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British Pugwash Group - report on discussion meeting: 18/April/2000.
British Institute of Radiology, London, U. K.
"The effects of low level radiation"
Chair: Sebastian Pease.
Roger Clarke (Chair, International Commission on Radiological Protection)
spoke on "Low level radiation". Less than a year after the discovery of
X-rays by Roentgen (1895), guidelines to prevent dermal burns were
developed by Fuchs. Serious international efforts had to await the end of
WWI. In 1934 the accepted limit was set at 0.2 roentgens/day - about 25
times the level deemed acceptable today. In those days and for some time
thereafter (the reporter has seen recent colour TV footage of people
sitting in abandoned US uranium mines 'for their health') low levels of
radiation and radioactivity were regarded as beneficial (radioactive
underwear was the rage...). After the bombs everything changed. By 1955 it
was recognised that for at least two groups of exposed victims -
radiologists themselves and the survivors of Hiroshima and Nagasaki -
cancer (esp. leukemia) risks were increased.
Now the ICRP guidelines are that "any risk must be kept much smaller than
that from other hazards" and "the probability of developing
radiation-dependent diseases, characteristically cancers, is directly
proportional to the dose received". That is, there is no threshold. By the
late 1970's the question had become one as to what is 'reasonable'.
Utilitarian cost-benefit analysis was in vogue. The key questions were seen
as: How many lives will be saved? What will it cost? Protect society, it
was thought, and the individual WILL be protected. But by the time the
1990's arrived the emphasis had changed. A concern for individual risk was
uppermost. An important question was that of inequity. It was not
acceptable if a single individual was at high risk even if the population
at large were relatively safe. Standards must therefore address the
question of the individual risk.
Now that we are in the 2000's the focus has become one of looking at
individual risks, sometimes from single sources. But the threshold effect
is still debated. The French Academy (the reporter notes the dependence of
French industry upon nuclear power and of French military prestige upon
nuclear weapons) has produced a report that says such a threshold exists.
In the US Senate, Sen. Domenici(sp?) has introduced a resolution demanding
recognition of such a threshold by bodies such as ICRP. Yet, says, ICRP,
there is no threshold.
There are two ways of looking at the evidence:
(a) the epidemiological. For A-bomb survivors we have data down to 50-100
mGy (milligrays). It is argued that there are no excess cancer cases at
these levels (some say below 200 mGy). We may note that the average
"natural" background is 3 mGy for a lifetime exposure of about 200 mGy. For
radium workers we have data at similar levels. No definable risk can be
demonstrated at low doses although some have found that risks in utero
increase for exposures as low as 10 mGy. As Jos Rotblat pointed out in the
discussion, the numbers of such cases (both populations and victims of
disease) are too low for statistics to tell us anything reliably one way or
the other.
(b) the molecular biological. DNA is the target. The cell can repair
damaged DNA. But only single strand breaks in the double stranded material
can reliably be repaired. Double breaks (common from radiation 'hits') can
leave the molecule damaged or mutated. Under such conditions the
probability of cancer seems to be increased for a single mutation. Hence,
no threshold. The cell engages in adaptive responses to insult
("hormesis"). This, together with evidence for radiation-induced changes in
apoptosis (controlled cell death) and immune surveillance, has suggested
that low levels of damage may actually be advantageous to the tissue or at
least unthreatening (radioactive underwear makes a come-back??).
Nonetheless in Clarke's view no evidence at the cellular level is available
seriously to challenge the ICRP position of 'no threshold'.
In the new era of 'equity-based ethics' individuals have acquired 'rights'
to certain levels of protection - how much, the 'stakeholders' themselves
must decide, not the experts or the government. Protect the individual, we
now say, and society will automatically be protected - a reversal of the
older doctrine. The result? The maximum dosage is now set at 0.3 mSv
(millisieverts), giving a possible cancer risk (assuming no threshold) of
1:10^5 and amounting to 10% of the 3 mSv natural background exposure. But
note that on Cornish granite the natural exposure goes to 10 mSv or even to
100 mSv in some pockets of radon accumulation. Those of us who take
international flights may or may not wish to be reminded that that gives a
substantial added 'natural'(?) exposure - possibly of greatest concern in
the case of flight crews.
The rules require continuous dialogue. Assessment of risks as a percentage
of natural background may be the most useful. This then also enables us to
consider the question of environmental radiation protection policy - an
area which current human-focussed guidelines do not address. Because the
environment is not one of individuals, such risks are direct and not
statistical in nature. What will be the effect on oak trees? Or shellfish?
Note that some organisms are much less sensitive to radiation than are
human beings (cockroaches are the famous example) but others more so
(including some plants and perhaps trees).
But justifying acceptable levels of radiation involves invoking more than
science; it is also a matter of policy into which technical radiological
issues are but a minor input. At the moment all we can say technically is:
(i) we must control doses to all those most exposed to risk; and,
(ii) such doses must be ALARP (as low as reasonably practical).
In discussion this reporter was surprised to hear that there seem to be no
firm guidelines as to acceptable levels of radionuclides in consumer
products. Some, of course, are deliberately radioactive (e. g. smoke
alarms), others by accident (newsprint a possible case). There is a
voluntary code but not governmental instructions. The National Radiological
Protection Board (of which Dr. Clarke is Director) does regularly monitor
the air, food samples and public water samples for us. Whatever comfort
that provides...
Douglas Holdstock (Secretary, Medact) then dealt with the specific question
of "Depleted Uranium". Depleted uranium (DU), left over after weapons or
reactor 235U has been extracted, contains 99.8% 238U ('natural' uranium is
99.3% 238U, 0.7% 235U and a small amount of 234U). 300 tons of DU were
released in the second Gulf War and about 7-10 tons in Kosovo. It is not a
reactor product and contains no fission products. DU shells release up to 1
kg. of burning dust on impact, giving possible rise to both chemical and
radiological effects.
What are the chemotoxicity dangers? U is a heavy metal like a number of
others (lead, cadmium etc.) and 1 mg. is dangerous for kidney function. But
to get 1 mg. U to the kidney 50 mg. would have to be inhaled, an amount not
likely to be taken up by anyone other than an unfortunate crew member of a
stricken tank. In any case the description of 'Gulf War syndrome' illnesses
does not include kidney-related complaints.
What are the radiological dangers? 238U has a half life of 4.5 byr, and
235U of 0.71 byr compared to 24 kyr for 239Pu. This means that 238U, and
even 235U are hardly radioactive (the weapons - explosive - effect is due
to nuclear fission, quite a different process). Still, what radioactivity
there is involves alpha-emission, a possible inducer of 'genomic
instability', as discussed by Dr. Clarke. But 100 mg. of U would be needed
for a significant radiation dose and the descriptions of 'Gulf War
Syndrome' suggest a pattern of multiple causes to which the indiscriminate
use of insecticides inside tents and the injection of anti-nerve gas
cocktails including substances like prostigmine are the most likely major
contributors. The reported symptoms reminded Dr. Holdstock of the
recognized syndrome suffered by farmers exposed to extensive amounts of
sheep dip chemicals.
Should then DU be banned from weapons? There is an inhumane weapons
convention. The use of any weapon must pass the 'principle of
justification'. The reporter notes that some military authorities or
services have decided against using DU, perhaps because their own personnel
are uncomfortable about it - but good can be done by stealth. It seems
therefore not to be seen as militarily decisive. Although it may not be as
poisonous as some think, it is, even just as a weapon, unpleasant or
'unknightly' (the occupants of an attacked tank have little opportunity of
surrender). Its use blurs the distinctions between conventional, chemical
and nuclear weapons. The absence of any preceding discussion of its
development at civilian levels (our knowledge of its existence may have
come courtesy of a sharp-eyed Gulf reporter and a talkative soldier) was
another indication of failed civilian control of the military. A ban may
therefore be a political as much as an ethical desirability. But doubtless
the debate will continue.
References.
1. Clarke, R. H., & Holdstock, D. (2000) Summaries (British Pugwash
Group, 63A Gt. Russell St., London WC1B 3BJ, UK).
2. Fetter, S., & von Hippel, F. (1999) Bull. Atomic Scient. 55, #6, 42-45.
and, for another set of viewpoints:
3. Laka Foundation (1999) Depleted Uranium: a post-war disaster for
environment and health. (Laka Foundation, Ketelhuisplein 43, 1054 RD
Amsterdam, Netherlands).
Reporter: Peter Nicholls.
Peter Nicholls, Department of Biological Sciences,
Central Campus, University of Essex,
Wivenhoe Park, Colchester, CO4 3SQ, England.
Tel.: +44-1206-873776 (office) +44-1206-873333 (ex. 3015) (Lab)
Fax : +44-1206-872592
e-mail : pnicholl@essex.ac.uk
http://www.essex.ac.uk/bcs/staff/nicholls/
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