Do levels of radioactivity in the United States follow the levels being released from the Japanese reactor site?

You are not
alone in your concern about radioactivity released in Japan reaching the United
States and the potential impact it might have. We all occupy a globe of finite
dimensions, and we share some common environmental transport paths through
which materials generated on part of our planet may be carried by prevailing
forces to locations very remote from the source.

As we discuss
this issue, I should first note that one great advantage we have with respect
to our assessment of radioactive materials, as opposed to many nonradioactive
toxic species, is that we often have much greater sensitivity for detecting the
radioactivity by way of the radiations that the material emits than we do for
most nonradioactive materials. Thus, even when the concentrations of radioactive
atoms are so low as to represent no health concerns, the material may still be
detectable using the instrumentation that has been developed and is currently
available and operational in many laboratories throughout our country and the
world. That is the situation we presently have regarding detection of
radioactive fission products that have been transported from Japan on the winds across the Pacific
Ocean.

The diluting
power of the atmosphere is extremely large, and the airborne concentrations of
some fission products that have reached our shores from the Fukushima Daiichi
site are very low. As the radionuclides reach our country they may remain
airborne, some may deposit from the air directly on to soil, vegetation, and
bodies of water, and some may be washed out of the atmosphere to the earth with
natural precipitation. In all cases, resulting levels have been extremely low,
not adding any meaningful increment to the radiation doses that we already
receive from natural background radiation sources.

If the
situation in Japan should worsen such that higher levels of radioactivity were
to be released to the atmosphere, and the prevailing wind patterns remained as
they have been, then we might expect to see the concentrations of some
radionuclides increase in our country, but I cannot imagine a scenario in which
such levels would reach a point where they presented any significant health
concern.

We must keep
in mind that the reactors have been shut down and some fission products of
initial concern, especially the radioactive iodines, of which ¹³¹I
is the most important, are decaying with rather short half-lives—e.g., ¹³¹I
has an 8-day half-life, which means that every eight days any previously
existing ¹³¹I would have been reduced in amount by a factor of two.
Unless something changed drastically for the worse in Fukushima—in particular,
a new fire that affected fuel in the reactors or greater losses of cooling
water that allowed the fuel temperature to increase markedly—I would not expect
levels in this country to reach markedly higher levels than we are now
measuring.

We should
keep in mind that there may be local occurrences at the Japanese reactor sites
that may produce temporary increases in releases of some radioactive species—e.g.,
the releases of radioactive materials into the ground and sea water associated
with leakage of contaminated water through the recently discovered crack in a
concrete pit. Such events may produce notable localized increases of
radioactivity and associated radiation levels in some environmental media in
the Fukushima
area, but may result in no increases in radioactivity in our country. In order
for us to experience increased radioactivity levels, not only must there be increases
in levels released from the Japanese site, but there must also be an effective transport
mechanism to get the material to our country. Atmospheric transport is the most
likely means for transporting material here, but this is only effective if the reactor
products are released to the air. Material that is released to the ground or
ground water in Japan and ultimately may reach the ocean will be partly
sequestered by silts and other possible biota and/or be diluted to such a great
extent that we would not expect to see measurable amounts in sea water near our
shores.

What we see
in the way of radioactive contaminants reaching our country is clearly related
to what is happening in Japan, but there is not a one-to-one correlation
between amounts released there and what we measure here because of the
intervening factors that affect the distribution and migration of material in
the environment. The physical form and properties of the released material—gas or solid or liquid—and radioactive half-life, chemical properties, affinity
of inert and bio-materials for uptake of the material, and available transport
pathways affect the amounts that will reach us. The radioactivity that has been
able to escape from the reactors into the air environment and be transported to
remote locations has been volatile components that were volatilized at elevated
temperatures when some water coolant was lost, thus allowing the fuel to heat
up to the point of being partially damaged with an attendant loss of some of the
cladding that provides a barrier against leakage of fission products from the
fuel matrix. This radioactivity includes primarily some radioactive noble gases,
of which ¹³³Xe is an example (5.2-day half-life), radioactive
iodines, of which ¹³¹I (8-day half-life) is the most notable, and
radioactive isotopes of cesium, primarily ¹³⁴Cs (2.1-year half-life)
and ¹³⁷Cs (30-year half-life).

Naturally,
there is a greater concern on our part with certain food products produced in sections
of Japan, where levels of contamination in soil, vegetation, and water might be
relatively high, that might be imported into the United States. Our country has
banned imports of fresh vegetables, fruits, and milk from Japan. It is also
requiring radiation monitoring, upon arrival, of other food products from Japan.

In summary,
your inferences about the relationships between levels of radioactivity being
released from the Fukushima site and levels being measured here have some
validity, but the present situation does not seem to portend ever-increasing
releases from Japan and, in the event of continuing and/or increasing releases
from the debilitated reactors, the levels that we will experience in this
country may vary significantly with the characteristics of the radioactivity
released and any changes in environmental conditions that influence transport
of the material from Japan to the United States. There is no reason to believe
that future levels will present any notable health impact to citizens in this
country.

Naturally, we
are all hoping for the safest and most expeditious resolution and minimization
of the threats caused by the extreme events that have transpired in Japan. The direct
catastrophic impacts of the earthquake and the tsunami have wrought terrible
consequences that have been a cause of great grief for Japanese survivors as
well as the world community and will require massive commitments of manpower
and resources to remediate. The nuclear events involving the reactors at the
Fukushima Daiichi site present an added burden that will require continuing
efforts and resources to minimize the effects on safety and health of the Japanese
workers and general population. The likely permanent losses of several of the
reactors as electrical generators present another significant loss that might
negatively affect Japan’s
overall well-being and recovery. We must trust that the United States, along
with much of the developed world, will continue to provide assistance in the
forms of financial aid, materials, technical resources, and expert manpower
to assist Japan in its recovery.

George
Chabot,
PhD, CHP