[ RadSafe ] Radon: Raabe and Cohen

[Chris Hofmeyr]

Dear Proff Raabe and Cohen, Radsafers,

Prof Cohen's US-wide county-based radon studies caused quite a stir since 1995,
mainly because of the apparent inverse relationship between lung cancer
mortality and average radon concentrations. However, Cohen's main conclusion
was that the result was at variance with the linear-no threshold (LNT) model.
My own analysis of the data sets for two periods kindly provided by Prof Cohen
showed adamantly that there was in fact NO indication of a dependence on
average radon concentration up to the maximum recorded. Such a finding would
concur with Raabe's model of protracted low-intensity exposure (HPJ, July
2011).  Human lifespan is too short to show discernible lung cancer induction
from domestic radon concentrations in the USA. 

However, uncertainty remains with respect to the question of the apparent
inverse relationship in Cohen's data between lung cancer mortality rates and
average county radon concentration, which some people wanted to interpret as
proof of hormesis. Significantly, in a 2006 paper on cancer risk from low level
radiation, Cohen did not cite his own radon data in support of hormesis or even
rejection of LNT.  In Cohen's data average county radon concentration was to
some degree anti-correlated with smoking prevalence, thus explaining the
inverse relationship in the uncorrected (for smoking) data. The smoking
correction to the data was consequently important for the 'real' dependence
curve. Unfortunately it was not possible to analyse the correctness of the
smoking correction, nor associated uncertainties, but I became convinced that
Cohen was not able to correct the data adequately for smoking, possibly
resulting in the persistent apparent inverse dependence of the 'corrected'
data.
 
A stark illustration of the overwhelming importance of extraneous factors -
most probably smoking - is to compare the female lung cancer data sets 1970-79
with 1979-94. There was a mortality increase of almost a factor of 2, whereas
male lung cancer declined very slightly between the two data sets (during
1970-79 it was about a factor of 5 higher than the female figure).
Regards.
Chris Hofmeyr
chris.hofmeyr at webmail.co.za

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