Re: Radiation hormesis

["Gregg Claycamp" <hgc2+@pitt.edu>]

While physics exercises are fun (and I am guilty as the next of making
simple comparisons for illustration), there should be a little room for
biology in this LNT thread.  The "it's all energy" thread takes Paracelcus'
(1500's?) dictum "it's the dose that makes the poison" to extremes.   (Sorry
Latin fans, but that's the popular mis-translation!) Just as important as
the energy "exposure" to organisms is the nature of the "poison" at the
target cell/tissue/organ and the biological tolerance mechansims in those
target cell/tissue/organs.  Clearly, the mechanism of energy desposition and
the biological mechanisms of tolerance are strikingly different in moving up
the spectrum from heat to sunlight to ionizing radiation.   One shouldn't
ignore the very real biological side to the LNT issue just because the
physical agents share the same dimensions (energy/mass) in their dose
concepts.

Just to keep it short, I' take one example -- the one indicating that 200
hops 0.5 ft does not carry the same risk of death as one hop (fall) from 100
ft. Here the author treats the 200 hops as independent events that don't
have a cumulative effect of a 100-ft hop.  True, but what if each hop were
to the next higher rung on a 100-ft ladder that had only 199 steps? (Watch
out for the last hop!!) By analogy, there is biological plausibility for
cumulative dose-risk relationships, not only for ionizing radiation but for
chemical hazards as well.  For example, lung cancer risk is  from cigarette
smoking is very clearly linear with "pack-years" of exposure rather than
"packs per day."

What the target cell thinks about a the equivalent of a 0.5-ft hop over the
long run is just as important as dealing with energy relationships.  There
is evidence for significant levels of tolerance (reducing cumulative
effectiveness) and there is evidence for cumulative effects that include,
perhaps, a heightened sensitivity to the next hop (increment of dose).  Thus
far mechanistic studies cannot definitely exclude LNT hypotheses.
Politically charged as it might be, there remains a reasonable biological
basis for the health protection POLICY.  The magnitude of the policy slope,
is certainly subject to debate.

I'll resist commenting on the mixing of end points (cancer, erythema, etc.),
which BTW, means that the models,   *biologically* based LNT and threshold
effects, are being mixed.  (it's a fair trade for the "fun with analogies.")

H. Gregg Claycamp, Ph.D., C.H.P.
University of Pittsburgh
hgc2+@pitt.edu


-----Original Message-----
From: tmohaupt@wright.edu <tmohaupt@wright.edu>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Thursday, May 06, 1999 2:07 PM
Subject: Re: Radiation hormesis


>Radsafers,
>
>Glen presents an interesting point of view.  Since ionizing radiation
>is simply a form of energy, it can be readily compared with other
>forms of energy and their effects.  Keep in mind that there is no
>type of energy that is safe in high levels.  Radiation is the only
>one to which a LNT is applied.  The LNT is a political
>position and, most likely, not an accurate description of reality.
>Personally, I'd like to see radiation regulated to prevent real
>damage, much the way we do with other forms of energy, rather than
>treat it like the witchcraft trails of the late 17th century in New
>England.
>
>An example:  Sunlight is known to cause cancer, cataracts, and a host
>of other detrimental effects.  If, out of precaution for the health and
>well being of the general public, a Solar Regulatory
>Commission decided to apply a linear no-threshold model to solar
>radiation risk, we would probaby have to close beaches and other
>outdoor activities to keep exposure limits within acceptable limits.  Even
on a
>cloudy day you would be exposed, and that may be unacceptable, unless
>you have a need to be outside that overrode the risk.  If a lifeguard
>gets melanoma 20 years later, can he/she sue his employer to a
>hazardous working environment?  But wait, sunlight is essential for
>life!  Being exposed 60 times in a day for 1 minute each time is
>beneficial (i.e., promotes Vitamin D), where one exposure of 60
>minutes can result in sunburn, which is a significant risk factor for
>skin cancer.  How does one assure that recurrent exposures to trace
>levels of sunlight do not cause sun cancer?
>What about potential energy (ie altitude)?  If a person falls from
>100 feet, there's a strong liklihood the person would die.  The LNT
>would say that if you hop to a height of 6 inches, one out of
>200 hops you would die.  That's not true.  It's called exercise and
>it is promoted as a salubrious effect.  Once again the LNT doesn't fit
>and shouldn't be applied.
>Name the energy, electricity, UV radiation, heat, impact, wind, etc.,
>Each has levels where truly harmful effects can be observed.  And
>each has lower levels which are either beneficial or inconsequential.
>Ionizing radiation is no different.
>How does this apply to the proposed rules for setting an allowance
>limit for releasing metals for recycling to the public domain?  The
>proposed release values will result in exposures that are fractions
>of background or inconsequential compared to the natural variability
>of background.  We cannot prove radiation is safe in low levels; however
>we do know that low levels are NOT UNSAFE, which is the same
>criteria we apply to all other forms of energy that we commonly
>experience.
>Tom
> >In a message dated 5/4/99 6:04:57 PM EST, 7pe@ornl.gov writes:
> >
>><< Why should the public take on any additional risk, no matter how
trivial in
> > some people's opinion, to assist the nuclear/defense industry in getting
> > rid of their contaminated scrap?  The only measurable cost benefit is to
> > industry, none to the public (unless there IS a hormetic effect). >>
> >
> >Even IF there is a demonstrable hormetic effect, how does one assure that
the
> >"beneficial" dose from contaminated scrap metal plus nuclear power plants
> >plus fossil-fuel power plants plus radwaste disposal facilities plus
> >household radon plus doctors' offices plus dentists' offices plus
high-flying
> >airliners plus...plus...plus...is still "beneficial"?
> >
> >An exposure which ALONE might have a beneficial effect, might have a
> >detrimental effect when combined with all other exposures.  Unless the
> >proponents of radiation hormesis can assure that their proposed
contribution
> >to the recipient's total exposure still has a cumulative hormetic effect,
> >hormesis should remain an interesting, but practically useless phenomena.
> >
> >Glenn
> >GACarlson@aol.com
>Tom Mohaupt, MS, CHP
>Wright State University
>Radiation Safety Officer
>
>
>

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