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Canadian Nuclear Safety Commission

Information Updates

Health of nuclear workers and people living near nuclear power stations in Canada

July 3, 2009

The Canadian Nuclear Safety Commission (CNSC) wishes to respond to the article “Nuke plants hike cancer risk” which appeared in The Saskatoon StarPhoenix on June 23, 2009.

The CNSC offers the following comments and analysis:

Quick Facts:

Nuclear workers in Canada experience a lower rate of cancer and live longer than the general population.
There is no evidence that people living near nuclear power stations have increased risk of any diseases, including leukemia.
Current radiation protection practices are in place to protect workers and members of the public.
There are minimal health effects to workers at nuclear power plants.
The Canadian data component of the IARC study is being reviewed.

Nuclear Workers

Nuclear workers in Canada experience a lower rate of cancer and live longer than the general population.

Image: Two nuclear workers at the Bruce A nuclear power plant located near Kincardine, Ontario

The 15-country study by the International Agency for Research on Cancer (IARC study) showed that Canadian workers have a 24% lifetime lower risk of mortality from all cancers and 38% lifetime lower risk of mortality from all causes of death compared to the Canadian population of similar age and gender. These findings are also supported by a Canadian study by Dr. Zablotska published in 2004 (Zablotska et al. 2004).

Current radiation protection practices are in place to protect workers and members of the public.

As a result of good occupational practices and effective regulatory oversight, the radiation levels experienced by Canadian nuclear workers are low, and thus the risk of developing a cancer as a result of occupational radiation exposure is also low. Further, radiation emissions from nuclear power plants are controlled and monitored, such that public doses are orders of magnitude below the limit of 1 mSv per year.

Further, radiation emissions from nuclear power plants are controlled and monitored, such that public doses are orders of magnitude below the limit of 1 mSv per year.

There are minimal health effects to workers at nuclear power plants.

The paper quoted in the newspaper article mistakenly concludes that the “15-country study of nuclear-power workers found the employees are twice as likely to die from all causes of cancer than the general public because of the extra radiation exposure”

Based on the IARC findings, there was an excess risk to workers for all cancer mortality of 0.97 per Sievert (a sievert, or Sv, is a measure of radiation dose).

This means that for every Sv of radiation dose, the worker’s risk of cancer increases by 0.97. Mathematically this can be expressed as:

Risk of cancer due to occupational radiation exposure = Dose (in Sv) X 0.97

Given that the average worker in the IARC study was exposed over a lifetime to a cumulative radiation dose of 0.0194 Sv, this means an increased risk of cancer mortality of approximately 2% compared to those with zero dose.

In other words, there is a very low risk of nuclear workers contracting cancer due to occupational radiation exposure.

The Canadian data component of the IARC study is being reviewed.

In the Zablotska study, analysis of the Canadian data alone showed an excess risk of 2.80 per Sv. In this study, the cumulative lifetime dose for Canadian workers was 0.0135 Sv, leading to an increased risk of cancer of 4%.

Reanalysis of the IARC study without the Canadian data resulted in an excess risk for all causes of cancer of 0.58 per Sv. In this situation, nuclear workers with cumulative lifetime doses of 0.0195 Sv would have a 1% increase risk of cancer death.

In recognition of this finding, the CNSC initiated a detailed analysis.

One finding was that Ontario Hydro workers were excluded from the IARC study. These workers represent over half of Canadian nuclear workers so their exclusion substantially affected the Canadian findings.

Also, historic dose records were missing from Canadian workers’ employment histories which may have biased the Canadian risk estimates. These historic records are now included in the Canadian study file and further analyses of their impact are underway to get a more accurate estimate of cancer risk among Canadian nuclear workers.

As a result, the CNSC is currently arranging for an international workshop to re-analyze the Canadian data, and will publish an update as soon as possible.

People living near nuclear power plants

There is no evidence that people living near nuclear power stations have increased risk of any diseases, including leukemia.

Childhood leukemia near nuclear facilities has to be measured in relation to such occurrence in the general public.

It is now known that the background risk is uneven - the most extreme childhood leukemia cluster is many miles from a nuclear facility. Those clusters reported near nuclear sites could very well have the same cause as those far away from nuclear sites.

The German study of childhood leukemia referred to in Dr. Lemstra’s report does indeed indicate an increased risk of childhood leukemia, but the authors also point out that while the results do support a relationship between childhood leukemia incidence and distance from nuclear power plants, the excess incidence of leukemia has not been related to radiation exposure.

They also point out that radiation dose estimates from emissions from the nuclear power plants were orders of magnitude below the level at which any regional excess of childhood leukemia would be expected and that similar childhood leukemia clusters have been found in other locations unrelated to nuclear power.

At present, the reasons why these excesses occurred are not known; however, the German Commission on Radiological Protection assessed the German childhood leukemia study and ruled out radiation exposures from nuclear power plants as a cause for the childhood leukemia cluster.

Recent British and French studies used the same methodology as the German childhood leukemia study and did not find any increase in risk in their populations.

The CNSC has conducted several independent studies on potential health effects of nuclear emission on humans, especially children, living in the near vicinity of nuclear facilities in Canada.

These studies looked at childhood leukemia, birth defects and infant mortality in children as well as all causes of death and cancer incidence in people of all ages. These studies provide no evidence of an association between health effects and proximity to Canadian nuclear facilities.

Local health departments have also conducted studies of communities living near nuclear facilities. In particular, the Durham Regional Health Department, which is unique since approximately 300,000 people live within 10 km of two nuclear generating stations (Darlington and Pickering NGS), has conducted several studies examining rates of cancer incidence and mortality, congenital anomalies and other health outcomes.

In general, the rates of cancer incidence and mortality were similar to those in Ontario and prevalence of birth defects was significantly lower than those in the rest of Ontario.

Canadian Nuclear Safety Commission

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Health of nuclear workers and people living near nuclear power stations in Canada

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