WSU Environmental Sciences student, Chris Nielsen, has employed a combination of histopathological stains and autoradiography to study the microdistribution of plutonium nitrate in the lungs of a USTUR Registrant and beagle dogs from historical studies. Mr. Nielsen’s work found that 38 years post-intake, the retained Pu had congregated as "stars" that were predominantly located in the pleura. Mr. Nielsen’s master’s thesis study titled, "An analysis of the microdistribution and long-term retention of 239Pu(NO3)4 in the respiratory tracts of an exposed plutonium worker and experimental beagles," was successfully defended in January 2012. His findings have been published in Cancer Research (link to article).
The laboratory work for this collaborative study was carried out by Mr. Nielsen with the assistance of Dr. Xihai Wang, a visiting researcher. Both Mr. Nielsen and Dr. Wang were employed by the Pacific Northwest National Laboratory (PNNL), Richland, WA, and members of Dr. Bill Morgan’s Radiation Biology and Biophysics research team. PNNL provided Mr. Nielsen’s and Dr. Wang’s labor and all necessary equipment and supplies. USTUR provided laboratory space. Mr. Nielsen’s graduate committee chair was Dr. Allan S. Felsot.
In October 2012, Mr. Nielsen initiated work on his Ph.D. to expand this study to address a specific research need of the European Communities’ SOLO (Epidemiological Studies of Exposed Southern Urals Populations) project.
The following images are pictures of autoradiography slides from Mr. Nielsen’s study. In each of them, retained plutonium emitted alpha particles in a “star” pattern, seen when the autoradiography film was developed.
Master’s Thesis: An analysis of the microdistribution and long-term retention of 239Pu(NO3)4 in the respiratory tracts of an exposed plutonium worker and experimental beagles
Christopher E. Nielsen, Xihai Wang, Dulaney A. Wilson, Gerald E. Dagle, Antone L. Brooks, Stacey McCord, William J. Bair, Anthony C James, Sergei Y. Tolmachev and William F. Morgan.
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 Hanford worker and in the lungs of experimentally exposed beagle dogs with varying initial lung depositions were determined. Autoradiographs of selected histological lung, lymph node, trachea, and nasal turbinate tissue sections were made to determine the location of plutonium within the tissues. A variety of specific stains were used to detect apoptosis and connective tissue generation. These studies showed that fibrotic scar tissue effectively encapsulated the plutonium and prevented its clearance from the body or translocation to other tissues. Alpha activity from deposited plutonium in the human case was observed primarily along the sub-pleural regions and strongly associated with the deposition of a carbon material, thought to be cigarette residue. No alpha activity was seen in the tracheobronchial lymph nodes of the exposed human. However, high activity levels in the tracheobronchial lymph nodes of the beagle dogs indicated they were more effective in clearing deposited plutonium from the lung tissues to the tracheobronchial lymph nodes. In both the human and beagle dogs, the appearance of bound plutonium was inconsistent with current biokinetic models for soluble forms of plutonium. The presence of sequestered plutonium in the beagle dogs suggested similar retention in the human case may not have been totally from cigarette smoking. The findings presented here provide additional support for a need to revise the lung model and include a bound plutonium fraction occurring after inhalation of plutonium nitrate, qualitatively not unlike that occurring after inhalation of insoluble plutonium oxide particles which also have been reported as being sequestered in pulmonary scar tissue. This bound fraction will have a marked effect on the dose to the lungs and the potential increase in cancer risk. It is suggested that the observation of long term retention of inhaled soluble plutonium nitrate in lungs be reflected in biokinetic models for radiation protection purposes.
Excerpt from Mr. Nielsen’s proposal (posted July 7, 2011)
Progress Report presented at the 2011 EURADOS meeting (posted February 17, 2011)
Poster presentation at the 2012 Radiation Research Society Meeting (October 1-3, 2012)