Updated analysis of the Eldorado uranium miners' cohort: Part I of the Saskatchewan Uranium Miners' Cohort Study (RSP-0205)

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, possibly damaging the living cells lining the lung.

Learn more about radon.

Quick facts:

  • This study looks at the relationship between lung cancer (deaths and new cancer cases) in relation to radon progeny exposures in a group of 17,660 Eldorado uranium workers who started working at the Beaverlodge and Port Radium mine sites and the Port Hope radium and uranium facility between 1932 and 1980 and followed up through 1999.
  • It is an update of the original Eldorado study group, or cohort, that looked at mortality at the Beaverlodge (Howe et al, 1986) (Howe and Stager, 1996) and Port Radium (Howe et al, 1987) mine sites and Port Hope radium and uranium facility.
  • This study concludes that:
    • Overall, uranium mining and processing workers were as healthy as the general Canadian male population.
    • Lung cancer was the only disease that consistently showed significantly higher death and cancer incidence rates among uranium mine workers.
    • Overall, the excess risk of lung cancer death and cancer incidence increased linearly with increasing radon progeny exposure.
    • There was no statistically significant evidence of a relationship between RDP exposure and any other disease (other than lung cancer).

  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

  • Understand the relationship between RDP exposure and the risk of lung cancer or any other disease.
  • Compare cancer incidence and mortality rates of the updated cohort with the general Canadian population
  • Analyze lung cancer incidence and mortality rates associated with RDP exposure in the updated cohort
  • Analyze cancer incidence and mortality rates for diseases other than lung cancer associated with RDP exposure and gamma ray exposure

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Background

  • In 1993, a joint federal-provincial panel on uranium mining developments examining proposed uranium mines in Northern Saskatchewan recommended that ongoing health 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 Saskatchewan Uranium Miner's Cohort (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 to fulfill its task: Part I is this current study (updating the original Eldorado cohort of uranium workers) and Part II is a feasibility study looking at the health of modern day (post 1975) uranium miners.
  • The original Eldorado study found an excess of lung cancer deaths among Beaverlodge and Port Radium miners. This was due to the high levels of RDP exposures in these mines. Male workers in the Port Radium mine received the highest levels of RDP exposures, approximately 900 mSv throughout their career.
  • The original study also found that there was no unusual mortality among the Port Hope radium and uranium workers. This was most likely due to the very low RDP exposures received at this site.

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Methods

  • This study updates the original Eldorado study of 17,660 uranium workers who started working between 1932 and 1980.
  • Employees' job histories and radiation exposures were collected up until 1999. As expected, early operations resulted in higher radiation exposures (mean cumulative exposures) as compared to more modern times.
  • The update adds a further 19 years of mortality data (totaling 50 years) and 31 years of cancer incidence (new cancer cases) data not considered in the original study.

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Main results and conclusions

  1. Overall, uranium mining and processing employees were as healthy as the general Canadian male population.
  2. Lung cancer was the only disease that consistently showed significantly higher death and cancer incidence rates among uranium mine workers.
  3. Overall, the excess risk of lung cancer death and cancer incidence increased linearly with increasing RDP exposure.
  4. There was no statistically significant evidence of a relationship between RDP exposure and any other disease (other than lung cancer).

Read more on the study conclusions.

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Next steps

  • Seventy five percent (75 percent) of the uranium workers in the Eldorado cohort were still alive at the end of 1999 and many workers were still 65 years of age or younger. This is important since these workers could still be working at a modern mine today and could provide the opportunity for future studies.
  • Future mortality and cancer incidence follow-up and analysis of the Eldorado uranium workers and joint analysis with other uranium miner studies should shed more light on the health effects of low RDP exposure as experienced by current uranium workers as well as help to understand and address the health risks associated with residential radon.

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: Overall, uranium mining and processing employees were as healthy as the general Canadian male population.

Supporting evidence:

  • The reduction in risk for cancers, other than lung cancer, likely represents a healthy worker effect.
  • Miners have a physically strenuous job and thus may be expected to be more physically active then the general population.
  • The cohort had similar lower mortality for non-cancer causes such as heart disease presumably for similar reasons.
  • High mortality rates for the mine site employees (Beaverlodge and Port Radium) included alcohol-related deaths and external causes such as homicides, suicides and accidents. Lifestyle factors and the remote northern environment could have contributed to these deaths.

Conclusion 2: Lung cancer was the only disease that consistently showed significantly higher death and cancer incidence rates among uranium mine workers.

Supporting evidence:

  • Port Radium and Beaverlodge workers had significantly higher lung cancer death and incidence rates compared to the Canadian male population.
  • The excess lung cancer death and incidence rates seen in Port Radium and Beaverlodge can be largely attributed to the high RDP exposure found in historic mines.
  • Port Hope workers had lung cancer death rates and lung cancer incidence rates similar to the Canadian male population.
  • Lung cancer is the only known health effect related to RDP exposure.
  • Poor ventilation and lack of radiation protection programs led to very high RDP exposures during early mining operations among uranium miners.

Conclusion 3: Overall, the excess risk of lung cancer death and incidence increased linearly with increasing RDP exposure.

Supporting evidence:

  • Workers' RDP exposure was calculated to determine its effect on lung cancer incidence and mortality.
  • The risk estimates for lung cancer and RDP exposure were not statistically significant for Port Hope workers
  • Three important modifying factors affected the risk of lung cancer. The risk of lung cancer decreased with increasing time since the exposure, increasing age and decreasing exposure rate.
  • Similar to the mortality data, the risk of lung cancer incidence increases with increasing RDP exposure; this relationship is also statistically significant.

Conclusion 4: There was no statistically significant evidence of a relationship between RDP exposure and any other disease (other than lung cancer).

Supporting evidence:

  • The findings of the updated Eldorado study are supported by other research. “Lung cancer is by far the most important long-term health consequence of exposure to RDP experienced by underground miners. In fact, there is little, if any, evidence of any other serious long-term health effect arising from such exposure” (Darby et al, 1995).
  • Gamma ray doses, which were also studied, provided no statistically significant evidence of a relationship with any cancer or cause of death.
  • It is known that high doses of gamma rays can increase the risk of a number of cancers (UNSCEAR, 2000), with leukaemia being one of the most likely. However, in the present study, the average gamma ray dose of the Eldorado workers was fairly low, and health effects are not expected at these low doses. It is important to note though, that this study lacks statistical power to detect an effect of exposure to gamma rays because exposures are so low.

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Additional information

  • No data was available on smoking behaviour or other risk factors for cancer among the cohort. 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.
  • This update shows similar results to the original Eldorado study and provides further evidence that the only known health effect of from RDP exposure is lung cancer.
  • The total radiation doses received by today's uranium mine workers are very low (averaging 0.5 mSv/year), well below the regulatory limits. It is important to note that current uranium mines have extensive radiation protection programs, strict dose limits, and ALARA programs, all of which result in very low doses as compared to historic mine operations.
  • These findings are consistent with the results of other uranium miner studies and a combined analysis of the data from 11 underground miner studies (BEIR VI Report).  They are also consistent with the conclusions of a recent report (UNSCEAR, 2009) that provides a comprehensive review and summary of all radon-related research.
ALARA signifies keeping worker doses As Low As Reasonably Achievable social and economic factors taken into account.

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

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