Quantitative plutonium microdistribution in bone tissue of vertebra from a Mayak worker.

The purpose of this study was to obtain quantitative data on plutonium microdistribution in different structural elements of human bone tissue for local dose assessment and dosimetric models validation. A sample of the thoracic vertebra was obtained from a former Mayak worker with a rather high plutonium burden. Additional information was obtained on occupational and exposure history, medical history, and measured plutonium content in organs. Plutonium was detected in bone sections from its fission tracks in polycarbonate film using neutron-induced autoradiography. Quantitative analysis of randomly selected microscopic fields on one of the autoradiographs was performed. Data included fission fragment tracks in different bone tissue and surface areas. Quantitative information on plutonium microdistribution in human bone tissue was obtained for the first time. From these data, the quantitative relationships of plutonium decays in bone volume to decays on bone surface in cortical and trabecular fractions were defined as 2.0 and 0.4, correspondingly. The measured quantitative relationship of decays in bone volume to decays on bone surface does not coincide with recommended models for the cortical bone fraction by the International Commission on Radiological Protection. Biokinetic model parameters of extrapulmonary compartments might need to be adjusted after expansion of the data set on quantitative plutonium microdistribution in other bone types in humans as well as other cases with different exposure patterns and types of plutonium.

Use of air monitoring and experimental aerosol data for intake assessment for Mayak plutonium workers.

One of the major uncertainties in reconstructing doses to Mayak Plutonium (Pu) workers is the unknown exposure patterns experienced by individuals. These uncertainties include the amounts of Pu inhaled, the temporal exposure pattern of Pu air concentration, the particle-size distribution and solubility of the inhaled aerosols. To date, little individual and workplace-specific information has been used to assess these parameters for the Mayak workforce. However, extensive workplace-specific alpha activity air monitoring data set has been collated, which, if coupled with individual occupational histories, can potentially provide customised intake scenarios for individual Mayak workers. The most available Pu air concentration data are annual averages, which exist for over 100 defined work stations at radiochemical and chemical-metallurgical manufacturing facilities and basically for the whole period of Mayak production operations. Much sparser but more accurate data on Pu concentrations in workers' breathing zone are available for some major workplaces and occupations. The latter demonstrate that within a working shift, Pu concentrations varied over a range of several orders of magnitude depending on the nature of the operations performed. An approach to use the collated data set for individual intake reconstruction is formulated and its practical application is demonstrated. Initial results of ongoing experimental study on historic particle size at Mayak PA and their implications for intake estimation are presented.

Comparisons of the skeletal locations of putative plutonium-induced osteosarcomas in humans with those in beagle dogs and with naturally occurring tumors in both species.

Osteosarcomas occur from exposures to bone-seeking, alpha-particle-emitting isotopes, particularly plutonium. The skeletal distribution of putative 239Pu-induced osteosarcomas reported in Mayak Metallurgical and Radiochemical Plutonium Plant workers is compared with those observed in canine studies, and these are compared with distributions of naturally occurring osteosarcomas in both species. In the Mayak workers, 29% and 71% of the osteosarcomas were in the peripheral and central skeleton, respectively, with the spine having the most tumors (36%). An almost identical distribution of plutonium-induced osteosarcomas was reported for dogs injected with 239Pu as young adults. This distribution of osteosarcomas is quite different from the distributions of naturally occurring osteosarcomas for both species. In the Cooperative Osteosarcoma Study Group in humans (1,736 osteosarcomas from all ages), over 91% of the tumors occurred in the peripheral skeleton. In the Mayo Clinic group of older individuals (>40 years old), over 60% of the osteosarcomas appeared in the peripheral skeleton. The distribution of naturally occurring osteosarcomas in the canine is similar to that in the adult human. The similarities of the distributions of plutonium-associated osteosarcomas in the Mayak workers with those found in experimental studies suggest that many of the reported osteosarcomas may have been associated with plutonium exposures. These results also support the experimental paradigm that plutonium osteosarcomas have a preference for well vascularized cancellous bone sites. These sites have a greater initial deposition of plutonium, but also greater turnover due to elevated bone remodeling rates.

The development of the plutonium lung clearance model for exposure estimation of the Mayak production association, nuclear plant workers.

The purpose of this study was to develop a biokinetic model that uses urinary plutonium excretion rate data to estimate the plutonium accumulation in the human respiratory tract after occupational exposure. The model is based on autopsy and urinalysis data, specifically the plutonium distribution between the respiratory tract and the remainder of the body, taken from 543 former workers of a radiochemical facility at the Mayak Production Association (MPA) plant. The metabolism of plutonium was represented with a compartmental model, which considers individual exposure histories and the inherent solubility properties of industrial plutonium aerosols. The transport properties of plutonium-containing aerosols were estimated by experimentally defining their in vitro solubility. The in vitro solubilities were found by dialysis in a Ringer's solution. Analysis of the autopsy data indicated that a considerable fraction of the inhaled plutonium is systemically redistributed rapidly after inhalation. After the initial dynamic period, a three-compartment model describes the retention in the respiratory tract. One compartment describes the nuclide retained in the lungs, the second compartment describes a plutonium lung concentration that exponentially decreases with time, and the third compartment describes the concentration in the pulmonary lymph nodes. The model parameters were estimated by minimizing sum squared of the error between the tissue and bioassay data and the model results. The parameters reflect the inverse relationship between plutonium retention in lungs and the experimentally derived aerosol transportability. The model was validated by comparing the autopsy results with in vivo data for 347 cases. The validation indicates that the model parameters are unbiased. This model is being used to estimate individual levels of nuclide accumulation and to compute radiation doses based upon the urinary excretion rates.

The historical and current application of the FIB-1 model to assess organ dose from plutonium intakes in Mayak workers.

One of the objectives of the Joint Coordinating Committee for Radiation Effects Research Project 2.4 is to document the methodology used to determine the radiation doses in workers from the Mayak Production Association who were exposed to plutonium. The doses have been employed in numerous dose response studies measuring both stochastic and deterministic effects. This article documents both the historical (pre-1999) and current ("Doses 1999") methods used by the FIB-1 scientists to determine the doses. Both methods are based on a three-chamber lung model developed by the FIB-1 scientists. This method was developed in partial isolation from the West and has unique characteristics from the more familiar ICRP biokinetic models. Some of these characteristics are the use of empirically based transportability classifications and the parameter modification for chelation-therapy-enhanced excretion data. An example dose calculation is provided and compared to the dose that would be obtained if the ICRP models were used. The comparison demonstrates that the models are not interchangeable and produce different results.