Radiation doses and health risks from radionuclides released into the Clinch River in support of the Oak Ridge dose reconstruction project

The purpose of this work is to estimate off-site radiation doses and health risks (with uncertainties) associated with the release of radionuclides from the X-10 site (now called the Oak Ridge National Laboratory) on the Oak Ridge Reservation. The X-10 facility was originally designed to operate only one year as a pilot plant for the Hanford, Washington operation. The radioactive wastes generated from the plant were intended to be stored in large tanks. The original intent was changed, and in 1944 the first radioactive effluents were released to White Oak Creek and flowed into White Oak Lake. White Oak Lake acted as a final settling basin for the released contaminants. The radionuclides remaining in the water column were released over White Oak Dam, which is located one kilometer upstream from the Clinch River.

Following an initial screening analysis, the exposure pathways of interest included fish ingestion, drinking water ingestion, the ingestion of milk and meat, and external exposure from shoreline sediment. Four representative locations along the Clinch River, from the White Oak Creek Embayment to the city of Kingston, were chosen. Reference individuals were determined with respect to the pathways involved.

The doses and risks estimated in this study for individuals consuming fish exceeded dose and risk estimates for all other pathways. The category I consumer of fish (1-2.5 meals per week) at Clinch River Mile 20.5, received the highest doses. The central valves of the cumulative doses for 1944 through 1991 for specific organs ranged from 0.31 cSv (skin) to 0.81 cSv (bone) for males. The excess lifetime risk of cancer incidence was estimated based on cancer incidence data from the Japanese Atomic bomb survivors and the background incidence of cancer for East Tennessee. For males, the highest risk is to the red bone marrow (central value of 3.7 x 10^-5 ); for females, the highest risks are for the breast and red bone marrow (central values of 5.5 x 10^-5 and 2.8 x 10^-5 , respectively). Although differences between the highest and lowest organ-specific doses at any one location was only a factor of 2 to 4, the difference between risks is about a factor of 70 to 80 for females and 40 for males.

For the Category I consumer of fish near Jones Island, the 95% uncertainty range of the total excess lifetime risk of cancer incidence for all radionuclides and organs was 3.6 x 10^-5 to 3.5 x 10^-3 (2.8 x 10^-3 central value) for males and 2.9 x 10·5 to 2.8 x 10·3 (2.3 x 10^-4 central value) for females. The variation in fish across genders primarily reflects the difference in ingestion rates. For both males and females, the largest contribution to the total risk was from ¹³⁷Cs (about 90%).

The doses and risks estimated in this study are not significant enough to cause a detectable increase in health effects in the population. In most cases, the organ doses are - well below the limits of epidemiological detection (1 to 30 cSv) for radiation-induced health outcomes. Therefore, it is unlikely that exposure to radionuclides released from the X-10 site is responsible for an increased number of cancers to populations utilizing the Chinch River after 1944.