McDonald E. Wrenn

Metabolism of ingested U and Ra.

The literature on metabolism of U and Ra for man relevant to deriving drinking water standards has been reviewed and summarized. Radium is well understood, but significant gaps remain in our knowledge about U metabolism. Limits should be based on an equilibrium model where a constant relationship between intake and organ burden is established, using the best and most likely metabolic parameters. For the skeleton we conclude that the best estimate of skeletal burden expressed in days equivalent intake are 25 days for 226Ra, 10 days for 228Ra, and 0.3 days for 224Ra. For long-lived isotopes of U, we chose 11 days, with a range between 1 and 35 days. The committee believes that intake of natural U in water should be limited by considerations of toxicity to the kidney, and we believe that the metabolic model of Spoor and Hursh with a modified gastrointestinal (GI) absorption (1.4%) should be used to infer kidney content. Our review and analysis of the world literature leads us to believe the average human GI absorption of U is most likely 1-2% and is probably reasonably independent of age or the mass of U ingested. Using a safety factor of 50-150, the committee recommends a limit of U in water of 100 micrograms/l in order to limit toxic effects in the kidney. One hundred micrograms/liter is equivalent to 67 pCi/l of long-lived alpha-emitting natural U isotopes. Further research into the distribution of U in the human body is desirable, especially at natural levels in kidney and skeleton, the time-dependent pharmacokinetics of U in animals, the GI absorption of U in man from water and food, toxicological and U distribution studies in animals under conditions of chronic oral U intake, and metabolic model error propagation.

ANALYSIS OF THE ACTIVITY OF RADON DAUGHTER SAMPLES BY WEIGHTED LEAST SQUARES.

A new mathematical method employing weighted least-squares has been developed for the analysis of air samples for radon daughters. This method allows calculation of the concentrations in air of the daughter products of both 220Rn and z22Rn based upon the radioactive decay of a sample. I t employs observations of the total counts of alpha particles from the sample during various periods of time, rather than estimates of the counting rate at any particular time. There is no upper limit to the number of observations that may be used in the computations. Errors are estimated based upon the statistical limitations of the data. The method has been tested on radon daughter samples taken in uranium mines under conditions both of equilibrium and extreme disequilibrium and compared to the commonly employed Tsivoglou method. Filters were counted in the mines using a combination of ZnS phosphor, photomultiplier tube, and scalar. The concentrations of radium A, B, and C were calculated with both methods. The results of this comparison indicate major advantages of the new technique in research applications, including greater accuracy and clearly defined estimates of errors. INTRODUCTION in nature, 222Rn with a half-life of 3.85 days and IN ORDER to analyze the radon daughter 220Rn with a half-life of 51 sec. Environmental activities of numerous and varied samples of a air samples may contain one or both of these radon daughter atmosphere, a new analytic isotopes. technique has been developed. This was The most striking example of elevated, necessary because no general and direct pronaturally occurring, concentrations of 222Rn is cedures have been previously developed employfound in uranium mines. Generally the 220Rn ing gross alpha activity measurements. (hereafter called thoron) content in uranium Radon is an element with the atomic number mine atmospheres is negligible. Knowing the of 86; two isotopes are commonly encountered relative equilibria among the radon daughters in mines may be important for a variety of of “working levels” present, studying the effect Commission during tenure of a U.S.A.E.C. Fellowship in the Department of Radiation Biology and of ventilation, and research into other means of Biophysics, University of Rochester, Rochester, New York. removal of radon and its daughters. Other applications include laboratory studies of the t Research supported in part by the U.S. Public U.S.A.E.C. under Contract No. AT-(30-1)-3086, and studies Of exposure to radon and its is part of a center program supported by the Division daughters where evaluation of the state of of Environmental Health Sciences,National Institutes equilibrium is important. Thoron can also be of Health, Grant No. ES00260. measured by these techniques. * Research supported by the U.S. Atomic Energy reasons, among them evaluating the number Health Sewice Contract No. PH86-66-149, by the Physics Of the radon daughter and

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.

Design of a Continuous Digital-Output Environmental Radon Monitor

A new field instrument for the continuous measurement of radon concentrations has been developed to investigate the magnitude and variability of environmental levels of 222Rn. Passive diffusion of radon, but not its daughters, occurs through an open pore polyurethane foam into a sensitive volume where a static electric field directs the positively ionized radon daughter products to a central collecting electrode. Pulses in a ZnS(Ag) scintillator, resulting from the alpha emission of 218Po and 214Po, are observed with a photomultiplier tube and counted using standard NIM electronics. The detector unit has been fabricated into a small, convenient package for indoor air sampling without the use of air movers or pumps. The unit is unobtrusive and acceptable into a daily routine without disrupting normal family or business activities. The monitor can detect as little as 0.5 pCi/l for a 40-min. count (¿=.05). The equilibrium detection efficiency of the instrument is 0.7 cpm/pCi/l.

Distribution of polonium-210 in the human lung.

Polonium-210 has been measured in the tracheobronchial tree and parenchyma of cigarette smokers and nonsmokers in order to determine whether this ..cap alpha.. emitter is retained in smokers. The ratio of /sup 210/Po concentration in the tracheobronchial tree (T) to that in the lung parenchyma (P) in nonsmokers is T/P = 2.7 +- 0.5. The ratio in smokers is T/P = 1.1 +- 0.2. The difference in these ratios can be related to retention of /sup 210/Po, or its /sup 210/Pb precursor in the parenchymal tissue. About 5 pCi deposited and retained on alveolar surfaces and an average excess of 0.3 pCi /sup 210/Po retained on the tracheobronchial tree is estimated for smokers. Measurements in exsmokers result in a ratio (T/P) = 0.8 +- 0.4 and is possibly related to long-term retention of deposited /sup 210/Pb in alveolar tissue.

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.

Cancer incidence and lifespan vs. alpha-particle dose in beagles

Young adult beagles were injected with graded activities of 239Pu, 241Am, 228Th, 228Ra or 226Ra and observed throughout their lifespans. The vast majority of the dose was from alpha particles. The lifetime incidence of bone sarcoma increased with average skeletal dose, more or less linearly up to high incidence for 239Pu, 241Am, 228Th and 226Ra, but sigmoid fashion for 228Ra. Based on average skeletal dose, the toxicity of the emitters relative to 226Ra = 1.0 was 239Pu = 16.6 +/- 4.5, 241Am = 5.4 +/- 1.6, 228Th = 8.5 +/- 2.3 and 228Ra = 2.0 +/- 0.5. At the lowest doses, the average lifespans were 97% +/- 3% of that in the controls. If beneficial effects occurred, they may have been overwhelmed by the destructiveness of the densely ionizing alpha particles. A cell nucleus 5 micron in diameter receives a mean dose of about 1 Gy (100 rad) when traversed by a single alpha particle. We found no evidence that alpha-particle doses suppressed cancer or lengthened lifespan in beagles.

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)

Estimation of skeletal burden of "bone-seeking" radionuclides in man from in vivo scintillation measurements of the head.

A method for estimating the skeletal burden of various “bone-seeking” lowenergy photon-emitting radionuclides, e.g. ”‘Pb, 241Am, and 238,9Pu, has been developed utilizing the technique of in vivo scintillation measurement of photon activity from the skull bones. In this procedure, the head (skull), which represents a structure comprising more than 12% of the skeletal mass, is surrounded by three NaI(Tl)CsI(Tl) dual crystal scintillation detectors to maximize counting efficiency and minimize detection variablity. In addition to measuring the low-energy photons (<lo0 keV) of important radionuclides known to deposit in or on the surfaces of bone, these detectors are employed to simultaneously monitor the higher energy gamma-ray spectra of “natural” radioactivity such as 40K. From this information it has been possible to optimize the accuracy of background correction, thereby minimizing the detectable levels of a “bone-seeking’’ contaminant. In addition, considerations of accurate “phantom” head construction and the precision of head counting methodology have been investigated. Once the amount of activity deposited in the skull bones has been determined, it is possible to estimate the contribution from the nuclide in the thoracic skeleton to in vivo measurements of activity in the lungs

Chelation of

Investigations have been performed to evaluate DTPA effectiveness in the removal of241 Am from the adult baboon. By administering therapy at long as well as at shorter times after single iv injecti...