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Americium-241 whole body and internal biokinetics were experimentally investigated in the euryhaline diamond sturgeon Acipenser gueldenstaedtii during its uptake from water and food, in fresh (FW) and brackish water (BW; 9 psu). Whole-body uptake rates of 241 Am from water and subsequent depuration rates were quantified over 14 and 28 days, respectively, and assimilation efficiency (AE) of 241 Am from diet (chironomid) was determined over 28 days. FW reduced the biological half-life of 241 Am following aqueous uptake by an order of magnitude. In contrast BW greatly reduced 241 Am assimilation efficiency (AE) from diet (chironomid) by several orders of magnitude (from an AE of 8.5% (FW) down to 0.003% (BW)). Hence, salinity per se is indicated as a major environmental variable in determining the radiological exposure of A. gueldenstaedtii to 241 Am. During aqueous exposure BW appreciably increased 241 Am activity concentrations in most body components, but aqueous or dietary exposure pathway at either salinity did not determine marked differences in how 241 Am was distributed among six body components. The highly mineralized skin of A. gueldenstaedtii recurred as a major repository of 241 Am in all experimental treatments, as high as 50% among body components, due to its internal transfer from diet, surface adsorption and/or active absorption from water. The indicated prominence of the aqueous, compared to the dietary, exposure pathway for 241 Am accumulation by A. gueldenstaedtii suggests its radiological exposure would be enhanced by BW as it leads to its greater long-term retention, due to a much longer biological half-life., Competing Interests: Declaration of competing interest The authors have no competing interests to declare., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

NCRP Report 156 describes soluble radionuclide retention kinetics in a wound, segregated into four retention categories: weak (W), moderate (M), strong (S), and avid (A). An alternate single-parameter model, the negative power function, t, is presented in this paper to describe the time behavior of radionuclide retention. With this mathematical description, γ is a single parameter that can be used to assign the wound retention category rapidly. Using the power function description of wound retention, the various wound categories present as straight lines on log scales with different slopes corresponding to the various retention categories. Regression analysis of average retention values in NCRP 156 shows γ = 0.735 ± 0.132, 0.514 ± 0.015, 0.242 ± 0.016, and 0.053 ± 0.023 for the weak, moderate, strong, and avid categories, respectively. A case study is presented (REAC/TS Registry case 1284) where a power function is shown to fit retention data in a Pu/Am hand wound up to 2,000 d (5.4 y) post-accident.

Biokinetics underlies the basis for assessment of internal exposures. This paper develops a biokinetic method on simultaneous intake of radionuclides from multiple intake scenarios in internal exposures. With numerical techniques that transform the whole biokinetics between the coupled and decoupled representations of the same problem, this method applies to coupled biokinetics with complex structures and has no restrictions of practical importance on the number of intake scenarios, the number of intake parent radionuclides and decay products, and the complexity of decay relationships between parent and progeny nuclides. For illustration, this method is applied to an assumed case of mixed inhalation and ingestion of weapon-grade plutonium material for reference workers that is focused on Pu and Am. Due to coupled biokinetics between the direct intake and ingrowth parts in different intake pathways, the multiple intake results (the contents of lungs, daily excretions, and cumulative contents) display richer behaviors as compared to single intake cases. This method benefits both the prospective and retrospective assessment of internal exposures for complex intake cases in actual applications.

Chelating agents are administered to treat significant intakes of radioactive elements such as plutonium, americium, and curium. These drugs may be used as a medical countermeasure after radiological accidents and terrorist acts. The administration of a chelating agent, such as Ca-DTPA or Zn-DTPA, affects the actinide's normal biokinetics. It enhances the actinide's rate of excretion, posing a dose assessment challenge. Thus, the standard biokinetic models cannot be directly applied to the chelation-affected bioassay data in order to assess the radiation dose. The present study reviews the scientific literature, from the early 1970s until the present, on the different studies that focused on developing new chelation models and/or modeling of bioassay data affected by chelation treatment. Although scientific progress has been achieved, there is currently no consensus chelation model available, even after almost 50 y of research. This review acknowledges the efforts made by different research groups, highlighting the different methodology used in some of these studies. Finally, this study puts into perspective where we were, where we are, and where we are heading in regards to chelation modeling.

Americium (Am) biodistribution data obtained after wound contamination in rats were analysed to evaluate and quantify the influence of different physicochemical forms of Am in the presence or absence of plutonium (Pu). The biodistribution data were individual Am daily urinary excretion and tissue retention. The data were analysed with STATBIODIS, a statistical tool developed in the laboratory and based on the R language. Non-parametric methods were selected to comply with the data characteristics. Am systemic tissue retention and urinary excretion data were much greater for contamination with soluble physicochemical forms than insoluble forms. Meanwhile, Am relative biodistribution between the main retention tissues (skeleton, liver and kidney) remained the same. Hence, after absorption into blood the radionuclide behaviour was independent of the physicochemical form. The presence of Pu did not change the Am biodistribution. Comparisons of the biodistribution data from the laboratory with mean values published by other laboratories showed that soluble to moderately soluble forms of Am resulted in similar urine excretion after contamination, whether it was intravenous, intramuscular, subcutaneous injection or incision. Findings from this work will contribute to improve the understanding and interpretation of wound contamination cases with different physicochemical forms and mixtures of actinides including Am.

Digital autoradiography with the ionizing radiation quantum imaging detector is used at the US Transuranium and Uranium Registries for visualizing the microdistribution of alpha particles from Am and quantifying the activity. The radionuclide spatial distribution was investigated within cortical and trabecular regions of bone samples from US Transuranium and Uranium Registries case 0846. Multiple specimens from the humerus proximal end, humerus proximal shaft, and clavicle acromial end were embedded in plastic, and 100-μm-thick sections were taken and imaged using the ionizing radiation quantum imaging detector. The detector images were superimposed on the anatomical structure images to visualize Am distribution in cortical bone, trabecular bone, and trabecular spongiosa. Activity concentration ratios were used to characterize Am distribution within different bone regions. The trabecular-to-cortical bone and trabecular-spongiosa-to-cortical bone activity concentration ratios were quantified in both humerus and clavicle. The ionizing radiation quantum imaging detector results were in agreement with those obtained from radiochemical analysis of the remaining bone specimens. The results were compared with International Commission on Radiological Protection default biokinetic model predictions. Digital autoradiography was proven to be an effective method for microscale heterogeneous distribution studies where traditional counting methods are impractical.

Physicochemical properties of actinides highly influence internal intake and biodistribution. An a priori knowledge of the dissolution properties of compounds involved in accidental exposure would be of great help in early dose assessment. However, this information is rarely available, leading to difficulties in interpreting excretion data from contaminated victims. We developed an in vitro acellular assay to predict in vivo bioavailability of actinides and improve medical handling of the victims. Various actinides of different physicochemical properties were used to validate the reliability of the assay to mimic in vivo behavior of the contaminants. Our assay was designed as a dynamic muticompartmental system in which an agarose gel represents the retention compartment of actinides and a dynamic phase the transfer compartment. Relevant physiological conditions were obtained by introducing various components both in the static and dynamic phases. The proposed model may provide a good prediction of in vivo behavior and could be used as a first assessment to predict the fraction of actinides that could be potentially transferred from retention compartments, as well as the fraction available to chelating drugs., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this work, a baseline compartmental model of the distribution and retention of americium in the rat for a systemic intake was derived. The model was derived from data obtained from a study designed to evaluate the behavior of americium in the first 28 days after incorporation. A pharmacokinetic (PK)-front-end modeling approach was used to specify transfer to and from the extracellular fluids (ECF) in the various tissues in terms of vascular flow and volumes of ECF. Back-end rates representing transport into and out of the cells were determined empirically. Uncertainties in transfer rates were investigated using Markov chain Monte Carlo (MCMC). The combination of PK-front-end model and the back-end model structure used allowed for extrapolation to the earliest times with small uncertainty. This approach clearly demonstrated the rapid transfer of material from ECF to liver and bone. This model provides a baseline for modeling the action of decorporation agents, such as DTPA.

The biokinetic model for systemic americium (Am) currently recommended by the International Commission on Radiological Protection (ICRP) for application to occupational intake of Am is based on information available through the early 1990s. Much additional information on Am biokinetics has been developed in the past 25 y, including measurements of retention and excretion of 241 Am in many workers with 241 Am burdens and post mortem measurements of 241 Am in tissues of some of those workers. The ICRP's current Am model is reasonably consistent with the updated information, with the main exception that the current model apparently overestimates 24-hour urinary Am as a fraction of skeletal or systemic Am at late times after intake. This paper provides an overview of current information on the systemic kinetics of Am in adult human subjects and laboratory animals and presents an updated biokinetic model for systemic Am that addresses the discrepancies between the current database and current ICRP systemic model for Am. This model is applied in Part 4 (to appear) of an ICRP series of reports on intake of radionuclides by workers called the OIR (Occupational Intake of Radionuclides) series.

Distribution, retention, and excretion of intramuscularly injected Am citrate have been investigated in cynomolgus and rhesus nonhuman primates (NHP). Bioassay and retention data, obtained from experiments done by Patricia Durbin and her colleagues at Lawrence Berkeley National Laboratory, were evaluated against the International Commission on Radiological Protection (ICRP 67) Am systemic model coupled with to the National Council on Radiation Protection and Measurement wound model (NCRP 156). The default transfer rates suggested in these models were used with the urine and feces excretion data to predict the intake as well as liver and skeleton tissue contents at the time of death. The default models adequately predict the animals' urine bioassay data, but the injected activities were overpredicted by as much 4.41 times and underpredicted by as much as 0.99 times. Poor prediction has been observed in all cases using fecal excretion. The retained activity in the liver and skeleton were investigated using the same approach. It appears that the models predict the amount of the activity retention in the skeleton more accurately than in the liver. The fraction of predicted to measured activity at the time of death in the skeleton was over 1.0 in most cases, and accurate predictions were obtained in seven cases. The predicted activity in skeleton for these cases ranged from 2.7 to 17% overestimated activity and from 9 to 14% underestimated activity. NHPs' urine data and organ retention were compared with data from previously modeled baboons and beagle dogs. About 6% of the injected activity in baboons and beagle dog was excreted in urine and approximately 0.1% in feces in the first 24 h. The results from NHP are not different from excreta analysis in these other species. Urinary excretion in the cynomolgus, rhesus, and baboon NHP is the dominant pathway of Am clearance; however, fecal excretion is considered dominant in beagle dogs. The comparison between NHPs and humans is difficult due to the differences in the number of activities translocated or deposited in the liver tissue and nonliver tissues (primarily skeleton), in addition to the physiological differences between the NHPs and humans.

An americium solution injected intramuscularly into several nonhuman primates (NHPs) was found to behave differently than predicted by the wound models described in the NCRP Report 156. This was because the injection was made along with a citrate solution, which is known to be more soluble than chlorides, oxides, or nitrates on which the NCRP Report was based. A multi-exponential wound model specific to the injected americium solution was developed based on the retention in the intramuscular sites. The model was coupled with the americium systemic model to interpret the urinary excretion data and assess the intake, and it was determined that the models were adequate to predict early urinary excretion in most cases but unable to predict late urinary excretion. This was attributed to the differences in the systemic handling of americium between humans and nonhuman primates. Information on the type of wounds, solubility, particle size, mass, chemical form, etc., should always be considered when performing wound dosimetry.

Between 1960 and 1985, Patricia Durbin and colleagues performed studies on the distribution of intravenously and intramuscularly injected Am citrate with dosages ranging from 16 to 32 kBq kg in 30 male and female non-human primates (NHP). Dr. Durbin died unexpectedly in March of 2009, leaving much of the extensive serial blood, bioassay, and autopsy data from these NHP studies unanalyzed. As part of the experimental design, serial blood samples were taken, and urine and feces samples were collected separately for the duration of the study. The measurements of urine, fecal excretion, blood samples, and organ burden data obtained from the animals were used to evaluate the transfer rates of the ICRP 67 biokinetic model for Am. Seven cases, in which the primates were administered Am citrate by intravenous injection, were evaluated using the ICRP 67 systemic model. There were differences ranging from 51.4% underestimated to 102.7% overestimated activity between the predicted intake, which was calculated using IMBA Professional Plus software and based upon the urine bioassay data and the actual activity. The difference between the predicted activity at the time of death in the liver and skeleton using IMBA professional software and the value of the measured activity at the time of death were also compared. Generally, the ratios of predicted activity in the liver and skeleton at the time of death to the measured activity were consistently more than 1. However, the ratios were less than 1 in the skeleton for animals that were sacrificed 2,199 and 973 d post injection. The posterior probability distributions for model parameters derived using WeLMoS method were inconsistent with the ICRP 67 default parameters. The prediction made based on the posterior probability distributions for model parameters derived using WeLMoS gave the best fit to these data; however, the modified parameters overestimated the activity in almost all cases. The difference between the predicted Am activity and the value of the measured activity may be due to the physiological age-related characteristics relative to the age of the animal at the time of the injection and early and long scarified time.

Generally, plutonium has been manufactured to support commercial and military applications involving heat sources, weapons, and reactor fuel. This work focuses on three typical plutonium mixtures while observing the potential of Am ingrowth and its effect on internal dose. The term "ingrowth" is used to describe Am production due solely to the decay of Pu as part of a plutonium mixture, where it is initially absent or present in a smaller quantity. Dose calculation models do not account for Am ingrowth unless the Pu quantity is specified. This work suggested that Am ingrowth be considered in bioassay analysis when there is a potential of a 10% increase to the individual's committed effective dose. It was determined that plutonium fuel mixtures, initially absent of Am, would likely exceed 10% for typical reactor grade fuel aged less than 30 y; however, heat source grade and aged weapons grade fuel would normally fall below this threshold. Although this work addresses typical plutonium mixtures following separation, it may be extended to irradiated commercial uranium fuel and is expected to be a concern in the recycling of spent fuel.

The increasing threats of nuclear terrorism have made the development of medical countermeasures a priority for international security. Injectable formulations of diethylenetriaminepentaacetic acid (DTPA) have been approved by the FDA; however, an oral formulation is more amenable in a mass casualty situation. Here, the diethyl ester of DTPA, named C2E2, is investigated for potential as an oral treatment for internal radionuclide contamination. C2E2 was synthesized and characterized using NMR, MS, and elemental analysis. The physiochemical properties of solubility, lipophilicity, and stability were investigated in order to predict its oral bioavailability. Finally, an animal efficacy study was conducted in Sprague Dawley rats pre-contaminated by intramuscular injection with (241)Am(NO3)3 to establish effectiveness of the therapy via the oral route. Synthesis of C2E2 yielded a crystalline powder with high solubility and improved lipophilicity over DTPA. The ester was stable in both simulated gastric and intestinal fluids over the anticipated time course of absorption. Capsules containing C2E2 were demonstrated to be stable for 12 months under accelerated stability conditions. After a single dose, C2E2 enhanced the elimination of (241)Am in a dose-dependent manner. Significant improvement was seen in both total (241)Am decorporation and reduction of (241)Am liver and skeletal burden. C2E2 was concluded to be effective when orally administered to (241)Am-contaminated rats. It may therefore have potential for medical countermeasure in treating humans contaminated with (241)Am or other transuranic elements. An oral capsule or powder for reconstitution may be suitable formulations for future development based on the physiochemical properties and anticipated dose required for efficacy.

In case of internal contamination with plutonium materials, a treatment with diethylene triamine pentaacetic acid (DTPA) can be administered in order to reduce plutonium body burden and consequently avoid some radiation dose. DTPA intravenous injections or inhalation can start almost immediately after intake, in parallel with urinary and fecal bioassay sampling for dosimetric follow-up. However, urine and feces excretion will be significantly enhanced by the DTPA treatment. As internal dose is calculated from bioassay results, the DTPA effect on excretion has to be taken into account. A common method to correct bioassay data is to divide it by a factor representing the excretion enhancement under DTPA treatment by intravenous injection. Its value may be based on a nominal reference or observed after a break in the treatment. The aim of this study was to estimate the influence of this factor on internal dose by comparing the dose estimated using default or upper and lower values of the enhancement factor for 11 contamination cases. The observed upper and lower values of the enhancement factor were 18.7 and 63.0 for plutonium and 24.9 and 28.8 for americium. For americium, a default factor of 25 is proposed. This work demonstrates that the use of a default DTPA enhancement factor allows the determination of the magnitude of the contamination because dose estimated could vary by a factor of 2 depending on the value of the individual DTPA enhancement factor. In case of significant intake, an individual enhancement factor should be determined to obtain a more reliable dose assessment.

The fate of radionuclides in the environment is a cause of great concern for modern society, seen especially in 2011 after the Fukushima accident. Among the environmental compartments, seawater covers most of the earth's surface and may be directly or indirectly impacted. The interaction between radionuclides and the marine compartment is therefore essential for better understanding the transfer mechanisms from the hydrosphere to the biosphere. This information allows for the evaluation of the impact on humans via our interaction with the biotope that has been largely undocumented up to now. In this report, we attempt to make a link between the speciation of heavy elements in natural seawater and their uptake by a model marine organism. More specifically, because the interaction of actinides with marine invertebrates has been poorly studied, the accumulation in a representative member of the Mediterranean coralligenous habitat, the sponge Aplysina cavernicola, was investigated and its uptake curve exposed to a radiotracer (241)Am was estimated using a high-purity Ge gamma spectrometer. But in order to go beyond the phenomenological accumulation rate, the speciation of americium(III) in seawater must be assessed. The speciation of (241)Am (and natural europium as its chemically stable surrogate) in seawater was determined using a combination of different techniques: Time-Resolved Laser-Induced Fluorescence (TRLIF), Extended X-ray Absorption Fine Structure (EXAFS) at the LIII edge, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) and the resulting data were compared with the speciation modeling. In seawater, the americium(III) complex (as well as the corresponding europium complex, although with conformational differences) was identified as a ternary sodium biscarbonato complex, whose formula can be tentatively written as NaAm(CO3)2·nH2O. It is therefore this chemical form of americium that is accumulated by the sponge A. cavernicola.

The paper is devoted to determination of α-emitting radionuclides of 238, 239 + 240Pu and 241Am in liver, lungs, muscular and bone tissues of the boars on the territory of the Belarusian part of the ChNPP exclusion zone. It is shown that the content of Pu and Am isotopes in boar organs and tissues decreases in the following order: liver > bone tissues > lungs ≥ muscular tissues. The results received allow evaluation of penetration of 238, 239 + 240Pu and 241Am through the biological chain "soil-ration-organs and tissues". It is calculated that 1.7% of a boar's ration falls on the soil getting into the stomach with food. Translocation and accumulation coefficients characterizing the transfer of radionuclides through the chain "soil-vegetation-organs and tissues" were calculated. The conclusion about accumulation of Pu in the boar's body is made.

In 1983, a young man inhaled accidentally a large amount of plutonium and americium. This case was carefully followed until 2013. Since no decorporation measures had been taken, the undisturbed metabolism of Pu and Am can be derived from the data. First objective was to determine the amount of inhaled radionuclides and to estimate committed effective dose. In vivo and excretion measurements started immediately after the inhalation, and for quality assurance, all types of measurements were performed by different labs in Europe and the USA. After dose assessment by various international groups were completed, the measurements were continued to produce scientific data for model validation. The data have been analysed here to estimate lung absorption parameter values for the inhaled plutonium and americium oxide using the proposed new ICRP Human Respiratory Tract Model. As supplement to the biokinetic modelling, biological data from three different cytogenetic markers have been added. The estimated committed effective dose is in the order of 1 Sv. The subject is 30 y after the inhalation, of good health, according to a recent medical check-up., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Novel decorporation agents are being developed to protect against radiological accidents and terrorists attacks. Radioactive americium is a significant component of nuclear fallout. Removal of large radioactive materials, such as 241Am, from exposed persons is a subject of significant interest due to the hazards they pose. The objective of this study was to evaluate the dose-related efficacy of daily doses of NanoDTPA™ Capsules for decorporating Am administered intravenously as a soluble citrate complex to male and female beagle dogs. In addition, the efficacy of the NanoDTPA™ Capsules for decorporating 241Am was directly compared to intravenously administered saline and DTPA. Animals received a single IV administration of 241Am(III)-citrate on Day 0. One day after radionuclide administration, one of four different doses of NanoDTPA™ Capsules [1, 2, or 6 capsules d(-1) (30 mg, 60 mg, or 180 mg DTPA) or 2 capsules BID], IV Zn-DTPA (5 mg kg(-1) pentetate zinc trisodium) as a positive control, or IV saline as a placebo were administered. NanoDTPA™ Capsules, IV Zn-DTPA, or IV saline was administered on study days 1-14. Animals were euthanized on day 21. A full necropsy was conducted, and liver, spleen, kidneys, lungs and trachea, tracheobronchial lymph nodes (TBLN), muscle samples (right and left quadriceps), gastrointestinal (GI) tract (stomach plus esophagus, upper and lower intestine), gonads, two femurs, lumbar vertebrae (L1-L4), and all other soft tissue remains were collected. Urinary and fecal excretion profiles were increased approximately 10-fold compared to those for untreated animals. Tissue contents were decreased compared to untreated controls. In particular, liver content was decreased by approximately eightfold compared to untreated animals. The results from this study further demonstrate that oral NanoDTPA™ Capsules are equally efficient compared to IV Zn-DTPA in decorporation of actinides.

Monitoring preparation for internal contamination with actinides (e.g. Pu and Am) is required to assess internal doses at nuclear fuel cycle-related facilities. In this paper, the authors focus on skull counting in case of single-incident inhalation of (241)Am and propose an effective procedure for skull counting with an existing system, taking into account the biokinetic behaviour of (241)Am in the human body. The predicted response of the system to skull counting under a certain counting geometry was found to be only ∼1.0 × 10(-5) cps Bq(-1) 1y after intake. However, this disadvantage could be remedied by repeated measurements of the skull during the late stage of the intake due to the predicted response reaching a plateau at about the 1000th day after exposure and exceeding that in the lung counting. Further studies are needed for the development of a new detection system with higher sensitivity to perform reliable internal dose estimations based on direct measurements., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Purpose: Americium-241 ((241)Am) presents a potential risk for nuclear industry workers associated with reactor decommissioning and aging combustible materials. The purpose of this study was to investigate Am renal retention after actinide contamination by wounding in the rat., Materials and Methods: Anesthetized rats were contaminated with Mixed Oxide (MOX) (7.1% Plutonium [Pu] by mass and containing 27% Am as % total alpha activity), Pu or Am nitrate following an incision wound of the hind leg. Times of euthanasia ranged from 2 hours to 5 months after contamination. Pu and Am levels were quantified following radiochemistry and alpha-spectrophotometry., Results: Initial data show that over the experimental period the proportion of Am in kidneys as a fraction of total kidney alpha activity was elevated as compared to MOX powder indicating a specific retention in this organ. The percentage of Pu was similar to the powder. After MOX contamination, kidney to liver ratios appeared to increase more markedly for Am (from 0.2 at 7 days to 0.6 at 90 days) as compared with Pu (0.1 at 7 days to 0.2 at 90 days). In accordance with tissue actinide retention the dose from Am to the kidney increases with time. For comparison, the ratio of estimated equivalent doses due to Am to kidney is 1.5-fold greater than for Pu (around 90 versus 60 mSv)., Conclusion: After actinide contamination of wounds, Am is concentrated in the kidneys as compared to Pu leading to potential exposure of renal tissue to both alpha particles and gamma radiation.

Purpose: To improve the dosimetry of incorporated americium (Am) and to contribute to radiation protection by characterizing the absorption kinetics of inhaled Am compounds., Material and Methods: In vitro dissolution tests, animal experiments and human contamination cases published in the literature were reviewed. The data were analyzed with biokinetic models consistent with the current publications of the International Commission on Radiological Protection., Results: Material-specific dissolution parameter values with consequent assignment to absorption Types are proposed as well as representative central values for the different chemical forms of Am., Conclusions: The absorption of Am oxide is consistent with the moderate absorption Type M while Am nitrate appears more soluble. Am associated with plutonium oxide usually follows its slow absorption Type S. However, the large variability observed stresses the value of investigating the specific absorption kinetics for Am compounds which represent a significant risk of internal exposure.

Unlabelled: Abstract Purpose: To compare data on the whole-body distribution of americium-241 ((241)Am) in rats following intravenous injection (IV), inhalation, and wound (intramuscular injection, IM)., Material and Methods: Following exposure, each rat was placed in an individual metabolism cages for the duration of the study, 28 days (d). Urine and feces were collected daily. Tissues and organs were collected and measured., Results: Liver and skeleton were the main sites of deposition for all routes of exposure but the content differed substantially. By 28 d, (241)Am content in liver was similar for IV and IM administrations (12 ± 4% and 14 ± 5%, respectively), which was 3-fold higher compared to inhalation. Americium-241 content in skeleton was 27% by the end of the IV study; which was 50% higher compared to the IM study and 6-fold higher compared to inhalation. The cumulative excretion in 28 d was 54% for IV (44% by feces and 10% by urine); 38% for IM (34% by feces and 4% by urine); and 84% for inhalation (83% by feces and 1% by urine)., Conclusion: Unperturbed rat models for the three routes of administration are the baseline for evaluating the efficacy of chelating agents.

An internal contamination with (241)Am was detected in a worker during a routine monitoring of workers from a company producing Am sources for smoke detectors and Am-Be neutron sources. During the 4-year period after the exposure, the number of urine and faecal samples from the worker were analysed; in vivo measurements were also performed. Specific values for absorption parameters of the human respiratory tract model and particle transport values were applied to improve the model fit to the measurement data. A good agreement of the bioassay data with the so-modified model predictions was obtained.

Americium-241 (²⁴¹Am) is the second most significant radiation hazard after ²³⁹Pu at some of the Mayak Production Association facilities. This study summarizes current data on the accumulation, distribution, and excretion of americium compared with plutonium in different organs from former Mayak PA workers. Americium and plutonium were measured in autopsy and bioassay samples and correlated with the presence or absence of chronic disease and with biological transportability of the aerosols encountered at different workplaces. The relative accumulation of ²⁴¹Am was found to be increasing in the workers over time. This is likely from ²⁴¹Pu that increases with time in reprocessed fuel and from the increased concentrations of ²⁴¹Am and ²⁴¹Pu in inhaled alpha-active aerosols. While differences were observed in lung retention with exposures to different industrial compounds with different transportabilities (i.e., dioxide and nitrates), there were no significant differences in lung retention between americium and plutonium within each transportability group. In the non-pulmonary organs, the highest ratios of ²⁴¹Am/²⁴¹Am + SPu were observed in the skeleton. The relative ratios of americium in the skeleton versus liver were significantly greater than for plutonium. The relative amounts of americium and plutonium found in the skeleton compared with the liver were even greater in workers with documented chronic liver diseases. Excretion rates of ²⁴¹Am in ‘‘healthy’’ workers were estimated using bioassay and autopsy data. The data suggest that impaired liver function leads to reduced hepatic ²⁴¹Am retention, leading to increased ²⁴¹Am excretion.

Uncertainty analyses have been performed on the biokinetic model for americium currently used by the International Commission on Radiological Protection (ICRP), and the model for plutonium recently derived by Leggett, considering acute intakes by ingestion by adult members of the public. The analyses calculated distributions of doses per unit intake. Those parameters having the greatest impact on prospective doses were identified by sensitivity analysis; the most important were the fraction absorbed from the alimentary tract, f(1), and rates of uptake from blood to bone surfaces. Probability distributions were selected based on the observed distribution of plutonium and americium in human subjects where possible; the distributions for f(1) reflected uncertainty on the average value of this parameter for non-specified plutonium and americium compounds ingested by adult members of the public. The calculated distributions of effective doses for ingested (239)Pu and (241)Am were well described by log-normal distributions, with doses varying by around a factor of 3 above and below the central values; the distributions contain the current ICRP Publication 67 dose coefficients for ingestion of (239)Pu and (241)Am by adult members of the public. Uncertainty on f(1) values had the greatest impact on doses, particularly effective dose. It is concluded that: (1) more precise data on f(1) values would have a greater effect in reducing uncertainties on doses from ingested (239)Pu and (241)Am, than reducing uncertainty on other model parameter values and (2) the results support the dose coefficients (Sv Bq(-1) intake) derived by ICRP for ingestion of (239)Pu and (241)Am by adult members of the public.

The lung counting system at Kalpakkam, India, used for the estimation of transuranics deposited in the lungs of occupational workers, consists of an array of three large area germanium detectors fixed in a single assembly. The efficiency calibration for low energy photons was carried out using ²⁴¹Am and ²³²Th lung sets of Lawrence Livermore National Laboratory phantom. The muscle equivalent chest wall thickness (MEQ-CWT) was derived for the three energies 59.5, 75.95 (average energy of ²³²Th) and 238.9 keV for the series of overlay plates made of different adipose mass ratios. Efficiency as a function of MEQ-CWT was calculated for individual detectors for the three energies. Variation of MEQ-CWT from 16 to 40 mm resulted in an efficiency variation of around 40 % for all the three energies. The array efficiency for different MEQ-CWT ranged from 1.4×10⁻³ to 3.2×10⁻³, 1.5×10⁻³ to 3.3×10⁻³ and 1.1×10⁻³ to 2.3×10⁻³ for 59.5, 75.95 and 238.9 keV, respectively. In the energy response, efficiency was observed to be maximum for 75.95 keV compared with 59.5 and 238.9 keV.

Three facilities (CIEMAT, HMGU and HML) have used their in vivo counters to compare two leg phantoms. One was commercially produced with (241)Am activity artificially added to the bone inserts. The other, the United States Transuranium and Uranium Registries' (USTUR) leg phantom, was manufactured from (241)Am-contaminated bones resulting from an intake. The comparison of the two types of leg phantoms showed that the two phantoms are not similar in their activity distributions. An error in a bone activity estimate could be quite large if the commercial leg phantom is used to estimate what is contained in the USTUR leg phantom and, consequently, a real person. As the latter phantom was created as a result of a real contamination, it is deemed to be the more representative of what would actually happen if a person were internally contaminated with (241)Am.

In order to understand the bioaccumulation of (241)Am and (134)Cs in scallops living in sediments, the uptake and depuration kinetics of these two elements were investigated in the king scallop Pecten maximus exposed via seawater, food, or sediment under laboratory conditions. Generally, (241)Am accumulation was higher and its retention was stronger than (134)Cs. This was especially obvious when considering whole animals exposed through seawater with whole-body concentration factors (CF(7d)) of 62 vs. 1, absorption efficiencies (A(0l)) of 78 vs. 45 for seawater and biological half-lives (T(b½l)) of 892 d vs. 22 d for (241)Am and (134)Cs, respectively. In contrast, following a single feeding with radiolabelled phytoplankton, the assimilation efficiency (AE) and T(b½l) of (134)Cs were higher than those of (241)Am (AE: 28% vs. 20%; T(b½l): 14 d vs. 9 d). Among scallop tissues, the shells always contained the higher proportion of the total body burden of (241)Am whatever the exposure pathway. In contrast, the whole soft parts presented the major fraction of whole-body burden of (134)Cs, which was generally associated with muscular tissues. Our results showed that the two radionuclides have contrasting behaviors in scallops, in relation to their physico-chemical properties., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Freshwater fishes (Carassius auratus gibelio, crucian carp) were fed through catheter with homogenized biomass of submerged macrophytes labeled with transuranium element 241Am. The intensity of excretion of americium and its accumulation in organs and tissues of fishes were investigated. The highest release of americium (up to 70%) was recorded on the second day after feeding. 94-98% of americium were excreted during 3-4 days; however, americium was also recorded in the excrements after 11 days. Americium was registered in organs and tissues of fishes, including those tissues that had no direct contact with americium (bones and muscles). This implies assimilation of americium via digestive tract. The activity concentration of americium in bones (11 Bq/kg, fresh mass) was twice as high as that in muscles, heads and external tissues and organs (skin, scales and fins). The highest activity concentration of americium was registered in viscera (33 Bq/kg, 48% of the total activity in the body). Accumulation of americium in muscles enhances the probability of the further transfer of americium along a food chain.

After inhalation of plutonium oxides containing various percentages of americium in rats, we identified an acellular transient pulmonary compartment, the epithelial lining fluid (ELF), in which a fraction of actinide oxides dissolve prior to absorption and subsequent extrapulmonary deposit. Chelation therapy is usually considered to be poorly efficient after inhalation of actinide oxides. However, in the present study, prompt pulmonary administration of diethylenetraminepentaacetic acid (DTPA) as a dry powder led to a decrease in actinide content in ELF together with a limitation of bone and liver deposits. Because americium is more soluble than plutonium, higher amounts of americium were found in ELF, extrapulmonary tissues and urine. Our results also demonstrated that the higher efficacy of DTPA on americium compared to plutonium in ELF induced a preferential inhibition of extrapulmonary deposit and a greater urinary excretion of americium compared to plutonium. All together, our data justify the use of an early and local DTPA treatment after inhalation of plutonium oxide aerosols in which americium can be in high proportion such as in aged compounds.

Three workers incurred inhalation exposures to Am oxide as a result of waste sorting and compaction activities. The exposure magnitudes were not fully recognized until the following day when an in-vivo lung count identified a significant lung deposition of Am in a male worker, and DTPA chelation therapy was initiated. Two additional workers (one female and one male) were then identified as sufficiently exposed to also warrant therapy. In-vivo bioassay measurements were performed over the ensuing 6 mo to quantify the 241Am activity in the lungs, liver, and skeleton. Urine and fecal samples were collected and showed readily detectable 241Am. Clinical lab tests and medical evaluations all showed normal results. There were no significant adverse clinical health effects from the therapy. The estimated 241Am inhalation intakes for the three workers were 1,800 Bq, 630 Bq, and 150 Bq. Lung retention showed somewhat longer pulmonary clearance half-times than standard inhalation class W or absorption Type M assumptions. The three subjects underwent slightly different therapy regimens, with therapy effectiveness factors (defined as the ratio of the reference doses without therapy relative to the final assessed doses) of 4.5, 1.9, and 1.7, respectively.

Plutonium isotopes (239Pu and 238Pu, and 241Am) with a total activity of 269 kBq were accidentally deposited in a puncture wound of the right index finger of a nuclear worker at the Mayak Production Association. Tissues surrounding the wound site contaminated with radionuclides were excised 4.5 h after the injury. Residual contamination within the wound amounted to 0.05% of the initial contamination. The 10-d therapy with CaNa3-diethylene triamine pentaacetate acid (CaNa3-DTPA) was performed in parallel with in vivo measurements of the wound site and daily urine bioassays. The wound intake of radionuclides was consistent with two forms of radioactive materials detected within the wound site, i.e., soluble compounds and a large fragment, which was completely removed by excision. On day 9 after the injury, the clearance rate from the wound site was 1.8 times higher than the rate predicted by the National Council on Radiation Protection and Measurements (NCRP) model for soluble compounds of plutonium and americium. The NCRP model parameters of transfer rates from the colloid and intermediate state (CIS) into soluble, and particles, aggregates and bound state (PABS) compartments were modified to eliminate any difference. As a result, a difference between the observed wound site radionuclide content and the value predicted by the modified wound model did not exceed 14% up to 9 days after the injury. For a longer period from 7 to 24 months, the value predicted by the modified model was consistent with results of the corresponding in vivo measurements. The treatment reduced the effective dose (50 years) from internal exposure by at least 480 times. The dose estimated (without accounting for a contribution of exposure dose to the regional lymph nodes draining the wound site) did not exceed 11 mSv.

The aim of this study is to propose a single modeling structure to describe both plutonium and americium decorporation by DTPA, which is based on hypotheses mostly validated by experimental data. Decorporation efficacy of extracellular retention depends on the concentration ratio of DTPA vs. actinides and varies in each compartment according to the amount of biological ligands and their affinity for actinides. By contrast, because the relatively long residence time of DTPA after its cell internalization and the stability of actinide-DTPA complexes, intracellular decorporation efficacy is mainly controlled by a DTPA/actinide ratio, which is specific to each retention compartment. Although the affinity of DTPA is much lower for americium than for plutonium, a larger decorporation of americium can be obtained, which is explained by different biological ligands and/or their affinity for the actinide. Altogether, these results show that the relative contribution of intra vs. extracellular decorporation varies depending on the actinide, the chemical form of radionuclides, the galenic formulation of DTPA, and the treatment schedule.

A 1985 plutonium puncture wound resulted in the initial deposition of 48 kBq of transuranic alpha activity, primarily 239+240Pu and 241Am, in a worker's right index finger. Surgical excisions in the week following reduced the long-term residual wound activity to 5.4 kBq, and 164 DTPA chelation therapy administrations over 17 mo resulted in urinary excretion of about 7 kBq. The case was published in 1988, but now 24 y of follow-up data are available. Annual bioassays have included in-vivo measurements of 241Am in the wound, skeleton, liver, lung, and axillary lymph nodes, and urinalyses for plutonium and 241Am. These measurements have shown relatively stable levels of 241Am at the wound site, with gradually increasing amounts of 241Am detected in the skeleton. Liver measurements have shown erratic detection of 241Am, and the lung measurements indicate Am but as interference from activity in the axillary lymph nodes and skeleton rather than activity in the lung. Urine excretion of Pu since termination of chelation therapy has typically ranged from 10 to 20 mBq d, with Am excretion about 10% of that for 239+240Pu. Annual routine medical exams have not identified any adverse health effects associated with the intake.

A group of workers internally contaminated with Am have been followed for about 12 years. The source of contamination was AmO2 powder used for production of AmBe neutron sources and other applications. The production of some radionuclide sources included chemical treatment of the original material, which transformed the americium into the nitrate, but mostly powder metallurgy was used for production of sources for smoke detectors. In vivo measurement of the workers was performed with two LEGe detectors placed near the head of the measured person. Calibration was performed with four different physical skull phantoms of different origin and a voxel phantom with Monte Carlo simulation, which was developed to fit the head sizes of individual persons. Samples of urine and feces were analyzed by means of radiochemical separation followed by alpha-spectrometry. Separation of 241Am from mineralized excreta was performed by combined anion exchange and extraction chromatographic techniques. As a tracer, 243Am was used. When the measured data (83 data on skeletal activity, activity in 389 bioassay samples) were compared with International Commission on Radiological Protection's and Leggett's biokinetic models of americium, it was found that in most cases, after more than 15 y since the intake, the excretion rate was lower (or skeletal activity higher) than predicted. On the other hand, the ratio of excreted activity in urine and feces agrees well with model predictions.

Commonly used water-soluble polyaminocarboxylic acid (PACA) chelators, such as EDTA and DTPA, require intravenous or subcutaneous administration due to their poor bioavailability. The bioavailability of PACAs can be improved by the addition of differing lengths of alkyl side chains that alter amphipathic properties. Orally administered amphipathic triethylenetetramine pentaacetic acid (TT) compounds are efficacious for decorporation of plutonium and americium. The synthesis, efficacy, binding affinities, and some initial pharmacokinetics properties of amphipathic TT chelators are reviewed. C-labeled C12TT and C22TT chelators are reasonably well absorbed from the intestine and have a substantial biliary/fecal excretion pathway, unlike DTPA, which is mostly excreted in the urine. Whole body retention times are increased as a function of increasing lipophilicity. Neutron-induced autoradiography studies demonstrate that the oral administration of the chelators can substantially inhibit the redistribution of Pu in skeletal tissues. In summary, amphipathic TT-based chelators have favorable bioavailability, have a significant biliary excretion pathway, have demonstrated efficacy for americium and plutonium, and are thus good candidates for further development. Furthermore, some of the pharmacological properties can be manipulated by changing the lengths of the alkyl side chains and this may have some advantage for decorporation of certain metals and radionuclides.

The biodistribution of plutonium and americium has been studied in a rat model after inhalation of two PuO(2) powders in lungs and extra-pulmonary organs from 3 d to 3 mo. The main difference between the two powders was the content of americium (approximately 46% and 4.5% of total alpha activity). The PuO(2) with a higher proportion of americium shows an accelerated transfer of activity from lungs to blood as compared to PuO(2) with the lower americium content, illustrated by increased urinary excretion and higher bone and liver actinide retention. The total alpha activity measured reflects mostly the americium biological behavior. The activity contained in epithelial lining fluid, recovered in the acellular phase of broncho-alveolar lavages, mainly contains americium, whereas plutonium remains trapped in macrophages. Epithelial lining fluid could represent a transitional pulmonary compartment prior to translocation of actinides to the blood and subsequent deposition in extra-pulmonary retention organs. In addition, differential behaviors of plutonium and americium are also observed between the PuO(2) powders with a higher dissolution rate for both plutonium and americium being obtained for the PuO(2) with the highest americium content. Our results indicate that the biological behavior of plutonium and americium after translocation into blood differ two-fold: (1) for the two actinides for the same PuO(2) aerosol, and (2) for the same actinide from the two different aerosols. These results highlight the importance of considering the specific behavior of each contaminant after accidental pulmonary intake when assessing extra-pulmonary deposits from the level of activity excreted in urine or for therapeutic strategy decisions.

A calibration phantom was developed at the University of Cincinnati (UC) to determine detection efficiency and estimate the quantity of activity deposited in the axillary lymph nodes of a worker who had unknowingly sustained a wound contaminated with 241Am at some distant time in the past. This paper describes how the Livermore Torso Phantom was modified for calibrating direct, in vivo measurements of 241Am deposited in the axillary lymph nodes. Modifications involved milling a pair of parallel, flat bottom, cylindrical holes into the left and right shoulders (below the humeral head) of the Livermore Torso Phantom in which solid, 1.40-cm-diameter cylindrical rods were inserted. Each rod was fabricated using a muscle tissue substitute. One end of each rod contained a precisely known quantity of Am sealed in a 1-cm-diameter, 2.54-cm-deep well to simulate the axillary lymph nodes when inserted into the modified Livermore Torso Phantom. The fixed locations for the axillary lymph nodes in the phantom were determined according to the position of the Level I and the combined Level II + III axillary lymph nodes reported in the literature. Discrete calibration measurements for 241Am in the simulated axillary lymph nodes located in the right and left sides of the thorax were performed using pairs of high-resolution germanium detectors at UC and Lawrence Livermore National Laboratory. The percent efficiency for measuring the 59.5 keV photon from Am deposited in the right and left axillary lymph nodes using a pair of 3,000 mm2 detectors is 2.60 +/- 0.03 counts gamma-1 and 5.45 +/- 0.07 counts gamma-1, respectively. Activity deposited in the right and left axillary lymph nodes was found to contribute 12.5% and 19.7%, respectively, to a lung measurement and 1.2% and 0.2%, respectively, to a liver measurement. Thus, radioactive material mobilized from a wound in a finger or hand and deposited in the axillary lymph nodes has been shown to confound results of a direct, in vivo measurement of the lungs.

The current levels and distribution of the remaining transuranic contamination present in the terrestrial area affected by the nuclear Palomares accident have been evaluated through the determination of the Pu-isotopes and (241)Am concentrations in soils collected 35 years after the accident. In addition, after confirming that most of the contamination is present in particulate form, some bioavailability laboratory-based experiments, based on the use of single extractants, were performed as an essential step in order to study the behaviour of the Pu contamination in the soils from the affected areas.

The human and animal data on the biokinetics of (242)Cm and (244)Cm are reviewed and shown to be very similar to those for (241)Am. Liver and skeleton are the main organs of deposition and the retention of curium in the skeleton is very prolonged in all the species examined. Retention of both curium and americium in the liver appears to be species-dependent, being relatively rapidly removed from the liver of rats, and probably humans, but being tenaciously retained in dogs and some other species. The radiotoxicity of curium is also reviewed and it is shown that, as with (241)Am, lung and bone tumour induction are the major hazards from inhaled and systemically deposited (244)Cm. The use of chelating agents for the treatment of accidental contamination of the human body with (242,244)Cm is also discussed.

A 70-day experiment was performed with Daphnia magna exposed to waterborne Am-241 on a range of concentrations (from 0.4 to 40 Bq ml(-1)) in order to test chronic effects of internal alpha irradiation on respiration, somatic growth and reproduction over three successive generations. Changes in Am-241 concentrations were followed in the water and in daphnid tissues, eggs and cuticles. Corresponding average dose rates of 0.3, 1.5 and 15 mGy h(-1) were estimated. This study confirmed that oxygen consumption increased significantly in the first generation (F0) after 6 days of exposure to a dose rate >or=1.5 mGy h(-1). Consequences were limited to a reduction in body length (5%) and dry mass of females (16%) and eggs (8%) after 23 days of exposure, while mortality and fecundity remained unaffected. New cohorts were started with neonates of broods 1 and 5, to examine potential consequences of the reduced mass of offspring for subsequent exposed generations. Results strongly contrasted with those observed in F0. At the highest dose rate, an early mortality of 38-90% affected juveniles while survivors showed delayed reproduction and reduced fecundity in F1 and F2. At 0.3 and 1.5 mGy h(-1), mortality ranged from 31 to 38% of daphnids depending on dose rate, but was observed only in generation F1 started with neonates of the brood 1. Reproduction was affected through a reduction in the proportion of breeding females, occurring in the first offspring generation at 1.5 mGy h(-1) (to 62% of total daphnids) and in the second generation at 0.3 mGy h(-1) (to 69% of total daphnids). Oxygen consumption remained significantly higher at dose rates >or=0.3 mGy h(-1) than in the control in almost every generation. Body size and mass continued decreasing in relation to dose rate, with a significant reduction in mass ranging from 15% at 0.3 mGy h(-1) to 27% at 15 mGy h(-1) in the second offspring generation.

Data on the distribution and redistribution patterns in the laboratory rat of three trivalent elements with a similar ionic radius have been compared. This showed that these distributions for the two ions with the same ionic radius (111 pm), i.e., those of promethium (a lanthanoid) and curium (an actinoid), were indistinguishable and that americium, with a slightly larger ion size (111.5 pm), behaved similarly. The results are consistent with the suggestion that ion size is the only important factor controlling the deposition and redistribution patterns of trivalent lanthanoids and actinoids in rats. The result is important because it suggests that the same radiological protection dosimetry models should be used for trivalent actinoids and lanthanoids, that human volunteer data generated for lanthanoid isotopes can be used to predict the behavior of actinoids with the same ion size, and that appropriate pairs of beta-particle-emitting lanthanoid and alpha-particle-emitting actinoids could be used to study the relative toxicity of alpha and beta particles in experimental animals.

In case of chronic exposure or long time after an acute intake of (241)Am as a consequence of an incident, the assessment of internal dose might be realised by estimating the total activity content of this element in the skeleton. For this purpose, a new methodology has been developed at the Whole Body Counting Laboratory of CIEMAT. In vivo measurements of this bone-seeker radionuclide in the knee are performed using four low energy germanium detectors inside a shielded room. The sensitivity study of this technique resulted in a minimum detectable activity of 7 Bq, for a counting time of 1800 s. Extrapolation to the total activity in the bone has been carried out by taking into account that the bone content of the knee calibration phantom is equivalent to 10.7% of the whole skeleton mass. The results of in vivo measurements of population and the procedure for internal dose evaluation are presented here.

Internal contamination of workers with 241Am has occurred a few times since the beginning of the 1970s, mainly in the workplace where radionuclide sources were produced, and later on, also during liquidation of radioactive waste. Contamination in workers was measured in vivo and bioassay was performed. Solubility of aerosol in lungs was studied by in vitro dissolution test with a simulant solution of the extracellular airway lining fluids. Model calculation for the estimation of intakes was done with the experimentally obtained parameters of aerosol, with modified times of intake, with scattering factors, including Types A and B errors, and with corrections on skull size for in vivo measurements. For most cases, an acceptable fit to the experimental data was obtained; for two cases with intakes taking place long time ago ( approximately 30 y), some changes in the model are necessary.

Calibration phantoms for in vivo measurements of low-energy photons should be anatomically realistic to minimise the uncertainties in the activity assessment. The calibration of the detection system can be performed using computational techniques based on numerical phantoms. The purpose of this work is to approach a numerical calibration by Monte Carlo (MC) technique of a Germanium detection system for the determination of 241Am in the knee. A specific voxel phantom was built from a computerised tomography of the calibration Spitz knee phantom. The phantom and the procedure to generate the associated input file for the MC code, namely MCNPX, have been described, as well as the characterisation of the detectors according to the manufacturer data and the energy calibration curves of the spectrometer. The detection efficiency and the pulse-height distribution have been determined for a homogeneous contamination of 241Am in bone.

The general criteria and the scientific approach adopted for an 'International comparison on Monte Carlo modelling for in vivo measurement of Americium in a knee phantom' that is being organised within the EU Coordination Action CONRAD (Coordinated Network for Radiation Dosimetry) are described her. Detection system and a knee voxel phantom based on a computerised axial tomography of the Spitz anthropometric knee phantom with a homogeneous distribution of 241Am in bone have been considered for the simulation of three specific situations: (a) a single Low Energy Germanium detector for a point 241Am source in air; (b) the calculation of photon fluence spectra in air around the voxel phantom; and (c) the calculation of the energy distribution of pulses and peak detection efficiency in the real detection system geometry.

Biokinetic models are the scientific underpinning of internal dosimetry and depend, ultimately, for their scientific validation on comparisons with human bioassay data. Three significant plutonium/americium bioassay databases, known to the authors, are described: (1) Sellafield, (2) Los Alamos and (3) the United States Transuranium Registry. A case is made for a uniform standard for database format, and the XML standard is discussed.

The interpretation of individual activity measurement after a contamination by 241Am or its parent nuclide 241Pu is based on the reference americium (Am) biokinetic model published by the International Commission on Radiological Protection in 1993 [International Commission on Radiological Protection. Age-dependent doses to members of the public from intake of radionuclides: Part 2 Ingestion dose coefficients. ICRP Publication 67. Ann. ICRP 23(3/4) (1993)]. The authors analysed the new data about Am biokinetics reported afterwards to propose an update of the current model. The most interesting results, from the United States Transuranium and Uranium Registries post-mortem measurement database [Filipy, R. E. and Russel, J. J. The United States Transuranium and Uranium Registries as sources for actinide dosimetry and bioeffects. Radiat. Prot. Dosim. 105(1-4), 185-187 (2003)] and the long-term follow-up of cases of inhalation intake [Malátová, I., Foltánová, S., Becková, V., Filgas, R., Pospísilová, H. and Hölgye, Z. Assessment of occupational doses from internal contamination with 241Am. Radiat. Prot. Dosim. 105(1-4), 325-328 (2003)], seemed to show that the current model underestimates the retention in the massive soft tissues and overestimates the retention in the skeleton and the late urinary excretion. However, a critical review of the data demonstrated that all were not equally reliable and suggested that only a slight revision of the model, possibly involving a change in the balance of activity between massive soft tissues, cortical and trabecular bone surfaces, may be required.

Radiation monitoring with whole body counter (WBC) has a series of advantages, as this technique is efficient and is considerably cheaper than indirect urine bioassay method. Experience of WBC operation in the system of Mayak PA worker internal radiation monitoring as well as qualitative analysis of the obtained results is considered. The groups of workers under study are described, and a brief analysis of data obtained in comparison with individual exposure parameters is presented. The number of individuals with 241Am is higher among the workers employed in the early years of Mayak PA operation. Fraction of 241Am in total body burden relative to sum of actinides is higher for workers who started to work in conditions of exposure in the last decade (1990-2000) and sometimes is as high as 25%.