and 1958, the United States conducted 67 atmospheric tests of nuclear
weapon designs on the Bikini and Enewetak atolls of the Marshall
Islands. After this testing ended in the late 1950s, residents who
had been relocated from these atolls began asking to return to their
going home proved to be not so simple. At Enewetak, for instance,
islands continued to be used for other defense programs through
the 1960s and 1970s. Finally, in 1978, an extensive radiological
survey was conducted of the northern Marshall Islands, including
those in the Bikini and Enewetak atolls. An aerial survey determined
the external gamma exposure rate. Samples of soil, food crops, animals,
well water, seawater, fish, and more were collected to evaluate
the radionuclide concentrations in the atoll environment. About
the same time, the U.S. launched a massive cleanup and rehabilitation
program on the Enewetak Atoll, scraping off about 76,400 cubic meters
of surface soil from 6 islands and sealing it off in a crater on
the atolls Runit Island.
cleanup focused primarily on removing and containing plutonium and
other heavy radioactive elements from a group of islands in the
northwest corner of the atoll where most of the tests were conducted
and the highest levels of local fallout were found. Yet, even during
this early cleanup, questions arose about whether these efforts
would be adequate to protect the returning Enewetak population.
Predictive assessments based on the extensive radiological survey
showed that ingestion of cesium-137 and other fission products from
eating locally grown food and drinking the local water was the most
significant exposure pathway. Cesium-137 fallout from the tests
was more widely distributed than plutonium.
and scientists had already had an opportunity to discover what happened
when islands were resettled without adequately addressing the ingestion
portion of the equation. In 1969, the people of Bikini had resettled
their home islands. Once the locally planted food crops had matured
and island residents began including the resulting fruits in their
diet, the amount of cesium-137 in their bodies (the body burden)
increased dramatically. The people of Bikini once again had to leave
their islands and have yet to return.
southern portion of the Enewetak Atoll was resettled in 1980. Today,
scientists in Lawrence Livermores Marshall Islands Dose Assessment
and Radioecology Program work to minimize exposure through ingestion
and other pathways for the Marshallese now living on or wishing
to return to their islands. The program, directed by Livermore environmental
scientist Terry Hamilton, continues research begun nearly 30 years
agocharacterizing radiological conditions on affected islands
and developing strategies to minimize radiological exposure to a
people wishing to resettle. The program also supports Marshallese
efforts to implement radiation protection programs for residents
wishing to track their exposure to radionuclides from fallout contamination
that still lingers on the islands.
scientists continue work begun more than a quarter century ago
in the Marshall Islands, assessing and evaluating the various
exposure pathways for radiological dose and developing ways
to limit the dose. Experiments to reduce the uptake of cesium-137
by coconut trees and other food crops have been conducted on
Bikini Island. (inset) Fish collected on annual sampling trips
are analyzed for radionuclides at Livermore.
Doing the Groundwork
When islanders from Bikini and Enewetakand,
later, Rongelapbegan asking questions about residual fallout
contamination on their islands, U.S. officials decided that more
knowledge of the conditions of the atolls was needed before resettlement
could begin. (See box below.) Livermore scientists conducted large-scale
environmental surveys of the radionuclide distribution to gather
data for analyzing the health risks the island residents might face
if they resettled. Questions to answer included: What would be the
long-term radioactive exposure from eating crops grown on the islands?
From drinking the water? From eating fish caught in the lagoons?
For more than 25 years,
Livermore scientists have collected over 70,000 samples of edible
food crops, vegetation, soil, water, marine life, and animals to
evaluate the various exposure pathways for radiological dose. They
combined the radionuclide inventory from the samples, a diet model
for the population, and biokinetic models to determine the dose
due to ingestion. (See S&TR, January/February
Exposure to Radiation.) At several atolls, they also evaluated
external exposure to gamma radiation and studied how the resumption
of human activity might cause nuclides in the surface soil to be
resuspended in the air and thus inhaled. Results indicated that
ingestion was the most significant exposure pathway, with external
exposure to gamma radiation being the next most significant. The
dose from ingestion contributed 70 to 90 percent of the dose to
island residents, mostly through uptake of cesium-137 into island-grown
foods such as coconut, pandanus, breadfruit, and papaya.
One of the most significant
things we discovered from this research is that the uptake of cesium-137
is very different for plants grown in Marshall Islands soils than
for plants grown in North American and European soils, says
Hamilton. The uptake of cesium-137 in continental soilsthe
measurement used in most previous studiesis much lower. Such
uptake can be expressed by the soil-to-plant transfer factor, that
is the ratio of becquerels (units of radioactive activity) per kilogram
of dry weight plant to becquerels per kilogram of dry weight soil.
For cesium-137, the soil-to-plant transfer factors for tropical
fruits grown on Bikini range between 2 and 40; for vegetation grown
on continental soils in temperate zones, the factors range between
0.005 and 0.5. The reason for the difference lies in the different
compositions of the soils.
Unlike continental soils,
island coral soils have little clay and low concentrations of potassium.
With no clay for the cesium to bind to and plants essentially starving
for potassium, the plants take up cesium as a replacement for the
potassium. Once we knew this, we could more reliably predict
the dose for returning residents and develop a strategy to limit
the availability and uptake of cesium-137 into the crops,
Among the methods considered
was removing contaminated soil that contains most of the cesium-137.
However, the surface soil layer supplies all the nutrients for plants
and controls the amount of water held in the soil. Removing this
top layer wholesale would lead to severe environmental effects and
a long-term commitment to rebuild the soil and revegetate an island.
After examining other methods
for eliminating cesium from the soil or reducing its uptake into
food crops, the team settled on a remediation technique of applying
potassium fertilizer and using limited soil removal in housing and
village areas. It developed this method on results of large-scale
field experiments conducted by Livermore on Bikini Island. The added
potassium reduces the cesium-137 taken up by plants by nearly 90
percent, lowering the associated ingestion dose to about 5 to 10
percent of the pretreatment levels. The fertilizer has an added
benefit as wellsupporting the growth and increasing the productivity
of the plants.
In 2000, when activities
began to prepare Rongelap Island for resettlement planned for 2003,
scientists took the agricultural fix developed on Bikini and combined
it with a procedure designed to reduce external exposure rates and
inhalation or ingestion of contaminated soil containing plutonium.
This procedure involves removing surface soil down to about 25 centimeters
in and around the housing and village areas and replacing it with
crushed coral. A detailed in situ gamma radiation survey of the
entire area, conducted during May 2001 by Livermore scientists,
found that the average external dose from cesium-137 within the
service and village areas was reduced by more than 20-fold to less
than 1 millirem a year. To put this dose in perspective, the average
person in the U.S. receives a dose of about 46 millirems per year
from natural terrestrial gamma radiation.
The results of the fertilization
work on Rongelap are still pending, although the data from monitoring
resettlement workers suggest that internal doses from cesium-137
ingestion in the resettled population will be extremely low. In
this case, says Hamilton, the use of potassium will,
we hope, provide an added assurance to the people that the island
is suitable for resettlement.
Hamilton added that, for
the islanders who return, the situation should only improve with
time. Rainfall transports cesium-137 out of the root zone of plants
and into the groundwater. In the longer term, this will reduce cesium-137
levels in local food crops and reduce dose estimates even further.
Livermore researchers are now exploring how long the beneficial
effects of a single potassium treatment lasts and evaluating the
rate of environmental loss of cesium-137 in the atoll ecosystem
as a whole.
|Plates inserted into soil
collect water that will help scientists determine the removal
rate of radionuclides due to rainfall. One area of current research
in the Marshall Islands involves determining the environmental
factors that remove radionuclides from the immediate environment.
For instance, rainfall is leeching cesium-137 from the soil
into the groundwater and out into the lagoons. Scientists are
discovering that this process is actually more important than
radiological decay in decreasing the dose over time.
The story of fallout and its repercussions in the Marshall
Islands can be summed up by looking at events in three
of the northern atollsBikini, Enewetak, and Rongelap.
Soon after World
War II ended, the United States examined several possible
locations for conducting tests for its growing nuclear
weapons program. The coral atolls in the northern Marshall
Islands in the Pacific Ocean appeared to offer the best
advantages of stable weather conditions, fewest inhabitants
to relocate, isolation, andwith hundreds of miles
of open ocean to the westminimum radioactive fallout
onto populated areas. Residents were relocated from islands
in the Bikini and Enewetak atolls before testing began.
The most significant
contaminating nuclear test conducted in the Marshall Islands
was the CastleBravo Event on March 1, 1954. The
explosive yield of Bravo exceeded expectations and resulted
in unexpected radioactive fallout over the inhabited islands
of the Rongelap and Utitrik atolls and other areas east
little consideration was given to the potential health
and ecological effects of fallout contamination beyond
the immediate vicinity of the test sites. Sixty-four people
on Rongelap received significant exposure from Bravo and
had to be evacuated for medical treatment. The Rongelap
community spent the next three years living on Ejit Island
in the Majuro Atoll before returning home in 1957.
Rongelap was the
first atoll to experience an early wave of resettlement.
Bikini was next, with islanders settling on their homelands
in 1969, planting food crops,
and returning to their island lifestyle. But trouble bloomed
in paradise. Once the planted food crops in Bikini matured
and started to produce fruit, the fruit became part of
the inhabitants diets, and the amount of cesium-137
in the Bikini residents bodies increased dramatically.
In 1978, the people of Bikini left their islands a second
time. A similar turn of events occurred in Rongelap, where
growing concerns about the possible health effects of
exposure to residual fallout contamination prompted residents
to relocate again in 1985. The Rongelap community continued
to express a strong desire to return. In 1996, the U.S.
Congress approved a resettlement agreement that included
an initiative to reduce the level of radiation exposure
on the island using a cleanup strategy developed by Livermore
As for Enewetak,
it continued to be used for defense programs until cleanup
began in 1977. The southern part of Enewetak was successfully
resettled in 1980, and islanders continue to live there.
From 1980 to 1997, scientists from Brookhaven National
Laboratory periodically monitored the resettled population
for internally deposited radionuclides, a program that
then moved under the purview of Lawrence Livermore.
The work on the
Marshall Islands continues, with Livermore playing a number
of key roles, including characterizing the radiological
conditions at the various atolls; determining the transport,
uptake, and cycling of radionuclides in the ecosystem;
and estimating the potential radiological doses and risk.
Republic of Marshall Islands consists of 34 atolls scattered
over 1.3 million square kilometers and clustered in two
main groups: the Ratak and the Ralik chains. The atolls
consist of numerous coral reefs. Kwajalein is the largest
atoll, and Majuro is the capital island. The dashed line
and shaded areas near Bikini and Rongelap atolls show
the fallout pattern from the Bravo Event. The Rongelap
and Utirik communities were among those relocated after
being exposed to fallout from Bravo. The Utirik community
returned to its atoll about three months after the test
and continues to inhabit the atoll today.
Each Person's Dose
Another goal of the Livermore
effort is developing individual radiation protection programs that
ensure doses to island residents remain at or below acceptable safety
standards. The cornerstone of this activity rests on whole-body
counting systems and a new Livermore-developed technique to measure
extremely small amounts of plutonium in urine.
Whole-body counting systems
measure the gamma rays coming from radionuclides such as cesium-137,
cobalt-60, and potassium-40 deposited in the body and internal organs.
The total amount of a radionuclide measured in this manner is converted
into a dose estimate using specially designed commercial software.
Hamilton explains that the main pathway for exposure to residual
fallout contamination in the northern Marshall Islands is through
ingestion of cesium-137, and whole-body counting is a simple and
effective method for determining the quantity of cesium-137 taken
up by an individual. This part of the program offers island
residents an unprecedented level of radiation protection monitoring,
he adds. With these systems in place, residents dont
have to rely on assumptions made about their intake of locally grown
foods. They get real measurements on a person-by-person basis.
When measurements are combined with environmental monitoring data,
individuals can make informed decisions about eating habits and
Local Marshallese technicians
trained at Lawrence Livermore operate whole-body counting facilities
on Rongelap and Enewetak. Livermore scientists provide technical
assistance and advanced training and perform detailed quality assurance
appraisals on the data before they are released.
Plutonium urinalysis is a
sensitive measurement technique for estimating a persons exposure
to plutonium. Urine is collected from an individual over a 24-hour
period and turned into a powder that scientists analyze by counting
the number of plutonium atoms in a sample. All of us have
a small amount of plutonium in our bodies from exposure to worldwide
fallout contamination, notes Hamilton. The Livermore
teams job is to compare the amount of plutonium detected in
Marshall Islands residents with that seen elsewhere to assess likely
intakes associated with resettlement.
Plutonium urinalysis can
detect extremely small amounts of plutonium. The technique, developed
at Livermores Center for Accelerator Mass Spectrometry as
part of a Laboratory Directed Research and Development project,
is about a hundred times more sensitive than techniques used in
U.S. occupational monitoring programs. Data from the studies show
that residents and island workers exposures to plutonium
are low. People get a higher dose of radiation taking an airplane
from the Bay Area to one of these islands than they get while working
there, says Hamilton.
A recent comparison exercise
organized by the National Institute of Standards and Technology
for determining low-levels of plutonium in synthetic urine gave
high marks to the mass spectroscopy technique. In fact, Livermores
laboratory was the only one to meet the American National Standards
Institute (ANSI) quality performance criteria for both precision
and bias at all test levels.
Over the past three years,
memorandums of understanding between the U.S. Department of Energy,
the Republic of the Marshall Islands, and the EnewetakUjelang
and Rongelap Local Atoll Government have been signed, leading to
the design and construction of radiological laboratories on Enewetak
and Rongelap atolls. A third facility is slated for construction
in 2003 on the capital island of Majuro and will be available to
residents of Utirik and other outlying islands.
|Livermores new technology
to measure extremely small amounts of plutonium isotopes and
other long-lived radioisotopes came out of research conducted
at the Center for Accelerator Mass Spectrometry. This sensitive
measurement technique has possible applications beyond the Marshall
Islands work, in areas such as nuclear isotopic forensics and
counterterrorism, risk assessments, and dose reconstruction
for exposed nuclear workers.
|Marshallese technicians trained
at Livermore run whole-body counting facilities on Rongelap
and Enewetak. The facility at Enewetak is shown in the background.
the Marshall Islands, societal fear of radiation conflicts with
a desire to resettle native homelands, concludes Hamilton.
The work the Livermore team is doingproviding environmental
measurement data and dose assessmentshas the goal of finding
ways to minimize the exposures of returning residents. First, there
is the remediation. Then theres whole-body counting and the
accelerator mass spectrometry measurements. As communities return
and settle into these islands, we hope that the programs will provide
a level of reassurance to the residents that the amount of radiation
they receive is smallwell below the standards set by their
own governmentand becoming smaller.
Key Words: accelerator
mass spectrometry, Bikini Atoll, Bravo Event, Center for Accelerator
Mass Spectrometry (CAMS), cesium-137, dose assessment, Enewetak
Atoll, Marshall Islands resettlement, Nuclear Test Program, plutonium,
Rongelap Atoll, whole-body counting.
For further information contact Terry Hamilton (925) 422-6621 (firstname.lastname@example.org).