URINARY EXCRETION OF PLUTONIUM IN MAYAK WORKERS DURING AND AFTER CA-DTPA ADMINISTRATION.

Chelation therapy is sometimes used after potential exposures to plutonium to increase urinary excretion of the radionuclide to improve the accuracy of bioassay measurements. The purpose of this report is to describe the enhancement of urinary excretion of plutonium during and after the administration of the trisodium salt of calcium diethylenetriaminepentaacetate (Ca-DTPA) daily for 3 d to a group of male and female plutonium workers from the Mayak Production Association in Ozyorsk, Russia. One-hundred and two cases (18 females and 84 males) were selected where urinary contents of plutonium, prior to chelation, exceeded the detection threshold. Daily urine collections were obtained during the 3 d of Ca-DTPA treatments. In addition, 58 of these cases had urine bioassays at 1-45 d after chelation. The daily enhancement over baseline values excretion of plutonium was found to be 50.4×/1.4 (geometric mean and geometric standard deviation); 58.9×/1.2; 72.9×/1.4 in the first, second and third days of Ca-DTPA administration. The mean enhancement for the 3-d period was 60.1×/1.7. The rate of plutonium excretion from 1 to 45 d after chelation decreased with a half-period of 3.9 d and the chelation enhancement factor (Кenh-i) is described by the function Кenh-i = (0.79 ± 0.24) + (42.9 ± 1.2) × e-(0.18 ± 0.01) × day.

The effects of chronic diseases on plutonium urinary excretion in former workers of the Mayak Production Association.

The radiochemical analysis of plutonium activity in urine is the main method for indirect estimation of doses of internal exposure from plutonium incorporation in professional workers. It was previously shown that late-in-life acute diseases, particularly those that affect the liver, can promote accelerated rates of release of plutonium from the liver with enhanced excretion rates. This initial study examines the relationships of some chronic diseases on plutonium excretion as well as the terminal relative distribution of plutonium between the liver and skeleton. Fourteen cases from former workers at the Mayak Production Association (Mayak PA) who provided from 4-9 urine plutonium bioassays for plutonium, had an autopsy conducted after death, and had sufficient clinical records to document their health status were used in this study. Enhanced plutonium excretion was associated with more serious chronic diseases, including cardiovascular diseases and other diseases that involved the liver. These chronic diseases were also associated with relatively less plutonium found in the liver relative to the skeleton determined by analyses conducted after autopsy. These data further document health conditions that affect plutonium biokinetics and organ deposition and retention patterns and suggest that health status should be considered when conducting plutonium bioassays as these may alter subsequent dosimetry and risk models.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS-2016): INTERNAL DOSIMETRY RESULTS AND COMPARISON WITH MWDS-2013.

Differences in results from the new Mayak Worker Dosimetry System (MWDS-2016) vs the previous MWDS-2013 are described. Statistical characteristics are shown for the distribution of accumulated absorbed doses to organs for 8340 workers with bioassay data. Differences in mean values of accumulated doses and their relative standard uncertainties calculated by MWDS-2016 and MWDS-2013 were analysed separately for various types of industrial compounds of plutonium, specifically nitrates, mixtures and oxides. Within the range of accumulated doses >1 mGy, lung doses for nitrates and mixtures decreased by 41 and 15%, respectively, and remained at the same level for oxides. Accumulated liver doses within the range >1 mGy increased for nitrates and mixtures by 13 and 8%, respectively, and decreased for oxides by 7%.

The Mayak Worker Dosimetry System (MWDS-2013): Plutonium Binding in the Lungs-An Analysis of Mayak Workers.

Estimates of plutonium lung doses from urine bioassay are highly dependent on the rate of absorption from the lungs to blood assumed for the inhaled aerosol. Absorption occurs by dissolution of particles in lung fluid followed by uptake to blood. The latter may occur either rapidly or dissolved ions may first become temporarily bound within airway tissue. The presence of long-term binding can greatly increase lung doses, particularly if it occurs in the bronchial and bronchiolar regions. Analyses of autopsy data from Beagle dogs and USTUR Case 0269, obtained following exposure to plutonium nitrate, suggest that a small fraction of 0.2-1.1 and 0.4-0.7%, respectively, of plutonium becomes permanently bound within the lungs. The present work performs a further analysis using autopsy data of former plutonium workers of the Mayak Production Association to determine values of the bound fraction that are supported by these data. The results suggest a bound fraction value of 0-0.3%. The results also indicate that the Mayak worker population median values of the particle transport clearance parameters from the alveolar-interstitial region are largely consistent with expected values, but suggest the rate from the alveolar region to the interstitium may be lower than initially thought.

Use of in vivo counting measurements to estimate internal doses from (241)Am in workers from the Mayak production association.

Comparisons between results of in vivo counting measurements of americium burden and results from radiochemical analyses of organ samples taken at autopsy of 11 cases of former Mayak workers were made. The in vivo counting measurements were performed 3-8 y before death. The best agreement between in vivo counting measurements for americium and autopsy data was observed for the skull. For lungs and liver, the ratios of burden measured by in vivo counting to those obtained from radiochemical analyses data ranged from 0.7-3.8, while those for the skull were from 1.0-1.1. There was a good correlation between the estimates of americium burden in the entire skeleton obtained from in vivo counting with those obtained from autopsy data. Specifically, the skeletal burden ratio, in vivo counting/autopsy, averaged 0.9 ± 0.1. The prior human americium model, D-Am2010, used in vivo counting measurements for americium in the skeleton to estimate the contents of americium and plutonium at death. The results using this model indicate that in vivo counting measurements of the skull can be used to estimate internal doses from americium in the Mayak workers. Additionally, these measurements may also be used to provide a qualitative assessment of internal doses from plutonium.

Mayak Worker Dosimetry System 2008 (MWDS-2008): assessment of internal dose from measurement results of plutonium activity in urine.

A new modification of the prior human lung compartment plutonium model, Doses-2005, has been described. The modified model was named "Mayak Worker Dosimetry System-2008" (MWDS-2008). In contrast to earlier models developed for workers at the Mayak Production Association (Mayak PA), the new model more correctly describes plutonium biokinetics and metabolism in pulmonary lymph nodes. The MWDS-2008 also provides two sets of doses estimates: one based on bioassay data and the other based on autopsy data, where available. The algorithm of internal dose calculation from autopsy data will be described in a separate paper. Results of comparative analyses of Doses-2005 and MWDS-2008 are provided. Perspectives on the further development of plutonium dosimetry are discussed.

Accumulation, organ distribution, and excretion kinetics of ²4¹Am in Mayak Production Association workers.

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.

Development of an Inhalation Intake Model for 241Am Based on Mayak Production Association Worker Data.

ABSTRACT: Americium-241 is a significant radiation hazard at facilities that handle or reprocess spent nuclear fuels. An inhalation intake model for 241Am was developed using autopsy data obtained from former workers at the Radiochemical and Plutonium Production Plants at the Mayak Production Association (Mayak PA), Ozyorsk, Russia. Accumulation of 241Am in the body can occur though direct exposure to 241Am (termed here "exogenous" exposures), usually as an inhaled aerosol, or though exposure to 241Pu that decays inside the body to 241Am (termed here "endogenous" exposures). Metabolism of endogenous and exogenous 241Am can differ, with endogenous 241Am being initially related to the behavior of 241Pu. For the model, it was assumed that intakes of 241Am and 241Pu were functionally associated with intakes of 239Pu. The current Mayak Worker Dosimetry System model (MWDS-2008) was used to describe metabolism of plutonium and americium in the respiratory tract. The ICRP-30 model was used for the gastrointestinal tract, the ICRP-67 model was used for metabolism after absorption into the blood for americium, and the "Leggett modification" of the ICRP-67 model for plutonium was used for systemic, non-pulmonary organs. The proposed inhalation intake model for americium provides estimates for internal doses from 241Am from both exogenous and endogenous sources.

238Pu: accumulation, tissue distribution, and excretion in Mayak workers after exposure to plutonium aerosols.

The alpha spectrometry measurements of specific activity of 238Pu and 239Pu in urine from bioassay examinations of 1,013 workers employed at the radiochemical and plutonium production facilities of the Mayak Production Association and in autopsy specimens of lung, liver, and skeleton from 85 former nuclear workers who died between 1974-2009, are summarized.The accumulation fraction of 238Pu in the body and excreta has not changed with time in workers involved in production of weapons-grade plutonium production (e.g., the plutonium production facility and the former radiochemical facility). The accumulation fraction of 238Pu in individuals exposed to plutonium isotopes at the newer Spent Nuclear Fuel Reprocessing Plant ranged from 0.13% up to 27.5% based on the autopsy data. No statistically significant differences between 238Pu and 239Pu in distribution by the main organs of plutonium deposition were found in the Mayak workers. Based on the bioassay data,the fraction of 238Pu activity in urine is on average 38-69% of the total activity of 238Pu and 239Pu, which correlates with the isotopic composition in workplace air sampled at the Spent Nuclear Fuel Reprocessing Plant. In view of the higher specific activity of 238Pu, the contribution of 238Pu to the total internal dose, particularly in the skeleton and liver, might be expected to continue to increase, and continued surveillance is recommended.

238Pu: a review of the biokinetics, dosimetry, and implications for human exposures.

Plutonium-238 (238Pu) has a half-life of about 87.7 y and thus a higher specific activity than 239Pu. It is used in radioisotope thermoelectric generators and is a substantial source of plutonium alpha-radiation in spent nuclear fuels. Early animal studies demonstrated differences in the biokinetics of inhaled oxides of 238Pu and 239Pu with 238Pu having a substantially more rapid translocation from the lungs to the systemic organs, particularly the skeleton. This resulted in the predominant occurrence of skeletal cancers in animals exposed to 238Pu oxides but lung cancers in those with exposures to 239Pu oxides. The anatomical distribution of osteogenic sarcomas seen in animal studies was similar to that observed with 239Pu and also in plutonium workers but differed from naturally occurring tumors. The in vivo "solubility" of 238Pu has been associated with the relative amounts of 238Pu/239Pu in the particles and calcination temperatures during the preparation of the dioxides. There is experimental evidence of in vivo 238Pu particle fragmentation attributed to nuclear recoil during radioactive decay. The resulting conversion of microparticles to nanoparticles may alter their interactions with macrophages and transport across epithelial barriers. There are few documented cases of human exposures, but the biokinetics appeared to depend on the chemical and physical nature of the aerosols. Robust human biokinetic and dosimetric models have not been developed, due in part to the lack of data. With the acceleration of nuclear technologies and the greater demand for reprocessing and/or disposal of spent nuclear fuels, the potential for human exposure to 238Pu will likely increase in the future.