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 [(239)Pu (NO(3))(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.

Figure 1.

Anatomic regions of the respiratory tract that were sampled for Human Case 269 (*, denotes areas of plutonium deposition). Multiple sections were prepared from each general area listed.

Figure 2.

Autoradiographs of Human Case 0269 Respiratory Tissues. All of the above panels are 90-day exposed autoradiographs of Human Case 0269. A, an aggregate of alpha activity and cigarette residue is shown sequestered near a pulmonary blood vessel. B, alpha star aggregate of plutonium localized within connective tissue along the pleura. C, seen in this autoradiograph of Human case 0269 are alpha stars associated with the pleura as well as subpleural (parenchymal scar) fibrosis. Cigarette residue (black materials) is present as well. D, trichrome stain of same location as in A shows an increase in collagen (appears as the darker purple/blue color) in areas that contain alpha activity and a decrease in collagen the further from sites containing plutonium.

Figure 3.

Autoradiographs of experimental beagles respiratory tissues. All of the above panels are 90-day exposed autoradiographs of experimentally irradiated beagles. A, thickened bronchiole wall with associated aggregate of plutonium. Alveoli are also present with thin interalveolar septa between them with surrounding scattered alpha tracks. B, large concentration of alpha activity encapsulated by scar tissue in the tracheobronchial lymph node of a beagle exposed to a low level of Pu. C, plutonium aggregates engulfed by alveolar macrophages, radiation related fibrosis is present in the surrounding tissues. D, aggregate of alpha activity in the tracheobronchial lymph node.