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Feasibility study: Saskatchewan Uranium Miners Cohort Study (Part II)(RSP-0178)

Overview

Radon and radon decay products (RDP) also referred to as “radon progeny” emit types of radiation that are hazardous to people's health. The Canadian Nuclear Safety Commission (CNSC) protects the health of uranium workers by regulating radon and RDP in Canada's nuclear facilities by strictly controlling and monitoring exposures to workers and concentrations of radon and RDP in air.

Radon is an odourless, colourless radioactive gas that occurs naturally in the environment as a result of the radioactive decay of uranium in soils and rocks. Radon decays through a series of very short-lived elements (polonium-218, lead-214, bismuth-214 and polonium-214) called radon decay products.  RDP are not gases, but solid electrically charged particulates that will become suspended in the air, most attaching to dust particles or the surface of solid materials; some may remain unattached. Both attached and unattached fractions may be inhaled. If deposited in the lungs these decay products emit alpha radiation and possibly damaging the living cells lining the lung.

Learn more about radon.

Quick facts:
  • This study is Part II of the Saskatchewan Uranium Miners Cohort (SUMC) Study. It is a feasibility study to assess whether a modern miners' study could detect excess lung cancers due to the relatively low workplace RDP exposures in modern mines (1975 onward).
  • The specific risk of interest is the increased risk of lung cancer due to RDP exposure. Factors such as smoking and residential radon exposure are considered as potential confounding factors of the relationship between lung cancer and RDP.
  • This study concludes that:
    • Today's Saskatchewan uranium miners have RDP exposures that are significantly lower than those of past miners because of dose limits, improved mining techniques and other radiation protection practices.
    • The study calculated that about 24,000 workers will have spent time working at a uranium mine by the year 2030. During this period, 141 miners could be expected to develop lung cancer, primarily from tobacco smoking. Only one (1) additional miner could expect to get lung cancer from exposure to RDP in the workplace.
    • The study concluded that it would not be feasible to investigate the risk of excess lung cancer in modern miners because exposures are so low. It would also be practically impossible to accurately correct for the effects of smoking and residential radon, factors that could greatly impact the study results.
    • The CNSC continues to carefully monitor the occupational exposures of uranium miners to ensure they remain at low levels. Exposure records are maintained indefinitely by the National Dose Registry (NDR).
  1. Purpose of the study
  2. Background
  3. Methods
  4. Main results and conclusions
  5. Next steps
  6. Detailed study conclusions

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Purpose of the study

  • Determine if it is scientifically possible to assess the number of excess lung cancers from the relatively low RDP exposures in modern miners from 1975 onward.

Background

  • In 1993, a joint federal-provincial panel on uranium mining developments in Northern Saskatchewan recommended that epidemiological studies of past, present and future uranium miners should be conducted.
  • The panel felt it necessary to study whether working in the uranium industry affects health – especially the association between lung cancer and RDP exposure.
  • As a result of the above recommendation, the SUMC study group was formed and included members of provincial and federal governments (including the CNSC), industry and worker representatives.
  • The SUMC conducted two studies. The first study, initiated in 2000, updated the historic Eldorado uranium miners study (including Beaverlodge and Port Radium uranium miners, and Port Hope uranium workers) providing more than 50 years of mortality and 30 years of cancer incidence follow-up. The second study was a feasibility study to assess whether it was possible to conduct a study of modern day uranium miners.
  • This summary deals only with the second study (feasibility study).

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Methods

  • This study used current levels of employment, RDP and other workplace exposures, existing lung cancer risk estimates, provincial cancer rates and miners' age distribution (assuming these would remain consistent) to calculate the expected number of excess lung cancers until the year 2030.
  • Residential radon, other mining experience and miner's smoking habits were also considered.
  • Dose and demographic information was provided by the mining companies and the NDR.
  • A linear relative risk projection model based on the Ontario uranium miners study was used to estimate the increased risk of lung cancer from occupational RDP exposure for modern Saskatchewan miners.
  • The BEIR VI model, based on the combined analysis of eleven (11) miner cohort studies was also used to estimate the increased risk of lung cancer from occupational RDP exposure for modern Saskatchewan miners.

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Main results and conclusions

  1. Today's Saskatchewan uranium miners have RDP exposures that are significantly lower than those of past miners because of dose limits, improved mining techniques and other radiation protection practices.
  2. The study calculated that about 24,000 workers will have spent time working at a uranium mine by the year 2030. During this period, 141 miners could be expected to develop lung cancer, primarily from tobacco smoking. Only one (1) additional miner could expect to get lung cancer from exposure to RDP in the workplace.
  3. The study concluded that it would not be feasible to investigate the risk of excess lung cancer in modern miners because exposures are so low. It would also be practically impossible to accurately correct for the effects of smoking and residential radon, factors that could greatly impact the study results.
  4. The CNSC continues to carefully monitor the occupational exposures of uranium miners to ensure they remain at low levels. Exposure records are maintained indefinitely by the NDR.

Read more on the study conclusions.

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Next steps

  • Based on the conclusions and recommendations of the study and peer reviewers, the CNSC, the Government of Saskatchewan, workers and management from the mining companies agreed to continue to carefully monitor the occupational exposures of uranium miners to ensure they remain at the current low levels.
  • Records of these exposures will be maintained for the indefinite future by the NDR. However, an ongoing health study of modern Saskatchewan uranium miners will not be conducted.

Return to main health studies webpage.

To obtain a copy of the report (in English only), contact the CNSC.

 

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Detailed study conclusions

Conclusion 1: Today's Saskatchewan uranium miners have RDP exposures that are significantly lower than those of past miners because of dose limits, improved mining techniques and other radiation protection practices.

Supporting evidence:

  • Today's miners receive an average effective dose of less than 2.5 mSv per year.
  • Previous epidemiological studies of miners occupationally exposed to RDP have indicated a relationship between lung cancer risks and RDP.
  • The study found modern uranium miners may receive more RDP exposures from their homes and the natural environment than from occupational exposures.
  • Available data indicates that ventilation and work practices have been and continue to be successful in maintaining dust levels at a small fraction (typically <10 percent) of the workplace limits established by Saskatchewan Labour.

Conclusion 2:  The study calculated that about 24,000 workers will have spent time working at a Saskatchewan uranium mine by the year 2030. During this period 141 miners could be expected to develop lung cancer, primarily from tobacco smoking. Only one (1) additional miner could expect to get lung cancer from exposure to RDP in the workplace.

Supporting evidence:

  • The general population of Saskatchewan's lung cancer rates and today's uranium miners' RDP exposures have been used to calculate expected and predicted lung cancer deaths for the general population and uranium miners, respectively.
  • The “expected” number of lung cancer deaths is what is expected to occur in the reference population in the absence of any incremental risk from workplace RDP exposure.
  • The “predicted” number of lung cancer deaths includes both the expected number and an incremental number potentially attributable to workplace exposures.

Conclusion 3: The study concluded that it would not be feasible to investigate the risk of excess lung cancer in modern miners because exposures are so low. It would also be practically impossible to accurately correct for the effects of smoking and residential radon, factors that could greatly impact the study results.

Supporting evidence:

  • A study with adequate statistical power (about 80 percent) would have a high probability of detecting an excess risk of lung cancer.
  • However, because of the very low workplace RDP exposures, current knowledge of the health effects of RDP, the relatively small population of miners, and the effects of tobacco smoking and residential radon, the statistical power of a study of today's uranium miners to detect an excess risk of lung cancer as a result of occupational RDP exposure would be very low (about 3 percent).

Conclusion 4: The CNSC continues to carefully monitor the occupational exposures of uranium miners to ensure they remain at low levels. Exposure records are maintained indefinitely by the NDR.

Supporting evidence:

  • Any higher-than-normal lung cancer death rates from such low exposures would be virtually impossible to measure, therefore, an ongoing health study of modern Saskatchewan miners is not feasible.
  • The feasibility study was completed October 2003 and reviewed by three internationally respected radiation epidemiologists. The reviewers agreed with the study's conclusion that it is not scientifically feasible to conduct a study of present and future miners who work in modern Saskatchewan uranium mines (1975 onward) because exposures are so low.

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Additional information

  • The best source of information on the effect of RDP continues to be the updating of existing uranium miners studies such as the Eldorado and Ontario uranium miners studies.
  • The SUMC working group believes that a cohort study of modern Saskatchewan miners is unlikely to contribute significantly to the science because of the issues discussed above.
  • The sex distribution of uranium miners was about 10 percent female and 90 percent male.
  • Tobacco smoking is the number one cause of lung cancer in Canada. It is responsible for 30 percent of all cancer deaths and is related to more than 85 percent of lung cancer cases in Canada. Exposure to radon and RDP is the leading cause of lung cancer in non-smokers and further increases your risk of developing lung cancer if you smoke. Thus, it is important to consider the potential impact of smoking on risk estimates when interpreting studies such as this.
To obtain a copy of the report (in English only), contact the CNSC.

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