Re: Absence of Evidence II -Reply

[Charles Willis <CAW@nrc.gov>]

Fritz,

I cannot quarrel with the thrust of your argument, but I have a problem with your
ready acceptance of "zero dose equals zero effect."  This sort of relationship seems
almost self-evident in physics but not in biology.  For example, in physics, "zero
force equals zero acceleration,"  "zero mass means zero gravitational attraction,"
etc.  In biology, however, the situation generally is more complex; the effect
depends on the amount (dose) and too small a dose can be as bad as too larger a
dose.  For example, consider stable iodine: if the dose is about right, the thyroid
functions properly, if the dose is too large nodular goiter develops and, if the dose
is too small, colloidal goiter is the result.  That is for "normal" people; some
people are allergic to iodine and for such people a slightly too large dose can be
lethal in short order.  In pharmacodynamics, the general expectation is expressed
by the Arndt-Schulz Law: "small doses exercise a stimulating, medium doses a
depressing, and large doses a destructive effect."  

With radiation, of course, zero dose is unattainable so we can only guess what
would be its effect.  In the laboratory, deleterious effects have been demonstrated
from below normal radiation doses.  Beneficial effects of above normal radiation
doses are seen in humans.  Face it.  Biology is complex.

Charlie Willis
caw@nrc.gov

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html