Radiation Exposure and Cancer Incidence (1990 to 2008) around Nuclear Power Plants in Ontario, Canada

This study, by staff of the Canadian Nuclear Safety Commission purports to show that radioactive emissions from nuclear power plants in Ontario are not harming Canadians. It may in fact show the opposite. We offer the following observations about this study:

The Pickering results are suspect.  The authors should have noted that emissions of nuclear substances from the six, 500-megawatt operating reactors at Pickering over the period of the study were less than from the four, 900-megawatt reactors at Darlington or the eight, 800-megawatt reactors at Bruce.  But they did not.


Inclusion of Pickering skews the study.  The very large population living within 25 km of the Pickering facility would be subject to many other influences on cancer incidence, including positive factors. 


The authors should have looked at a smaller radius around Pickering – say, 10-15 km.  In general, the study would have been much stronger had they done variable radii around all three reactor sites.


Also, the positive associations between cancer incidence and proximity to the Bruce and Darlington reactors are much stronger that the weak (and spurious) negative association in the Pickering data.

From the study:

“However, the number of cases varies considerably between the three
NPPs due to the large differences in population size of people living
within 25 km of Pickering, Darlington and Bruce NPPs (1,580,000;
380,000; and 24,500 respectively, based on the 2006 census year).”
(quote from p. 893).

Table 10, Bruce – 9% significant increase in incidence of all
cancers, 17% significant increase in incidence of lung cancer, 17%
significant increase in incidence of colon and rectal cancer.  Total
observed cancers – 2570.  Total expected cancers – 2362.  Excess
cancers – 208 out of a population of 24,500.

Table 9, Darlington – 8% significant increase in incidence of all
cancers, 12% significant increase in incidence of lung cancer, 7%
significant increase in incidence of colon and rectal cancer, 8%
significant increase in incidence of thyroid cancer, 19% significant
increase in in incidence of bladder cancer, 26% significant increase
in in incidence of leukemia.  Total observed cancers – 24,707. Total
expected cancers – 22,853.  Excess cancers – 1,854 out of a
population of 380,000.

Excess cancers at Bruce and Darlington – 2,062 over an 18-year
period in a population at the end of that period of 404,500 – more
than a 0.5% increase of cancer.

Table 8, Pickering – The much larger population (1,580,000) within 25
km of the Pickering NPPs – which includes portions of Scarborough,
Ajax and Whitby – showed a lower overall cancer incidence than the
Ontario average, although incidence of thyroid cancer was
significantly increased (by 41%).

Our comment:

Lane et al. dismiss radiation as an explanation for the elevated
cancer incidence around Bruce and Darlington because “public doses
from environmental releases of radionuclides from Ontario NPPs
represent a very small fraction of natural background radiation (1.338
and 2.02 mSv/year) in the regions where the NPPs are located.”  Based
on their “dose” calculations, they say that “Therefore, on the basis
of current radiation risk estimates and the supporting epidemiological
literature, radiation is not a plausible explanation for any excess
cancers observed within 25 km of any Ontario NPP.”

In fact it would appear that there is clear evidence of excess
cancers within 25 km of the Bruce and Darlington nuclear reactor
sites, but that the authors dismissed radiation as a cause of these
cancers because that would conflict with “current radiation risk
estimates”.

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