The Mayak Worker Dosimetry System (MWDS 2013): Soluble Plutonium Retention in the Lungs of An Occupationally Exposed USTUR Case

Plutonium in Manhattan Project workers: Using autopsy data to evaluate organ content and dose estimates based on urine bioassay with implications for radiation epidemiology

PURPOSE

Radiation dose estimates in epidemiology typically rely on intake predictions based on urine bioassay measurements. The purpose of this article is to compare the conventional dosimetric estimates for radiation epidemiology with the estimates based on additional post-mortem tissue radiochemical analysis results.

METHODS

The comparison was performed on a unique group of 11 former Manhattan Project nuclear workers, who worked with plutonium in the 1940s, and voluntarily donated their bodies to the United States Transuranium and Uranium Registries.

RESULTS

Post-mortem organ activities were predicted using different sets of urine data and compared to measured activities. Use of urinalysis data collected during the exposure periods overestimated the systemic (liver+skeleton) deposition of 239Pu by 155±134%, while the average bias from using post-exposure urinalyses was -4±50%. Committed effective doses estimated using early urine data differed from the best estimate by, on average, 196±193%; inclusion of follow-up urine measurements in analyses decreased the mean bias to 0.6±36.3%. Cumulative absorbed doses for the liver, red marrow, bone surface, and brain were calculated for the actual commitment period.

CONCLUSION

On average, post-exposure urine bioassay results were in good agreement with post-mortem tissue analyses and were more reliable than results of urine bioassays collected during the exposure.

USTUR WHOLE-BODY CASE 0212: 17-YEAR FOLLOW-UP OF PLUTONIUM CONTAMINATED WOUND

The National Council of Radiation Protection and Measurements' (NCRP) wound model was applied to the bioassay data from a United States Transuranium and Uranium Registries' whole-body tissue donor, Case 0212. This individual was exposed to plutonium nitrate as a result of an occupational wound injury and he underwent extensive chelation treatment with Ca-DTPA. All major soft tissues and bones were collected post-mortem and radiochemically analyzed for 238Pu, 239,240Pu and 241Am. The 239,240Pu activity in the total body was estimated to be 232.0 Bq, with 80.3 Bq retained in the liver, 115.1 Bq in the skeleton and 14.3 Bq in the wound. The maximum likelihood method was used to simultaneously fit the 'post-treatment' urinary excretion and post-mortem liver and skeleton retention data. It was demonstrated that the deposited material was predominantly a strongly retained soluble compound (nitrate) with a 22% fraction of plutonium particles. The residual intake, the amount of plutonium deposited in the wound that was not removed from the system by Ca-DTPA, was estimated to be 288 Bq. The resulting committed effective dose was 134 mSv. Accounting for plutonium eliminated in the urine during chelation therapy, the actual 'untreated' intake was 1204 Bq, and the projected committed effective dose was 567 mSv. Hence, DTPA treatment reduced the dose by a factor of 4.

THE MAYAK WORKER DOSIMETRY SYSTEM (MWDS 2013): A RE-ANALYSIS OF USTUR CASE 0269 TO DETERMINE WHETHER PLUTONIUM BINDS TO THE LUNGS

Radionuclides in ionic form can become chemically bound in the airways of the lungs following dissolution of inhaled particulates in lung fluid. The presence of long-term binding can greatly increase lung doses from inhaled plutonium, particularly if it occurs in the bronchial and bronchiolar regions. However, the only published evidence that plutonium binding occurs in humans comes from an analysis of the autopsy and bioassay data of United States Transuranium and Uranium Registries Case 0269, a plutonium worker who experienced a very high (58 kBq) acute inhalation of plutonium nitrate. This analysis suggested a bound fraction of around 8 %, inferred from an unexpectedly low ratio of estimated total thoracic lymph node activity:total lung activity, at the time of death. However, there are some limitations with this study, the most significant being that measurements of the regional distribution of plutonium activity in the lungs, which provide more direct evidence of binding, were not available when the analysis was performed. The present work describes the analysis of new data, which includes measurements of plutonium activity in the alveolar-interstitial (AI) region, bronchial (BB) and bronchiolar (bb) regions, and extra-thoracic (ET) regions, at the time of death. A Bayesian approach is used that accounts for uncertainties in model parameter values, including particle transport clearance, which were not considered in the original analysis. The results indicate that a long-term bound fraction between 0.4 and 0.7 % is required to explain this data, largely because plutonium activity is present in the extra-thoracic (ET2), bronchial and bronchiolar airways at the time of death.