November 27, 2001
By GINA KOLATA
In their efforts to protect Americans from the hazards of
radiation, federal agencies have found themselves in a
quandary. People are constantly exposed to radiation from
natural sources - from cosmic rays, radon seeping out of
the earth and radioactive substances in soil, water, food
and even from potassium in the human body itself.
Compared with this radiation, the amounts coming from human
efforts like nuclear plants are, relatively, minuscule. So,
the question is, How closely must this radiation be
regulated?
Up to now, regulators have typically acted as if every bit
of excess exposure is potentially hazardous. But some
scientists question this assumption.
The issue is becoming increasingly pressing as more than
100 nuclear power plants are being relicensed so they can
continue to operate. At the same time, the country faces a
growing predicament of what to do with nuclear waste from
power plants and weapons sites.
"The issue rages because we are regulating doses that are
lower than the natural background of radiation," said Dr.
Arthur Upton. A radiation expert and former director of the
National Cancer Institute, Dr. Upton is a professor of
environmental and community medicine at the University of
Medicine and Dentistry of New Jersey.
In a report last year on radiation standards, the General
Accounting Office, the investigative arm of Congress, said:
"The standards administered by E.P.A. and N.R.C. to protect
the public from low-level radiation exposure do not have a
conclusive scientific basis, despite decades of research."
The situation is further confused, experts say, because
regulatory standards are a hodgepodge.
The Environmental Protection Agency advocates a standard
for all radiation exposure from a single source or site at
15 millirem a year, with no more than 4 coming from ground
water. A standard chest X-ray, in comparison, gives about
10 millirem to the chest, which is equivalent to 1 or 2
millirem to the whole body. The Nuclear Regulatory
Commission sets its acceptable level of radiation exposure
from any one source at 25 millirem a year. In contrast, the
natural level of background radiation in the United States,
on average, is about 350 millirem a year, and in some areas
of the country it is many times higher than that.
In New York, for example, people absorb about 100 millirem
of radiation each year from cosmic rays alone, said Dr.
John Boice Jr., a radiation expert, who is the scientific
director of the International Epidemiology Institute in
Rockville, Md. In Denver, exposure from cosmic rays
averages 200 millirem a year, he said, and natural
variation in radiation exposure is many times the amounts
of radiation that are being disputed by regulatory
agencies.
"We eat, breathe and drink low levels of radiation," Dr.
Boice said.
At the same time, said Dr. Fred Mettler, chairman of the
radiology department at the University of New Mexico
medical school, major medical sources of radiation, like
CAT scanners, have fallen outside the purview of any
regulatory agency.
"A whole lot of places aren't regulated at all," Dr.
Mettler said. "It's a bit of a nightmare."
"When you look at the exposure of the population from
radiation, about two-thirds is due to natural background
and about 15 percent is due to your friendly doctors and
chiropractors," Dr. Mettler said. "Everything else is, to
tell you the truth, very minimal. Less than a couple of
percent is from all the nuclear reactors and all the
research industry."
But, asked Dr. John Evans, a risk analyst at the Harvard
School of Public Health, Why should the level of background
radiation matter to the question of how much additional
risk from human-generated sources is acceptable? "Why isn't
the more relevant question, How much of this risk can be
mitigated at what cost to you?" he asked.
The quandary over how to set radiation levels does not
result from a lack of research or analysis, scientists say.
"Radiation's effects on people have been studied for over a
century," Dr. Mettler said. "There's a vast literature.
There are probably more studies on the harmful effects of
radiation than for any other toxic or noxious agents in the
environment."
And as scientists studied radiation, committees to evaluate
the data proliferated.
"We have national and international standing committees
that periodically review the world's literature on ionizing
radiation," said Dr. Boice, who is a member of many such
groups. "At the International Committee on Radiological
Protection, we just celebrated our 75th anniversary and we
meet two or three times a year."
Then, he said, there is the United Nations Scientific
Committee on the Effects of Atomic Radiation. "That started
in 1955," Dr. Boice said. "We meet every year in Vienna and
we publish volumes."
In the United States, the Environmental Protection Agency,
the Nuclear Regulatory Commission and the National Council
on Radiation Protection and Measurements wrestle with the
radiation standards question, and the National Academy of
Sciences has been called upon periodically since the 1950's
to weigh in with its committee, called the Biological
Effects of Ionizing Radiation committee. The Department of
Energy and the National Institutes of Health conduct
extensive research.
The science has grown rapidly. In 1980, Dr. Boice set up
the radiation epidemiology section at the National Cancer
Institute with just a handful of researchers. Now, he said,
while he moved on to form the International Epidemiology
Institute, which conducts research for industry and the
government, the cancer institute's radiation department is
no longer a section, it is a branch, and one of the largest
branches there, with hundreds of scientists.
"A lot of people say, `Gee, we don't know a lot about the
risks of radiation,' " Dr. Boice said. "I say: `We know a
whole lot. We've studied populations all over the world
since the turn of the last century. We know what happens at
high doses. We know what happens at medical doses. And we
know that at low doses the risks are low. The controversy
is just how low are they. Are they really low or are they
really, really low?' "
As with other toxic substances in the environment, the
stricter the standards, the more it costs to meet them.
The G.A.O. report last year, which had the subtitle
"Scientific Basis Inconclusive, and E.P.A. and N.R.C.
Disagreement Continues," gave some examples of the costs of
complying with standards setting different levels of
radiation. The cost of cleaning soil around reactors and
nuclear weapons facilities could range from thousands of
dollars to more than $100 million, depending on whether the
standard was an exposure of 15 or 25 millirem a year, the
report said.
The report said that for groundwater, the cost of going
from the Nuclear Regulatory Commission's limits of 25
millirem a year to the level that the Environmental
Protection Agency wants could be billions of dollars.
Scientists usually rely on a mathematical model in
estimating radiation risk. The most widely used model is
known as the linear-nonthreshold dose-response model. It
assumes that there is no safe dose of radiation and that
the risk of getting cancer or genetic damage increases
along with radiation exposure.
"For better or worse, that is our model," said Stephen
Page, the director of the environmental agency's office of
radiation and indoor air. And with that model, he said,
"the E.P.A. has tried to be as protective as possible." The
agency, he added, uses that model to make sure the risk
from radiation is within the allowable range from toxic
chemicals, 1 in 10,000 to 1 in a million chance of
developing cancer.
Some say that the linear model is the best way to estimate
radiation risk, but others say that there is, in fact, a
threshold below which radiation poses no hazard to health.
And still others say that low doses of radiation are
actually beneficial.
The linear hypothesis had its origin in 1927, when the
geneticist Dr. H. J. Muller published a paper on his work
eliciting gene mutations in fruit flies by bombarding them
with radiation from X-rays. In a paper published in the
journal Science, Dr. Muller showed that the number of
mutations in fruit flies was proportional to the dose of
X-rays that had struck the insects.
"He said: `Aha! There's a linear relationship,' " said Dr.
Dade W. Moeller, a radiation expert and professor emeritus
at Harvard who runs a consulting company, Dade Moeller &
Associates in New Bern, N.C. Yet, Dr. Moeller points out,
those studies by Dr. Muller used very high doses of
radiation, and he elicited gene mutations, not cancer. But
the idea that radiation's effects were directly
proportional to its dose caught hold and soon was being
used to predict cancer cases. The difficulty was in
demonstrating it.
The risks of getting cancer from exposure to radiation
increase with dose. But since a third of all people get
cancer anyway, at some time in their lives, the problem is
to find evidence that low doses of radiation cause cancers
that would not have otherwise occurred. Even for people
exposed to large radiation doses, like the 80,000 to 90,000
survivors of the atomic bombs exploded over Hiroshima and
Nagasaki, it has been hard to find excess cancers.
"They were exposed in 1945 and nearly half are still
alive," Dr. Moeller said.
Dr. Mettler said the latest data show that 12,000 of these
atomic bomb survivors had died from cancer. He said the
number of excess cancers in the group is about 700.
Those data, Dr. Mettler said, show that there is a small
risk of cancer with an exposure of tens of thousands of
millirem of radiation.
"There's a group that says that if you can't see it, it
doesn't exist," Dr. Mettler said. "Then there's another
group that says, `That's nice, but it doesn't mean it
doesn't happen.' "
Now, some scientists even say low radiation doses may be
beneficial. They theorize that these doses protect against
cancer by activating cells' natural defense mechanisms. As
evidence, they cite studies, like one in Canada of
tuberculosis patients who had multiple chest X-rays and one
of nuclear workers in the United States. The tuberculosis
patients, some analyses said, had fewer cases of breast
cancer than would be expected and the nuclear workers had a
lower mortality rate than would be expected.
Dr. Boice said these studies were flawed by statistical
pitfalls, and when a committee of the National Council on
Radiation Protection and Measurement evaluated this and
other studies on beneficial effects, it was not convinced.
The group, headed by Dr. Upton of New Jersey, wrote that
the data "do not exclude" the hypothesis. But, it added,
"the prevailing evidence has generally been interpreted as
insufficient to support this view."
In the meantime, the regulatory agencies are at a
stalemate, continuing to disagree on radiation standards.
And the committee reports and committee meetings on
radiation standards go on.
A recent report, issued in June by the National Council on
Radiation Protection and Risks, is 287 pages long and
devoted entirely to evaluating the linear-nonthreshold
model. It explains that the council "has sought to leave no
significant aspect of the subject unaddressed."
Its conclusion?
For lack of a better model, it recommends
keeping the linear one.
"There is not conclusive evidence on which to reject" the
model, the report says, adding that "it may never be
possible to prove or disprove the validity of the linear
nonthreshold assumption."
Copyright 2001 The New York Times Company