Re: Low doses (was Re: HPS objectives)

["David W. Lee" <lee_david_w@lanl.gov>]

At 05:14 PM 08-08-97 -0500, you wrote:
>David Lee wrote, in part:
>
>>Thus a question back to David Scherer:  How low-level must the exposure
>>rate or dose be before you declare an "unnecessary" exposure to be so
>>trivial as to not concern yourself with it anymore?
>
>Just because I pose the question, do I have to have an answer? :^)
>
>The whole point of my posts is that there is no unique answer to this
>question.  The question asks about values, not science.  My scientific
>training has not equipped me to address this question.  How has society
>assigned responsibility in the past when the risks were uncertain?  Even
>more important, what is the rationale for assigning this responsibility?
>This may be heretical, but I don't believe HPs have any greater standing
>than other members of the public in addressing these questions.
>
>Dave suggests a multiple of background, claiming there is no health defect
>from background.  I would ask how he knows there is no health defect.  We
>can say that no health consequence have been detected given our statistical
>tools.  That's what the LNT debate is about.  Are you saying you have
>conclusive evidence of a threshold at a certain dose?  I personally would
>be very happy to learn that there is an absolute threshold at some given
>dose, but I believe a defensible number for that value is not available at
>present.
>
>You pick a value of 2 or 3 times background.  Why is this better than 1/3
>background (NRC limit for the public)?  You pick this by some tradeoff in
>your mind.  That's what we should discuss: not the numerical limit, but the
>reasoning behind this limit or that.  Don't get me wrong.  I personally do
>not advocate chasing every last millirem.  (For example, we don't give
>whole body badges to people performing bench top chemistry.)  It is pretty
>clear to me when doses are trivial (mrem) and when they are not (rem).  It
>is ground in between that I find difficult.  If people talk about the basis
>for a limit, especially the tradeoff in values that is involved, maybe
>we'll get a littler closer to agreement.
>
>Since you mention background, I would like to respond to a comment I have
>heard in several forms.  We require employers to measure and control
>exposures from their operations even if it is less than or comparable to
>background.  Sometimes people say that this is because we view background
>as "good" radiation while occupational exposure is "bad."  I would suggest
>that the reason we treat them differently turns on responsibility.  The
>employer is responsible for the workplace, not for Mother Nature.  No
>matter what exposures nature gives, the employer is still responsible for
>his addition.  Radiation standards are not graded on a curve.
>
>I will be out of the office for a week (loud cheers from radsafe land) but
>I'll be interested to read your comments when I get back.
>
>Dave Scherer
>scherer@uiuc.edu
>
>

	I thank Ron Kathern for catching my typographical error.  As he correctly
states, I certainly meant "600-900 millrem (mrem), not "rem."

	In response to David Scherer's excellent commentary, I certainly
acknowledge that just because he poses the question, does not mean that he
has to have the answer.  The issue of formulating a de minimus level or
some other figure related to the natural radiation background dose level is
controversial and has thus far not been amenable to any one "right" answer.
 I think that efforts in this regard should continue, as Ron recommends,
and as discussed below.

	I appreciate Ron recalling Robley Evans' guidance--would you let your
unborn child, children, grandchildren be exposed to such levels, etc.
Regarding the 2 to 3 times the mean natural radiation background proposal,
I think the answer is "yes."  After all, we routinely work, play,
procreate, etc., all the while sustaining approximately 300 mrem/yr from
the natural background, and this "mean" background level varies across the
world by easily a factor of 2 to 3.  Thus, some people in this world, to
include unborn children, are exposed to 600--900 mrem/yr anyway, just from
background.

	David Scherer asks if I have any "conclusive" evidence of a threshold at a
certain level and if I claim there is no health "defect" from natural
radiation background dose/dose levels.  It would appear that David would
not accept any evidence, such as epidemiological studies, as being
"conclusive" so long as such studies used statistics to make inferences,
something short of direct measurements of some type.  If my understanding
of David's use of the word "conclusive" is correct, then in his
"conclusive" sense, I have no such "conclusive" evidence of a threshold.  I
would suggest, however, that the dose/dose rate of the natural radiation
background, operationally, is as close to a "threshold" as most of us could
want in that it is a level, public health-wise, at which no "ill health"
effects have ever been found.

	I do not know precisely what David means by the word "defect"; I do claim
as have others, however, that there is no evidence of any "ill health"
produced by the "mean" annual natural radiation background dose/dose rate;
that certain segments of the world population are exposed annually to
multiples of the "mean" background dose also with no discernible "ill
health" effects.  Thus, I would suggest that the "mean" natural radiation
background and even small multiples thereof constitute ionizing radiation
dose and dose rates to which living things have had to come to terms with,
evolution wise, e.g., developing a cellular radiation damage repair
mechanism.  One may refer to Eisenbud & Gesell, 4th Ed., Environmental
Radioactivity wherein the authors speak of epidemiological studies done in
India and China on large numbers of people exposed to multiples of the
"mean" natural radiation background, with no discernible "ill health."
Perhaps what David means by health "defect" may be what Ron alluded to in
an earlier response, e.g., that some chromosomal changes have been observed
in people exposed to substantially higher than the "mean" natural radiation
background.  But as Ron also stated, there is no clear link between such
microscopic chromosomal activity and overall, macroscopic "ill health."

	David Scherer stated that I picked a value of 2 to 3 times background.
"Why is this better than 1/3 background (NRC limit for the public (100
mrem/yr))"?  I suggested this multiple of the natural radiation background
for the above reasons of no discernible ill health effects and precisely
because it was a "multiple" of the background level, not a mere FRACTION of
it as is the NRC's value.

	The NRC's public dose limit value has become a "de facto" operational
standard to which radiation safety programs must benchmark much of their
radiation safety measures.  For example, in the DOE world, we must under
federal law (10 CFR 835) provide individual external and internal dosimetry
to a worker if they are likely to receive in excess of 100 mrem (external)
or 100 mrem CEDE (internal) per year.  This means for example in the case
of internal nuclides that we must be able to detect 100 mrem CEDE of Pu,
which basically is atom amounts of Pu due to the long effective half-life
(Class Y).  Thus, this 100 mrem/yr public dose standard has now become a
detection limit which must be attained.  Our "old" alpha spectrometry urine
Pu analysis system could detect only down to approximately 9000 mrem CEDE @
180 days post-intake.  The 100 mrem/yr standard drove the development of a
much more expensive, manpower-intensive, but more sensitive technique of
thermal ionization mass spectrometry (TIMS) which has a detection limit of
approximately 260 mrem @ 180 days.  But this technique still is not as
sensitive as the University of Utah/Brookhaven fission track technique with
a detection limit of approximately 30 mrem @ 180 days.  The point is that
this "public" protection limit operationally is also a major de facto
detection limit in the radiation safety program simply as a result of it
being specified as any kind of "public" limit at all by the NRC/DOE.  The
above described, rather Promethean efforts to develop more sensitive
bioassay techniques for Pu would not have been necessary has the "public"
protection limit been of a more realistic, reasonable value, e.g., some
multiple of the natural background dose.  The problem with this limit is
that it apparently ignores the natural background dose that every member of
the public unavoidably sustains; that the mean background dose is 300%
higher than this "public" limit; and that as a result, radiation safety
programs must chase after 100 mrem amounts of radioactivity that impart
doses well below the level that the same members of the public already
sustain for which no radiation safety effort is undertaken.

	David Scherer states that the reason we HPs treat the dose from natural
background differently compared to similar doses in the workplace turns on
"responsibility"; no matter what mother nature gives, the employer is still
responsible for his addition.  This seems to me to be a polemic which
attempts to rationalize why we ignore 300 mrem/yr from natural background
on the one hand, yet avidly chase after the same dose/dose rate in the
workplace.  Surely the radiobiologists in RADSAFE land will be willing to
confirm that from the standpoint of the cell, a dose is a dose no matter
where it comes from.  To ignore the dose from natural background, and even
resist accepting it as a "natural" threshold for which no ill health has
ever been found, and yet choose to play Don Quixote over the same dose in
the workplace seems to me to be philosophically hypocritical.

	In summary, since we don't hang dosimeters on ourselves and monitor our
natural background dose and apply ALARA to it, why do we persist in
monitoring occupational doses that approximate the background dose that we
all unavoidably sustain?  Background dose or occupational dose is still
dose; we don't get bent out of shape about 300 mrem/yr from background;
what sense does it make to chase after doses even less than 300 mrem/yr in
the occupational setting?  What sense does it make to have any sort of
"public" dose limit that is substantially less than what the same public
already unavoidably sustains from background, itself?

	I'm not cheering that David Scherer is out of his office for a week; I
look forward to his return and to his reply.

	As a point of further discussion, I think it might be interesting to
discuss the WHY of why do we in the ionizing radiation safety field NEED to
have a separate dose limit for the public at all?  In contrast, the
non-ionizing field has for years had only single standards to limit
occupational exposure to non-ionizing radiation.  If you show up to the
door of a "non-ionizing" radiation use facility, you are simply "informed"
that such sources exist inside the facility.  Having been "informed," your
exposure limits are then exactly the same as for the "occupationally
exposed" workers working therein--no difference, case closed.

Best regards  David

 

	 

	 


David W. Lee
Los Alamos National Laboratory
Radiation Protection Services Group (ESH-12)
PO Box 1663, MS K483
Los Alamos, NM  87545
PH:   (505) 667-8085
FAX:  (505) 667-9726
lee_david_w@lanl.gov