A restatement of the natural science evidence base concerning the health effects of low-level ionizing radiation.

This paper has the stated aim of restating the evidence available on the health effects of low level ionizing radiation. It reports that it is known that high levels of radiation are detrimental to the health of organisms including humans but that it is less clear at low levels (low doses or doses delivered at a low rate) with some arguing that current radiological protection standards are too lax and others arguing that they are too severe.

The authors penned a draft review of the data which they discussed at a one day workshop. Here they classified the data sets according to their view of the strength and consistency of the evidence presented. The review was revised and then circulated to a wider circle of experts in the low level radiation field for comment and further revision.

I particularly like figure 2 of the paper (available as a download) which shows a number of datasets of measured effect against dose. It is clear that there is a trend for effect to increase with dose but much less clear that this trend is well behaved at low levels. This figure and the paper summarises the issue nicely. What is happening at low dose and low dose rates?

ResmodelThe diagram shown is figure 3 from the paper. It shows a number of different potential risk models that can be compared to the data. These include the linear no threshold model (LNT), which postulates a straight line through the origin and the linear with threshold, which postulates that there is a level of dose below which no harm is experienced. The former is used by ICRP and a number of other international authorities as a plausible and conservative assumption. The threshold argument also has its proponents who believe that LNT leads to excessive spend on pointless dose avoidance.

Hormesis is an interesting one. It is based on the suggestion that small amounts of radiation can be good for you.

The caption to the diagram states that “at sufficiently low doses, all models are consistent with available datasets”.

The paper provides a brief discussion of a number of studies:

  • Variations in natural background in different places across the world;
  • Acute high level exposures;
  • Low level exposures;
  • The Japanese life span study (recognised as the “gold standard” for learning);
  • Chernobyl workers and exposed members of the public;
  • Fukushima;
  • Workers;
  • Medical exposures;
  • In-vitro studies.

It provides a number of interesting headlines for each category but, deliberately refuses to come to any conclusion.

This is a useful and interesting paper resulting from some careful and systematic work. I am grateful to the authors for producing it and I recommend it as a good read.

Reference: McLean AR et al. 2017. A restatement of the natural science evidence base concerning the health effects of low-level ionizing radiation. Proc. R. Soc. B 284: 20171070. http://dx.doi.org/10.1098/rspb.2017.1070

Author: Keith Pearce

Emergency Planning and Health Physics consultant and author

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