Uncertainties associated with assessing Ontario uranium miners' exposure to radon daughters.

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.

Non-targeted effects and radiation-induced carcinogenesis: a review.

Exposure to ionising radiation is clearly associated with an increased risk of developing some types of cancer. However, the contribution of non-targeted effects to cancer development after exposure to ionising radiation is far less clear. The currently used cancer risk model by the international radiation protection community states that any increase in radiation exposure proportionately increases the risk of developing cancer. However, this stochastic cancer risk model does not take into account any contribution from non-targeted effects. Nor does it consider the possibility of a bystander mechanism in the induction of genomic instability. This paper reviews the available evidence to date for a possible role for non-targeted effects to contribute to cancer development after exposure to ionising radiation. An evolution in the understanding of the mechanisms driving non-targeted effects after exposure to ionising radiation is critical to determine the true contribution of non-targeted effects on the risk of developing cancer. Such an evolution will likely only be achievable through coordinated multidisciplinary teams combining several fields of study including: genomics, proteomics, cell biology, molecular epidemiology, and traditional epidemiology.

Leukemia, lymphoma and multiple myeloma mortality (1950-1999) and incidence (1969-1999) in the Eldorado uranium workers cohort.

Uranium workers are chronically exposed to low levels of radon decay products (RDP) and gamma (γ) radiation. Risks of leukemia from acute and high doses of γ-radiation are well-characterized, but risks from lower doses and dose-rates and from RDP exposures are controversial. Few studies have evaluated risks of other hematologic cancers in uranium workers. The purpose of this study was to analyze radiation-related risks of hematologic cancers in the cohort of Eldorado uranium miners and processors first employed in 1932-1980 in relation to cumulative RDP exposures and γ-ray doses. The average cumulative RDP exposure was 100.2 working level months and the average cumulative whole-body γ-radiation dose was 52.2 millisievert. We identified 101 deaths and 160 cases of hematologic cancers in the cohort. Overall, male workers had lower mortality and cancer incidence rates for all outcomes compared with the general Canadian male population, a likely healthy worker effect. No statistically significant association between RDP exposure or γ-ray doses, or a combination of both, and mortality or incidence of any hematologic cancer was found. We observed consistent but non-statistically significant increases in risks of chronic lymphocytic leukemia (CLL) and Hodgkin lymphoma (HL) incidence and non-Hodgkin lymphoma (NHL) mortality with increasing γ-ray doses. These findings are consistent with recent studies of increased risks of CLL and NHL incidence after γ-radiation exposure. Further research is necessary to understand risks of other hematologic cancers from low-dose exposures to γ-radiation.

Impact of environmentally based chemical hardness on uranium speciation and toxicity in six aquatic species.

Treated effluent discharge from uranium (U) mines and mills elevates the concentrations of U, calcium (Ca), magnesium (Mg), and sulfate (SO4 (2-) ) above natural levels in receiving waters. Many investigations on the effect of hardness on U toxicity have been experiments on the combined effects of changes in hardness, pH, and alkalinity, which do not represent water chemistry downstream of U mines and mills. Therefore, more toxicity studies with water chemistry encountered downstream of U mines and mills are necessary to support predictive assessments of impacts of U discharge to the environment. Acute and chronic U toxicity laboratory bioassays were realized with 6 freshwater species in waters of low alkalinity, circumneutral pH, and a range of chemical hardness as found in field samples collected downstream of U mines and mills. In laboratory-tested waters, speciation calculations suggested that free uranyl ion concentrations remained constant despite increasing chemical hardness. When hardness increased while pH remained circumneutral and alkalinity low, U toxicity decreased only to Hyalella azteca and Pseudokirchneriella subcapitata. Also, Ca and Mg did not compete with U for the same uptake sites. The present study confirms that the majority of studies concluding that hardness affected U toxicity were in fact studies in which alkalinity and pH were the stronger influence. The results thus confirm that studies predicting impacts of U downstream of mines and mills should not consider chemical hardness. Environ Toxicol Chem 2015;34:562-574. © 2014 The Authors. Published by Wiley Periodicals, Inc. on behalf of SETAC.