Re: Radiation hormesis, thresholds, etc

[Bernard L Cohen <blc+@pitt.edu>]

On Fri, 3 Sep 1999 Christoph_Hofmeyr/CNS1@cns.co.za wrote:

> 1.  It might be useful to point out that from an RP perspective the LNT is
> extremely convenient, allowing concepts like collective dose to be used
> 'constructively'.  The concept of a threshold would require a very
> significant adaptation in thinking and doing.  Collective dose
> (man-Sieverts) would become meaningless as an expression of risk, except
> where individual doses are well in excess of the threshold.  Then, to a
> dose accrued over what period would the threshold apply?  When are the
> counters reset?  Does it apply to acute or chronic exposures?  If it is a
> lifetime phenomenon, and incremental dose is deleterious once you have
> passed the optimum?  These questions would have to be addressed
> satisfactorily before a new RP strategy can be developed.  Health Physics
> might well change to Health Math.

	--My response to this, submitted for publication in Health Physics
Newsletter, is as follows:

	IS LINEAR-NO THRESHOLD THEORY JUSTIFIABLE FOR REGULATORY PURPOSES

	Bernard L. Cohen
	University of Pittsburgh

	A former ICRP Chairman supports the linear-no threshold theory
(LNT) because it simplifies bookkeeping. LNT is certainly convenient for
making health physics calculations. It allows us to calculate the risk
from any given radiation exposure in quantitative terms, which is the goal
of any risk analysis. Without LNT, the risk to a person from a given dose
depends on the concentration of radon in his home, his experiences with
medical X-rays, etc; effectively, there is a synergism between a given
exposure and all other radiation exposures. Since most of the latter are
unregulated, it is impractical to take them into account. If we abandon
LNT, we largely abandon quantitative risk assessment, which might seem to
make regulation more difficult.
	But is this really a very serious problem?  It is a problem that
occurs in nearly every other area of environmental concern. For example,
LNT is not used for air pollution. There are regulations on releases and
on ambient levels of SO2, of NOx, of total suspended particulates, of fine
particulates, of ozone, of lead, etc. For none of these can the risk of
each additional exposure be calculated quantitatively., even if no other
pollutants are present.  No consideration is given to synergisms between
these various pollutants, although such synergisms are quite likely to be
important.  By the standards we apply to radiation, the scientific bases
for air pollution regulations are mediocre at best.
	But they work quite successfully. They prevent catastrophes and
generally avoid identifiable deaths. Most importantly, they give the
public confidence that it is being protected. This confidence is not even
shaken by studies concluding that tens of thousands of Americans die
annually from air pollution1. The Media give scant attention to these
studies, and the public shows little interest as long as no victims are
identifiably tied to the pollution..
	Is this situation reprehensible? I think not. It allows our
technology to progress and to increase SocietyUs wealth, and technology
and wealth create health, far outstripping the harm to health done by the
pollution. Air pollution reduces our life expectancy by something like 30
days2, whereas technology and the wealth it has created have increased our
life expectancy by 30 years in this century.
	We thought we could do much better with radiation, using LNT to
calculate risks in quantitative terms. For every little bit of radiation,
we calculate the number of deaths, and killing is something the Media are
quick to report. People are moved by such reports and view these deaths as
real, perhaps even afflicting themselves or their loved ones. The public
has thus  been driven insane over fear of radiation, losing all contact
with reality. As a result, we have largely lost the benefits of nuclear
power which could be averting tens of thousands of deaths per year from
air pollution (and also solving other environmental problems like global
warming, acid rain, etc). We are losing many other benefits of radiation
such as food irradiation which could be averting millions of cases of food
poisoning, saving thousands of lives, each year. We are wasting our
SocietyUs wealth on ridiculous clean-up programs at nuclear facilities;
this wasted wealth could save thousands of lives each year if it were
spent on biomedical research, on public health programs, or on highway
safety.
	Our passion for doing much better for radiation than has been done
for air pollution by using LNT has backfired horribly, costing our Society
dearly. Perhaps it could be argued that we must be honest and scientific
at all costs. But is accepting LNT honest science? I have reviewed this
question in detail in a recent paper3 and concluded that it is not. The
Health Physics Society Position Paper of January 1996 concludes that the
science does not exist for supporting LNT in the low dose region. The
situation is the same as for low levels of air pollution -- the science
just isn't there. The best they can do is regulate by assuming a threshold
for harm, and that is the best we can do for regulating radiation. Far
from making regulation of radiation more complicated as is often assumed,
this would greatly simplify our regulatory process
	Thus, there is no honest scientific reason why radiation should be
treated differently than air pollution in the low dose region  We should
abandon this phony effort to be more scientific in our regulatory
practices. That way we would be more honest, and we would have a much more
positive impact on the Society we serve.

REFERENCES
1. H. Ozkaynak and J.C. Spengler, Analysis of health effects resulting
from population exposure to acid precipitation,   Environmental Health
Perspectives 63:45ff; 1985

2. B.L. Cohen, Catalog of risks extended and updated, Health Physics
61:317-335; 1991

3. B.L. Cohen, Validity of the linear-no threshold theory of radiation
carcinogenesis in the low dose region, Technology 6:43-61; 1999


Bernard L. Cohen
Physics Dept.
University of Pittsburgh
Pittsburgh, PA 15260
Tel: (412)624-9245
Fax: (412)624-9163
e-mail: blc+@pitt.edu


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