The estimation and potential radiobiological significance of the intake of 228Ra by early Ra dial workers in Illinois.

We made radiochemical determinations of 226Ra and the 228Ra-decay product, 228Th, in samples of bone from former Ra dial workers who belonged to a major cohort of Ra-exposed persons under study for health effects at our institution. Most of the former workers were long-term residents of two communities supplied with drinking water containing elevated natural levels of 228Ra and 226Ra, so determinations also were made of radioactivity in samples of bone from long-term residents not occupationally exposed to Ra. The 228Th activity of the bones of the former workers, after correction for the presence of natural radioactivity, showed that some had significant occupational intakes of 228Ra, contrary to published reports that 228Ra was never used by the Illinois company that had employed the cohort of early workers. For 14 workers hired in the years 1920-23, the calculated ratio of the occupational intake of 228Ra to 226Ra activity averaged 0.15 (coefficient of variation 0.65), whereas for three workers hired in 1924, it was not significantly different from zero (mean 0.05, coefficient of variation 1.5). The risk of radiogenic cancer for the typical worker hired before 1924 may have been nearly twice that incurred in the absence of the 228Ra component of the Ra intakes.