Radiation standards: “hormesis” explained

US Nuclear Regulatory Commission (NRC): Consultation. Dr Ian Fairlie Consultant on Radioactivity in the Environment LONDON United Kingdom www.ianfairlie.org, 28 Aug 15, 

Introduction On June 26 2015, the US Nuclear Regulatory Commission (NRC) stated it was seeking public comments by September 8, on petitions stating that the Linear No Threshold theory of radiation’s effects was not a valid basis for setting radiation standards and that the hormesis model should be used instead.

In more detail, the NRC has received three petitions for rulemaking requesting that the NRC amend its “Standards for Protection Against Radiation” regulations and change the basis of those regulations from the Linear No-Threshold (LNT) model of radiation protection to the hormesis model. (See the Appendix for details of the petitions.) The LNT model assumes that biological damage from radiation is linearly related to exposure and is always harmful, ie without a threshold.

The hormesis model assumes that exposures to low radiation levels is beneficial and protects the human body against deleterious effects of high levels of radiation. The NRC has stated it is examining these petitions to determine whether they should be considered in rulemaking and is requesting public comments.

US environmental groups are concerned that, if the NRC agreed with the petitions, it would introduce rules to weaken radiation protection standards at US nuclear facilities. On the other hand, according to two NRC staffers (Brock and Sherbini, 2012), the NRC apparently pays attention to the evidence on risks of low levels of radiation………

No evidence below 100 mSv? It is necessary at this point to directly address the argument often raised by hormesis advocates – that there is little evidence of effects below 100 mSv.

This is incorrect.Older evidence exists -see http://www.ianfairlie.org/news/a-100-msv-threshold-forradiation-effects/for a list of studies and the newer evidence, as we have just seen, clearly shows this fact as well. B. Radiobiological Evidence Current radiobiological theory is consistent with a linear dose-response relationship down to low doses (ie below ~10 mSv). The radiobiological rationale for linearity comes from the stochastic nature of energy deposition of ionising radiation. It was explained by 15 of the world’s most eminent radiation biologists and epidemiologists in a famous article (Brenner et al, 2003) as follows: “1. Direct epidemiological evidence demonstrates that an organ dose of 10 mGy of diagnostic x-rays is associated with an increase in cancer risk………..

The Importance of LNT in Radiation Protection Regardless of dissenting views on LNT, the reality is that most concepts used in radiation protection today are fundamentally based on the LNT theory. For example, LNT underpins the concepts of absorbed dose, effective dose, committed dose, and the use of dose coefficients (ie Sv per Bq of a radionuclide). It also allows radiation doses (i) to be averaged within an organ or tissue, (ii) to be added from different organs, and (iii) to be added over time.

LNT also permits annual dose limits; optimization -ie comparison of practices; radiation risk assessment at low and very low doses; individual dosimetry with passive detectors; collective dose, and dose registers over long periods of time. 9 In fact, the LNT underpins all legal regulations in radiation protection in the US and in the rest of the world.

Indeed, if the LNT were not used, it’s hard to imagine our current radiation protection systems existing at all. However this statement should not be misconstrued to mean that the LNT is used just because it’s convenient: the LNT is used because the scientific evidence for it is comprehensive, cogent and compelling……..

 

Conclusions

(i) the debate The validity or otherwise of LNT and hormesis have been the subject of hundreds of scientific articles and debates over several decades. Unfortunately, much of the literature on hormesis or adaptive response is based on faulty science or on misconceptions, or on misinterpretations, or on all three.

HormesisThis is particularly the case with several US and UK journalists who write with confidence on how radiation risks are exaggerated. Their knowledge and experience of radiogenic risks are limited to say the least, but these journalists, almost on a weekly basis, misinform and mislead the public about radiation risks, so the existence of the US petitions is perhaps unsurprising.

However real scientists are increasingly standing up and opposing the poor science used by hormesis advocates. Very recently, four Swiss scientists from the Institute of Social and Preventive Medicine at the University of Bern; the Swiss Tropical and Public Health Institute, Basel and the University of Basel published a study which revealed that exposure to high rates of background radiation resulted in increased cancer risks to children (Spycher et al, 2015).http://ehp.niehs.nih.gov/1408548/

In reply, 17 scientists (Siegel et al, 2015) mostly from the US, some of whom were members of a hormesis pressure group “Scientists for Accurate Radiation Information” objected to these findings. They alleged that the government would have to evacuate children living in higher radiation areas and relocate them to lower radiation areas. They stated that studies like this should not be taken seriously without public health policy implications being examined. (http://ehp.niehs.nih.gov/1510111/)
The Swiss scientists in turn responded (http://ehp.niehs.nih.gov/1510111R/) that the proposed evacuation was “nonsensical” in view of the very low numbers involved. In a spirited rejoinder, they refuted the poor science cited and added that “the Scientists for Accurate Radiation Information a priori exclude the possibility that low-dose radiation could increase the risk of cancer. They will therefore not accept studies that challenge their foregone conclusion”.
(ii) the petitions After briefly examining the three US petitions, my conclusion is that they do not merit serious consideration. It seems that the petitioners, who may or may not have axes to grind about radiation risks, have seized on the possible phenomenon of hormesis 11 to make ill-considered claims that radiation is protective or even good for you.

In other words, the petitions appear to be based on preconceptions, or even ideology, rather than the scientific evidence which points in the opposite direction. The petitions should not be used by the NRC to justify weakening regulatory standards at US nuclear facilities. A question remains whether the NRC should have accepted the petitions for review. Presumably the NRC has discretion not to review or to refer back spurious, mischievous, or ill-founded petitions.

 The NRC should seek guidance from the five US scientific agencies and Government departments mentioned above whose scientists have published evidence on the matter. Credits. Thanks to Dr Jan Beyea, Cindy Folkers, Dr Alfred Körblein, Xavier Rabilloud, Dr Marvin Reznikoff and Dr Gordon Thompson for comments on drafts. Any errors are my responsibility.References…….. http://www.ianfairlie.org/wp-content/uploads/2015/08/US-NRC-Consultation-4-1.pdf  (NRC):

 

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