Microdistribution and Long-term Retention of 239Pu (NO3)4 in the Respiratory Tracts of an Acutely Exposed Plutonium Worker and Experimental Beagle Dogs

Abstract

The long-term retention of inhaled soluble forms of plutonium raises concerns as to the potential health effects in persons working in nuclear energy or the nuclear weapons program. The distributions of long-term retained inhaled plutonium-nitrate [239Pu (NO3)4] deposited in the lungs of an accidentally exposed nuclear worker (Human Case 0269) and in the lungs of experimentally exposed beagle dogs with varying initial lung depositions were determined via autoradiographs of selected histologic lung, lymph node, trachea, and nasal turbinate tissue sections. These studies showed that both the human and dogs had a nonuniform distribution of plutonium throughout the lung tissue. Fibrotic scar tissue effectively encapsulated a portion of the plutonium and prevented its clearance from the body or translocation to other tissues and diminished dose to organ parenchyma Alpha radiation activity from deposited plutonium in Human Case 0269 was observed primarily along the subpleural regions while no alpha activity was seen in the tracheobronchial lymph nodes of this individual. However, relatively high activity levels in the tracheobronchial lymph nodes of the beagles indicated the lymphatic system was effective in clearing deposited plutonium from the lung tissues. In both the human case and beagle dogs, the appearance of retained plutonium within the respiratory tract was inconsistent with current biokinetic models of clearance for soluble forms of plutonium. Bound plutonium can have a marked effect on the dose to the lungs and subsequent radiation exposure has the potential to increase cancer risk.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

“…However, while it enabled good fits to be made to the experimental data, including this bound fraction had little effect on dose. (838) More recent studies indicate the presence of a small, but very long-term, bound state for plutonium (e.g. James et al., 2007; Nielsen et al., 2012), which could potentially increase equivalent doses to the lungs significantly, particularly if it occurs in the BB and bb regions. Consideration is therefore only given here to such a long-term bound state.…”

ICRP Publication 150: Cancer Risk from Exposure to Plutonium and Uranium

“…The concentration of plutonium activity was not uniform in the various lung regions, but was significantly less than the average lung concentration in the bronchovascular interstitial tissue of the bronchi and the lumen of the conducting airway, and significantly higher in parenchymal and non-parenchymal scars, with a density of particles approximately 14 times the average of the lung. Similarly, Nielsen et al (2012) observed long-term retention of plutonium in an autopsied Hanford worker (USTUR Case 0269 mentioned above) to be concentrated in parenchymal scar tissue. Some of the fixed deposit of plutonium in the respiratory tract may therefore correspond to plutonium encapsulated in scar tissue.…”

“…Measurements of the activity concentration in the BB, bb, and AI regions of the lung of Case 0269 showed uniform distribution between the three regions; the activity concentration in each region was not statistically different from the average lung concentration (Tolmachev et al., 2017). However, autoradiographs of selected lung tissue sections obtained from this donor showed that the microdistribution was non-uniform (Nielsen et al., 2012). An alpha ‘star’ aggregate of plutonium was measured in the connective tissue of the bronchioles, which indicates that the plutonium was localised rather than diffused within the region.…”

A comparison of CFPD, compartment, and uniform distribution models for radiation dosimetry of radionuclides in the lung

“…In its later revision [71], the clearance was suggested to result from a balance between mucociliary transport and blood absorption, and the residual amount should be time-varying. Also, radioactive materials are prone to accumulate in the tracheobronchial lymph nodes [72]; their potential importance in evaluating inhalation hazards has yet to be evaluated. Second, the respiratory system in the VIP-Man phantom is assumed to be a homogeneous mixture of air and water with 0.26 g cc −1 density.…”