Ecological Research Series
PLUTONIUM UPTAKE BY PLANTS FROM SOIL
CONTAINING PLUTONIUM 238 DIOXIDE
PARTICLES
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
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This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
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EPA-600/3-77-052
May 1977
PLUTONIUM UPTAKE BY PLANTS FROM
SOIL CONTAINING PLUTONIUM-238 DIOXIDE PARTICLES
By
K. W. Brown and J. C. McFarlane
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not con-
stitute endorsement or recommendation for use.
ii
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ABSTRACT
Three plant species—alfalfa, lettuce, and radishes—were grown in soils
contaminated with plutonium-238 dioxide (238puQ2) at concentrations of 23,
69, 92, and 342 nanocuries per gram (nCi/g). The length of exposure varied
from 60 days for the lettuce and radishes to 358 days for the alfalfa. The
magnitude of plutonium incorporation as indicated by' the discrimination
ratios for these species, after being exposed to the relatively insoluble
Pu02, was similar to previously reported data using different chemical forms
of plutonium.
Evidence indicates that the predominant factor in plutonium uptake by
plants may involve the chelation of plutonium contained in the soils by the
action of compounds such as citric acid and/or other similar chelating agents
released from the plant roots.
iii
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FOREWORD
Protection of the environment requires effective regulatory actions which
are based on sound technical and scientific information. This information
must include the quantitative description and linking of pollutant sources,
transport mechanisms, interactions, and resulting effects on man and his
environment. Because of the complexities involved, assessment of specific
pollutants in the environment requires a total systems approach which trans-
cends the media of air, water, and land. The Environmental Monitoring and
Support Laboratory-Las Vegas contributes to the formation and enhancement of
a sound integrated monitoring data base through multidisciplinary, multimedia
programs designed to:
. develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment
demonstrate new monitoring systems and technologies by
. applying them to fulfill special monitoring needs of
the Agency's operating programs
This report describes the plutonium transfer between soil and plant
systems. The purpose is to better predict and understand the behavior of
plutonium in plant-soil systems. Radiobiologists should find this report
of value. If further information is needed on this subject, the Pollutant
Pathways Branch of the Monitoring System Research and Development Division,
U.S. Environmental Protection Agency's, Environmental Monitoring and Support
Laboratory, Las Vegas, Nevada, should be contacted.
PI p
George B! Morgan
Director
Environmental Monitoring and Support Laboratory-LV
iv
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ACKNOWLEDGMENTS
The authors express their appreciation to Dr. 0. G. Raabe and Dr. R. 0.
McClellan of the Inhalation Toxicology Research Institute, Lovelace Foundation,
for providing the plutonium-238 dioxide microspheres used in this study.
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INTRODUCTION
The use and production of transuranic elements by the expanding nuclear
power industry, along with the release of many of these elements into the
biosphere during periods of atmospheric nuclear testing, have prompted the
need for assessing their behavior in biological systems. Of the transuranic
elements being utilized and produced in these energy- and weapons-related
programs, many investigators, including McKay (1961), Saenz and Ramos (1973),
and Fraser (1967), consider plutonium, because of its long half-life, to be
one of the most radlologically and biologically toxic radioelements. Seaborg
(1970) estimated that industrial and medical applications may utilize from
60 to 80 tons (54 to 73 metric tons) of plutonium-239 and up to 6 tons (5.4
metric tons) of plutoniura-238 by the end of this century. The small portion
of this plutonium which escapes containment may pose a serious threat to
human health.
A review of the pertinent literature concerning the uptake and trans-
location of plutonium within biological systems by Mullen and Mosley (1976)
showed that the amount of plutonium-239 deposited worldwide on the first few
centimeters of surface soils from past weapons tests and nuclear accidents
alone would comprise approximately 1 part per trillion (ppt) of the soil
volume. They further reported that air samples collected from numerous
locations around the world in 1963 had plutonium-239 concentrations of
10-15 Ci/m3. This was higher than the concentration of 10~16 to 10~17 Ci/m3
in air samples collected in 1965 at various locations in the United States.
The critical pathway of plutonium from its source to man is generally
considered to be by inhalation. The environmental dissolution of plutonium
particulates, which may become accidentally incorporated into man's metabolic
system either by inhalation or ingestion, necessitates determining the reten-
tion and absorption characteristics of plutonium from sites of deposition.
One such study, an i.n vitro investigation to determine the solubility of
plutonium-238 and plutonium-239 dioxides, was conducted by Raabe et al.
(1973). They found that after an exposure to a serum simulant, similar in
chemical composition to blood serum, small amounts of the plutonium dioxides
were dissolved and carried off in the serum stream. Although the plutonium-
238 and plutonium-239 dioxide particles were relatively insoluble, the
solubility rate was about two orders of magnitude higher for the plutonium-
238 dioxide particles than for the plutonium-239 dioxide particles. If this
difference in solubility occurs in environmental plutonium contaminants,
there are important problems facing radlobiologists. For instance, contami-
nation predictions must be modified to reflect different plutonium isotopes.
Also, many pathway studies using plutonium^-238 will be invalid in predicting
plutonium-239 behavior.
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The pathway of plutonium to man by his ingestion of vegetative material
is considered to be a much smaller risk than inhalation. However, in 1955,
Rediske et al. indicated that of the radioactive isotopes that become incor-
porated into biological systems, most have entered initially via plants.
Investigations concerning this mode of biological entry have been primarily
designed to determine the pathways and rates of radionuclide transfer among
the many soil, soil-plant and plant components of both native and agricultural
ecosystems. Many of these studies have been initiated in the field following
accidental releases or during continual releases of radioactive pollutants
into the environment, while others have been conducted in the laboratory under
controlled conditions. Both types of investigations have added to our under-
standing and knowledge of the complexity of transuranic pollutants pathways.
The available literature identifying both the physical and biological
parameters for assessing the amount of plutonium assimulated by plants via
a soil rooting media is limited. In most controlled studies, plutonium is
uniformly mixed in soil. As a result, the data from these experiments would
not necessarily be correlatable to data collected from native vegetation
growing in soils where the plutonium is deposited on the soil surface. Inves-
tigations by Romney et al. (1970) have indicated that plutonium is normally
quite immobile and tends to remain in the upper few centimeters of the soil;
therefore, it is not readily available for plant uptake. Nevertheless, the
results of laboratory investigations where plutonium is uniformly mixed in
the rooting media are valuable in understanding the contamination of culti-
vated vegetation grown on plowed lands and in identifying the mechanisms
which control its uptake and distribution in plants.
The use and/or the production of the common oxide of plutonium, plutonium
dioxide (PuO^) in fast breeder reactors (Pigford, 1974), as fuel for the nu-
clear power system (SNAP devices) for space explorations (Adams and Fowler,
1974), and the results of investigations by a small number of researchers
such as Dr. 0. G. Raabe were instrumental in the initiation of this investi-
gation. This study was designed to obtain information regarding the differ-
ences in isotopic uptake by plants. However, only the portion dealing with
plutonium-238 is complete and is reported in this paper.
CONCLUSIONS
The results of this study have shown that plutonium in the form of
plutonium-238 dioxide is taken up and translocated to the aerial portions
of three commonly cultivated plant species. The magnitude of assimilation
and translocation of this chemical form of plutonium by these plants appears
to be in about the same proportion as the incorporation of other chemical
forms of plutonium by a variety of other plants, including both aquatic and
terrestrial species. The long-term exposure of the alfalfa did not show
any increase in the specific activity of plutonium in the plant tissue, even
though the root mass increased. This increase in root mass would normally
enhance the probability of a contaminant assimilation as the chance of phys-
ical contact with the soil-borne pollutants would increase.
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As the behavior of 238puQ2 in soils, as indicated in this study, par-
allels other chemical forms of plutonium as far as plant assimilation, the
rate and means of uptake may be largely determined by the effect of root
exudates. A number of investigators, including Romney et^ a^. (1970),
Schultz et^ al. (1976), Rhodes (1957), and Price (1972), have indicated that
the biological availability of plutonium is largely governed by its solubility
and also to the numerous chemical reactions which occur in soils. These
reactions, which are enhanced by the soil microflora, as shown by Au (1974),
involve and affect soil pH and the rates of natural and/or induced chelation.
As such, the effects of chelation, additions of various soil dressings and a
changing soil pH on the availability of plutonium transfer from soils to
plants are important factors that merit further study.
METHODS AND MATERIALS
This investigation was designed to.determine the extent and magnitude
of plutonium assimilation by plants growing in soils. The chemical form and
the isotopes of plutonium selected for this study,. 238puQ2 and 239pu()2, were
based primarily on the observations made by Dr. 0. G. Raabe and his research
associates in 1973. However, only sized particles of 238puc>2 were available
at the scheduled start of this study.
238
Monodisperse Pu02 particles were obtained from the Inhalation Toxi-
cology Research Institute, Lovelace Foundation, located in Albuquerque,
New Mexico. The particles had a geometric mean diameter of 0.32 micrometers
(urn) and were prepared initially in December of 1973. They were stored dry
on stainless steel foil inside a screw-capped plastic centrifuge tube. The
amount obtained for this study consisted of 2.6 mCi of-238Pu with a trace
amount of ytterbium-169 (850 nCi as of November 15, 1974). The specific
alpha activity of these particles was 13.6 Ci/g. The' chemical composition
by mass was 97% Pu02 and 3% ytterbium trioxide (169Yb203). The plutonium
contained 90% 238Pu and 10% 239pu by mass. The particles were further
identified as being from segment number 16, LAPS soil number 1, production
run number 73337.
The soil selected for the rooting media was a silty loam consisting of
57.6% sand, 36.8% silt, and 5.6% clay. It has a pH of 7.9 and a cation
exchange capacity of 12.23 milliequivalents (meq)/100 g. This soil which
had been sieved through a 0.417-mm standard sieve and the plutonium dioxide
were shipped to the Nuclear Chemistry Division at the Naval Weapons Center,
White Oak, Maryland, for mixing.
The initial procedure for preparing the rooting media was to remove the
particles from the foil and suspend them in a suitable solution. This proce-
dure was previously described by Raabe et al. (1975).. Basically this method
involves adding 50 ml of a 0.02% surfactant solution (Triton® X-100) to
the centrifuge tube, thereby submerging the stainless steel foil. The cen-
trifuge tube was then placed into an ultrasonic water bath to dislodge the
plutonium particles from the stainless steel foil. After a 4-hour period of
ultrasonic agitation, the foil was removed.
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Because of the necessity of dry mixing to obtain a homogeneously mixed
rooting media, aliquots of the surfactant solution containing the plutonium
particles were added to a slurry of talc, H2Mg3(8103)4. The talc, which
readily absorbed the liquid, was then dried under an infrared lamp. The talc
mix, which dried into a brittle conglomerate, was transferred in toto to a
16-quart (30-liter) capacity Patterson-Kelley Twin Shell ® blender. The mix-
ing action of the soil particles broke down the talc conglomerate into a
fine powder.
The homogeneity of the soil-plutonium mix was determined over a 20-hour
blending period by taking soil samples from the blender at various times and
analyzing for the 169yb content using a gamma scintillation detector. Four
different soil-plutonium concentrations (mixes) were made for this study, each
consisting of approximately 5,100 g. After mixing, each of the four soil
mixes was divided into six nearly equal portions, put into 1,000-g volume
plastic bottles, and then placed into a 2R type radioactive material shipping
container.
The transfer of the potting soil into specially designed 5-inch (127-
millimeter) greenhouse pots was completed at the Las Vegas Laboratory. This
procedure was accomplished in a standard radiation glovebox. Before trans-
ferring the soil, 25 g of vermiculite was added to each of the 24 plastic
bottles to prevent excessive soil compaction during plant growth. The bottles,
which contained approximately 850 g of the plutonium-contaminated soil, were
capped and then rotated by hand for approximately 5 minutes to mix the vermi-
culite into the soil. After mixing, all the soil from one of the bottles
was poured into one of the 5-inch pots. This procedure was duplicated until
all 24 pots were filled. The pots were transferred from the glovebox into a
self-contained environmental growth chamber. As previously stated, the pots
were specially designed as shown in Figure 1. The pots were designed to
contain the plutonium over an extended period. To prevent loss of the plu-
tonium particles by leaching, a nylon reinforced Acropor ® filter with a
pore size of 0.20 \na was cemented over the drain holes. To protect the
Acropor filter from damage by roots and to prevent it from being plugged
by soil particles, a Microsorban ® filter was placed in the bottom of the
pot to act as a prefilter. To reduce the loss of the plutonium particles
by upward migration via capillary action, the soil surface was covered by
a Whatman® filter that had been impregnated with seeds. The Whatman filter
was then covered with a 3.0-cm deep layer of 0.3-cm diameter polystyrene
beads.
Further safety precautions included the construction of a fiberglass-
lined wooden tank measuring 115 x 115 x 18 cm which was placed in the growth
chamber to hold the pots. Once the pots were placed in the tank, handling
of the contaminated material was eliminated except during harvesting. Also,
an automatic irrigation system, as shown in Figures 2 and 3, was designed.
Features of this system included the recycling of the evapotranspired water,
exterior controls, and a safety float installed in the fiberglass-lined tank.
The safety float was installed to shut off the pump, timer, and solenoid if
an excessive amount of water occurred in the tank. To ensure a fairly even
distribution of water to each pot, four manifolds were used, each distributing
water to six pots (Figure 3). Each pot was irrigated with approximately
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POLYSTYRENE BEADS
CHAPIN WATERING LINE
WHATMAN
FILTER
MICROSORBAN
FILTER
DRAIN
ACROPOR FILTER
(Pore Size 0.20cm)
Figure 1. The design of five-inch plastic greenhouse pots used to hold
the 238Pu02 contaminated soil.
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('
<
-__/f unuw
[ m
A
' FLOAT
i i
7" 1
/
\
«GROWTH CHAMBER COOLING COILS
PUMP
SOLENOID
EVAPOTRANSPIRATION
WATER RECYCLED BACK
INTO IRRIGATION SYSTEM
DISTILLED
WATER
PUMP
SOLENOID
TO GROWTH CHAMBER (SEE FIGURE
Figure 2. Schematic of the irrigation system used to recycle
evapotranspired water, add nutrient solutions, and water
plants growing in 238Pu02 contaminated soil.
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AIR
EXHAUST
FROM
PUMP
mm///////////////////^^^^^^
^
FIBERGLASS
\xxLINED WOODEN
X «^. nnw
WATERING LINE
DISTILLED WATER AND
HYDROPONIC SOLUTION
CHAMBER DOOR
^GROWTH
CHAMBER
EXTERIOR
WALL
Figure 3. Design of the interior portion of the growth chamber showing
the irrigation system, pot emplacement and direction of chamber
air flow.
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180 ml of water per day. Plant nutrients were provided by irrigating once
every six weeks with a modified Hoagland solution as described by Berry (1971)
An air sampling system was constructed as a safety precaution to sample
the chamber air. The air was pumped from the chamber through a Millipore®
membrane filter having a pore size of 0.1 ym and then exhausted back in the
chamber. Figure 3 shows the intake and exhaust ports of this system along
with the direction of the air flow in relation to the pot placement within
the chamber. The chamber air was sampled for approximately 6 hours at a
flow rate of 12 liters per minute (1pm) This sampling was conducted 24 to
36 hours prior to entering the chamber. After the decay of naturally occur-
ring radon, the filter was counted to determine if any of the plutonium-238
had become airborne.
The environmental growth chamber used for this study was specially con-
structed to conduct soil-plant kinetic studies involving selected chemical
forms of radioisotopes. As a result, the chamber was virtually airtight
with all the controls on the exterior. Throughout this investigation a
chamber photo-period of 16 hours was maintained. The:light-dark tempera-
tures were kept at 25° C and 20° C, respectively. Carbon dioxide (C02) was
automatically injected into the chamber atmosphere to maintain a uniform
daytime concentration of 350 parts per million (ppm).
SAMPLES AND SAMPLE ANALYSIS
Soil samples were collected from each pot 2 days after the pots were
placed in the chamber. This 2-^day delay was to ensure that all of the soil
in the pots was damp due to irrigation. Samples were collected by inserting
a 10-cc disposable syringe', which "had the bottom (needle ^attachment) end cut
off, into the soil. The syringe was then withdrawn containing a 7- to 10-g
(dry weight) core of,soil; Using the syringe plunger, the soil core was
removed and placed into an-aluminum can. To avoid cross-contamination, 24
different syringes were vised. The wet weight of each,.soil sample was deter-
mined and then"they were dried in an oven at a temperature of 100° C to
determine the dry weight. The cans were then sealed and sent to the Eberline
Instrument Laboratories for plutonium-238 analysis.
The initial plant samples were collected on April 28, 1975. They were
collected by clipping with scissors and then were placed into a small pre-
weighed paper bag. The samples were weighed and then dried _at a temperature
of 75° C. The bags were individually sealed in aluminum cans and sent to the
Eberline Instrument Laboratory for plutonium-238 analysis. These samples
were not removed from the paper bag but were dissolved in toto. This proce-
dure eliminated additional handling of plant material and therefore increased
the precision of analysis. No attempt was made to separate the various plant
organs, for example, stems from leaves. Following a period of regrowth,
usually from 5 to 6 weeks, the plants were reharvested.
Basically, the analytical technique included decomposition of the soil
and plant material by potassium fluoride fusion and/or acid dissolution.
After decomposition, plutonium-236 was added as a tracer followed by the
separation of the plutonium by ion exchange or solvent extraction. The
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plutonium was electroplated and then counted by alpha spectroscopy,
RESULTS AND DISCUSSION
Two plant species, alfalfa, Medicago sativa, and lettuce, Lactuca sativa,
were originally planted. Twelve pots, three replications of each of the four
plutonium soil mixes, were sown with each species. All of the alfalfa germi^
nated; however, only 3 of the 12 pots of lettuce germinated. As a result,
after harvesting the lettuce, all 12 of the pots originally planted with this
species were resown with radish, Raphanus sativus,
As previously stated, different plutonium concentrations constituted the
four treatments used in this study. The soils were mixed in batches, divided
into individual pots, and then subsampled for analysis. The results of the
soil analysis for the soil plutonium-238 concentration are shown in Table 1.
In soil treatments 1 and 2, the standard deviations were 13% and 12% of the
means, and only 3% in treatments 3 and 4. These soil concentration values
compare closely with the soil concentrations calculated and analyzed by
gamma counting the 169Yb. The results based on the 169Yb concentration,
as analyzed and reported by the Naval Ordnance Laboratory, for the four
treatments were 24, 62, 94, and 310 nCi/g, respectively. The use of the
169Yb as an analytical tool for determining the plutonium-238 concentration
in the treatment 1 and 2 soils indicated that much less variation existed in
each of these two mixes when compared to the soil plutonium-238 analyses, as
the standard deviations were calculated to be only 7% and 6% of the means.
It is assumed that the larger variability (13 to 12%) was the result of the
238pu analysis rather than in the soil preparation techniques. The variation
in the treatment 3 and 4 soils was nearly identical after the two analyses.
TABLE 1. PLUTONIUM-238 CONCENTRATION IN SOILS
——— - ——
Treatment Pu Concentration (nCi/g)
1 23 ± 3*
2 69 ± 8
3 92 ± 3
4 342 ± 10
*Standard deviation, a, of six soil analyses.
Investigations involving the transfer of plutonium from soils to plants
via root assimilation have shown that a large discrimination ratio (DR)
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(DR) - Plutonium concentration in the plant nCi/8 dry exlat> Thig
v ' Plutonium concentration in the soil nCi/g dry
is presented in Table 2 for each of the three species. The high coefficient
of variability in the alfalfa (about 47%) is thought to be the result of im-
precision in plant analysis rather than variability of plant absorption. This
conclusion was based on observing similar variability in plutonium analysis
of aliquots of the same samples.
The magnitude of plutonium uptake appeared to be greater in both the
lettuce and radishes than it did in the alfalfa as indicated by the discrimi-
nation ratios shown on Table 2. However, the ratios calculated for these two
species are in most cases based on a single observation and are considered
to be inconclusive as an indication of species differences or trends in
plutonium incorporation.
TABLE 2. PLUTONIUM DISCRIMINATION RATIOS FOR ALFALFA, LETTUCE, AND RADISH
PLANTS GROWN IN SOILS CONTAMINATED WITH 238puQ2 SPHERES
Soil Concentration
(nCi/g)
23
69
92
342
Discrimination Ratios
Alfalfa
7.4 ±
7.5 ±
8.8 ±
7.4 ±
3.0*
4.0
4.0
3.8
x 10~5
x 10~5
x 10~5
x 10~5
Lettuce Radish
2.6 x 10~5 3.4
1.7 x 10~4 1.2
1.8 x 10~4 4.2
2.7
x 10~4
x 10~4
x 10~5
x 10~4
*Standard deviation, a, of ten discrimination ratios
Francis (1973) summarized the available literature and reported that the
discrimination ratio generally falls between 10~4 and 10~6. This large
discrimination against plutonium absorption by plants has more recently been
confirmed by Hansen (1975) and again summarized by Bernhardt and Eadie (1976).
The alfalfa discrimination ratios shown in Table 2 are similar in magnitude
to those previously reported. It is somewhat surprising to find that these
values, which represent the absorption and translocation of plutoniura from
soils contaminated with discrete spheres of relatively insoluble Pu02, are
similar to those in which ionic and chelate-complexed plutonium were applied
as the contaminant. Even experiments reported by McFarlane et_ al. (1976),
in which plant roots were treated with plutonium in solution cultures, show-
ed discrimination ratios against plutonium in the same general magnitude.
This suggests that the chemical reactions which occur at the root surface
predominate the kinetics of plutonium uptake and translocation in plants.
Plants are known to exude organic compounds such as citric and humic acids
which form strong chelates with plutonium. Based on the results of this
study and the results from other investigations (Romney e_t ad., 1970), it
seems possible that the release of citric acid and/or other similar chelating
10
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compounds may be responsible for plutonium uptake.
If the absorption of plutonium by plants is dependent on the release of
a particular compound or on the formation of some chemical complex at the
root surface, it would explain why plutonium solubility in soil, water move-
ment in plants, growth rate, and root contact potential appear to have little
impact on plant assimilation of plutonium. This would also explain the tight
grouping of discrimination ratios for dissimilar experiments where the chemis-
try of the contaminating plutonium was extremely different.
The growth rate (dry matter synthesis) of the alfalfa in this study
increased with each successive cutting. This increase is evidence that the
rooting systems were increasing in size, therefore, coming in physical contact
with more potentially absorbable plutonium. A proportionate increase in total
plutonium uptake and translocation was associated witfiin this increased plant
growth rate. However, the specific activity in the plant tissue remained un-
changed and was apparently independent of time or root exposure. At one point
in the experiment the growth chamber overheated due to a mechanical failure.
Severe wilting occurred followed by the harvesting of the alfalfa stems and
leaves. Subsequent growth was suppressed and damage to the root system was
suspected. Despite this stress, no detectable change occurred in the rate of
plutonium uptake, the specific activity, nor in the discrimination ratios.
For a number of reasons, a relatively few laboratory plant kinetics
studies involving plutonium are conducted over an extended period of time.
However, one study conducted and reported by Dr. Romney and his research
associates in 1970, was in many aspects similar to this investigation. In
their study, Nevada Test Site (NTS) soils contaminated with various chemical
forms of plutonium were used as the rooting media. Although the specific
chemical composition of plutonium in Dr. Romney's study was not known,
Bretthauer et. al. (1974), reported that NTS soils contain plutonium dioxide,
silicates and organic particles of plutonium having diameters of less than
0.5 urn. Close similarities between the two investigations were that both
were cropping studies conducted over a considerable length of time, and they
both utilized plant species belonging to the leguminosae family.
Dr. Romney et_ _al. (1970) reported that the Ladino clover that they grew
and cropped over an extended 5-year period had plutonium discrimination ratios
that varied from 1.9 x 10~5 to 14.0 x 10~5. They also reported that a trend
of increasing plutonium uptake by this plant species occurred with time.
Their data support the hypothesis that plutonium incorporation by plants may
be primarily dependent upon the release of chemical compounds from plant roots
and/or from microbial action. Even though the magnitude of plutonium incorpo-
ration by the alfalfa was similar to that taken up by the Ladino clover as
shown by the discrimination ratios, no similar increase of plutonium uptake by
the alfalfa as a function of time was evident. The absence of this trend may
have been due to the comparatively short duration of the alfalfa exposure which
would reduce the amount of soil chemical formation.
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REFERENCES
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of 238pu02 micr°spheres in an aquatic environment and the uptake of plutonium
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Second AEC Environmental Protection Conference, Albuquerque, New Mexico.
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Au, F. H. F. 1974. The role of soil microorganisms in movement of plutonium.
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Bernhardt, D. E., and G. G. Eadie. 1976. Parameters for estimating the up-
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Berry, L. W. 1971. Evaluation of phosphorus nutrient status in seedling
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Fraser, D. C. 1967. Health physics problems associated with the production
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McKay, H. A. C. 1961. Alpha emitters in reactor wastes. Atomic Energy
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-052
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
PLUTONIUM UPTAKE BY PLANTS FROM SOIL CONTAINING
PLUTONIUM-238 DIOXIDE PARTICLES
5. REPORT DATE
May 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
K. W. Brown and J. C. McFarlane
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, NV 89114
10. PROGRAM ELEMENT NO.
1FA628
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency—Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV 89114
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/07
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Three plant species—alfalfa, lettuce, and radishes—were grown in soils contami-
nated with plutonium-238 dioxide (238pu02> at concentrations of 23, 69, 92, and
342 nanocuries per gram (nCi/g). The length of exposure varied from 60 days for the
lettuce and radishes to 358 days for the alfalfa. The magnitude of plutonium incor-
poration as indicated by the discrimination ratios for these species, after being
exposed to the relatively insoluble Pu02> was similar to previously reported data
using different chemical forms of plutonium.
Evidence indicates that the predominant factor in plutonium uptake by plants may
involve the chelation of plutonium contained in the soils by the action of com-
pounds such as citric acid and/or other similar chelating agents released from
the plant roots.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Plutonium-238
Metabolism
Plant Growth
. Uptake from soil
07B
06C
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
20
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
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