Averaging - ICRP's fatal flaw
[adapted from a talk given by Richard Bramhall
to a Welsh AntiNuclear Alliance meeting
in Chepstow, Wales,
23rd February 2001]
The basic message of the Low Level Radiation Campaign is that nuclear pollution appears to be far more dangerous than the authorities have ever admitted. Consequently nuclear power and nuclear weapons are unacceptable, and even nuclear medicine is extremely questionable.
There is a great deal of evidence suggesting that what officials underestimate is hazard from low radiation doses, and that the problem lies with internal contamination.
The evidence is:
1) geographical clustering of leukaemia around nuclear plant and weapons factories;
2) studies of nuclear workers, showing that those who are (or who only may have been) internally contaminated have higher cancer risks and confer higher risks of leukaemia on their own children;
3) temporal clustering associated with periods of time when large amounts of radioactivity were injected into the environment - Chernobyl in 1986, and atmospheric weapons testing in the 1950s and '60s.
There is broad agreement that if (repeat if) internal radioactivity is to blame for the diseases, then risk factors are out by a factor of between 2 and 3 orders of magnitude - say, between 100 and a couple of thousand.
AEATechnology responded to a report Ref. of increased prostate cancer in its workforce by calculating that doses were 2000 times too small. Atkinson ref.
So of course they did not agree that radioactivity is to blame, but a new study Ref. designed to test the National Radiological Protection Board's risk factors confirms the scale of their error.
Agencies like NRPB predict the yield of diseases by multiplying the dose by standard risk factors. At the time of Chernobyl they said there was no significant threat to health in the UK, on the basis of the rad. doses they had measured.
In the case of infant leukaemia, doses from Chernobyl should have produced far less than one additional case in the populations of Wales and Scotland. (To spare you the mental anguish of trying to imagine a fraction of a case of leukaemia, I can tell you that all this mean is that you'd have to investigate the cancer registrations for a population more than 50 times as big in order to expect even a single baby with leukaemia caused by the radiation.)
But Busby and Scott Cato looked at the figures and found that the rate had jumped quite sharply - 14 babies were diagnosed in the two years following Chernobyl. The average in a two year period before it was 4.2, so finding 14 meant there were 9 or 10 extra cases
Column a represents the average number of cases in each 2 year period for a few years before the accident - it's 4.2
Column b represents that "usual" average rate, plus the extra predicted by NRPB's model - it's the thin black line just above the dotted line - it's very small - . I'll come back to the exact size in a minute.
Column c is the actual number of cases found in the two year period after the accident.
It's a great deal bigger than NRPB's prediction.
Now saying a great deal bigger sounds vague and not very scientific. But I have to say it because we don't know exactly how the radioactivity made these babies ill.
Was it because it crossed their mothers' placentas?
Or because it affected them after they were born?
Or because the dose to their fathers' balls had mutated the sperm before they were even conceived?
There are different risk factors for these different types of exposure route.
After doing some simple arithmetic with the figures in Busby and Scott Cato's paper we can display the implied errors like this:If the damage was done by the placenta-crossing dose, NRPB's prediction was about 72 times too small;
if it was the post-natal effect, the prediction was 132 times too small;
and if it was the preconception dose to the fathers' testes, NRPB was out by a whacking 2390.
Given that we are constantly bathed in radiation from natural sources, how can it be that anthropogenic radioactivity appears to be 100 times, or 2000-odd times as dangerous as NRPB says it is, without the human race having melted down into a soup of amino acids?
The important point is that the official risk agencies understand radiation dose as energy transfer averaged over substantial volumes of tissue. They think in terms of whole organs, the whole body, or even entire populations - as in the case of the collective doses from Chernobyl and NRPB's leukaemia predictions. But there is no doubt that the vital target for radiation damage is not the whole body but individual cells. This is admitted by the radiation protection community. Roger Clarke, Chairman of ICRP and Director of NRPB, has written"there is compelling evidence that cellular DNA present in the chromosomes of the cell nucleus acts as the principal target for spontaneously arising and carcinogen-induced tumours in humans and experimental animals. ... At present the evidence available supports the view that ionising radiation acts most strongly as the early initiating phase of tumour development by inducing specific gene loss in stem cells.DNA damage comes from discrete radiation tracks, and cells are either hit or are missed altogether (for the time being we'll ignore the newly discovered and poorly understood "bystander effects")
So the important effects are happening at the level of the individual cell, and we should remember that cancers are "monoclonal" - that is, if you do DNA analysis of cancerous tissue you find that all the cells are descended from a single mutated cell.
If you grasp the idea that it's at the cellular level, rather than the whole body level, that NRPB's averaging model breaks down it's much easier to visualise. (and for practical epidemiological purposes you could regard the entire human population of any given study area as one vast colony of cells.)
So where environmental contamination at low dose is concerned the real situation is not, as NRPB's model assumes, that whole body doses cannot vary much, so "No problem". What is really happening is that hot particles, or individual atoms of nuclides which decay sequentially, are causing huge local inhomogeneities of dose. Like the armed madman shooting at the crowd in the supermarket; he hits me; he misses you.
This is why depleted Uranium is such an important issue. The tiny glassy beads of Uranium oxide created by DU weapons float around in the air, are easily inhaled, and migrate to the lymph nodes, where they stay. It's not just us that says this - look at what one of the world's most important radiation biologists says about it:Burning uranium forms small particles of uranium oxides, between 0.1 and 10 microns wide, which can be inhaled. White blood cells scavenge the particles in the lungs and deposit them in the tracheobronchial lymph nodes. They are highly insoluble, and might not show up at all in urine, while still emitting intense local alpha and beta radiation. That could damage blood stem cells, causing leukaemia.This is quoted in New Scientist and it is completely out of step with what NRPB says - they take no account of these very "intense" local effects. How did this situation arise?
Well, it's because their understanding of hazard is based on studies of Hiroshima survivors - these studies are pivotal, NRPB says.
The survivors were people who were in the open when the bomb went off. So they were exposed to a single massive flash of gamma rays delivered from outside their bodies and evenly spread. The whole of their bodies would have got much the same amount - just think of a camera flash gun - it lights up everything in front of it!
So, right from the start, you have a type of exposure which tells you nothing about the local effects of internal contamination.
Then, as "science", it gets worse. To find out the effects of any type of influence or exposure you have to compare rates of disease in the "exposed" people with rates in an "unexposed", "control" group. The controls for Hiroshima were people who had been out of the city when the bomb exploded, or were sheltered underground or behind thick walls.
But both groups lived in the city, and were equally exposed to eating, drinking, and inhaling fallout, so the "controls" were equally contaminated. ALL the studies of the Japanese survivors are based on the same "exposed" and "control" groups. So NONE can ever tell ANYTHING about internal fallout.
But NRPB aren't too bothered about that.
Here's what they do.Going up the vertical axis we see increasing genetic damage;
going left to right along the bottom is increasing dose.
This is the famous Linear No Threshold model - damage is strictly proportional to "dose" or "energy deposition"; and there is no dose too small to do some damage - in theory.
But there are only two data points - the very high gamma doses at Hiroshima caused some leukaemia - and the line between those points and the "origin" - zero dose and no extra damage - is just an assumption. A guess. Professor Goodhead, who was quoted in the New Scientist slide I showed earlier, calls it a large area of uncertainty
And just to confirm it, here's what the top man at NRPB says:In the absence of directly informative data ... the shape of the low-dose response has to be judged on indirect data on the cellular mechanisms involved in the whole of this complex process. ClarkeNRPB is fond of saying that the straight line is supported by other studies. You can represent them with some extra dots on the graph, like thisBut these again are relatively high doses of external radiation, so the problem remains - it's guesswork at low dose.
What is the reality?
A substantial number of studies have been put together and show a curve like this.Now you can see that in the very low dose region, on the left hand side (that's what we are concerned with in environmental pollution)
genetic damage increases rapidly as sensitive cells are hit and mutated.
As dose increases a bit more the effect peaks, and begins to fall off. This is because the sensitive cells are being killed, rather than being mutated. Just as dead men tell no tales, dead cells don't multiply to become cancers.
As dose increases a bit more, the insensitive cells begin to be mutated, so that's why the curve begins to rise again. Note that this second upward slope parallels the LNT line - NRPB seems to have got it about right at these higher doses.
Eventually there would be a second falling off - but that represents the death of whole organisms (I mean "people") from acute radiation. That's at very high doses, but it's the very low doses on the left-hand side that interest us, and now we can see why there is such a huge error.At any level of dose - A - A for example - the size of NRPB's error is the distance between the straight "LNT" line and the wavy "biphasic" curve, compared with the distance between the LNT line and the bottom of the graph. That could easily be 100 fold.
What we have to note is that at higher doses the two curves agree.
The practical implication of this is that a lot of research is needed to identify which isotopes, and which physical and chemical forms of them, confer the biggest hazards [ it's possible that some forms of nuclear pollution are no more dangerous dose for dose than Natural Background Radiation] Only then can we develop rational and scientific standards for dealing with the legacy of radioactive junk the industry has bequeathed us.
On this note, I'd like to say something to the people who work in the nuclear industry, if there are any here tonight.
You may regard me as an enemy, but in fact I am not. What I am saying should mean (if we lived in a rational world) that generating electricity from nuclear power would never again be considered a valid option. That does not mean that you would be out of a job. For the other implication is that 50 years of playing with the atom has left us with a vast amount of debris which we have to clean up very carefully. That is a "jobs for life" situation rare in today's world.
Look at this cartoon illustrating the idiocy of average dose [You can print it out on one sheet of A4 and pin it on your wall]
References and notes
Roger Clarke, Chairman of International Commission on Radiological Protection and Director of National Radiological Protection Board Control of low-level radiation exposure: time for a change? J. Radiol. Prot. Vol. 19 No 2 107 - 115]
Atkinson, W. D., Marshall, M., Wade, B. O., Cancer risk has no effect on mortality BMJ 308: 268 (1994)
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