Estimation of radon exposures to workers at the Fernald Feed Materials Production Center 1952–1988

Abstract

The Feed Materials Production Center (FMPC) at Fernald, Ohio produced uranium metal products for use in Department of Energy defense programs. Radium-contaminated waste material was stored on-site in two K-65 silos on the west side of the facility and provided a source of 222 Ra. The initial objective of this study was to estimate radon exposures to employees at FMPC working from 1952 to 1988. A modified Gaussian plume model was used to estimate exposures to workers. In an effort to validate these model-based estimates, we used 138 CR-39 film assays from window glass sampled in buildings throughout the site. Results from the CR-39 assays indicated a second substantial source of radon, the smaller Q-11 silos located in the production area. A response-surface regression analysis using a cubic spline model was fit to the CR-39 data to estimate 210 Po surface activity levels at geographic coordinates throughout the facility. Knowledge of the age of the glass, the amount of contaminated waste in the Q-11 silos, and 210 Po decay rates were used to estimate annual exposures to radon decay products (WLM: working level months). Estimated WLM levels associated with the Q-11 source term indicated that employees working in the vicinity during the period when they were filled with radium-contaminated waste (1952)(1953)(1954)(1955)(1956)(1957)(1958) received substantially higher radon exposures than those from the K-65 source during this period. Results of the two models, corresponding to the K-65 and Q-11 sources, were combined to estimate WLM levels by year for each of the 7143 Fernald workers during the period 1952-1988. Estimated cumulative exposures to individual workers ranged from o0.5 to 751 WLM. Estimated radon exposures from this newly discovered source have important implications for future epidemiologic studies of lung cancer in workers at the Fernald facility.

Exposure assessment for a cohort of workers at a former uranium processing facility

“…Radon exposure was assessed by combining the FMPC cohort work history created for this study with a radon exposure matrix developed previously by Hornung et al 15 This radon exposure matrix was based on a Gaussian dispersion model coupled with a source term for the K-65 silos that was originally intended to estimate exposures to residents living near the FMPC. A detailed description of this atmospheric transport model and the development of the K-65 source term is described elsewhere.…”

“…A detailed description of this atmospheric transport model and the development of the K-65 source term is described elsewhere. 16--18 Hornung et al 15 modified this model by applying stratified meteorological measurements to annual average exposure at various locations at the facility. This resulted in radon exposure estimates that corresponded to work location and shift assignment (three shifts) for each worker at FMPC, thereby accounting for the 24-h variation in radon concentrations.…”

“…This resulted in radon exposure estimates that corresponded to work location and shift assignment (three shifts) for each worker at FMPC, thereby accounting for the 24-h variation in radon concentrations. 15 The exposure matrix consisted of files containing assigned location codes and annual cumulative working level months (WLMs). (A working level (WL) is a measure of the concentration of radon progeny in 1 liter of air that results in the emission of 1.3 Â 10 5 MeV of alpha particle energy.…”

“…Before combining with the cohort work history, annual cumulative WLM for each subject in the Hornung et al 15 cohort was divided by the number of days the person worked in that year to get the daily exposure. This allowed for combining the currently updated work history which may have varied somewhat from the work history assigned by Hornung et al 15 Thorium Thorium exposure was assessed qualitatively for workers determined to have potential for exposure to thorium. Work history for each member of the cohort was examined to determine whether it coincided with thorium production activities.…”

“…Patterns of annual internal uranium exposure were examined using estimates of daily uranium intake (in Bq/day) calculated from urine bioassay data. Radon exposures were estimated using the model described by Hornung et al 15 Normalization for each exposure variable was accomplished by dividing the yearly average value by the overall average between the years 1952 and 2004. Table 3 shows the cohort demographics and provides a description of the bioassay data used in the radiation organ dose assessment.…”