[Mill, 1879; Harre, 1985; Papineau, 1996]
Let us first define our question. It is this. What are the health consequences of exposure to novel internal radioisotopes at whole organ dose levels below 2mSv? Because we are looking at battlefield DU, we should add that in this case, although the element is ‘natural’, the exposure is novel, and due to internal sub-micron Uranium Oxide particles embedded in tissue.
Although risks from exposure to high levels of ionizing radiation are generally accepted, since they are fairly immediate and graphic, the situation with regard to low-level exposure is curious. There are now two mutually exclusive models describing the health consequences of exposure to low-level radiation. There is a nuclear establishment one, which is that which is presently used to set legislation on exposures and argue that DU is safe, and a radical one, which is espoused by the anti-nuclear movement and its associated scientists. I show these two models schematically in Fig 2.
The two models arise from two different scientific methods. The conventional model is a physics-based one because it was developed by physicists prior to the discovery of DNA. Like all such models it is mathematical, reductionist and simplistic, but because of this is of great descriptive utility. Its quantities, dose, are average energy per unit volume or dE/dV and in its application, the volumes used are greater than 1kg. Thus it would not distinguish between the average energy transferred to a person warming themselves in front of a fire and a person eating a red hot coal. In its application to the problem at hand, the internal, low-level, isotopic or particulate exposure, it has been used entirely deductively. The basis of this application is that the cancer and leukaemia yield has been determined following the external acute high-dose irradiation by gamma rays of a large number of Japanese inhabitants of the town of Hiroshima. Following this, arguments based on averaging have been used (quite spuriously) to maintain that there is a simple linear relationship (in the low-dose region) between dose and cancer yield. This Linear No Threshold (LNT) assumption enables easy calculations to be made of the cancer yield of any given external irradiation.
By comparison, the radical model shown in Fig.2 arises from an inductive process. There have been many observations of anomalously high levels of cancer and leukaemia in populations living near nuclear sites, especially those where the measurements show that there is contamination from man-made radioisotopes, e.g. reprocessing plants. In addition, populations who have been exposed to man-made radioisotopes from global weapons tests, downwinders living near nuclear weapon test sites and those exposed to these materials because of accidents (like the Chernobyl infant leukaemia cohort) or because of work in the nuclear industry or military. A review of these findings is available [Busby, 1995] and a more recent literature review of studies showing these effects if published by the Low Level Radiation Campaign [LLRC, 2000]. In addition, the radical model is based on biological considerations and considers each type of exposure according to its cellular radiation track structure in space and in time. It is not, therefore, possible to employ this model to predict risks from ‘radiation dose’ to ‘populations’ but only from microscopically described doses from specific isotopes or particles whose decay fractionations are considered to interact with cells which themselves respond biologically to the insults and may be in various stages of their biological development. The dose-response relationship following from this kind of analysis might be expected to be quite complex.
These models are at war: which one is correct? What considerations can we use to choose?
The answer is that the conventional LNT model must be rejected because it is not scientific. Its conclusions are based on deductive reasoning. It falsely uses data from one set of conditions, high-level, acute, external exposure to model low-level, chronic, internal exposure. It is scientifically bankrupt, and were it not for political considerations, would have been rejected long ago. On the other hand, it should be clear that the radical model conforms to all the requirements of the scientific method listed above. Man-made radioisotopes, often in the form of ‘hot particles’ are common contaminants to the areas near nuclear sites where there are cancer and leukaemia clusters, and to the downwinders, and to the fallout-exposed populations. This satisfies the Canon of Agreement. The contingency analysis tables with control populations for such studies show that the Canon of Difference is also satisfied: people living in more remote regions than the downwinders show lower levels of illness. We must by now also have some faith in a Principle of Instance Confirmation, since so many studies have shown that increases in cancer and leukaemia follow these exposure regimes at low dose. Indeed, the Gulf War Syndrome, might be considered as such an instance confirmation. We are left only with ‘Plausibility of Mechanism’, which I will address below.
Before I turn to the mechanistic arguments I will try to throw some light on how such a state of affairs continues to go unchallenged by quoting from an eminent and past member of the Royal Society, the Nobel-prize winner, Chemist and Economist Michael Polanyi.
Polanyi, was interested in the scientific method, and in scientists: his writings pre-dated the Science War philosophers like Kuhn and more recently Latour. He was aware that at any time, the scientific world view might be completely wrong. For as Montaigne wrote:
Since a wise man may be wrong, or a hundred men, or several Nations, and since even human nature, as we know it, goes wrong for several centuries on this matter or on that, how can we be certain that it occasionally stops going wrong and that in this century it is not mistaken?
Montaigne 1533-92, The Essays
In asking how we know anything at all and how we build up a picture of the ‘real world’ Polanyi saw many similarities between scientists and primitive witch-doctors like the Azande who had been studied by the anthropologist Evans Pritchard who wrote:
They reason excellently in the idiom of their beliefs, but they cannot reason outside, or against their beliefs, because they have no other idiom in which to express their thoughts. The contradiction between experience and one mystical notion is explained by reference to other mystical notions.
E. Evans Pritchard, Witchcraft, Oracles and Magic among the Azande, 1937
For the scientific world view, Polanyi concluded:
[For] the stability of the naturalistic system we currently accept, instead, rests on the same logical structure as Azande witchcraft beliefs. Any contradiction between a particular scientific notion and the facts of experience will be explained by other scientific notions. There is a ready reserve of possible scientific hypotheses available to explain any conceivable event. Secured by its circularity and defended by its epicyclical reserves science may deny or at least cast aside as of no scientific interest, whole ranges of experience which to the unscientific mind appear both massive and vital.
M. Polanyi FRS, Personal Knowledge, 1958
The Royal Society committee is invited to apply these considerations to the responses which followed the discovery by Yorkshire TV of the childhood leukaemia cluster near Sellafield, and bear them in mind whilst deliberating the effects of DU.