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Re: Risks of low level radiation - New Scientist Article
Re Norm Cohen on PNAS (paper full ref : Zhou et al. Radiation risk to low
fluencies of alpha particles may be greater than we thought, PNAS
98(14410-14415, Dec 4 2001)
Otto Raabe is right. There is no indication of supra-linearity at low
dose - or dose rates of alpha radiation. Otto mentioned the radium dial
painters. There are also thresholds at about 2 Gy (40,000 mSv) in Thorotrats
patients (Andersson, M.; Storm, H.H. Cancer incidence among Danish
Thorotrast-exposed patients, Journal of the National Cancer Institute,
84:1318-1325, 1992.). There are thresholds at about 0.8 Gy (1,600 mSv) for
lung cancer in workers exposed to plutonium at the Mayak (Urals) plant
(Tokarskaya Z. et al. Multifactorial analysis of lung cancer dose-response
relationship for workers at the Mayak Nuclear Enterprise, Health Physics
Vol. 73 No. 6, pp. 899-905, 1997).
Jim Nelson reminds us of BEIR VI and of the Iowa study; Otto of Bernie
Cohen's work. Radon epidemiology would be more instructive if real
uncertainties in exposures (and, if low radiation dose to the lung is the
cause of cancer, all non-radon lung doses - and associated errors - received
by uranium miners) were taken into account in determining comprehensive
error bars. Bernie Cohen's work has been criticized but I may have missed a
numerical refutation of his conclusions (how big should have been the
confounders and what correlation should there be between them to account for
the discrepancy with LNT predictions?).
Otto's on work shows that latency time increases with decreasing dose rate
and exceeds the lifespan of animals when it is low enough (practical
thresholds) See Raabe O.G. Three-dimensional model of risk from internally
deposited radionuclides, In: Raabe O.G. ed., Internal radiation dosimetry.
Medical Physics publishing, pp. 633-655, 1984).
Sanders (Sanders, C.L.; McDonald, K.E.; Mahafey, J.A. Lung tumor response
to inhaled Pu and its implications for radiation protection. Health Physics
Vol. 55, pp.455-462, 1988) showed thresholds at about 1 Gy for lung cancer
in rats after inhalation of PuO2.
Morlier et al. Morlier, J.P.; Morin, M.; Chameaud, J.; Masse, R.; Bottard,
S.; Lafuma J. Importance du rôle du débit de dose sur l'apparition des
cancers chez le rat après inhalation de radon. C.R. Acad. Sci. Paris, t.
315, Série III, 463-466, 1992) show that a low dose (about a lifetime indoor
exposure) of radon progeny delivered at a high dose rate induces lung
cancer. The same low dose given at low dose rate seems to decrease the risk
below that in controls.
Ron Mitchel et al. (R.E.J. Mitchel, B. Heinmiller, and J. S. Jackson,
Inhaled Uranium Ore Dust and Lung Cancer Risk in Rats, Health Physics, 76,
145-155 (1999) show that the risk of lung cancer in rats after inhalation of
very high grade (40% U) uranium ore dust is proportional to dose rate rather
than dose. Median survival time was higher in the lowest exposure group than
in the control group.
All the above (other examples can be found) contradict the affirmation that,
mutation rates observed at low fluences of alpha radiation (I quote Zhou et
al.) "...suggest(s) that the assumption of direct proportionality in
radiation risk assessment is seriously in error".
In vitro mutations as well as bystander effects are real but the acid test
for their extraploation to whole organisms is provided by experimental and
clinical observations in real people or animals, when confounders can be
measured or estimated with enough confidence and when normal cell and tissue
controle mechanisms are allowed to play their role. To date, the data seem
to indicate that there is no supra-linearity for cancer risk at low doses
(and dose rates) of alpha radiation. Examples of supra-linearity of alpha
radiation risk (in animal or people), with error bars that take all sources
of error into account are welcome.
Sorry for giving so many details!
Philippe Duport
International Centre for Low Dose Radiation Research
University of Ottawa
555 King Edward Ave.
Ottawa, ON, Canada, K1N 6N5
Tel: (613) 562 5800, ext. 1270
pduport@uottawa.ca
----- Original Message -----
From: "Otto G. Raabe" <ograabe@UCDAVIS.EDU>
To: "Norman Cohen" <ncohen12@HOME.COM>; <radsafe@list.vanderbilt.edu>
Sent: Tuesday, December 04, 2001 9:45 PM
Subject: Re: Risks of low level radiation - New Scientist Article
> December 4, 2001
> Davis, CA
>
> Don't waste your time reading this New Scientist Article.
>
> The fact that high LET alpha radiation can produce unique multiple
> double-strand DNA lesions and the existence of bystander effects do not
> imply anything about elevated risk. Cancer from alpha radiation is
> well-known to be a highly non-linear, threshold-like phenomenon that is
> only effective at very high doses (Evans, et al., radium-226 papers). In
> addition most normal background radiation exposure is associated with high
> energy alpha radiation to the lung tissues from radon decay products, and
> there is apparently little health risk from these exposures (Cohen's
> ecological studies).
>
> Otto
>
> **********************************************
> Prof. Otto G. Raabe, Ph.D., CHP
> Center for Health & the Environment
> (Street Address: Bldg. 3792, Old Davis Road)
> University of California, Davis, CA 95616
> E-Mail: ograabe@ucdavis.edu
> Phone: (530) 752-7754 FAX: (530) 758-6140
> ***********************************************
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