Improved Radiation Dosimetry/Risk Estimates To Facilitate Environmental Management of Plutonium Contaminated Sites

Technical Report · Fri Dec 10 00:00:00 EST 2004

OSTI ID:835026

Cheng, Yung-Sung; Zhou, Yue; Okladnikova, Nadezhda D

This report is comprised of a main section and two appendices (A, B) that contain two submitted papers developed with either partial or full support from this Environmental Management Science Program (EMSP) project. The project has focused on applying basic and applied scientific methods to improve both the characterization of plutonium (Pu) aerosol deposition in the human respiratory tract and the understanding of the associated health risks. Our modeling research has ranged from stochastic effects in cells (mutations, neoplastic transformation, apoptosis) to cancer induction in humans. Special attention has been given to cancer risk for low-dose exposure to alpha radiation from inhaled Pu-239. We have also conducted modeling research related to high-dose exposure to alpha radiation from inhaled Pu isotopes and the associated risks for deterministic effects. This research is especially timely given new concerns related to possible nuclear terrorist incidents in the United States and elsewhere. The methodology presented in one of our submitted papers (Appendix A) for characterizing the risk of radiation deterministic effects associated with exposure to large internal (alpha, beta, and gamma) and external (gamma) doses is being used by the International Atomic Energy Agency (IAEA) to develop guidance for managing radiological incidents (e.g., dirty bomb incidents) and by Sandia National Laboratories to assess the health consequences of the use of dirty bombs by terrorists. Our dosimetry modeling research has focused largely on weapons-grade Pu (WG Pu), which is comprised of several different isotopes that are primarily alpha emitters. We have mainly focused on the insoluble dioxide form. Our mechanistic modeling research has lead to a revised model for low-dose, radiation induced, neoplastic transformation (an early step in cancer induction). The revised model is called NEOTRANS3, and has facilitated evaluating the expected shape of the dose-response relationship for the relative risk (RR) for lung cancer induction in humans [Mayak Plutonium Facility Production Association (PA) workers in Russia] after combined exposure to alpha and gamma radiations. This is based on the published observation that RR for neoplastic transformation has a similar dependence on dose as for the RR of cancer induction. Based on our mechanistic model, low dose-rate exposure to low or moderate doses of gamma radiation is predicted to possibly protect adult humans from cancer occurrence, including cancer induction by low dose alpha-radiation and cigarette smoke. The gamma irradiation associated protection arises through gamma rays hitting many of the millions of normal cells in the irradiated tissue, which turns on intra- and intercellular signaling that leads to cleansing of tissue of neoplastically transformed and other genomically compromised cells (e.g., mutants, micronucleated cells, etc.) via a selective apoptosis mechanism. Using available cohort study data for Mayak PA workers chronically exposed to gamma rays in combination with alpha radiation from inhaled Pu-239, we can explain the hormetic-type, dose-response relationship for the RR for radiation-induced lung cancer seen in the workers as well as in tuberculosis patients receiving chronic X-ray irradiation. Based on currently available information, the linear nonthreshold (LNT) model appears to apply to chronic exposure to alpha radiation alone but, in adults, not to exposure to gamma radiation or combinations of gamma and alpha radiations. We found that linear extrapolation from high-dose data to low doses can introduce phantom (nonexistent) excess cancer risk in the case of combined exposure of adults to gamma and alpha radiations or exposure only to gamma rays. Because remediation of radionuclide-contaminated U. S. Department of Energy (DOE) sites is driven by risk-based considerations, and risks are assumed to increase according to the LNT model, it is important to understand under what circumstances risk would not be expected to increase linearly as dose increases. Results presented in this report facilitate making such assessments. We have developed and published a novel theoretical approach to characterizing the variability among different individuals associated with inhaled plutonium dioxide (PuO2). The approach is probabilistic and explains the large variability observed in association with worker exposure to 238PuO2 at Los Alamos National Laboratory during the March 16, 2000, accident in the Plutonium Processing and Handling Facility [Technical Area (TA) -55] involving a glovebox leak.

• Research Organization: Lovelace Biomedical & Environmental Research Institute (US)
• Sponsoring Organization: USDOE Office of Environmental Management (EM); USDOE Office of Science (SC) (US)
• DOE Contract Number: FG07-00ER62511
• OSTI ID: 835026
• Report Number(s): DOE/ER-62511; TRN: US200501%%404
• Resource Relation: Other Information: PBD: 10 Dec 2004
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRONMENTAL POLLUTANT EFFECTS ON LIVING ORGANISMS AND BIOLOGICAL MATERIALS
AEROSOLS
APOPTOSIS
CHRONIC EXPOSURE
DOSE-RESPONSE RELATIONSHIPS
DOSIMETRY
EXTRAPOLATION
GAMMA RADIATION
IRRADIATION
MANAGEMENT
NEOPLASMS
PLUTONIUM
PLUTONIUM DIOXIDE
RADIATIONS
ALPHA RADIATION
STOCHASTIC EFFECTS
DETERMINISTIC EFFECTS