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The Free-Radical Fallacy about Ionizing Radiation:
Demonstration That a Popular Claim Is Senseless
By John W. Gofman, M.D., Ph.D., September 1997
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* Part 1 -- The Free-Radical Fallacy: "Just Living"
Hurts DNA Much More than Ionizing Radiation
* Part 2 -- The Relative Frequency of DNA Damage-Events
* Part 3 -- Reality-Check for the "Same-Nature" Assumption
* Part 4 -- The Unique Power of Ionizing Radiation
[Polly wants to express a divergent view to tonight's channel 5 editorial]
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Part 1 * The Free-Radical Fallacy: "Just Living"
Hurts DNA Much More than Ionizing Radiation
1a * In some peer-review journals and various interviews
in the media, what we call the Free-Radical[1] Fallacy has been
employed in an effort to deny the menace of low-dose ionizing
radiation. Here, we will demonstrate why it is a fallacy.
1b * There is no doubt that routine metabolic chemistry
in each cell produces legions of free-radicals every hour, in the
process of "just living." And there is no doubt that exposure to
ionizing radiation produces some EXTRA free-radicals in irradiated
cells. And so radiation scientists such as Dr. Daniel Billen
(1990) have tried to argue that low-doses of ionizing radiation
must be inconsequential BECAUSE they add so few free-radicals to a
cell, by comparison with the number of free-radicals naturally in
each cell anyway.
1c * The hidden (and false) assumptions in such
reasoning are (1) that the nature of damage done by ionizing
radiation is the same as the nature of damage done by routine
metabolic free-radicals, and (2) that damage therefore can be
compared by comparing the relative numbers of free-radicals. The
erroneous "same-nature" assumption is at the heart of the
Free-Radical Refrain, and has been disseminated by statements like
"We are irradiating ourselves by living" (Dr. Bruce Ames 1994,
p.18; Ames 1995, p.5259).
1d * Using numbers from Dr. Billen's own presentation,
plus a reality-check with actual observations, we can demonstrate
that the nature of damage from ionizing radiation CANNOT POSSIBLY
BE THE SAME AS the nature of the damage from routine metabolic
free-radicals. We have not seen this demonstration elsewhere, but
perhaps someone else has put it forth, too. We use nothing but
simple multiplication and division (Part 3).
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Part 2 * The Relative Frequency of DNA Damage-Events
2a * Billen (1990, p.242) cites various mainstream
sources for two estimates in his free-radical argument: (1)
"Approximately 10,000 measurable DNA modification events occur per
hour in each mammalian cell due to intrinsic causes," and (2)
"About 100 (or fewer) measurable DNA alterations occur per
centi-Gray of low-LET radiation per mammalian cell." These two
values are made comparable in Part 2d, below.
2b * The goodness of both estimates, above, will surely
improve a great deal with future methods of measurement, but
neither Billen's argument nor its refutation depends on precision
in these two values. Billen's reference to "low-LET" radiation
includes x-ray, beta, and gamma radiations.
2c * Billen states his conclusion (p.242): "Therefore,
every HOUR, human and other mammalian cells undergo at least
50-100 times as much spontaneous or natural DNA damage as would
result from exposure to 1 centi-Gray of ionizing radiation."
Centi-Gray and "rad" are two names for the same amount of
radiation exposure. How much is one rad of exposure?
2d * On the average, it takes about 10 years for a
person to accumulate one rad of whole-body exposure from natural
background radiation. So Billen's numbers mean that the ratio of
damage-events PER UNIT OF TIME (per hour, or per day, or per year)
may be as large as 8.8 million endogenous damage-events for each
damage-event due to natural background radiation. A very large
difference ... but is it meaningful?
2e * The estimates presented by Billen of "DNA
modifications" and "DNA alterations" are estimated numbers PRIOR
to repair-work by the cell. Here (and elsewhere in the
literature), the term "damage-events" is preferred, to signal that
the event is not necessarily an unrepairable PERMANENT mutation of
the DNA.
2f * Billen's arithmetic is correct, but a reality-check
is needed for his assumption that the nature of DNA damage-events
is the same from routine cellular metabolism and from ionizing
radiation.
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Part 3 * Reality-Check for the "Same-Nature" Assumption
3a * According to Billen, a rad (centi-Gray) causes
about 100 or fewer measurable DNA damage-events per cell.
3b * According to Billen, the number of comparable
damage-events from intrinsic causes per cell, every HOUR, is 50 to
100 times higher, which means 5,000 to 10,000 damage-events every
hour from intrinsic causes, per cell. (Bruce Ames 1995, p.5259,
provides an estimate per DAY, not per hour: "The number of
oxidative hits to DNA per cell per day is estimated to be about
100,000 in the rat and roughly ten times fewer in the human." We
will include this estimate in Point 3e.)
3c * It follows from Billen that per DAY, the DNA
damage-events per cell from endogenous causes are either:
( 5,000 events/hr) x (24 hr/day) = 120,000 events/day, or:
(10,000 events/hr) x (24 hr/day) = 240,000 events/day ...
in each cell.
3d * And something else follows from Billen's assumption
that there is no important difference between the endogenous and
the radiation-induced damage-events. If correct, then the
DNA-based consequences from a radiation dose which delivers
120,000 or 240,000 damage-events each day, per cell, should be the
same as from 120,000 or 240,000 such events per cell each day,
from endogenous sources.
3e * The whole-body radiation dose per day required (by
Billen's numbers) to deliver 120,000 to 240,000 such DNA
damage-events per cell, each day, would be either:
(120,000 events) x (1 rad/100 events) = 1,200 rads, or:
(240,000 events) x (1 rad/100 events) = 2,400 rads. And:
If we substitute Ames' figure (from Point 3b), we would calculate
(10,000 events) x (1 rad/100 events) = 100 whole-body rads per day
to deliver DNA damage equivalent to daily damage from intrinsic
causes.
Bottom Line of the Reality-Check
3f * If there were equivalance between DNA damage by
free radicals from normal, intrinsic processes and DNA damage from
ionizing radiation, then whole-body doses of 100 rads to 2,400
rads per day EVERY day would be easily tolerated. Instead, such
doses are promptly lethal.
3g * For half the humans exposed, promptly-lethal doses
are estimated by the radiation community at 300 whole-body
internal-organ rads accumulated in one week or less (or 420 such
rads within a month).
3h * There is an additional observation worth noting.
The background rate of cancer (a disease widely acknowledged to be
DNA-related) is doubled by extra radiation doses of a few hundred
whole-body rads, or fewer, of accumulated exposure. According to
Billen (Point 3a), 300 rads cause about 30,000 or fewer DNA
damage-events per cell --- a number far exceeded in a single day
by intrinsic processes (Point 3b). If DNA damage from intrinsic
causes and from low-LET ionizing radiation were equivalent, it is
hard to see how anyone could escape having MULTIPLE clinical
cancers from intrinsic processes.
3i * From these two reality-based observations (acute
lethal doses and doubling-doses for radiation-induced cancer), we
have demonstrated that the nature of damage caused by ionizing
radiation CANNOT POSSIBLY BE THE SAME as it is from normal
metabolic processes and oxidative damage. Without an equivalence,
the Billen argument and its variations collapse. The Free-Radical
Refrain is just a Free-Radical Fallacy.
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Part 4 * The Unique Power of Ionizing Radiation
4a * The difference between free-radical damage from
routine metabolism and from ionizing radiation almost surely lies
in REPAIRABILITY. If DNA damage is perfectly repaired by a cell,
such damage has no health consequences. It is inconsequential. The
consequences arise only from injuries which are non-repairable or
mis-repaired.
4b * The demonstration in Part 3 supports other evidence
(and vice versa) that ionizing radiation can induce the special
kinds of complex DNA damage which CANNOT BE PERFECTLY REPAIRED. A
leading figure in this research is John F. Ward; see Reference
List.
4c * The power of ionizing radiation to induce the
complex injuries is not in dispute. Billen himself appears to
acknowledge it, but then to ignore it (Billen 1991, p.388).
4d * The power of ionizing radiation to induce
particularly complex and unrepairable genetic injuries is surely
related to a UNIQUE PROPERTY of this agent. Ionizing radiation
instantly unloads biologically abnormal amounts of energy at
random in an irradiated cell. Biochemical reactions in a cell
generally involve net energy-transfers in the ballpark of 10
electron-volts and below. By contrast, Ward reports (1988, p.103)
that the average energy-deposit from low-LET ionizing radiation is
thought to be about 60 electron-volts, all within an area having a
diameter of only 4 nanometers. (The diameter of the DNA
double-helix is 2 nanometers). In other words, ionizing radiation
produces violent energy-transfers of a type simply absent in a
cell's natural biochemistry.
4e * Because of its unique property, ionizing radiation
is a unique menace to our DNA and chromosomes. This fact needs
wide recognition, as mankind learns that FAR more health problems
are mutation-based than anyone could prove 15 years ago.
# # # # #
References:
* Ames 1994 (Bruce N.), interviewed by Russell Schoch in California
Monthly (Univ. of California, Berkeley), June 1994, at page 18.
* Ames 1995 (Bruce N.), "The Causes and Prevention of Cancer,"
Proceedings Natl Acad Sci USA Vol.92: 5258-5265.
* Billen 1990 (Daniel), (commentary) "Spontaneous DNA Damage and Its
Significance for the `Negligible Dose' Controversy in Radiation
Protection," Radiation Research Vol.124: 242-245.
* Billen 1991 (Daniel), (letter) "Response to Comments of K.F. Baverstock
and J.F. Ward," Radiation Research Vol.126: 388-389.
* Ward 1985 (John F.), "Mammalian Cells Are Not Killed by DNA
Single-Strand Breaks Caused by Hydroxyl Radicals from Hydrogen
Peroxide," Radiation Research Vol.103: 383-392.
* Ward 1988 (John F.), "DNA Damage Produced by Ionizing Radiation in
Mammalian Cells: Identities, Mechanisms of Formation, and
Reparability," Progress in Nucleic Acid Research & Molecular Biology
Vol.35: 95-125.
* Ward 1990 (John F.), "The Yield of DNA Double-Strand Breaks Produced
Intracellularly by Ionizing Radiation: A Review," International Journal
of Radiation Biology Vol.57: 1141-1150.
* Ward 1991 (John F.), (letter) "Response to Commentary by D. Billen,"
Radiation Research Vol.126: 385-387.
For more details on the unique action of ionizing radiation,
and on the repair-issue, see:
* Gofman 1990, Radiation-Induced Cancer from Low-Dose Exposure. 480
pages. Chapter 19 "The Special Interaction of Ionizing Radiation with
Living Tissue," and Chapter 20 "Various Radiation Sources: Primary
Electron-Tracks per Nucleus per Rad." Book available from CNR ($29.95),
and online at .
* Gofman 1995, "What Is Factually Wrong with This Belief: `Harm from
Low-Dose Radiation Is Just Hypothetical --- Not Proven'." 4 pages.
Available from CNR and online at
.
* Gofman 1996, Preventing Breast Cancer. 422 pages. Chapter 45 "Three
Remarkably Similar Reports on the Safe-Dose Fallacy." Book available
from CNR ($17), and online at .
* Gofman 1996, "Answers to Frequently-Asked-Questions about `Radiation'."
4 pages. Available from CNR and online at
.
1. Free-radicals are highly reactive molecules possessing an unpaired
electron. In our cells, such radicals can do injury (for instance,
oxidative damage) to proteins and other molecules --- including the DNA
molecules which encode the human genes.
# # # # #
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