Uncertainties associated with assessing Ontario uranium miners’ exposure to radon daughters

Abstract

The Ontario uranium miners study is a large (n = 28 546) cohort with low levels of radon exposure relative to other uranium miner cohorts. Multiple methods were used over time to estimate annual occupational exposure to radon daughters including: mine-specific extrapolations by mining engineers, area sampling in limited areas of the mines combined with approximate working time and lastly, consistent exposure sampling in different locations of the mine combined with workers’ time cards. Nonetheless, estimating exposures involves assumptions that lead to some uncertainty in occupational exposure characterisation arising from the assessment approach and variability within workplace, over time and by individual. An evaluation of the total uncertainty associated with radon daughter exposure estimation in Ontario miners over time has not been conducted. The objective of this study was to identify the contributing sources and assess the total uncertainty associated with estimating occupational radon daughter exposure among underground Ontario uranium miners over the course of uranium mining. The five sources of radon daughter exposure uncertainty evaluated were: natural variations in radon concentration, estimation of working time, precision of the radon measurement method, unintended errors during sampling, and record keeping and transcription of exposure data. These sources were examined separately for the period 1958 to 1967 and then 1968 onward due to changes in radon daughter concentration measurement practices between these periods. The magnitude of uncertainty associated with each of these sources over time were determined by reviewing historical literature on uranium mining in Ontario as well as through expert advice. Using the root sum square method, the total radon daughter exposure uncertainty was found to be 53 to 67% in the earlier period of uranium mining from 1958 to 1967. This decreased to 31 to 39% for the period 1968 to 1996 with natural variations of radon daughter concentrations in mines accounting for the largest percentage of uncertainty. This assessment provides an initial step in understanding the effect of exposure uncertainty on risk estimates. The impact of this uncertainty on the dose-response relationship between radon exposure and cancer risk will be assessed in future work.

Lung Cancer and Radon: Pooled Analysis of Uranium Miners Hired in 1960 or Later

“…The size of measurement errors decreased over time and became relatively small in the 1960s and later when compared with the early years of operation when contemporaneous measurements often were entirely lacking. 32 , 48 , 49 The impact of exposure measurement error, particularly associated with the early years of operation, has been a major concern in prior studies of radon exposure and lung cancer among underground miners. There also have been concerns that trends in data quality could influence not only an estimate of the overall radon-associated lung cancer risk coefficient but also estimates of parameters that describe the relationship of excess risk with time-related variables, such as exposure rate and time since exposure.…”

“…A major factor contributing to the relatively low-level exposures to radon progeny experienced by uranium miners employed in 1960 or later was the introduction of mechanical ventilation of uranium mines for air exchange that occurred around 1955 in the Czech, 31 German, 16 and French mines 13 and around 1960 in the Canadian and U.S. mining industry; these interventions were often accompanied by improvements in exposure monitoring for radiation protection purposes. 5 , 28 , 32 More than 90% of the employed working years in 1960 or later involved exposures to radon progeny at annual exposure rates of WL.…”

Radon exposure and risk of neurodegenerative diseases among male miners in Ontario, Canada: A cohort study

“…Radon assessment methods from the MMF database included mine‐specific extrapolations by engineers (early 1950s), the use of measurements with individuals’ approximate work time in limited areas (1958–1967), and more consistent area samples taken in different locations of the mines combined with individuals’ work time records (1968–1996). These methods have recognized uncertainties ranging from 31% to 67%, which has been extensively discussed by Navaranjan et al 41 However, the impact of data uncertainties may be low since it only possibly influenced a small proportion of the cohort.…”

“…22 . These methods have recognized uncertainties ranging from 31% to 67%, which has been extensively discussed by Navaranjan et al 41 However, the impact of data uncertainties may be low since it only possibly influenced a small proportion of the cohort.…”

Lung cancer and radon: Pooled analysis of uranium miners hired in 1960 or later

“…A major factor contributing to the relatively low-level exposures to radon progeny experienced by uranium miners employed in 1960 or later was the introduction of mechanical ventilation of uranium mines for air exchange that occurred around 1955 in the Czech, 31 German, 16 and French mines 13 and around 1960 in the Canadian and U.S. mining industry; these interventions were often accompanied by improvements in exposure monitoring for radiation protection purposes. 5,28,32 More than 90% of the employed working years in 1960 or later involved exposures to radon progeny at annual exposure rates of <1 WL.…”