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[cdn-nucl-l] It's time to do something about LNT controversy
I thought you might be interested to read the following guest editorial
which appears in the latest issue of the Health Physics Society Newsletter.
It was written by Dr. Don Higson, Editor, Newsletter of the Australasian
Radiation Protection Society.
IT'S TIME TO DO SOMETHING ABOUT THE LNT CONTROVERSY
It is generally agreed that the lowest dose at which a statistically
significant increase in the incidence of cancer has been shown to occur is
about 100 mSv. This risk has been observed from doses incurred at very high
dose rates, as in an atomic bomb explosion or from some medical procedures.
There is a wide range of disagreement about the biological effects of lower
doses and low dose rates. In recent years, it has become clear that many
scientists are concerned that the practices of radiation protection and
regulation, applied to low levels of radiation, are not consistent with the
The ICRP recommends using the assumption that the risk of cancer is
proportional to dose without a threshold, the "linear no-threshold (LNT)
hypothesis". This assumption is almost certainly not correct, but is claimed
by its advocates to be a reasonable and conservative approximation. Others
have criticised it as being seriously misleading in some applications. For
this criticism, readers need look no further than the article "LN-T and
politics" by Harald Rossi, published in the HPS Newsletter, January 2000.
Controversy about the health effects of low levels of ionising radiation,
and the LNT hypothesis in particular, has become polarised to an extent
which should be considered unacceptable in a rational community. On the one
hand, ICRP-adherents promote the view that LNT can be extrapolated reliably
over a range of four orders of magnitude in terms of dose, and over a much
greater range in terms of dose rate, to estimate cancer fatality risks from
dose rates down to 0.02 mSv per year (and less). Those who disagree tend to
be treated as heretics, deviants and a threat to society. It has even been
claimed that ICRP-recommended risk coefficients underestimate risks.
At the other extreme, there are claims that public fears about low level
radiation are being deliberately exploited for a variety of improper
purposes. One critic of LNT in the US has stated that the head of a national
radiation protection authority, at the international BRPS Conference (see
below), accused him of trying "to kill the golden goose".
The radiation protection profession is the meat in this sandwich. For its
members, the LNT hypothesis is a convenient tool, without which their work
would be difficult to perform. Most of them are not involved in research.
Their job is to apply nationally approved standards, not to question those
standards, evaluate the results of research or develop independent ideas
about radiological risks. But is it good enough to say, in effect, "we were
just obeying orders" when radiation protection measures that cost
(worldwide) literally billions of dollars each year are not achieving any
demonstrable benefit to society, except perhaps:
* to alleviate some public anxiety, which is due largely to belief in
the LNT hypothesis; and
* helping to keep the economy ticking over.
We cannot even be certain that protecting people from exposure to low levels
of radiation is not detrimental to their health. However, we can be certain
that the health effects, if there are any, are extremely small.
If any of my readers are, at this moment, in the process of deciding that
such thoughts represent a threat their livelihood, I would like to say to
them "please read your Code of Ethics - it is not there for fun". The HPS
"Professional statements made by members shall have a sound
scientific basis. Sensational and unwarranted statements of others
concerning radiation and radiation protection shall be corrected, when
The Australasian Radiation Protection Society's Code of Ethics, which can be
found at http://www.arl.gov.au/arps on the Internet, spells this out even
more explicitly. An IRPA Code of Ethics will, I hope, be promulgated after
the IRPA-10 Congress in Hiroshima.
I was surprised that there was no official attempt made to address and
resolve the LNT controversy during the IRPA-9 Congress in Vienna, four years
ago. Instead, the Sievert Lecture was used to attack the apostasy of
questioning ICRP recommendations on the matter. Since then, there have been
numerous conferences wholly or partly concerned with the science and
regulation of low level radiation. The most recent of these, pertinently
entitled "Bridging Radiation Policy and Science" (BRPS), took place at
Airlie in VA, USA, 1-5 December 1999. The Final Report of this conference is
available at http://www1.misinc.net/burkinc/.
The BRPS Conference appears to have addressed most aspects the controversy,
except radiation hormesis*, without making a great deal of progress. Its
recommendation that "the conference supports the evolving global framework
of the IAEA for the safe use of radiation" was hailed by some as a consensus
on LNT and an endorsement of the IAEA Basic Safety Standards, but it is
clear from the full report that no such consensus was reached. What is
notable is: how limited was the range of agreement that existed!
The conclusion of the BRPS Conference that "the effects of low-level
radiation below 1 mSv per year (100 mrem per year) above background
radiation cannot currently be distinguished from those of everyday natural
health hazards" is a truism, since an increment of 1 mSv per year is well
within the natural range of background radiation. If this conclusion had
related to 10 mSv per year, it would presumably have been necessary to note
the evidence of radiation hormesis. It is difficult to understand why this
matter was not addressed, because either:
* hormesis is a real phenomenon, in which case protection from low
(and perhaps intermediate) levels of radiation is not only a waste of time
and money but positively counterproductive and harmful; or
* the existence of hormesis can be disproved, in which case the
disproof should be clearly stated so that claims that hormesis exists can be
safely set aside, once and for all, and those who make them can be
* we simply do not know, in which case we surely need to find out.
Major funding should be applied to properly designed epidemiological studies
aimed at resolving the matter.
It seems to me that this is the most important issue faced by society and
our profession in bridging the gap between radiation policy and science.
* For newcomers to this controversy, "hormesis" is a short way of
saying "things go better with low level radiation". There is a huge amount
of information published on hormesis, including reports that relatively low
incidences of cancer occur where levels of background radiation are
relatively high. Without taking any position on this matter, I could provide
a short list of respectable references to anyone who needs them. Supporters
of LNT appear not so much to refute this evidence as ignore it.
Dr D J Higson
Editor, Newsletter of the Australasian Radiation Protection Society
260 Glenmore Road
Paddington, NSW 2021, AUSTRALIA