Microdistribution and localized dosimetry of the alpha-emitting radionuclides 239Pu, 241Am and 233U in mouse femoral shaft

PURPOSE

To analyse the temporal change in microdistribution of 239Pu, 241Am and 233U in mouse femur and to compare the calculated radiation doses with regions of the bone marrow thought to contain target cells for osteosarcoma and leukaemia with relative risk for those diseases.

MATERIALS AND METHODS

Neutron-induced and alpha-track autoradiographs were prepared from femora of the CBA/H mouse that had been injected with 40 kBq kg(-1) radionuclide between 1 and 448 days previously. Computer-based image analysis of the autoradiographs was performed and dosimetric methods applied to obtain radiation dose-rates to different regions of the marrow cavity.

RESULTS

Initially each radionuclide deposited on endosteal and periosteal bone surfaces; 241Am was additionally deposited on vascular canal surfaces. Redistribution resulted in 233U being incorporated into bone, while 239Pu and 241Am showed transfer into both bone volume and marrow. Accumulation in the central marrow peaked at 112-224 days post-injection, but subsequently was cleared by 448 days. Cumulative doses to both osteosarcomagenic and myeloid leukaemogenic target cell regions showed the trend 239Pu > 241Am > 233U.

CONCLUSIONS

Calculation of cumulative doses to a 10-microm layer of marrow adjacent to bone surfaces appears to be a suitable predictor for risk of osteosarcoma. Risks of myeloid leukaemia in the mouse are better predicted by considering the central marrow as the target region rather than average dose to all marrow.

Review and critical analysis of available in vitro dissolution tests

The procedures recommended in Publications 30 and 66 by ICRP for calculating radiation doses from inhaled or ingested radionuclides include classification of material on the basis of different parameters, among which transportability plays a major role, The allocation of transportable Classes or absorption Types should, whenever possible, be based on animal or human data. However, when such in vivo data are unavailable, it becomes appropriate to consider the use of other approaches, among which in vitro dissolution techniques are reasonable alternatives. This paper reviews and critically analyzes in vitro dissolution techniques that have been described historically and recommends methods shown to be useful in estimating the in vivo solubility of radioactive particles.

Efficacy of ethane-1-hydroxy-1,1-bisphosphonate (EHBP) for the decorporation of uranium after intramuscular contamination in rats

PURPOSE

To obtain compounds that will effectively reduce the fixation of uranium in its main target organs: bone and kidney. There is an urgent need for a chelating agent that is suitable and available for human use.

MATERIALS AND METHODS

The efficacy of ethane-1-hydroxy-1,1-bisphosphonate (EHBP), already in use as a therapeutic agent, was investigated in animal experiments. The effect of different treatment regimens was investigated on rats (EHBP: 50-100 micromol kg(-1); ligand/uranium ratio 2500 to 5000).

RESULTS

The present study shows that one prompt injection of EHBP reduced uranium deposition in kidneys by a factor of five after acute intramuscular contamination in rats. At the same time, the total body uranium in the treated animals was 70% of controls. When the treatment was delayed 30 min after contamination, the kidney content was still reduced by a factor of two.

CONCLUSIONS

EHBP has the advantage of clinical acceptance as a therapeutic agent for other purposes and its toxicity has been well studied. It therefore has a role in the treatment of human contamination with uranium.

[Percutaneous absorption of metallic cations: uranium particulates]

Washing is usually used to reduce the risk of a skin contamination. Skin biopsies were used and contaminations were realised with 1) soluble radioactive calcium 2) insoluble particles of uranium. The result obtained with different wash liquids are presented here. Water and soap had no effect but hypertonic DTPA was the better therapy to remove uranium from skin.

Implementation of ICP-MS protocols for uranium urinary measurements in worker monitoring

The uranium concentration in human urine spiked with natural uranium and rat urine containing metabolized depleted uranium was determined by ICP-MS. The use of ICP-MS was investigated without any chemical treatment or after the different stages of a purification protocol currently carried out for routine monitoring. In the case of spiked urine, the measured uranium concentrations were consistent with those certified by an intercomparison network in radiotoxicological analysis (PROCORAD) and with those obtained by alpha spectrometry in the case of the urine containing metabolized uranium. The quantitative information which could be obtained in the different protocols investigated shows the extent to which ICP-MS provides greater flexibility for setting up appropriate monitoring approaches in radiation protection routines and accidental situations. This is due to the combination of high sensitivity and the accuracy with which traces of uranium in urine can be determined in a shorter time period. Moreover, it has been shown that ICP-MS measurement can be used to quantify the 235U isotope, which is useful for characterizing the nature of the uranium compound, but difficult to perform using alpha spectrometry.

Distribution of uranium in rats implanted with depleted uranium pellets

During the Persian Gulf War, soldiers were injured with depleted uranium (DU) fragments. To assess the potential health risks associated with chronic exposure to DU, Sprague Dawley rats were surgically implanted with DU pellets at 3 dose levels (low, medium and high). Biologically inert tantalum (Ta) pellets were used as controls. At 1 day and 6, 12, and 18 months after implantation, the rats were euthanized and tissue samples collected. Using kinetic phosphorimetry, uranium levels were measured. As early as 1 day after pellet implantation and at all subsequent sample times, the greatest concentrations of uranium were in the kidney and tibia. At all time points, uranium concentrations in kidney and bone (tibia and skull) were significantly greater in the high-dose rats than in the Ta-control group. By 18 months post-implantation, the uranium concentration in kidney and bone of low-dose animals was significantly different from that in the Ta controls. Significant concentrations of uranium were excreted in the urine throughout the 18 months of the study (224 +/- 32 ng U/ml urine in low-dose rats and 1010 +/- 87 ng U/ml urine in high-dose rats at 12 months). Many other tissues (muscle, spleen, liver, heart, lung, brain, lymph nodes, and testicles) contained significant concentrations of uranium in the implanted animals. From these results, we conclude that kidney and bone are the primary reservoirs for uranium redistributed from intramuscularly embedded fragments. The accumulations in brain, lymph nodes, and testicles suggest the potential for unanticipated physiological consequences of exposure to uranium through this route.

The effects of the initial lung deposit on uranium biokinetics after administration as UF4 and UO4

This study was designed to assess the effect of the initial lung deposit (ILD) on uranium biokinetics in rats after intracheal instillation of biologically soluble uranium compounds. Rats received various doses of either UO4 or UF4 dust. The uranium content was determined in the kidneys, lungs, remaining carcass, urine and faeces at intervals of up to 30 days. The percentages of uranium absorbed into blood, transferred to tissues, and excreted in urine were independent of the uranium lung deposit for the two compounds. The K/K + U ratio 24 h after installation (K is the per cent of uranium retained in the kidneys and U the per cent excreted in urine) which can be used to evaluate kidney function, was essentially constant in the range from 0.02 to 12.5 microg U g(-1) kidneys.

Intracellular behaviour of uranium(VI) on renal epithelial cell in culture (LLC-PK1): influence of uranium speciation

The main objective of this work was to assess the potentiality of in vitro models to study and understand the uranium-induced cytotoxicity on renal cells. Cytotoxicity and morphological studies were performed in a tubular proximal original established cell line (LLC-PK1 cell line). Dose-dependent cytotoxicity response was obtained with the uranium bicarbonate complex. In vitro experiments revealed a toxicity of uranium-bicarbonate complexes after a 24-h exposition and for concentrations ranging from 7 x 10(-4) M to 10(-3) M. In contrast, a lack of cytotoxicity of uranium(VI) citrate complexes studied using the same experimental conditions was noticed. Furthermore, electron transmission microscopy and X-ray microanalysis studies, after exposition of LLC-PK1 cells to the uranium-bicarbonate system ([U] = 8 x 10(-4) M) revealed that uranium entered into the cells and it was precipitated within the cytoplasmic compartment as uranyl phosphate needles. Similar morphological studies conducted with citrate complexes did not show any intake of uranium by LLC-PK1 cells. Experiments conducted in phosphate free culture medium showed that uranium was incorporated as a soluble material and that the association of the metal with phosphate ions occurred in the cytoplasmic compartment of LLC-PK1 cells.

Inhaled uranium ore dust and lung cancer risk in rats

Using a nose-only inhalation system, male Sprague-Dawley rats were exposed 4.2 h d(-1), 5 days per week for 65 weeks to one of two concentrations of natural uranium ore dust aerosol (44% U, 50 mg m(-3) and 19 mg m(-3)) without significant radon content. After inhalation exposure ceased, the rats were allowed to live for their natural lifetime. Lung uranium burdens, measured at the time of death of each animal, declined exponentially after dust inhalation ceased, and the rate of decline was independent of the initial lung burden. Lymph node specific burdens ranged from 1 to 60 fold greater than the specific lung burden in the same animal. No lymph node tumors were observed. The frequency of primary malignant lung tumors was 0.016, 0.175 and 0.328 and primary non-malignant lung tumors 0.016, 0.135 and 0.131 in the control, low and high aerosol exposed groups, respectively. There was no difference in tumor latency between the groups. Absorbed dose to the lung was calculated for each animal in the study. The average doses for all the animals exposed to the low and high dust aerosol concentrations were 0.87 Gy and 1.64 Gy respectively, resulting in an average risk of malignant lung tumors of about 0.20 tumors per animal per Gy in both groups. The frequency of primary lung tumors was also calculated as a function of dose increment for both exposed groups individually and combined. The data indicate that, in spite of the above result, lung tumor frequency was not directly proportional to dose. However, when malignant lung tumor frequency was calculated as a function of dose rate (as measured by the lung burden at the end of dust inhalation) a direct linear relationship was seen (p < 0.01) suggesting dose rate may be a more important determinant of lung cancer risk than dose. Conversely, non-malignant lung tumors were significantly correlated with low lung burdens (p = 0.01). We conclude that chronic inhalation of natural uranium ore dust alone in rats creates a risk of primary malignant and non-malignant lung tumor formation and that malignant tumor risk was not directly proportional to dose, but was directly proportional to dose rate.

Acute toxicity, toxicokinetics, and tissue target of lead and uranium in the clam Corbicula fluminea and the worm Eisenia fetida: comparison with the fish Brachydanio rerio

The general objective of our work was to propose new reference material for chemical toxicity testing and new sentinel organisms for environmental quality survey programs (freshwater or soils). We also wanted to provide basic toxicological data on the environmental effects of uranium. Thus, we conducted a comparative study to establish the acute toxicity and toxicokinetics of lead (Pb) and uranium (U) to the bivalve mollusc Corbicula fluminea and the terrestrial annelid Eisenia fetida andrei and to compare these findings with those of the well-known teleost fish Brachydanio rerio. We then measured the concentration of these metals in various tissues of the clam and the worm after two periods of exposure (4 and 11 days) to identify the affinities of these tissues for Pb and U. Our results have shown that Pb and U are very toxic to Eisenia and relatively nontoxic to Corbicula. By comparison, Pb was relatively nontoxic and U appeared to be very toxic to the fish. The toxicokinetic studies indicated that the three species are able to accumulate Pb and U, the rate and level of accumulation depending both on the species and the metal. We also found that fish and clams depurate the two metals. Data collected for the worm were conflicting: Pb was not depurated whereas tissue concentrations of U declined after the eighth day of exposure. Our study has also shown that the tissue distribution of Pb in the mollusc and in the earthworm differs significantly from that of U, both after 4 and 11 days exposure. In conclusion, these three species showed potential as bioindicators of environmental contamination by metals. Indeed, they could be used in conjunction to test different compartments of an ecosystem: worms for soils, fish for the water column, and clams for the water/sediment interface.

Uptake of ingested uranium after low "acute intake"

The uptake of uranium, ingested as a soluble compound, was studied by monitoring the uranium level in urine by inductively coupled plasma mass spectrometry and through measurement of an isotopic tracer. The high sensitivity of this method allows measurement of uranium levels in urine samples from each voiding, therefore more detailed biokinetic studies are possible. To simulate low "acute intake," five volunteers with "normal" levels (5-15 ng L(-1)) of uranium in urine ingested a grapefruit drink spiked with 100 microg of uranium (235U/238U = 0.245%) as uranyl nitrate, and the level of uranium in their urine after ingestion was monitored. Two techniques were applied to estimate the extent of exposure: a) uranium levels above the normal level for each volunteer; and b) the deviation from natural isotopic ratio. Results were normalized relative to the creatinine concentration, which served as an indicator of urine dilution, to reduce effects due to diurnal changes. The results clearly indicate that currently accepted bio-kinetic models overestimate the time between ingestion of dissolved uranium and its excretion in urine, the maximum of which was found to be around 6-10 h. The uptake fraction was in agreement with recent studies, i.e., 0.1-0.5% of the ingested uranium for four of the subjects but above 1.5% for the fifth, and well below the 5% reported in International Commission on Radiation Protection Publication 54. Finally, partial results from the isotope dilution study indicate that uranium absorbed through the intestine interchanges with uranium retained in body organs. The time scale of this process is quite short, and the acute exposure led to a minimum in the isotopic ratio within hours, while recovery back to natural abundance due to low chronic exposure takes several days.

Interaction between chitosan and uranyl ions. Part 1. Role of physicochemical parameters

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.

Impact of the 235U series on doses from intakes of natural uranium and decay progeny

The doses from 235U series radionuclides have often been ignored in dose assessments involving natural uranium and progeny. This is due to the relatively low abundance of 235U in natural uranium (less than 5% on an activity basis). However, inclusion of the 235U series radionuclides, especially 227Ac and 231Pa, in dose calculations can have a substantial impact on estimated inhalation doses.

Environmental uranium and human health

Uranium from the environment enters the human body by ingestion with food and drink and by inhalation of respirable airborne uranium-containing dust particles or aerosols. Daily intake of uranium in food and water varies from approximately 1 to approximately 5 micrograms U/d daily in uncontaminated regions to 13-18 micrograms/d or more in uranium mining areas. A 70 kg, non-occupationally exposed 'Reference Man' living in Europe or in the United States has an estimated total body uranium content of about 22 micrograms. Uranium is absorbed from the intestine or the lungs, enters the bloodstream, and is rapidly deposited in the tissues, predominantly kidney and bone, or excreted in the urine. In the bloodstream, uranium is associated with red cells, and its clearance is relatively rapid. Renal toxicity is a major adverse effect of uranium, but the metal has toxic effects on the cardiovascular system, liver, muscle, and nervous system as well. Any possible direct risk of cancer or other chemical- or radiation-induced health detriments from uranium deposited in the human body is probably less than 0.005% in contrast to an expected indirect risk of 0.2% to 3% through inhaling the radioactive inert gas radon, which is produced by the decay of environmental uranium-238 in rocks and soil and is present in materials that are used to build dwellings and buildings where people live and work.

New agents for in vivo chelation of uranium(VI): efficacy and toxicity in mice of multidentate catecholate and hydroxypyridinonate ligands

Soluble uranyl ion [UO2(2+), U(VI)] is a kidney poison. Uranyl ion accumulates in bone, and the high specific activity uranium isotopes induce bone cancer. Although sought since the 1940's, no multidentate ligand was identified, until now, that efficiently and stably binds U(VI) at physiological pH, promotes its excretion, and reduces deposits in kidneys and bone. Ten multidentate ligands patterned after natural siderophores and composed of sulfocatechol [CAM(S)], carboxy-catechol [CAM(C)], or hydroxypyridinone [Me-3,2-HOPO] metal-binding units have been tested for in vivo chelation of U(VI). Ligands were injected intraperitoneally (i.p.) into mice 3 min after intravenous (i.v.) injection of 233U or (232+235)U as UO2Cl2 [ligand-to-metal molar ratio 75 to 92]. Regardless of backbone structure, denticity, or binding unit, all 10 ligands significantly reduced kidney U(VI) compared with controls or with mice given CaNa3-DTPA, and four CAM(S) or CAM(C) ligands also significantly reduced skeleton U(VI). Several ligands removed U(VI) from kidneys, when injected at 1 or 24 h. Injected at molar ratios > or = 300, 5-LIO(Me-3,2-HOPO) and TREN-(Me-3,2-HOPO) reduced kidney U(VI) to about 10% of control. Given orally to fasted mice at molar ratios > or = 300, those ligands significantly reduced kidney U(VI). In mice injected i.v. with 0.42 micromol kg(-1) of 235U and given 100 micromol kg(-1) of one of those Me-3,2-HOPO ligands i.p. daily for 10 d starting at 1 h after the U(VI)) loss of kidney U(VI) was greatly accelerated, and the kidneys of treated mice showed no microscopic evidence of renal injury. Crystals of uranyl chelates with linear tetradentate ligands containing bidentate Me-3,2-HOPO groups demonstrate a 1:1 structure. Considering low toxicity, effectiveness, and reasonable cost, the structurally simple linear tetradentate ligands based on the 5-LI backbone (diaminopentane) offer the most promising approach to a clinically acceptable therapeutic agent for U(VI). Work is in progress to identify the most suitable CAM or HOPO binding unit(s).

A sensitive method for the determination of uranium in biological samples utilizing kinetic phosphorescence analysis (KPA)

Kinetic phosphorescence analysis is a technique that provides rapid, precise and accurate determination of uranium concentration in aqueous solutions. This technique utilizes a laser source to excite an aqueous solution of uranium, and measures the emission luminescence intensity over time to determine the luminescence decay profile. The lifetime of the luminescence decay profile and the linearity of the log luminescence intensity versus time profile are indications of the specificity of the technique for uranium determination. The luminescence intensity at the onset of decay (the initial luminescence intensity), which is the luminescence intensity at time zero after termination of the laser pulse used for excitation, is proportional to the uranium concentration in the sample. Calibration standards of known uranium concentrations are used to construct the calibration curve between the initial luminescence intensity and uranium concentration. This calibration curve is used to determine the uranium concentration of unknown samples from their initial luminescence intensity. We developed the sample preparation method that allows the determination of uranium concentrations in urine, plasma, kidney, liver, bone spleen and soft tissue samples. Tissue samples are subjected to dry-ashing in a muffle furnace at 600 degrees C and wet-ashing with concentrated nitric acid and hydrogen peroxide twice to destroy the organic component in the sample that may interfere with uranium determination by KPA. Samples are then solubilized in 0.82 M nitric acid prior to analysis by KPA. The assay calibration curves are linear and cover the range of uranium concentrations between 0.05 micrograms l-1 and 1000 micrograms l-1 (0.05-1000 ppb). The developed sample preparation procedures coupled with the KPA technique provide a specific, sensitive, precise and accurate method for the determination of uranium concentration in tissue samples. This method was used to quantify uranium in different tissue samples obtained over a period of 90 days following a single intraperitoneal uranium dose of 0.1 mg kg-1 in rats.

Brewery yeast as a biosorbent for uranium

Yeast cells are capable of carrying out biosorption with various heavy metals. The biomass deriving from Saccharomyces cerevisiae coming from brewing industries is a by-product that is possible to be used in the purification of water contaminated with these ions. In this paper we show that yeast biomass from one of the city's breweries can adsorb uranium efficiently, up to 2.4 mmol of this metal per gram of dry biomass. It can also be seen that the temperature (between 10 degrees and 37 degrees C) has no effect on the biosorption, while pH does have an influence, 4.5 being the best value. When the concentrations of uranium range between 0.1 and 0.5 mol l-1 the yeast dry biomass is capable of adsorbing between 84% and 98% of this metal in solution.

The relationships between urinary elimination, airborne concentration, and radioactive hand contamination for workers exposed to uranium

The purposes of this study were to estimate the proportional contribution of uranium dust exposure to urinary excretion of the metal, and to examine the influence of hand contamination on the elimination of uranium from the urine of workers who performed different jobs. The study was based on records taken from a gaseous diffusion plant in 1956. Regression techniques were used to investigate the relationship between uranium concentration in urine and exposure variables, including the concentration of uranium dust and the incidence of hand contamination. The proportional contribution of airborne to urinary uranium was estimated by the slope of this relationship. It is concluded that the workers eliminated uranium at relatively constant rates per unit air concentration (0.67 to 1.27 micrograms/L per micrograms/m3). In addition to airborne uranium, hand contamination significantly contributed to the elimination among maintenance crew, but not among production workers. Furthermore, the production index was shown to be a useful surrogate for airborne and urinary uranium.

Assessment of radioactive systemic uptakes by deconvolution of individual monitoring results

The methods of interpretation presently available for evaluating individual radioactivity intakes from measured data involve difficulties connected with the adaptation of metabolic models to the situations encountered in practice. These difficulties essentially concern the definition of appropriate parameters for each encountered case, and very often- except for characterized incidents-erroneous appreciation of the time course of contamination episodes and of th routes of entry. These considerations led us to develop a simplified method of interpreting monitoring data, by considering separately the data relating to routes of entry and those concerning systemic contamination, i.e., the contamination occurring after the transfer of radionuclides to the blood. An approach to interpreting measurements of systemic contamination is proposed in this study. This method is to calculate, from these measurements, the values for the activity absorbed daily from the routes of entry into the blood using the appropriate retention and excretion functions. a day-to-day follow-up of the absorbed activity becomes possible, thus enabling its real-time evolution to be recorded and easy to consult. A few applications of the method are described, including cases of acute tritium and uranium contamination and of chronic contamination by tritium, uranium, and iodine. The conditions and constraints required to validate the proposed approach are indicated.

Uranium skeletal dosimetry and distribution in young adult beagles: a guide for calculating uranium skeletal doses in humans

Uranium isotopes were given via single intravenous injection into 22 young adult beagle dogs of both sexes to determine the metabolism of this element. Animals were given either 232U, 233U, 238U, or a combination of 232 (+) 233U. Calculations to assign a value of skeletal dose for each dog were performed using published radioactive properties of each uranium isotope and the metabolic data (including measured retention and skeletal distribution) derived from this study during a period of up to 2 y after injection. We believe that the procedures illustrated in this communication can serve as a useful pattern for estimating skeletal radiation doses to humans contaminated with 232U, 233U, or 238U.

PBK modeling for metals. Examples with lead, uranium, and chromium

Physiologically-based models for metals differ in several key respects from models for organic compounds. Although sequestration by binding to specific metal-binding proteins in liver, kidney, and red cell may be important, neither the magnitude and pattern of metabolism nor potential accumulation in fat is a component of models of metal kinetics. In addition, the long residence times of bone-seeking elements require that bone turnover and metabolism be incorporated into physiologically-based models for these elements. Three mechanism (rapid exchange at bone/blood interfaces, trapping or incorporation with forming bone and loss with resorbing bone, and slow exchange throughout the total bone volume) are potentially important in the overall interchange of bone-seeking elements between blood and bone. Three examples are given of applications of physiologically-based kinetic models for the bone-seeking elements lead, chromium, and uranium to assist in answering practical questions relating to bioavailability, distribution, and data interpretation.

Probabilistic risk assessment of nephrotoxic effect of uranium in drinking water

Assessments of the health effects of pollutants generally use models in which exposure variables and model parameters are point values, often chosen as conservative estimates. A more realistic approach is to characterize the uncertainty of each variable and parameter explicitly as a probability distribution. This paper presents a probabilistic version of an established model for metabolism of ingested uranium and characterizes the parameters of the model as distributions. It then characterizes the uncertainty of the threshold level for nephrotoxic risk of uranium, and uses distributions of the heterogeneity in drinking water intake of uranium in the U.S. to assess nephrotoxic risk. It further evaluates the implications of inadequate data on the heterogeneity of dietary intake.

Efficacy of 3,4,3-LIHOPO for reducing the retention of uranium in rat after acute administration

Decorporation therapy is the only known effective method of reducing the radiation dose to persons following accidental internal contamination with transportable radionuclides. Deposits of actinides in bone should be minimized because development of osteosarcoma appears to be related to internal exposure. In contrast with other actinides, such as plutonium or americium where chelating agent treatment is efficient, the therapeuric approaches used for cases of uranium contamination are widely ineffective. This is the first report on in vivo efficacy of a chelating agent, a siderophore analogue code named 3,4,3-LIHOPO, after systematic exposure to natural uranium in the rat. Using the classical antidotal therapy (sodium bicarbonate) for comparison, this ligand has been investigated for its ability to remove uranium from rats after intravenous or intramuscular injection as nitrate. Following an immediate single intramuscular or intravenous injection of 3,4,3-LIHOPO (30 mumol.kg-1) urinary excretion of uranium was greatly enhanced with a corresponding reduction 24 h later in kidney and bone uranium content (to about 20 and 50% of the control rat respectively). Under identical experimental conditions, sodium bicarbonate (640 mumol.kg-1) reduced the uranium content in kidney in kidney and bone only to about 90 and 70% of controls respectively, and there was less enhancement of uranium excretion. However, when treatment was delayed by 30 min and administered intraperitoneally, there was no marked difference in retention and excretion of uranium between the two compounds. As this ligand showed no apparent irreversible toxicity at effective dosages, it is concluded that the administration of the 3,4,3-LIHOPO chelating agent represents potentially a most significant advance for prompt treatment of uranium contamination, while a more detailed investigation is necessary on the possible advantage when treatment delayed.

A study of uranium lung clearance at a uranium processing plant

A study has been made of the retention of uranium in the lungs of persons exposed chronically to low levels of uranium aerosols at the Y-12 Plant. A new characterization of the workplace aerosols shows an activity median aerodynamic diameter of 8 microns to be representative of the uranium oxides handled at the Y-12 Plant. The usual ICRP respiratory-system model is employed in conjunction with bioassay data from worker exposures to deduce a new set of parameters to describe lung clearance of these aerosols. This new assessment leads to good agreement between in vivo estimates of uranium lung burdens.

Fractional absorption of ingested uranium in humans

This paper provides a review and reanalysis of data relating to gastrointestinal (GI) uptake of uranium in humans. Estimates of GI uptake of uranium in adult humans have been derived from results of three controlled experimental studies involving short-term oral intake of an elevated quantity of uranium in fluids, from a controlled balance study conducted in a metabolic research ward of a hospital, and from a variety of environmental studies in which urinary uranium could be related to total intake or total excretion of this element in the same population. For controlled studies, uptake values range from less than 0.1% to about 6% for individual subjects, with central values for different studies falling in the range 1-2.4%. Environmental studies yield central estimates in the range 0.3-3.2%. Expressed as a percentage of total intake of uranium in food and fluids, average GI uptake of uranium in adult humans appears to be about 1-1.5%. Limited intake and excretion data for environmentally exposed human subjects > or = 5 y of age do not reveal important differences with age in uranium uptake, but more definitive information is needed for children. More information is also needed to determine whether fractional uptake of uranium increases with decreasing levels of intake and whether uptake from drinking water is substantially higher than uptake from food. Data for laboratory animals indicate that fractional uptake of uranium depends strongly on the chemical form ingested and the length of time since the last intake of food.