WSU Student, Chris Nielsen, to Study Microdistribution of Plutonium Nitrate in Lung

July 7, 2011 – WSU Environmental Sciences student Chris Nielsen is conducting his master’s thesis study titled, “An Analysis and Comparison of the Microdistribution and Long-Term Retention of ²³⁹Pu(NO₃)₄ in the Respiratory Tracts of a Hanford Worker and Experimental Beagles.” The laboratory work is being carried out by Mr. Nielsen, a graduate research student, with the assistance of Dr. Xihai Wang, a visiting researcher who is employed by the Pacific Northwest National Laboratory (PNNL), Richland, WA.  Mr. Nielsen and Dr. Wang are members of Dr. Bill Morgan’s Radiation Biology and Biophysics research team.  PNNL provides Mr. Nielsen’s and Dr. Wang’s labor and all necessary equipment and supplies. USTUR provides laboratory space. Mr. Nielsen’s graduate committee chair is Dr. Allan S. Felsot.

Excerpt from Mr. Nielsen’s Proposal

According to the current recommendations of the International Commission on Radiological Protection (ICRP 1994a,b), inhalation of “soluble” forms of plutonium results in moderately rapid translocation (absorption) from the respiratory tract to other organs of the body (primarily the skeleton and liver). Indeed, all chemical forms of plutonium except insoluble oxides are assumed to have "Type M" (moderately rapid) absorption characteristics; i.e., 10% of the material deposited in the respiratory tract is absorbed at the rate of 100 d^-1 (half-time about 10 min) and the remaining 90% at the rate of 0.005 d^-1 (half-time about 140 d). However, lifetime follow-up of plutonium nitrate [²³⁹Pu(NO₃)₄] inhalations in both experimental animals (beagle dogs) and an accidentally exposed Pu worker indicated that tissues of the respiratory tract receive substantially higher doses than would be predicted for ‘Type M’ absorption behavior. Furthermore, a biokinetic modeling study of the human case indicated that unexpectedly long retention of “soluble” plutonium in respiratory tract tissue may result from a substantial amount of “chemical binding” of Pu in the parenchymal tissue (James et al. 2007), and thus, according to the current Human Respiratory Tract Model (HRTM: ICRP 1994a), also in bronchial and bronchiolar epithelium. In a recent review entitled “Plutonium Worker Dosimetry,” Birchall et al. (2010) stated that, “This study highlights areas where more research is needed to reduce biokinetic uncertainties, including more accurate determination of particle transport rates and long-term dissolution for plutonium compounds, a re-evaluation of long-term binding of dissolved plutonium, and further consideration of modeling for plutonium absorbed to blood from the lungs.” The proposed autoradiographic study of the form and distribution of nominally “soluble” plutonium retained in lung, lymph node, and bronchial/bronchiolar epithelial tissue for many years in human and beagle dog lungs is designed to address the issue of “long-term binding of dissolved plutonium.”

References

1. James, A.C., L. Sasser, et al (2007). USTUR Whole Body Case 0269: Demonstrating Effectiveness of I.V. Ca-DTPA for Pu. Radiation Protection Dosimetry. 127(1-4): 449-455.
2. Birchall A, M. Puncher, et al (2010). Plutonium Worker Dosimetry. Radiat. Environ. Biophys. 49:203-212.
3. International Commission on Radiological Protection.  Human Respiratory Tract Model for Radiological Protection. ICRP Publication 66. Ann. ICRP 24(1-3). (Oxford: Pergamon Press) (1994a).
4. International Commission on Radiological Protection.  Dose Coefficients for Intakes of Radionuclides by Workers. ICRP Publication 68. Ann. ICRP 24(4). (Oxford: Pergamon Press) (1994b).