More LNT

[NCRP <ncrp@ncrp.com>]

Radsafers:              


Charlie Meinhold has asked that this be entered on the RADSAFE listserver:
In view of the recent discussion of the various positions taken with regard
to the LNT discussions, I thought the following material might be useful.
It is based on material I prepared for the recent Wingspread Conference
which, unfortunately, I was unable to attend.

Perhaps the most important aspect of estimating low dose effects as they
relate to regulation is that of uncertainty.

If we knew for certain that John Gofman was right or that Warren Sinclair
was right or that Bernie Cohen was right, this would be easy.  Either avoid
all radiation, avoid unnecessary radiation or seek out some extra radiation.
Or to put it another way, EPA's drinking water standards are either (1)
appropriate, (2) EPA's drinking water standards are quite conservative and
could be based on 25 millirem per year assuming the full system of
protection is in place (justification and optimization) or (3) let's
reintroduce radiothor so we can all be healthy.

It would seem that the foregoing demonstrates that neither the NCRP, nor the
ICRP, nor the UNSCEAR are at either extreme in this issue.

This is the predominant reason that I abstain from "debates" and similar
symposia that claim to be fair when they place the position of NCRP/ICRP at
one end of the spectrum and the rest at the other end.  The fact, of course,
is that the NCRP/ICRP position is in the middle between the
threshold/hormesis proponents and those scientists who think the NCRP/ICRP
greatly underestimates the risk of radiation exposure.  This was brought
most clearly to my attention when both the French Academy of Science and
Greenpeace Organization were castigating the ICRP over their draft of
publication 60 in the late 1980's.  There are scientists on each side of the
NCRP/ICRP position who can select some data to establish their position.
The centrist approach is to look at all of the data and attempt to reflect
the most reasonable value for risk estimation.

I would like to go on somewhat, however, to examine what I think is the most
serious issue and that is one of public perception.  The problem is that
people do not consider the level of risk in their decisions about issues
involving radioactive materials.  The introduction of a waste depository in
my village sounds bad and I will fight it no matter what the risk if I
really don't want it.  Or, more importantly, if I really don't believe it is
necessary.  Reducing radon concentrations in my lovely home is unnecessary.
I like living here and can't afford expensive corrective actions.  

These views are prevalent everywhere.  The end result is that the actual
shape of the low dose  effect curve may be relatively unimportant for
regulations at low doses.  It is the same public perception which interferes
with scientifically based decision making.  What this public perception
issue leads to is the suggestion that the shape of the dose response curve
at low dose rates has virtually no 
impact on the public as long as there is even any suggestion that there is
some finite probability of cancer occurring from the transmutation of one
DNA molecule.  Sad as that reality may be.
Just as an example - EPA and the states have been fully aware that the basis
for their tritium drinking water concentration of 20,000 pCi per liter
should, in fact, be over 80,000 pCi per liter. based on a 
committed effective dose of 4 mrem but they are loath to acknowledge any
such change in their regulation.

As an additional example, I have watched with fascination the public contest
between EPA's Browner and NRC's Jackson on acceptable remediation levels.
EPA's position revolves essentially around 15 mrem per year and NRC suggests
25.  Looks like a factor of about 2 doesn't it? However, both accept the
same 5%/Sv fatal cancer risk value.  I would like to suggest there is
virtually no difference between these two agencies position in their
objective of protecting the public health.  EPA sets a limit of 15 mrem, NRC
selects a limit of 25 mrem.  NRC, however, has the ability and the
responsibility to require its licensees to demonstrate that its planned
operations are as low as reasonably achievable.  That is, they must reduce
all potential exposure pathways to values which can be demonstrated to meet
this requirement.  Given the limit of 25 mrem, it would be foolhardy  for a
licensee to plan its operations without at least a "safety" factor of 2 and
for environmental pathway assumptions even higher.  Thus, the NRC licensee
will design his operations so that he will expect certainly no more than 10
mrem or perhaps even less and the EPA limit has been assured.

It seems clear that the only way to get definite answers to the risk of low
dose rate exposure is through molecular biology.  This, of course, assumes
we have the scientific tools to extrapolate this information to human cancer
induction.  For now isn't the assumption of linearity at low dose and dose
rates the only reasonable approach to public health policy?

Perhaps a change can be made in public perception.  The action of
regulators, politicians and journalists have played a large role in
endorsing and encouraging the public concern over very low dose.  Let's work
on this as part of the problem.

James A. Spahn
Senior Staff Scientist,NCRP
email:ncrp@ncrp.com     
Fax:907-8768
Phone:301-657-2652