Evidence for a differential translocation of actinides across human lung epithelial cell monolayer in vitro according to their physicochemical properties and the presence of a chelating agent.

The epithelial cell plays a key role in the transfer of radionuclides from lungs to blood following pulmonary exposure. The present study was designed to evaluate the transfer across human lung epithelial cells of various actinides (plutonium, americium and uranium), the influence of the physicochemical properties of plutonium compounds and of the chelating agent diethylene triamine pentaacetic acid (DTPA). To address this question, Calu-3 cells grown in a bicameral culture system were used. The integrity of the epithelial barrier was evaluated by measuring transepithelial electrical resistance (TEER) and the passage of a fluorescent marker, lucifer yellow. Activity measurement in basal compartment following periodic collection of culture medium was made from 2 h to seven days. To facilitate data handling and analysis, the statistical tool STATBIODIS was used. The results indicate differences in transfer for the different elements, and according to Pu physicochemical properties. Though to various extents, the chelating agent DTPA always increased the transfer of Pu and Am across the epithelial cells, without altering the integrity of the epithelial barrier. This in vitro cell culture model, by mimicking translocation of actinides from lungs to blood, can represent a valuable tool to further understand the underlying mechanisms and properties controlling this process.

Evaluation of Uncertainties in lung measurements of actinides due to counting statistics.

Counting statistics is an important parameter that can introduce uncertainties in the lung activity measurements of actinides in radiation workers. Evaluation of uncertainties due to counting statistics is practically difficult as it requires monitoring various radiation workers having different levels of lung actinide content, multiple times, each for 50 min of monitoring period. However, different activities in lungs can be simulated by combining uncontaminated male data with LLNL phantom data acquired with 241Am and natural uranium lung sets at various short periods. Therefore, multiple measurements were carried out on realistic thorax LLNL phantom with 241Am and natural uranium lung sets for 15-600 s. The mean counts with the phantom at various time intervals, corresponds to different actinide activities in lungs, assuming they are obtained for 50 min of monitoring interval. Using propagation of error, standard deviations were evaluated for combined phantom and uncontaminated adult male data. The combined standard deviations and mean phantom counts are used to evaluate scattering factors (SFs) for uncertainties due to counting statistics for Phoswich and HPGe array detectors. The SFs due to counting statistics are found to be the function of lung activities of radionuclides as well as energies and yields of the photons emitted by radionuclides. SFs are found to increase with decrease in lung activity. For similar yields photons, SFs are found to be lower for higher energy photons compared to lower energy photons. For photons of similar energies, the SFs are lower when yield is higher compared to lower yield photons.

Mitigating the Psychological Harm from Actinide Intakes.

Investigations into possible actinide intakes, as well as the intakes themselves, may result in significant psychological harm that should be mitigated by the internal dosimetrist. Many aspects of this psychological impact are unique to actinide intakes and have not been discussed in the literature. This paper discusses some of these unique considerations and describes how the Internal Dosimetry Team at Los Alamos National Laboratory (LANL) has, with input and guidance from LANL psychologists, tried to address them. We feel that much of the psychological harm can be mitigated by educating employees specifically about internal dosimetry and internal doses, and by improving communication with radiation workers.

Hydroxypyri(mi)dine-based chelators as antidotes of toxicity due to aluminum and actinides.

This review is focused on recent developments on hydroxypyri(mi)dines, as aluminum and actinide chelating agents to combat the toxicity due to accumulations of these metal ions in human body resulting from excessive metal exposure. After a brief update revision of the most common processes of aluminum (Al) exposure, as well as the associated toxicities and pathologies, we will focus on the current available Al chelators and future perspective as potential antidotes of Al toxicity. Due to the similarity between Al and Fe, a major emphasis is given to the hydroxypyridinone and hydroxypyrimidinone chelators, since they are analogues of the current iron chelators in clinical use (DFP and DFO). This review includes issues such as molecular design strategies and corresponding effects on the associated physico-chemical properties, lipo-hydrophilic balance, toxicity, in vivo bioassays and current clinical applications. The hydroxypyri(mi)dine chelators are also suitable for other hard metal ions, such as the radiotoxic actinides, and so a brief review is included on the applications of these chelators in actinides scavenging.

Bone as target organ for metals: the case of f-elements.

The skeleton is a target organ for most metals. This leads to their bioaccumulation, either as storage of useful oligoelements or as a protection against damage by toxic elements. The different events leading to their accumulation in this organ, under constant remodeling, are not fully understood, nor the full subsequent impact on bone metabolism. This lack of knowledge is particularly true for lanthanides and actinides, whose use has been increasing over recent decades. These metals, known as f-elements, present chemical similarities and differences. After a comparison of the biologically relevant physicochemical properties of lanthanides and actinides, and a brief reminder of the main events of bone metabolism, this review considers the results published over the past decade regarding the interaction between bones and f-elements. Emphasis will be given to the molecular events, which constitute the basis of the most recent toxicological studies in this domain but still need further investigation. Ionic exchanges with the inorganic matrix, interactions with bone proteins, and cellular mechanism disturbances are mainly considered in this review.

Treatment of actinide exposures: a review of Ca-DTPA injections inside CEA-COGEMA plants.

Calcium diethylenetriamine pentacetate (Ca-DTPA) has been used for medical treatment of plutonium and americium contaminations in the CEA and COGEMA plants from 1970 to 2003. This paper is a survey of the injections Ca-DTPA administered as a chelating molecule and it will be a part of the authorisation process for Ca-DTPA by intravenous administration. Out of 1158 injections administered to 469 persons, 548 events of possible or confirmed contamination were reported. These employees were followed by occupational physicians according to the current French regulations. These incidents took place at work, were most often minor, not requiring follow-up treatment. The authors present (1) a synthesis of the most recent findings. Due to its short biological half-time and its limited action in the blood, Ca-DTPA does not chelate with plutonium and americium as soon as these elements are deposited in the target organs. It justifies an early treatment, even in cases of suspected contamination followed by additional injections if necessary (2) data concerning these 1158 injections (route of contamination, dosage, adverse effects, etc.) The authors also investigated a study on the efficacy of the product on a group of persons having received five or more injections. These results were compared with the efficacy estimated theoretically. Dosages and therapeutic schemes were proposed based on these observations. This synthesis is the result of a collective work having mobilised the occupational medicine departments, the medical laboratories inside a working group CEA-COGEMA-SPRA.

Actinide speciation in relation to biological processes.

In case of accidental release of radionuclides into the environment, actinides represent a severe health risk to human beings following internal contamination (inhalation, ingestion or wound). For a better understanding of the actinide behaviour in man (in term of metabolism, retention, excretion) and in specific biological systems (organs, cells or biochemical pathways), it is of prime importance to have a good knowledge of the relevant actinide solution chemistry and biochemistry, in particular of the thermodynamic constants needed for computing actinide speciation. To a large extent, speciation governs bioavailability and toxicity of elements and has a significant impact on the mechanisms by which toxics accumulate in cell compartments and organs and by which elements are transferred and transported from cell to cell. From another viewpoint, speciation is the prerequisite for the design and success of potential decorporation therapies. The purpose of this review is to present the state of the art of actinide knowledge within biological media. It is also to discuss how actinide speciation can be determined or predicted and to highlight the areas where information is lacking with the aim to encourage new research efforts.

Actinide and metal toxicity to prospective bioremediation bacteria.

Bacteria may be beneficial for alleviating actinide contaminant migration through processes such as bioaccumulation or metal reduction. However, sites with radioactive contamination often contain multiple additional contaminants, including metals and organic chelators. Bacteria-based bioremediation requires that the microorganism functions in the presence of the target contaminant, as well as other contaminants. Here, we evaluate the toxicity of actinides, metals and chelators to two different bacteria proposed for use in radionuclide bioremediation, Deinococcus radiodurans and Pseudomonas putida, and the toxicity of Pu(VI) to Shewanella putrefaciens. Growth of D. radiodurans was inhibited at metal concentrations ranging from 1.8 microM Cd(II) to 32 mM Fe(III). Growth of P. putida was inhibited at metal concentrations ranging from 50 microM Ni(II) to 240 mM Fe(III). Actinides inhibited growth at mM concentrations: chelated Pu(IV), U(VI) and Np(V) inhibit D. radiodurans growth at 5.2, 2.5 and 2.1 mM respectively. Chelated U(VI) inhibits P. putida growth at 1.7 mM, while 3.6 mM chelated Pu(IV) inhibits growth only slightly. Pu(VI) inhibits S. putrefaciens growth at 6 mM. These results indicate that actinide toxicity is primarily chemical (not radiological), and that radiation resistance does not ensure radionuclide tolerance. This study also shows that Pu is less toxic than U and that actinides are less toxic than other types of metals, which suggests that actinide toxicity will not impede bioremediation using naturally occurring bacteria.

Does mean lung dose calculated after inhalation of alpha emitters actually reflect the risk of induction of malignant lung tumours?

A comparison of incidence of lung tumours in rats after inhalation exposure to aerosols containing alpha emitters which have different physico-chemical properties has been performed. Aerosols of radon and progeny, uranium ore dust, NpO2, PuO2 or Cm2O3 were considered for intercomparison with similar or different particle sizes. Dose-effect relationships for the frequency of malignant lung tumours appear linear up to a few Gy and then become infralinear at higher doses delivered to the lungs. The initial slope of the curves reflects the risk of induction of a lung tumour. The highest slopes of incidence were observed for radon and uranium ore dust (about 70 and 20% Gy(-1) respectively) for which the most homogeneous alpha dose distribution to the lungs is expected. In a general trend, increasing the alpha-activity of deposited particles (higher specific activity of constituent radioisotopes or larger particle size) decreases the risk. The comparison of the reported data shows that the risk per Gy at 'low doses' could vary over more than one order of magnitude depending on the physico-chemical properties of the aerosols.

The United States Transuranium and Uranium Registries as sources for actinide dosimetry and bioeffects.

The United States Transuranium and Uranium Registries (USTUR) has analysed tissues collected at autopsies of over 300 former radiation workers from actinide processing sites throughout the US, in addition to collecting the medical and radiation exposure histories of those workers. These data are included in a large USTUR database and they are available to research scientists throughout the world, either as public records or through collaborative projects with the USTUR. The USTUR also operates the National Human Radiobiological Tissue Repository (NHRTR), in which portions of tissue samples collected at autopsy are kept. These samples, frozen at -70 degrees C, may be used for molecular studies of the effects of radiation. Medical and radiation exposure histories of the tissue donors are available, as are the results of radiochemical analyses of adjacent portions of the samples. These materials are available to researchers who have collaborative agreements with the USTUR, which can be established by accessing USTUR staff members through the website, http://www.ustur.wsu.edu.

[Specific parameters for the calculation of dose after aerosol inhalation of transuranium elements]. / Mesure de paramètres spécifiques pour le calcul de dose après inhalation d'aérosols renfermant des éléments transuraniens.

A review on specific parameter measurements to calculate doses per unit of incorporation according to recommendations of the International Commission of Radiological Protection has been performed for inhaled actinide oxides. Alpha activity distribution of the particles can be obtained by autoradiography analysis using aerosol sampling filters at the work places. This allows us to characterize granulometric parameters of "pure" actinide oxides, but complementary analysis by scanning electron microscopy is needed for complex aerosols. Dissolution parameters with their standard deviation are obtained after rat inhalation exposure, taking into account both mechanical lung clearance and actinide transfer to the blood estimated from bone retention. In vitro experiments suggest that the slow dissolution rate might decrease as a function of time following exposure. Dose calculation software packages have been developed to take into account granulometry and dissolution parameters as well as specific physiological parameters of exposed individuals. In the case of poorly soluble actinide oxides, granulometry and physiology appear as the main parameters controlling dose value, whereas dissolution only alters dose distribution. Validation of these software packages are in progress.

Ultrastructural lesions induced by neptunium-237: apoptosis or necrosis?

In this study, we are concerned with the 237 isotope of neptunium (237Np), which is a by-product of uranium in nuclear reactors. To study ultrastructural lesions induced by this element, a group of rats were injected with a solution of 237Np-nitrate once a day for 14 weeks. Lesions observed in liver and kidney are described using electron microscopy. Ultrastructural alterations of cellular membranes and intracellular organelles demonstrated the existence of neptunium toxicity. This toxicity was characterized by various lesions, such as cytoplasmic clarification, disappearance of mitochondrial cristae, swollen mitochondria, abnormal condensation of nuclear chromatin, and nuclear fragmentations. This study demonstrated the probable induction of apoptosis by neptunium both in liver and kidneys.

[The effect of dose distribution on risk of lung cancer after inhalation of actinide oxides]. / Influence de la distribution de dose sur le risque d'apparition de cancers pulmonaires après inhalation d'oxydes d'actinides.

The aim of this work was to estimate risk of lung tumour occurrence after inhalation of actinide oxides from published studies and rat studies in progress. For the same delivered dose, the risk increases when homogeneity of irradiation increases, i.e., the number of particles deposited after inhalation increases (small particles and (or) low specific alpha activity). The dose-effect relationships reported appear linear up to a few gray, depending on the aerosol considered, and then the slope decreases. This slope, which corresponds with the risk, can vary over one order of magnitude depending on the aerosol used. An effective threshold at about 1 Gy was not observed for the most homogeneous dose distributions. A dosimetric and biological approach is proposed to provide a more realistic risk estimate.

Chemical toxicity of some actinides and lanthanides towards alveolar macrophages: an in vitro study.

PURPOSE: To compare the toxicity of lanthanides (cerium, gadolinium) with actinides (thorium, neptunium, uranium) added in soluble form to rat alveolar macrophage cultures. MATERIALS AND METHODS: The metals were added 1 day after seeding alveolar macrophages extracted by pulmonary lavage, and the metal toxicity was scored 3 days later. Cell death was measured after vital staining to distinguish between apoptosis and necrosis; relative cell density was also quantified. The physico-chemical form of the metals in the culture medium was characterized using filtration and radioactive measurements. RESULTS: Except for thorium, induction of cell death was observed for all the elements studied and the death mechanism involved was apoptosis. Graduated toxicity was observed from uranium to neptunium, cerium and gadolinium, in the range of concentration from 10(-3)-10(-6) M. From pilot experiments, it was hypothesized that soluble compounds were mainly involved in lanthanide toxicity, whereas insoluble forms were mainly involved in actinide toxicity. CONCLUSION: This study demonstrates that the toxicity of neptunium and uranium was concomitant with the presence of insoluble forms in the culture medium. Further studies are needed to characterize the cell death mechanisms involved and the potential synergistic effects of chemical toxicity and irradiation.

Comparison of the carcinogenicity of radium and bone-seeking actinides.

The relative effectiveness of nine bone-seeking radionuclides with their progeny for the production of malignant skeletal tumors (mostly osteogenic sarcoma), principally by chronic alpha-particle irradiation, is examined with available data obtained from lifetime studies at three laboratories of pure-bred beagles exposed to graded dosages in controlled experiments. The lifetime tumor dose-rate/time-response relationships observed in beagles injected with 226Ra at the University of California at Davis, in which 123 cases of bone cancer (98% osteosarcoma) have been observed for dose rates between 0.05 and 20 rad/day, provide the basis for comparing the induction of bone cancer by the other radionuclides. All nine radionuclide studies were found to demonstrate with high precision (sigma g less than 1.2) a three-dimensional lognormal response relationship represented in two dimensions by the equation of the time to death from bone cancer t = KD-s, where t is the elapsed time to death, D is the average skeletal dose rate, K is a parameter characteristic of the radionuclide, risk level and exposure details, and S observed to be 0.29 (0.01 SE) and suggested to be exactly one-third for all the nine radionuclides. The results show the relative biological effectiveness (RBE) for bone-cancer induction potency with respect to radiation exposure from 226Ra to be 3.0 for 228Ra , 6.4 for 241Am, 6.6 for 249Cf , 252Cf and 253Es , 9.0 for 239Pu, 10.7 for 228Th , and 15.5 for 238Pu. The observed RBE values are interpreted in terms of the relative exposure of sensitive cells of the skeleton since they all involve primarily alpha irradiation. Scaling to people is accomplished using a response ratio (RR) of 3.6 with respect to beagles.

Some historical highlights and portents for the future of biomedical research on radium and the actinides.

Radiobiological research on the actinide elements has been a continuum since the first cryptic report by Hamilton at Berkeley, California, in February 1944. Yet certain landmarks in the work, certain people and certain organizations were responsible for the equivalent of quantum jumps in our concepts and understanding. This paper will review very briefly a few of these. Among them will be the realization of the biochemical and consequent biological differences between plutonium and radium, the first demonstration of carcinogenicity of the actinides, their behavior in bone, their relative toxicity, carcinogenesis after inhalation, the genesis of the "king-size" experiments to investigate their long-term effects, "hot particles" in lung, highlights of research with the transplutonics, and several others. To the extent possible, the review will consider not only the research findings, but their bearing on standard setting and the general operations in place at the time. Some of the past and current polemics will be touched upon.