v>EPA
United States
Environmental Protection
Agency
Environmental Monitoring
and Support Laboratory
P.O. Box 15027
Las Vegas NV 89114
EPA-600/3-79-026
March 1979
Research and Development
Ecological
Research Series
Plutonium-239 and
Americium-241 Uptake
by Plants From Soil
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped Into nine series. These nine broad categories
were established to facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously planned to foster
technology transfer and a maximim interface in related fields. The nine sereies are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy—Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans.plant and animal species, and
materials. Problems are assessed for their long-and short-term influences. Investiga-
tions include formations, transport, and pathway studies to determine the fate of
pollutants and their effects. This work provided the technical basis for setting standards
to minimize undesirable changes in living organisms in the aquatic, terrestrial, and
atmospheric environments.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161
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EPA-600/3-79-026
March 1979
PLUTCNIUM-239 AND AMERICIUM-241 UPTAKE BY PLANTS FROM SOIL
By
Kenneth W. Brown
Monitoring Systems Research and Development Division
Environmental Monitoring and Support Laboratory
P. 0. Box 15027
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 consti-
tute endorsement or recommendation for use.
11
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FOREWORD
Protection of the environment requires effective regulatory actions
which are based on sound technical and scientific information. This infor
mation 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 transcends the media of air, water, and land. The Environmental
Monitoring and Support Laboratory-Las Vegas contributes to the formation
and enhancement of a sound monitoring data base for exposure assessment
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 and americium transfer between
soil and plant systems. The purpose is to better predict and understand
the behavior of plutonium and americium in plant-soil systems. Radiobiolo
gists should find this report of value. If further information is needed
on this subject, the Pollutant Pathways Branch of the Monitoring Systems
Research and Development Division, U.S. Environmental Protection Agency's,
Environmental Monitoring and Support Laboratory, Las Vegas, Nevada, should
be contacted.
George B. Morgan
Director
Environmental Monito-ring and Support Laboratory
Las Vegas
ill
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ABSTRACT
Alfalfa was grown in soil contaminated with plutonium--239 dioxide
( PuOz) at a concentration of 29.7 nanocuries per gram (nCi/g). In addi-
tion to alfalfa, radishes, wheat, rye, and tomatoes were grown in soils con-
taminated with americium'-241 nitrate [ 41Am(NO3)3] at a concentration of
189 nCi/g. The length of exposure varied from 52 days for the radishes to
237 days for the alfalfa.
The magnitude of plutonium incorporation by the alfalfa as indicated by
the concentration ratio, 2,5 x 10 , was similar to previously reported data
using other chemical forms of plutonium. The results did indicate, however,
that differences in the biological availability of plutonium isotopes do
exist.
All of the species exposed to americium-241 assimilated and translocated
this radioisotope to the stem, leaf, and fruiting structures. The magnitude
of incorporation as signified by the concentration ratios varied from
0.1 x 10 ** for the wheat grass to 15.2 x 10~3 for the radishes. An increase
in the uptake of americium also occurred as a function of time for four of
the five plant species.
Evidence indicates that the predominant factor in plutonium and ameri-
cium uptake by plants may involve the chelation of these elements in soils by
the action of compounds such as citric acid and/or other similar chelating
agents released from plant roots.
iv
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ACKNOWLEDGMENTS
The author-would like to express his appreciation to Dr. 0. G. Raabe
and Dr. R. 0. McClellan of the Inhalation Toxicology Research Institute,
Lovelace Foundation, for providing the plutonium-239 dioxide microspheres
used in this study. Also, to Mr. C. Feldt and Mrs. R. O. Houston for their
support and work during this investigation.
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INTRODUCTION
Many of the longest lived radioactive pollutants being released into
our environment are the transuranic elements. Jacobs and Gera (1969) pro-
jected that the activity of a small number of these elements and their decay
products from United States sources alone would exceed 1,000 megacuries by
the year 2020. The anticipated production, use, and release of most trans-
uranic elements into the biosphere during periods of atmospheric nuclear
testing and by the expanding nuclear power industry have prompted the need
for assessing their behavior in biological systems.
Of the transuranic elements used in the nuclear industry, the highly
radioactive plutonium isotopes are generally considered to be of primary im-
portance. Of the large number of plutonium isotopes used and produced,
plutonium-239 is, as summarized by Mullen and Mosley (1976), the isotope most
utilized. One means by which plutonium-239 is produced is by the irradiation
of uranium-238 in nuclear reactors.
In addition to the concern caused by the possible environmental impact
of plutonium-239, the scientific community has become increasingly aware of
the environmental consequences of the formation and release of americium into
the biosphere. Of the 12 americium isotopes, americium-241 is generally con-
sidered to present the most serious hazard. This isotope enters the environ-
ment primarily as a decay product of plutonium-241, which is released into
the biosphere as a by-product of both the nuclear testing program and the
nuclear power industry.
Reviews of the pertinent literature concerning the uptake and transloca-
tion of plutonium-239 and americium-241 by plants have been completed by
Mullen and Mosley (1976), Price (1973), Frances (1973) , Romney and Davis
(1972), Brown (1976), and Bernhardt and Eadie (1976). These reviews have
shown that these two isotopes do accumulate in both the plant and edaphic
portions of our environment. They also appear in a variety of chemical forms
and will accumulate in one of the many trophic levels of a biological system.
Although identification of both the physical and biological parameters for
assessing the amount of their assimilation by plants via a soil rooting media
is limited, the foregoing reviews do show that their movements are, in gen-
eral, very slow. As reported by Price (1973) , the final assessment of envi-
ronmental impact will show that pollutants such as plutonium and/or americium
which have long residence times will increase in relative importance with
time, especially in areas where they are uncontained within the biosphere.
In most plant kinetics studies, the americium and/or plutonium have been
uniformly mixed in the soil rooting media. As a result, the data from these
experiments would not necessarily correlate with data collected from
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vegetation growing in soils where the plutonium is deposited on the soil sur-
face. Investigations by Romney et al. (1970) have indicated that transuranic
elements are normally quite immobile and tend to remain in the upper few cen-
timeters of the soil; therefore, they are not readily available for plant as-
similation. Nevertheless, the results of laboratory investigations where
plutonium and americium are uniformly mixed in the rooting media are valuable
in understanding the contamination of cultivated vegetation grown on plowed
lands and also in the identification of the mechanisms which control their
uptake and distribution in plants.
Public awareness concerning the possible biological impact of plutonium
has increased because of its anticipated production and use in breeder re-
actors (Pigford, 1974) and as fuel for the numerous nuclear power systems.
Also, the projected impact of americium as suggested by Poet and Martell
(1972) and Major et al. (1974), and the results of investigations by a small
number of researchers such as Dr. 0. G. Raabe and his research associates in
1973, were instrumental in the initiation of this investigation.
This study was designed to determine the extent and magnitude of pluto-
nium-239 and americium-241 assimilation by plants growing in soils. It was
also conducted to obtain additional data concerning the isotopic differences
in plant uptake between plutonium-238 and plutonium-239 oxides. The initial
investigation which dealt with the plant assimilation of plutonium-238 oxide
was previously reported by Brown and MeFarlane (1977),
CONCLUSIONS
The results of this study have shown that plutonium in the form of plu-
tonium-239 dioxide is taken up and translocated to the aerial portions of the
commonly cultivated plant species, alfalfa. Based on the concentration
ratios, the amount of plutonium assimilated and translocated by this plant
species 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. However, there do appear to be dif-
ferences in the amount of plutonium assimilated between different isotopes.
For example, previous studies by Brown and MeFarlane (1977) using identical
plant species grown under nearly identical physical and environmental condi-
tions showed that plutonium-238 dioxide is more readily available for plant
uptake.
The long-term exposure of the alfalfa did not cause any increase in the
concentration of plutonium in the plant tissue, even though the root mass in-
creased. This increase in root mass would normally enhance the probability
of a contaminant assimilation as the chance of physical contact with the soil-
borne pollutants would increase. Since the behavior of 239PuO2 in soils, as
indicated in this study, parallels other chemical forms of plutonium as far
as plant assimilation, the rate and means of uptake are probably determined
by the effect of root exudates. A number of investigators, including Romney
et al. (1970), Schultz et al. (1976a), Rhodes (1957), and Price (1972), have
indicated that the biological availability of plutonium is largely governed
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by its solubility and also by the numerous chemical reactions which occur in
soils.
Americium in the form of 2^-Am(N03)3 was also shown to be taken up and
translocated to the aerial organs of five species of commonly cultivated crop
and pastureland plants. The amount of americium assimilated and translocated
by these plant species appeared to be similar in magnitude to that assimilated
by other plant species under a variety of conditions.
The long-term exposure of these species -did show an increase in the con-
centration of americium in the plant tissues. This behavior, of americium
availability, similar to the biological availability of plutonium over a
period of time as reported by Romney et al. (1970), is governed by its solu-
bility and by the chemical reactions occurring in the soils.
The reactions which are enhanced by the soil microflora, as reported 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 changing soil pH on the availability of plutonium and americium
transfer from soils to plants are important factors that merit additional
study.
METHODS AND MATERIALS
As previously stated this investigation was designed to determine the
extent and magnitude of plutonium and americium assimilation by plants
growing in soils. The chemical form and the isotope of plutonium selected
for this study was 239PuO2- It was selected for investigation primarily on
the basis of observations made and reported by Dr. O. G. Raabe and his re-
search associates in 1973. The chemical form and isotope of americium used
was 2ttlAm(NO3) 3.
Monodisperse PuC>2 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 0.44 micrometers (ym) .
They were stored dry on a stainless steel foil inside a screw-capped plastic
centrifuge tube. The amount obtained for this study was 100 microcnaries (yCi)
The ^^Am (1^03) 3 was obtained from a commercial source and consisted of 3.0
millicuries (mCi) in a solution of 0.5 M HNC>3.
The soil selected for the rooting media for both isotopes was a silty
loam consisting of 57.6 percent sand, 36.8 percent silt, and 5.6 percent clay.
It had a pH of 7.9 and a cation exchange capacity of 12.23 milliequivalents
(meq)/100 g. The soil, which had been sieved through a 0.417-millimeter (mm)
standard seive, and the two isotopes were shipped to the Nuclear Chemistry
Division at the Naval Weapons Center, White Oak, Maryland, for mixing.
The initial procedure for preparing the plutonium-239 rooting media was
to remove the particles from the foil and suspend them in a suitable solution.
The procedure used was previously described by Raabe et al. (1975) and used
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by Brown and McFarlane (1977). Basically, this method involves adding 50 ml
of a 0.02 percent surfactant solution (Tritor®X-100) to the centrifuge tube,
thereby submerging the stainless steel foil. The centrifuge tube is 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
soil was removed.
Because of the necessity of dry-mixing to obtain a homogenously mixed
rooting media, the surfactant solution containing the 23^PuC>2 particles was
added to a slurry of talc, H2Mg3 (SiOs) 4.. The 24^Am(N03)3 in nitric acid was
also added to a separate talc slurry. The talc, which readily absorbed the
liquid, was then dried under an infrared lamp. These brittle talc conglom-
erates were then transferred in toto to a 30-liter capacity Patterson-Kelley
twin shell® blender where the mixing action of the soil particles broke down
the talc conglomerate into a fine powder. The two isotopic-talc conglomerates
were mixed separately, each with a different batch of soil.
The length of blending time to obtain a homogenous soil mix had been pre-
viously determined by using 23^PuO2 tagged with ytterbium-169. The 169Yb con-
centration was determined from aliquots of soil collected from the blender
over a 20-hour period. The precise methods and procedures used in the soil
mixing techniques were reported by Brown and McFarlane (1977). After mixing,
the plutonium soil mix was divided into 3 nearly equal portions and the
americium soil mix into 16 nearly equal portions. Each portion was then
placed into a 1,000 ml plastic bottle, put into an appropriate shipping con-
tainer and shipped to the U.S. Environmental Monitoring and Support Laboratory
in Las Vegas.
The transfer of the potting soil into specially designed 127-mm green-
house pots was completed at the Las Vegas Laboratory. This procedure was
accomplished in a standard radiation glovebox. Before transferring the
soil, 25 g of vermiculite were added to each of the 19 plastic bottles to
prevent excessive soil compaction during plant growth. The bottles, which
contained approximately 860 g of the plutonium and americium contaminated
soil, were capped and then rotated by hand for approximately 5 minutes to mix
the vermiculite into the soil. After mixing, all the soil from one of the
bottles was poured into one of the greenhouse pots. This procedure was du-
plicated until all 19 pots were filled. The three pots containing the plu-
tonium were transferred from the glovebox into a self-contained environmental
growth chamber. The remaining 16 pots containing the americium were trans-
ported from Las Vegas to the greenhouse facility located at the U.S. Environ-
mental Protection Agency's experimental farm on the U.S. Department of
Energy's Nevada Test Site.
As previously stated, the pots were specially designed as shown in
Figure 1. The pots were designed to contain the plutonium and americium over
an extended period. To prevent loss, a nylon reinforced Acropor® filter
with a pore size of 0.20 ym was cemented over the drain holes. To protect
the Acropor®filter from damage by roots and to help 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 and
Registered trademark
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POLYSTYRENE BEADS
CHAPIN WATERING LINE
SEEDS
WHATMAN
FILTER
f ^MICROSORBAN
«T FILTER
DRAIN
ACROPOR FILTER
(Pore Size 0.20 |im)
Figure 1. The design of the 127 millimeter plastic greenhouse pots used
to hold the plutonium-239 and americium-241 contaminated soils.
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americium by upward migration via capillary action, the soil surface was
covered by a Whatman® filter that had been impregnated with seeds. The
WhatmarPfilter was then covered with a 3.0-centimeter (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 and greenhouse 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 was designed. Features of
this system included the recycling of the evapotranspired water, exterior con-
trols, and a safety float installed in the fiberglass-lined tank. The safety
float was installed to shut off the pump, timer, and solenoid if excessive
amounts of water occurred in the tank. To ensure a fairly even distribution
of water to each pot, manifolds were used, each distributing water to a pre-
selected number of pots. Each pot was irrigated with approximately 180 ml of
water per day. Plant nutrients were provided by irrigating- once every 6
weeks with a modified Hoagland solution as described by Berry (1971).
An air sampling system was constructed as a safety precaution to sample
both the greenhouse and chamber air. The air was pumped from the chamber and
greenhouse through a Millipore© membrane filter having a pore size of 0.1 pm
and then exhausted back in the greenhouse and growth chamber. The air was
sampled at a flow rate of 12 liters per minute (1pm). This sampling was con-
ducted prior to entering the growth areas. After the decay of naturally
occurring radon, the filter was counted to determine if any of the plutonium
and/or americium had become airborne.
The environmental growth chamber used for the plutonium study was spe-
cially constructed 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 investiga-
tion a chamber photo-period of 16 hours was maintained. The light-dark tem-
peratures were kept at 25 C and 20 C, respectively. Carbon dioxide (CC>2)
was automatically injected into the chamber atmosphere to maintain a uniform
daytime concentration of 350 parts per million (ppm).
The greenhouse used for the americium study was fairly small, measuring
approximately 3 meters long, 2 meters wide, and 2.5 meters in height. Light
banks plus two portable heating and cooling units were installed in the green-
house prior to the initiation of this study. The photo-period and the light-
dark temperatures were kept nearly identical to those in the growth chamber.
SAMPLE COLLECTION AND ANALYTICAL PROCEDURES
Soil samples were collected from the plutonium-soil pots 2 days after
placement into the growth chamber, and from the americium-soil pots 1 day
after placement into the greenhouse. This delay was to ensure that all of
the soil in the pots was damp due to irrigation. Samples were collected by
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inserting a 10-cubic centimeter (cm3) 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, 19 different syringes were used. The wet
weight of each soil sample was determined 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 located in Albuquerque,
New Mexico for analysis.
The initial plant samples were collected from the plutonium and americium
soil pots 51 and 52 days, respectively, after planting. They were collected
by clipping with scissors and then were placed into a small preweighed 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, similar to the
soil samples, to the Eberline Instrument Laboratories for analysis. These
samples were not removed from the paper bag but were dissolved in toto. This
procedure eliminated additional handling of plant material and therefore in-
creased the precision of analysis. No attempt was made to separate the various
plant organs in the plutonium portion of this investigation. It was, however,
done in the americium portion; i.e., stems, leaves, and fruit were collected
and analyzed separately.
Basically, the analytical technique for the plutonium analysis 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 plutonium was electroplated and then counted by alpha spec-
troscopy.
The analytical methods for the americium analysis included dissolving
the samples in nitric and hydrofloric acids. Prior to decomposition, amer-
icium-243 was added as a tracer followed by two successive solvent extraction
steps and one cation exchange resin step. The americium was then electro-
plated and counted by alpha spectrometry.
RESULTS AND DISCUSSION
Plutonium
Alfalfa, Medicago sativa, was planted in each of three pots. As stated,
the soil had been mixed in one batch and then divided into three portions.
The plutonium-239 concentration of the soil was 29.7 ± 2.1 nCi/g. This cal-
culated concentration represented the mean and standard deviation of three
soil analyses from the three soil aliquots sampled from each pot.
Stem and leaf tissues were collected over an 8-month period representing
237 days. After clipping, the alfalfa was allowed to regrow. Reharvesting
occurred 6 additional times thereafter, usually within a 31- to 38-day growth
period.
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Investigations involving the transfer of plutonium from soils to plants
via root assimilation have shown that a large concentration ratio (CR)
__ concentration in the plant nCi/g dry .
t-«- = r—7~: : rr— —rt ——. ; exists. The alfalfa concentration
concentration in the soil nCi/g dry
ratio is shown in Table 1.
TABLE 1. PLUTONIUM CONCENTRATION RATIO FOR ALFALFA PLANTS GROWN IN SOIL
CONTAMINATED WITH 239Pu02 SPHERES
Soil Concentration Concentration Ratio
(nCi/g) (x 10~6)
29.7 ± 2.1* 2.5 ± 1.5t
*Standard deviation, s, of three soil analyses.
tStandard deviation, s, of seven concentration ratios.
The magnitude of plutonium uptake by alfalfa was greater during the
first half of this investigation, 0 to 104 days, than during the latter por-
tion, 105 through 237 days. The amounts of 2^Pu assimilated per gram of
dry tissue during the first and second portions of this study were 0.2 and
0.02 picocuries (pCi), respectively. This is surprising in view of the fact
that the growth (dry matter) of the alfalfa increased with each successive
cutting. This increase in tissue is evidence that the rooting system was
increasing in size, thereby, coming in physical contact with more potentially
absorbable plutonium. A proportionate increase in plutonium uptake was asso-
ciated with this increased plant growth rate. However, the concentration
in the plant tissue remained unchanged; in fact, it decreased somewhat during
the latter portions of this study.
Evidence indicates that the absorption of plutonium by plants is perhaps
dependent upon the release of a particular compound or upon the formation of
some chemical complex at the root surface. This could explain, in part, the
lack of plutonium assimilation by these plants over the 237-day growth period.
In another experiment conducted by Brown and McFarlane (1977) similar results
were obtained. They reported that alfalfa grown in soils contaminated with
spheres of 2^8PuO2 and cropped over a 358-day growing period did not show
any significant increase in plutonium assimilation with time. They hypoth-
esized that plutonium solubility in soils, water movement in plants, growth
rate, and root contact potential appear to have little impact on plant as-
similation of plutonium. The results of this study and the previous one con-
ducted by Brown and McFarlane (1977) suggest that chemical reactions occurring
at the root surfaces predominate the kinetics of plutonium uptake and trans-
location in plants. Plants are known to exude organic compounds such as
citric and humic acids which form strong chelates with plutonium. Based upon
the results of this study and the findings of other investigators (Romney
et al., 1970), it appears that the release of citric acid and/or other similar
chelating compounds may be responsible for plutonium uptake.
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Further evidence supporting this hypothesis is that Francis (1973) sum-
marized the available literature_and reported that plutonium concentration
ratios generally fall between 10 ** and 10 6- This large discrimination
against plutonium absorption by plants was confirmed by Hansen (1975) and
again summarized by Bernhardt and Eadie (1976). In addition to the studies
cited by these investigators in which many different chemical forms and both
ionic and chelated-complexed plutonium were applied to the rooting media, the
same general magnitude of plutonium assimilation by plants was reported by
McFarlane et al. (1976) following a root exposure to plutonium in solution
cultures.
A number of studies, such as those conducted by Raabe et al. (1973) in-
dicated that plutonium isotopes vary in solubility. They reported that
during an in vitro study using plutonium-238 and plutonium-239 dioxide par-
ticles exposed to a serum stimulant, similar in chemical composition to blood
serum, the solubility rate was about two orders of magnitude higher for
the plutonium-238 dioxide particles than for the plutonium-239 dioxide par-
ticles. If this solubility difference between the two isotopes occurred
during other biological reactions, environmental contaminant priorities would
have to be selected and based upon additional criteria.
To furnish additional data concerning the possible differences existing
between the solubility of plutonium-238 and plutonium-239 in plant-soil
systems, this investigation was conducted in many aspects identical to the
previously mentioned study by Brown and McFarlane (1977). The mixing pro-
cedures, plant species, soil, and the environmental conditions were the same
for each study. Plutonium-238 dioxide particles measuring 0.32 ym in di-
ameter were used for the previous investigation. In addition, the PuC>2
soil concentration was slightly lower, 23 ± 3 nCi/g. Even though a direct
comparison between the two isotopes cannot be made because of the variation in
particle size, differences in plant assimilation of the two isotopes were
evident. Based upon the concentration ratios during the initial growing
period, 51 days for the 23^PuO2 exposure and 55 days for the 238PuO£ exposure,
4.0 ± 2.7 x 10 6 and 2.0 ± 1.1 x 10 k, respectively, the plutonium-238 incor-
porated into the aerial plant portions exceeded the amount of plutonium-239
assimilated by 50 times. This trend continued through both studies. For
example, at the end of the 237-day growing period for the plutonium-239 study,
which can be correlated with a 242-day growing period for the plutonium-238
study, the relationship between the concentration ratios was nearly identical,
6.7 x 10 ' and 3.0 x 10 ^, respectively, to those ratios calculated for the
51- and 55-day exposures.
Americium
Five plant species, alfalfa, radish, Raphanus sativusf rye grass, Seoale
oereale, wheat, TTitiaian sp., and tomatoes, Lyoopersictm sp. were planted in
the americium-241 soil mix. As previously described, the americium-241 con-
taminated soil was divided into 16 nearly equal portions and then transferred
into 16 greenhouse pots. Three of the pots were planted with alfalfa, three
with radish, three with rye, and three with wheat. The remaining four pots
were planted with tomatoes. The americium-241 concentration in the soil was
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189 ± 31 nCi/g. This calculated concentration represented the mean and the
standard deviation of 16 soil analyses from 15 soil aliquots sampled from
each pot.
Stem leaves, and fruiting structures were collected over an 8-month
period representing 236 days. The initial plant sampling occurred 52 days
after sowing. Three species, alfalfa, rye, and wheat, were allowed to regrow
after each harvest. The radishes were replanted once following the initial
harvest. Investigations concerning the assimilation of americium by plants
via root uptake similar to those conducted on plutonium incorporation have
shown concentration ratios that vary between lo"1 and 10~7. This large vari-
ation has been shown to be due in part to differences in soil pH, and the
addition of various soil dressings such as lime and the chelating agent
diethylenetriaminepentaacetic acid (DTPA) (Wallace, 1974 and Schulz, 1977).
The americium-241 concentration ratios for the five plant species at
each harvesting period are shown in Table 2. Because of the fairly long
duration of this study, indications of increased uptake over time were
observed. Figure 2 shows the concentration of americium-241 in the stem and
leaf tissues of the alfalfa and tomato plants, and Figure 3 shows the ameri-
cium concentration in the rye and wheat grasses. As is shown on these two
figures, the amount of americium-241 assimilated by these plants at the end
of the growing period for all four species was of the same general magnitude.
Perhaps the most interesting observation is that even though all four species
showed an increase in americium uptake, the rate of assimilation was greater
in the grass species than in the alfalfa and tomato plants.
The maximum amount of americium-241 taken up and accumulated in the
radishes varied between a high of 288.2 pCi/g (dry) and a low of 50.7 pCi/g
(dry). The maximum concentration in the radishes occurred during the initial
52-day growth period. The decrease in the amount of americium assimilated
during the second planting and growth period, which was 86 days, cannot be
explained.
TABLE 2. CONCENTRATION RATIOS FOR FIVE PLANT SPECIES_ GROWN IN
SOILS CONTAMINATED WITH AMERICIUM-241 (x lO"^)
Harvesting Period Plant Species
(Days After Planting)
Alfalfa Radish Rye Wheat Tomato
52
75
102
125
138
145
188
216
236
1.910.6
1.610.3
1.2±0.3
2.3±0.4
1.110.3
3.2+0.5
35.0+22.0
11.016.0
152.0130.0
2.7+0.4
3.511.9
2.2+0.6
2.9+1.8
0.6+0.2
1.7+0.4
8.1+4.1
9.716.5
0.110.0
4.512.3
3.611.3
7.012.2
8.214.3
1.110.6
0.7+0.2
0.610.5
1.410.7
1.110.9
21.0+4.0
10
-------
1000n
TJ
O)
\
O
o 1 00-
+••
2
+-*
c
0)
o
c
o
o
Alfalfa •——-
Tomato ^~
\
38
l l
75 113
Time (Days)
150
190
Figure 2. Concentration of americium-241 in the stem and leaf tissues of
alfalfa and tomato plants.
11
-------
100CH
100-
O)
\
o
Q.
.0
2
+••
c
0)
g 10-
o
O
• Rye
^—A Wheat
0 38 75 113 150
Time (Days)
190
Figure 3. Concentration of americium-241 in the stem and leaf tissues of
rye and wheat grass.
12
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An increase in americium uptake exhibited by four of the plant species
as a function of time is perhaps associated with a number of parameters.
The most obvious one is the increase in root mass which was verified by an
increase in the growth rate (dry matter synthesis) of the stem and leaf
tissues, which occurred with each successive cutting. Other parameters af-
fecting americium solubility and uptake could have been the exuding of vari-
ous organic compounds by the plant roots such as citric and humic acids which
may form strong chelates with the americium. These processes, in addition to
the affects of various chelating agents and other soil dressings on the bio-
logical availability of selected transuranic elements, have been previously
'reported by Wallace (1974), Romney (1970), Au (1974), and Schulz (1977).
Americium was also translocated to the fruiting structures of each
species. The fruiting structures of the grass species accumulated the great-
est amount of americium-241 when compared to the concentration in the stem
and leaves. The percentage compositions of the fruiting structures of the
rye and wheat grasses when compared to their respective stem and leaf tissues
were 9 percent to 91 percent and 46 percent to 54 percent. The high ratio,
46 percent of the americium-241 accumulated by the wheat grass heads, cannot
be explained as none of the other species exhibited this trait. Harvesting
of the fruiting structures of these two grass species was completed only one
time during this investigation, as such, trends of americium translocation
with time could not be made.
Tomatoes were harvested and analyzed three separate times during this
study. Table 3 shows the amount of americium-241 assimilated by the stem and
leaf tissues and translocated to the tomatoes at each collection period. Also
shown is the percentage composition provided by each portion.
TABLE 3. AMERICIUM-241 CONCENTRATIONS IN THE STEM AND LEAF TISSUES AND IN
THE FRUITING STRUCTURE OF TOMATO PLANTS
Growing Time Americium-241 pCi/g (dry)
(Days) Stem
52 20
149 383
164 267
and Leaves
.510.0
.4161.0
.7160.4
Fruit
5.211.6
31.3+17.7
9.2+3.4
Percentage Composition (%)
80
20
92
8
96
4
As shown in Table 3, the percentage translocated to the fruit was
greater during the initial growing period than during the subsequent growing
and harvesting periods. The apparent decrease of americium translocated to
the tomatoes when compared to the stem and leaf tissues during each growth
and harvesting period cannot be explained. The magnitude of americium incor-
poration into the fruit does, however, compare with other reported values
(Schulz et al., 1976b; and Romney et al., 1976).
13
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REFERENCES
Au, F. H. F. 1974. The Role of Soil Microorganisms in Movement of
Plutonium. NVO-142. The Dynamics of Plutonium in Desert Environments.
Nevada Applied Ecology Group Progress Report, pp. 135-141.
Bernhardt, D. E., and G. G. Eadie. 1976. Parameters For Estimating the
Uptake of Transuranic Elements by Terrestrial Plants. ORP/LV-72-2. Office
of Radiation Programs—Las Vegas Facility. U.S. Environmental Protection
Agency, Las Vegas, Nevada 89114.
Berry, L. W. 1971. Evaluation of Phosphorus Nutrient Status in Seedling
Lettuce. J. Amer. Horti. Soc. 96;(3) 341-344.
Brown, K. W. 1976. Americium—Its Behavior in Soil and Plant Systems.
USEPA Ecological Research Series. EPA 600/3-76-005. Ecological Research
Series. Environmental Monitoring and Support Laboratory, U.S. Environmental
Protection Agency, Las Vegas, Nevada 89114.
Brown, K. W., and J. C. McFarlane. 1977. Plutonium Uptake by Plants
From Soil Containing Plutonium-238 Dioxide Particles. USEPA Ecological
Research Series. EPA 600/3-77-052. Ecological Research Series.
Environmental Protection Agency, Las Vegas, Nevada 89114.
Frances, C. W. 1973. Plutonium Mobility in Soil and Uptake in Plants:
A Review. J. EnV;-'Qual. 2; (1) .67-70.
Hansen, W. C. 1975. Ecological Considerations of the Behavior of
Plutonium in the Environment. Health Phys. 28;529.
Jacobs, D. G. and Ferruccio Gera. 1969. Development of Criteria for
Long-term Management of High-level Radioactive Wastes. Health Physics
Division, Annual Progress Report, Oak Ridge National Laboratory, Oak Ridge,
Tennessee. ORNL-4446. pp. 1-40.
Major, W. J., K. D. Lee, R. A. Wessman, and C. H. Heitz. 1974. A Rapid
Method for Radiochemical Analysis of Americium-241. Environmental Analysis
Laboratories, Richmond, California. T.L.W. 6116. pp. 1-8.
McFarlane, J. C., A. R. Batterman, and K. W. Brown. 1976. Plutonium Uptake
by Plants Grown in Solution Culture. EPA Ecological Research Series.
Environmental Monitoring and Support Laboratory, U.S. Environmental
Protection Agency, Las Vegas, Nevada 89114.
14
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Mullen, A. A., and R. E. Mosley. 1976. Availability, Uptake, and Trans-
location of Pu Within Biological Systems: A Review of the Significant
Literature. EPA-600/3-76-043. Ecological Research Series. Environmental
Monitoring and Support Laboratory, U.S. Environmental Protection Agency,
Las Vegas, Nevada 89114.
Pigford, T. H. 1974. Radioactivity in Plutonium, Americium, and Curium in
Nuclear Reactor Fuel. A study for the Energy Policy Project of the Ford
Foundation. June. pp. 1-48.
Poet, S. E. and E. A. Martell. 1972. Plutonium-239 and Americium-241
Contamination in the Denver Area. Health Phys. 23:537-548 .
Price, K. R. 1972. Uptake of 237Np, 239Pu, 21tlAm, and 2k^Cm. from Soil
by Tumbleweed and Cheatgrass. DNWL-1688. Battelle Pacific Northwest
Laboratories, Richland, Washington, pp. 1-14.
Price, K. R. 1973. A Review of Transuranic Elements in Soils, Plants, and
and Animals. J. Env. Qual. _2_: (1) 62-66.
Raabe, O. G., G. M. Kanopilly and H. A. Boyd. 1973. Studies of the In_
Vitro Solubility of Respirable Particles of 238Pu and 239Pu Oxides and
9 3 Q
Accidentally Released Aerosol Containing 03Pu. Annual Report of the In-
halation Toxicology Research Institute/ Lovelace Foundation for Medical
Education and Research, Albuquerque, New Mexico. LF-46. pp. 24-30.
Raabe, 0. G., H. A. Boyd, G. M. Kanopilly, C. J. Wilkinson, and G. J.
Newton. 1975. Development and Use of a System for Routine Production of
Monodisperse Particles of 238Pu02 and Evaluation of Gamma Emitting Labels.
Health Phys. 28:655-667.
Rhodes, D. W. 1957. The Effect of pH on the Uptake of Radioactive Isotopes
from Solutions by a Soil. Soil Sci. Soc:•Amer; Proc. 21:389-392.
Romney, E. M., H. M. Mork, and K. H. Larson. 1970. Persistence of
Plutonium in Soils, Plants, and Small Mammals. Health Phys. 19:487-491.
Romney, E. M., and J. J. Davis. 1972. Ecological Dissemination of
Plutonium in the Environment. Health Phys. 22:551.
Romney, E. M., A. Wallace, R. 0. Gilbert, and Jean E. Kinnear. 1976.
239'. 2lfOpu an(j 241^ contamination of Vegetation in Aged Fallout Areas.
In: Transuranium Nuclides in the Environment. IAEA-SM-199. pp. 479-491
Romney, E. M., A. Wallace, P. A. T. Wieland, and J. E. Kinnear. 1976.
Plant Uptake of 239-2itOPu an<3 241Am Through Roots Containing Aged Fallout
Materials. Report UCLA 12-1056. pp. 1-15.
Schulz, R. K. 1977. Root Uptake of Transuranic Elements In: Proceedings
of A Symposium at Gatlinburg, Nevada Applied Ecology Group. U.S. Energy
Research and Development Administration. NVO-178.
15
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Schulz, R. K., G. A. Tompkins, and K. L. Babcock. 1976. Uptake of
Plutonium and Americium by Barley from Two Contaminated Nevada Test Site
Soils. J. Env. Qual. 5_: 406-410.
Schulz, R. K., G. A. Tompkins, and K. L. Babcock. 1976a. Uptake of
Plutonium and Americium by Plants from Soils. Transuranium Nuclides in
the Environment. IAEA, Vienna pp. 303-310.
Wallace, A. 1974. Behavior of Certain Synthetic Chelating Agents in
Biological Systems. Report UCR 34. pp. 1-37.
U. S. GOVERNMENT PRINTING OFFICE: 1979-684-480
16
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-79-026
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Plutonium-239 and Americium-241 Uptake By Plants from
Soil
5. REPORT DATE
March 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Kenneth W. Brown
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
Alfalfa was grown in soil contaminated with plutonium-239 dioxide (239PuO2) at a
concentration of 29.7 nanocuries per gram (nCi/g). In addition to alfalfa, radishes,
wheat, rye, and tomatoes were grown in soils contaminated with americium-241 nitrate
^1Am(N03)3] at a concentration of 189 nCi/g. The length of exposure varied from
52 days for the radishes to 237 days for the alfalfa.
The magnitude of plutonium incorporation by the alfalfa as indicated by the con-
centration ratio, 2.5 x 10 6, was similar to previously reported data using other
chemical forms of plutonium. The results did indicate, however, that differences in
the biological availability of plutonium isotopes do exist.
All of the species exposed to americium-241 assimilated and translocated this
radioisotope to the stem, leaf, and fruiting structures. The magnitude of incorporation
as signified_by the concentration ratios varied from 0.1 x 10 4 for the wheat grass
to 15.2 x 10 for the radishes. An increase in the uptake of americium also occurred
as a function of time for four of the five plant species.
Evidence indicates that the predominant factor in plutonium and americium uptake
by plants may involve the chelation of these elements in soils by the action of com-
pounds such as citric acid and/or other similar chelating agents released from plant
roots.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
Plutonium-238
Plutonium-239
Americium-241
Metabolism
Plant Growth
Uptake from Soil
07B
06C
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
24
20. SECURITY CLASS (Thispage}
UNCLASSIFIED
22. PRICE
A02
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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