data also suggest that 230Th is more available for accumulation in skeleton than would be supposed from its relative geochemical abundance.

Plutonium-239, 240 and plutonium-238 in sediments of the Hudson River estuary.

Plutonium-239,240 and plutonium-238 were determined in 59 Hudson River sediment dredge samples collected during 1973-77 in the vicinity of the Indian Point Nuclear Power Station. Acid leaching followed by solvent extraction, electrodeposition, and alpha-spectrometry were used to extract, purify, and quantitate plutonium isotopes present in these samples. Annual median plutonium-238/plutonium-239,240 isotopic activity ratios in surficial sediments were 0.032 (1973-74), 0.035 (1975), 0.042 (1976), and 0.040 (1977). The source of these nuclides in the estuary was identified by analysis of the sample isotopic activity ratios. On the basis of the sampling regimen and the methods used, it is concluded that no input, other than that of fallout, has contributed significantly to the plutonium burden in Hudson sediments. (1 map, 9 references, 9 tables)

Determination of Alpha Emitting Isotopes of Uranium in Bone

A radiochemical procedure for the determination of alpha emitting isotopes of uranium in bone has been developed. The method involves the dry ashing of bone followed by wet ashing. Uranium is coprecipitated as oxalate after it is reduced to tetravalent state with SnCl, and HI. The precipitate is heated at 550°C in a muffle furnace, cooled and dissolved in 10 Μ HCl. Uranium is then extracted into 20% tri-lauryl amine (TLA) solution in xylene, backextracted with an equal volume of 0.1 Μ HCl, electrodeposited and counted alpha-spectrometrically. The results indicate a radiochemical recovery of 85 ±6 percent and the precision is within the counting error. The decontamination of thorium and polonium, which may interfere in the alpha spectrum of uranium, exceeds 3 Χ 10 and 5 Χ 10, respectively.

Macro-distribution of naturally occurring alpha-emitting isotopes of U in the human skeleton.

Argonne National Laboratory (ANL) exhumed the remains of two individuals who had received Pu by intravenous injection, performed Pu analysis on these remains, and then sent portions of individual bones to our laboratory. We analyzed these bone samples to determine the macro-distribution of naturally occurring alpha-emitting isotopes of U (234U and 238U). We found that the sacrum contained the highest concentrations of 234U and 238U (4.9 +/- 0.3 mBq g-1 of bone ash). Different ribs contained varying concentrations of 234U and 238U ranging from 0.26 +/- 0.2 to 1.6 +/- 0.4 mBq g-1 of bone ash for 234U, and from 0.16 +/- 0.1 to 1.5 +/- 0.4 mBq g-1 ash for 238U. The upper and lower values differ significantly at p = 0.001. Concentrations of 234U and 238U in vertebral bodies were lower than in left ribs numbers 1 and 2, but were similar to the concentrations in the other left ribs. The concentration of 235U was below the detection limit in each bone (lower limit of detection (LLD) = 4 X 10(-4) Bq per sample). The results indicate that the distribution of U isotopes is not uniform throughout the skeleton. Thus, the skeletal burden of U estimated from determinations in an individual bone sample may be quite erroneous until the fraction of total skeletal U contained in each bone is known.

Uranium and thorium isotopes and their state of equilibria in lungs from uranium miners.

Radiochemical analysis of seven lungs obtained at autopsy show that concentrations ranged between 6 and 63 pCi/kg for 238U and 6-66 pCi/kg, for 234U. Similarly, 230Th ranged from 17 to 54 pCi/kg, two orders of magnitude higher than 230Th observed in the lungs of the general population from the Western mining region. For individual lungs, 238U and 234U were close to equilibrium with an average ratio of 238U/234U of 0.94 and a range of 0.80-1.02. Surprisingly, 230Th was close to equilibrium with 234U with a 230Th/234U ratio of 1.1 and a range from 0.54 to 2.6. Equilibrium between U and Th isotopes is in contrast to the disequilibrium reported in beagles which chronically inhaled carnotite, where the 230Th/234U ratio was observed to range from 5.4 to 7.4 with an average of 6.3. The average radiation dose rate to lung from each of the three radionuclides was calculated as follows: D = 18.7 CE where D = dose rate in mrad/year, C = activity concentration in tissue in pCi/g and E = energy absorbed per disintegration in MeV. The combined radiation dose rate (at death) due to three long-lived radionuclides 238U, 234U and 230Th varied from 2.5 to 14.2 mrad/yr with a mean of 9.6 mrad/yr. The concentration of 226Ra and daughters in the lung was not determined. An upper limit to the dose rate from the whole chain, calculated assuming 226Ra through 210Po are in equilibrium with 238U, 234U and 230Th, would be 30 mrad/yr.

Distribution of thallium and lead in children's blood.

Mean whole blood concentrations for lead and thallium were determined by atomic absorption spectrophotometric analysis for children residing in Newkark, NJ. Frequency distributions for the various concentration ranges for both metals were recorded. There is no noticeable correlation between the lead and thallium content of whole blood, which suggests that exposure to and/or absorption of these substances are different.

Utilization of femoral head for estimating the skeletal burden of U and Pu in humans

Uranium and Pu were determined in vertebrae, ribs and femoral head samples obtained from the same population. Vertebrae and rib samples were obtained at autopsy and femoral head samples were obtained from persons undergoing hip surgery. The results indicate that there was no statistically (p less than or equal to 0.05) significant difference between the mean concentration of 239,240Pu in vertebrae and ribs. Also, there was no significant difference between the mean concentration of 239,240 Pu in ribs and femoral head. Also, statistical tests were performed to see whether the mean concentrations of 238U and 234U in three different bones differ from each other. The results suggest that there was no statistically significant difference between vertebrae and ribs, vertebrae and head of the femur nor between ribs and femoral head. These results indicate that femoral head may be an appropriate substitute for vertebrae or ribs, the most commonly used bone for inferring the skeletal burden of U and Pu in human. Femoral head samples can be obtained from living persons undergoing hip surgery, while vertebrae and ribs are obtained only at autopsy.

The beagle: an appropriate experimental animal for extrapolating the organ distribution pattern of Th in humans.

The concentrations and the organ distribution patterns of 228Th, 230Th and 232Th in two 9-y-old dogs of our beagle colony were determined. The dogs were exposed only to background environmental levels of Th isotopes through ingestion (food and water) and inhalation as are humans. The organ distribution patterns of the isotopes in the beagles were compared to the organ distribution patterns in humans to determine if it is appropriate to extrapolate the beagle organ burden data to humans. Among soft tissues, only the lungs, lymph nodes, kidney and liver, and skeleton contained measurable amounts of Th isotopes. The organ distribution pattern of Th isotopes in humans and dog are similar, the majority of Th being in the skeleton of both species. The average skeletal concentrations of 228Th in dogs were 30 to 40 times higher than the average skeletal concentrations of the parent 232Th, whereas the concentration of 228Th in human skeleton was only four to five times higher than 232Th. This suggests that dogs have a higher intake of 228Ra through food than humans. There is a similar trend in the accumulations of 232Th, 230Th and 228Th in the lungs of dog and humans. The percentages of 232Th, 230Th and 228Th in human lungs are 26, 9.7 and 4.8, respectively, compared to 4.2, 2.6 and 0.48, respectively, in dog lungs. The larger percentages of Th isotopes in human lungs may be due simply to the longer life span of humans. If the burdens of Th isotopes in human lungs are normalized to an exposure time of 9.2 y (mean age of dogs at the time of sacrifice), the percent burden of 232Th, 230Th and 228Th in human lungs are estimated to be 3.6, 1.3 and 0.66, respectively. These results suggest that the beagle may be an appropriate experimental animal for extrapolating the organ distribution pattern of Th in humans.