What Is Factually Wrong with This Belief: "Harm from
Low-Dose Radiation Is Just Hypothetical — Not Proven"
By John W. Gofman, M.D., Ph.D.
- Part 1 — An "Open Letter" to Editors
of Major Journals and Newspapers, to Science Reporters and Physicians
- Part 2 — Some Introductory Information
- Part 3 — Where's the Controversy,
in View of Such Evidence?
- Part 4 — How Ionizing Radiation "Works"
- Part 5 — Human Studies Showing
Radiation-Induced Cancer from Minimal Doses
- Part 6 — A Five-Point Summary
The Author: John
W. Gofman, M.D., Ph.D, is Professor
Emeritus of Molecular and Cell Biology at the University
of California (Berkeley), former Associate Director of
the Livermore National Laboratory, and author of four
scholarly books on radiation health effects.
Part 1. An "Open Letter" to Editors of Major Journals
and Newspapers, to Science Reporters and Physicians
in identifying the causes of cancer and inherited
afflictions receive much attention in your publications and
broadcasts --- because you and your customers care very much
about preventing these miseries.
do not want mistakes slipping through your various
filters against misinformation. The mistake we address here is
the claim that harm from ionizing radiation, a proven carcinogen
and mutagen, is "only hypothetical" at low dose-levels. This
misinformation is routinely treated as credible and is disseminated
widely; recent conduits include the Journal of the Amer.
Medical Association (Skolnick 1995,
p.367, p.368), the Lancet (Hulka 1995,
p.885), the Wall Street Journal (Chase 1995,
p.B-1), Nuclear News (Sept.1995, p.26) --- and even a current
syllabus for residents in radiology (Goldberg 1995,
purpose of this communication is to show you, in
abbreviated fashion, the factual basis for rejecting the claim that
no harm has yet been proven from low-dose radiation --- and
for rejecting suggestions that your duty is to fight
"radio-phobia" over a carcinogen which "requires" high doses.
stakes are worth some of your time. How so?
Because ionizing radiation is not an exotic carcinogen and
mutagen which exposes a small segment of the population.
Low-dose ionizing radiation is received from natural
background sources, numerous medical procedures, nuclear
pollution, flying, and sometimes from occupational exposures.
How many other proven human carcinogens can you name to
which everyone is exposed on a daily and lifelong basis?
evidence that there is no safe dose-level of ionizing
radiation (no threshold dose) means that journals and other
media contribute to cancer (and inherited afflictions)
whenever they include disproven claims which encourage a
casual attitude toward extra exposures to low-dose ionizing
radiation. We believe that you want to help prevent such
Part 2. Some Introductory Information
in this communication are supported in detail, and with very
specific sourcing, in
21, 32, 33).
require the presence of damaged genetic
molecules in the single cells which turn malignant. Likewise,
inherited afflictions require the presence of damaged genetic
molecules in the single cell from which a baby develops. The
genetic molecules in a human cell-nucleus are the 46 human
chromosomes, each consisting of one double-strand DNA helix
plus associated proteins.
damage occurs to a genetic molecule, the cell
attempts to repair it. If the cell achieves perfect repair, the
genetic molecule regains its "mint quality" --- as if no damage
had ever occurred.
menace to health involves the genetic damage
which is unrepaired, unrepairable, or misrepaired. The
the damage is complex --- for example, when
the opposite strands of the double helix have been broken ---
pieces of the DNA double-helix sometimes end up in the wrong
place, or become permanently lost. These failures of repair are
not in dispute.
contrast, the cell is exquisitely efficient at repairing
injury to single strands of the double helix. It has been
estimated that, every day, each cell copes with at least 10,000
DNA injuries induced by routine chemical sources (including
free radicals produced by the cell itself). Such standard repairs
might be compared to replacing a lamp's broken light bulb with
a new bulb. After "repair," the lamp works perfectly again.
radiation has demonstrated beyond any doubt
its ability to break both strands of the DNA double helix at the
same time. This ability has made it "famous" among toxic
agents as a chromosome-breaker. (If only one DNA strand
breaks, the other strand holds the chromosome together.)
experiments have been done on cells to
measure the speed with which they repair radiation-induced
DNA damage, both single-strand and double-strand injuries.
Even after extremely high radiation doses, that repair which
does occur is complete within about 8 hours, and most of it is
complete within about 2 hours.
"extremely high radiation dose" can be understood
by comparison with the annual dose which everyone receives
from natural sources. Excluding radon, the natural dose per
year is about 0.1 rad. Therefore a common experimental dose to
cells of 100 rads, delivered in an instant ("acute" dose-delivery),
is about 1,000 times higher than the total annual natural
dose. And yet experiments show that human cells mobilize
enough repair capacity (repair enzymes) to cope with 100 rads
all at once. Indeed, repair capacity seems not overwhelmed
even at doses of 500 rads and more.
explanation for residual, post-repair damage is not
a lack of repair-capacity or time, but rather an inherent inability
of the repair-system to fix certain complex injuries to genetic
radiation-induced chromosome abnormality does not
always kill the cell in which it persists, nor does it always
prevent the cell from dividing. When the injured cell divides,
the same injury is replicated in the new cells. In the A-bomb
survivors, extra chromosome abnormalities have been observed
even 40 years after the bombings. Their radiation-causation is
indicated by the positive dose-response: The higher the
bomb-dose, the higher the frequency of abnormalities
unrepaired and misrepaired chromosome
damage in human blood samples, irradiated in lab dishes (in
vitro), is visually detectable at acute radiation doses as low as
2 rads, despite crude methods of observation
Moreover, the residual genetic damage which can not be
detected with such methods may swamp the amount detected.
residual damage also exist, after repair-time, if
low doses are received slowly by living humans (in vivo)?
Yes. For example, extra chromosome damage has been
observed among Alaskan natives from nuclear fallout, in spite of
very gradual accumulation of about 0.08 rad of extra exposure
per year for 10 years (AEC 1970);
extra chromosome damage has been observed among nuclear dockyard
workers exposed very slowly to less than 5 rads per year
(Evans 1979); extra
chromosome damage has been observed among various
populations living where the chronic natural dose from radiation
is above average (for example, see Barcinski 1975;
1976). [One rad is also called 0.01 Gray.]
Part 3. Where's the Controversy, in View of Such Evidence?
residual genetic damage has been observed even
from low radiation doses at slow dose-rates (para. L, above),
how can anyone still claim that evidence of harm at low doses is
"just hypothetical," or that harm requires high doses?
how. If challenged, they say: (1) Since a
connection is just hypothetical between real-world health effects
and misrepaired or unrepaired genetic injury from radiation,
the evidence of harm to health from low-dose radiation is
just hypothetical; and (2) Since there are radiation doses
lower than occupational doses, and lower than fallout
doses, and lower than any doses we can ever afford to study,
the harm at these lower doses will always remain unproven.
They suggest that maybe, at some extremely low dose or
dose-rate, "repair" becomes perfect.
recognized a method which could cope with both
difficulties. Beginning with Gofman 1971
(pp.275-277), it evolved in Gofman 1981
(pp.405-411), and Gofman 1986 (pp.6-14). In
we developed the method and the evidence in detail. Full presentation
70 pages --- not suitable for a journal. We wanted to know if the
threshold issue, for ionizing radiation, could be settled. Our
analysis proves, by any reasonable standard of scientific proof, that
there is no safe dose or dose-rate of ionizing radiation.
have found no refutation of our proof. On the
contrary, our method is extensively confirmed in the 1993 report
of the United Nations (UNSCEAR 1993, esp. pp.627-636,
p.681, p.696 Table 17).
readers to understand how our method overcomes
the obstacles described above (para. n), you need to know how
ionizing radiation "works." It works very differently from toxic
chemicals (para. cc, below).
Part 4. How Ionizing Radiation "Works"
radiation includes beta particles, alpha
particles, gamma rays, and x-rays; the term excludes radio,
microwave, infra-red, and visible radiations.
particles are electrons --- but they differ from
the ordinary non-beta electrons in the human body in one
important way. Beta particles are endowed with biologically
unnatural energy. This energy causes them to travel through the
cell (and beyond) at high speed, like tiny bullets.
radioactive atoms (called radio-nuclides,
radio-isotopes) decay into stable atoms by spitting out beta
particles --- or alpha particles, which are much larger.
Radio-nuclides often emit gamma rays too, in the process of
decaying into stable nuclides.
rays are photons --- a sort of light having too
much energy for humans to see. X-rays are like gamma rays,
except x-rays have less energy per photon. Both are generated
by "nature" and by man-made generators.
photons of x-rays and gamma rays do their damage
to cells by knocking electrons out of ordinary molecules and
causing them to become beta particles --- which travel
through the cell (and beyond) with biologically unnatural energy.
There are about 600 million typical cells in 1 cubic centimeter.
biological damage caused by ionizing radiation,
including gamma rays and x-rays, is due to high-speed
particles traveling through cells and unloading concentrated
amounts of energy in unnatural places at random. Each particle
creates a very narrow path of disturbance (called a primary
"ionization track") as it unloads energy at irregular intervals.
Alpha particles don't travel far; they unload their energy within
just a few cells. Since virtually no one claims any threshold
dose (safe dose) for alpha irradiation, our work involves
high-speed electrons (para. s + v, above).
amount of energy transferred in an instant, from
the high-speed electron to nearby molecules, is often many times
larger than the single energy-transfers which occur "anyway" in
normal cell chemistry and metabolism. This unique feature of
ionizing radiation probably explains why ionizing radiation is so
"good" at breaking chromosomes and inflicting other complex
injuries on the genetic molecules. Every track --- acting
without help from any other track --- has a chance of causing
an unrepairable carcinogenic injury in a cell.
high radiation doses, many tracks from
high-speed electrons pass through every cell-nucleus. We
focus on the nucleus because that is where the human's
genetic molecules are located. How many tracks? At 100
rads from medical x-rays, about 130 primary tracks cross every
1990; based on 30 KeV x-rays
on the average, from 90 kV peak). At 100 rads from gamma
rays, about 300 tracks cross every cell-nucleus (Gofman
1990; based on ~630 KeV gamma rays from radium-226 or
decay of cesium-137 into stable barium-137).
happens at low doses? When the total dose is about 0.75 rad
(750 milli-rads) from medical x-rays, the average number of tracks
per cell-nucleus is one track
20-M). At total doses of about 0.33 rad (330 milli-rads) from
radium-226 or cesium-137, the average number of tracks per
cell-nucleus is one track. At a total annual dose of 0.1
rad from natural background sources, the average number of tracks
per cell-nucleus is a fraction of one track during a year.
electrons can not be subdivided into
fractions. So, either a cell-nucleus experiences an
electron-track, or it does not. Yes or no. At very low total
doses, some nuclei experience one track or a few tracks, and
other nuclei experience no irradiation at all.
the average number of tracks per nucleus is
one track, 37% of the nuclei experience no track at all, 37%
experience one track, 18% experience two tracks, 6% experience 3
tracks (Gofman 1990,
are a special property making ionizing
radiation very different from toxic chemicals. Chemicals can be
present in a cell-nucleus at lower and lower concentrations. For
chemicals, there is no minimum concentration. But for ionizing
radiation, one track is the least possible invasion it can inflict
upon a cell-nucleus. At the cellular level, one track is the
lowest possible "dose," and one track presents the least possible
challenge for the repair-system. The split-second occurrence of
one track is also the slowest possible dose-rate.
human evidence shows health harm caused by
doses which deliver just one or a few tracks per cell-nucleus,
then such evidence wipes out the hope that "repair" can ever
deliver a threshold or safe dose (para. n, above).
Part 5. Human Studies Showing Radiation-Induced Cancer from Minimal Doses
the mainstream medical literature are quite a
number of epidemiological studies showing that even minimal
doses of ionizing radiation induce extra cases of
cancer. The references are flagged (#)
in the list.
the flagged studies, we figured out the average
number of tracks per nucleus caused by each exposure
average number of tracks through each cell-nucleus, per exposure,
ranged from 0.3 track to 12 tracks, with this distribution: 0.3;
0.7; 1.2; 1.3; 2.1; 6.2; 10; 12 tracks. In
other words, some studies meet a very strict definition
of lowest possible radiation dose (para. cc,
above), and others are
only the 6-track, 10-track, and 12-track studies
existed, someone would be sure to speculate that "maybe 6
tracks overwhelm a cell's repair-capacity. Maybe there is a
safe dose at 4 tracks." Six tracks (average) correspond with
radiation doses of 2 to 5 rads, so such speculation would be hard
to reconcile with evidence of abundant repair-capacity at 100 to
500 rads (see para. h, above). In
any case, such speculation is
ruled out by the studies showing excess cancer from even
lower track-averages per nucleus.
any reasonable standard of proof, the combination
of human epidemiology and track-analysis demonstrates that
there is no threshold dose or dose-rate below which "repair"
invariably prevents health harm.
is an error to assert that no human evidence exists of
harm to health at minimal dose-levels. It does exist (see
Reference List, flagged (#) entries). Cancer is a very serious
harm. The flagged studies rule out speculation that low-dose radiation
may be either risk-free or "good for you." Moreover, if
radiation carcinogenesis is the result of residual injury to the
genetic molecules, then the flagged studies strongly warn us
that there is no safe dose of gonadal irradiation with respect to
human inherited afflictions.
is especially powerful evidence when a common
result arises from a variety of radiation experiences. The
flagged studies include infants in-utero, children, adolescents,
young women, high-energy gamma rays, medical x-rays, acute
single doses, acute serial doses, and chronic occupational doses.
is worth noting that acute serial doses, in women
who received repeated low-dose chest fluoroscopies, occurred
with plenty of time for the repair-system to complete its work
on damaged molecules before the next x-ray exam (para. g, above). If
repair could always work flawlessly when the x-ray
dose is low, then such women would show no
radiation-induced cancer from the very high radiation doses
which they gradually accumulated. After flawless repair-work,
the women would never have any cancer-risk left from the
previous exposure when they received the next exposure in the
series. Each exposure would occur on a "clean slate."
evidence of excess breast cancer in the
fluoroscoped women is very solid, and shows a positive
dose-response. This evidence of radiation-induced human
cancer is widely acknowledged and cited --- but not many
people recognize that it is evidence of cancer-induction resulting
from nearly minimal doses of radiation per exposure (about 6
to 10 tracks per average cell-nucleus, per x-ray examination).
final point concerns the immune response. We've
heard people speculate like this: "Even if a fraction of low-dose
genetic damage is unrepaired, or unrepairable, or misrepaired at
the lowest dose-levels, the resulting cancers would be so few
that the immune system and the body's other defenses against
cancer would eliminate them." The evidence in the flagged
studies refutes that speculation, and so does logic. If a body's
natural defenses automatically eliminate single cancers, humans
would never develop cancer from any cause (including
high-dose radiation). But lots of people do develop cancer.
Fatal cancer. In the USA, 22% of all deaths are due to cancer.
Part 6. A Five-Point Summary
One: The radiation dose from x-rays, gamma rays,
and beta particles is delivered by high-speed electrons, traveling
through human cells and creating primary ionization tracks.
Whenever there is any radiation dose, it means some cells and
cell-nuclei are being traversed by electron-tracks. There are
about 600 million typical cells in 1 cubic centimeter.
Two: Every track --- without any help from
another track --- has a chance of inflicting a genetic injury if
the track traverses a cell-nucleus.
Three: There are no fractional electrons. This
means that the lowest "dose" of radiation which a cell-nucleus
can experience is one electron-track.
Four: There is solid evidence that extra human
cancer does occur from radiation doses which deliver just one or
a few tracks per cell-nucleus, on the average. See paragraphs ee-mm, above.
Five: Thus we know that there is no dose or
dose-rate low enough to guarantee perfect repair of every
carcinogenic injury induced by radiation. Some carcinogenic
injuries are just unrepaired, unrepairable, or misrepaired. The
It is factually wrong to believe or to
claim that no harm has ever been proven from very low-dose
radiation. On the contrary. Existing human evidence shows
cancer-induction by radiation at and near the lowest possible
dose and dose-rate with respect to cell-nuclei. By any
reasonable standard of scientific proof, such evidence
demonstrates that there
is no safe dose or dose-rate below which dangers disappear.
No threshold-dose. Serious, lethal effects from minimal
radiation doses are not "hypothetical," "just theoretical,"
or "imaginary." They are real.
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# # # # #
extent to which radiation-induced DNA damage may be correctly
repaired at very low doses and very low dose rates is beyond
the resolution of current experimental techniques. If DNA
double-strand breaks are critical lesions determining a range of
cellular responses, including perhaps neoplastic transformation,
then it may be that wholly accurate cellular repair is unlikely
even at the very low lesion abundance expected after low dose
and low-dose-rate irradiation."
UNSCEAR 1993 Report, p.634, para.74.
is highly unlikely that a dose threshold exists for the initial
molecular damage to DNA, because a single track from any ionizing
radiation has a finite probability of producing a sizable cluster
of atomic damage directly in, or near, the DNA. Only if the
resulting molecular damage, plus any additional associated damage
from the same track, were always repaired with total efficiency
could there be any possibility of a dose threshold for consequent
UNSCEAR 1993 Report, p.636, para.84.
effects are believed to arise predominantly from residual DNA
changes that originate from radiation damage to chromosomal
DNA. It is the repair response of the cell that determines its
fate. The majority of damage is repaired, but it is the
remaining unrepaired or misrepaired damage that is then
considered responsible for cell killing, chromosomal aberrations,
mutations, transformations and cancerous changes."
UNSCEAR 1993 Report, p.680-681, para.323.
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