Ionizing Radiation and Neurodegenerative-related Mortality in a Retrospective Uranium Processing Cohort: Assessing Confounding and Effect Modification by Co-Exposures

OBJECTIVE: To evaluate ionizing radiation exposure and neurodegenerative-related mortality experience by job category and assess potential confounding and effect modification by occupational co-exposures. METHODS: The Fernald uranium processing cohort has 6403 workers. Job titles were grouped into categories, with co-exposures assigned using a job exposure matrix. Logistic regression examined neurodegenerative mortality by job category, and Cox proportional hazards models assessed cumulative brain dose. Confounding and effect modification were evaluated by comparing effect estimates across co-exposure strata. RESULTS: Some job categories showed elevated neurodegenerative mortality odds. Annual cumulative brain dose was not associated with increased mortality at 10 mGy (hazard ratio, 1.01; 95% confidence interval, 0.96-1.06). No confounding was detected, though effect modification occurred, particularly with machining fluids. CONCLUSIONS: Findings suggest co-exposures may modify IR effects, underscoring their consideration in occupational radiation safety research and policy practice.