Epidemiology
“If one is going to study the effect on human health of a
phenomenon thought to be dangerous, it has to be done after the fact, right
Curmudge?”
“It’s called epidemiology,
Julie, and that’s what we will talk about today. As in the two previous postings, information will come from
Hiserodt’s book, which we may occasionally quote or paraphrase. Original references are found in
chapter 16. An early study by
Abbott (1983) of 4,000 nuclear workers, exposed in the workplace to an average
of 7 cGy (about 20 years of additional annual background radiation), revealed
that their cancer mortality was less than that of the population of Ontario.”
“But, Curmudge, those workers had to be healthier than the
average citizen even to be hired.
No wonder their cancer mortality was less.”
“That’s called the healthy
worker effect, Julie. Abbott
corrected for this by including a cohort of non-nuclear workers drawn from the
same population as the nuclear workers.
The cancer mortality of the non-nuclear workers was right up there with
the general population; for the nuclear workers it was much lower. Another study in Canada, by Gribbin et
al., compared leukemia mortality of unexposed Atomic Energy of Canada workers to
their colleagues who were exposed to an average of 4.9 cSv. The exposed workers had about half the
leukemia mortality of the controls.”
“Curmudge, even a reckless old buzzard like you should be
afraid of plutonium dust.
Plutonium emits alpha particles; they don’t go far, but I’ve always
envisioned their making big holes—sort of like Swiss cheese—in one’s lungs.”
“Hiserodt described the fate of 26 males exposed to
plutonium dust and fumes during atomic bomb development in 1944-45. Their health was checked every five
years starting in 1952. By 1986-87,
22 of the subjects were still alive at an average age of 66. Two had died of heart attacks, one in
an auto accident, and one—a pack-a-day smoker—died of lung cancer at the age of
72.”
“Someone has calculated—Hiserodt didn’t say who—that eight
of the atomic bomb workers (living at the end of 1987) had received a dose of
more than 2 times 10 to the 15th power alpha particles. Curmudge, I think I’ll have to revise
my mental picture of what alpha particles do inside lungs.”
“Don’t close the book yet, Julie. In chapter 19 Hiserodt describes what might have been the
definitive low-level radiation study.
In 1991 the U.S. Dept. of Energy contracted with Johns Hopkins
University to study ‘Health Effects of Low-Level Radiation in Shipyard
Workers.’ Workers were divided
into three groups: (1) The Control group of 33,352 workers whose duties did not
involve radiation. (2) The Low
group of 10,462 workers whose cumulative exposure was less than 500 mrem. (3) The High group of 28,542 workers
whose cumulative exposure was equal to or greater than 500 mrem. Results were reported as standardized mortality ratio (SMR),
which compares the death rate of a group in question with that of an
age-adjusted population of peers.
The control group had an SMR of 1.00 for death by all causes, which
corresponds with that of the general population.”
“That certainly sounds
rigorous, Old Guy. Tell me what
those academic statisticians found.”
“With one exception, the SMRs for both exposed groups were
lower (better) than those of the control group. The exception was mesothelioma, which is known to be caused
by amphibole asbestos. For all
causes of death, the difference between the exposed groups and the controls was
statistically significant. For
cancers other than mesothelioma (leukemia, lymphoma and hematopoietic cancers,
and lung cancer), the SMRs were lower than the controls but not significantly
lower. A reviewer (Prof. John
Cameron of UW-Madison) has stated that, ‘This study is probably the best
scientific evidence…to show that low levels of ionizing radiation are without
health hazard.’ “
“Wow, Curmudge!
I certainly feel better after reading that last sentence. It is especially interesting that this
study was initiated to show the adverse effects of low-level gamma radiation
and ended up showing no adverse effect.
It’s another nail in the LNT theory’s coffin. But why, after so many years, hasn’t the Department of
Energy issued a formal report on this work?”
“We can only speculate, Julie, and we will in a later posting.”
“I hope you haven’t forgotten, Senescent Senior, about the
unintentional epidemiological event in Taiwan (1). In 1982 several radioactive cobalt-60 orphan sources were
inadvertently recycled into 20,000 tons of steel, some of which was used to construct
apartment buildings housing 10,000 people.”
“It wasn’t forgotten, Julie; it was only a ‘senior
moment.’ The average cumulative
dose for the exposed residents was about 50 mSv. Twenty years later, only seven fatal cancers were observed
where 232 were expected.”
“Do you suppose, Curmudge, that the tenants’ rent was raised
to reflect the benefits of radiation hormesis?”
“My guess is that the tenants were evicted and the buildings
razed. It was probably government
policy to protect the residents from further exposure to radiation, whether it
was good or bad for them.”
Kaizen Curmudgeon
(1) Sanders,
C.L. Dose-Response 10, p.615 (2012).
