Radioactivity muddles the alphabet of DNA

[caraher]

22. I think there are two somewhat parallel lines of research here

The research in your OP is atomic-level computational work, and can be handy for identifying specific pathways for DNA change/damage. What's interesting about this study is its role as a sort of "existence proof" - that it is possible for damage to take a form not really considered before.

This would be potentially useful in guiding lab research on what happens on a cellular level, which would have implications for our understanding of why the dose response might be expected to take a particular form (whether the response is linear or not).

The particular C-14 decay mechanism they looked at probably doesn't translate well to radiation damage from things like nuclear waste because as I understand it, their concern is chiefly with the effects of a carbon atom transmuting into nitrogen within DNA (as opposed to the effect of a cell absorbing energy from a source external to the DNA). My understanding of the usual radiation damage pathway is that ionizing radiation creates free radicals, and the subsequent interaction of the free radicals with DNA causes most of the trouble. I think this is part of the claim to novelty in this research - it concerns effects of radioactive decay that originates in the DNA molecule itself. But it might be a great probe of what does and does not trigger repair mechanisms.

With respect to using LNT in radiation protection, I think what makes the whole issue complicated is that LNT is not based on ab initio chemistry and cell biology, but on epidemiology. Obviously one cannot ethically or even pragmatically do systematic controlled human studies of dose response so we're limited to trying to glean information from historical examples of mass exposure events. Except for a few cancers with obvious links to particular contaminants (e.g. I-131 and thyroid cancer), the "signal" is very hard to dig out of the high background cancer rate, which is why even the Chernobyl cancer death rate estimated by conventional LNT figures produces numbers that are hard to fish out of noise. The value of computational, in vitro and animal studies of radiation effects is that they might provide a sound theoretical basis for expected low-dose effects.

The last Biological Effects of Ionizing Radiation report, BEIR VII, came out in support of continued use of LNT:

Despite the challenges associated with understanding the health effects of low doses of low-LET radiation, current knowledge allows several conclusions. The BEIR VII committee concludes that current scientific evidence is consistent with the hypothesis that there is a linear dose-response relationship between exposure to ionizing radiation and the development of radiation-induced solid cancers in humans. The committee further judges it unlikely that a threshold exists for the induction of cancers but notes that the occurrence of radiation-induced cancers at low doses will be small. The committee maintains that other health effects (such as heart disease and stroke) occur at high radiation doses, but additional data must be gathered before an assessment can be made of any possible connection between low doses of radiation and noncancer health effects. Additionally, the committee concludes that although adverse health effects in children of exposed parents (attributable to radiation-induced mutations) have not been found, there are extensive data on radiation-induced transmissible mutations in mice and other organisms. Thus, there is no reason to believe that humans would be immune to this sort of harm.

The debate is ongoing. A medical physicist friend of mine who has studied this more than I have is quite convinced that a threshold model is more plausible (and he now works in ultrasound, so it's immaterial to his bread-and-butter). A good example of this line of argument is the unambiguously-titled editorial, "The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data", which was published with a less-noted rebuttal, "Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May Be (Almost) the Best We Can Do."