United States
             Environmental Protection
             Environmental Monitoring
             and Support Laboratory
             P.O. Box 15027
             Las Vegas NV 89114
March 1979
             Research and Development
Research Series
Plutonium-239 and
Americium-241  Uptake
by Plants From Soil


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
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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 species, and
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tions include formations, transport, and  pathway studies to determine the fate  of
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This document is available to the public through the National Technical Information
Service, Springfield, Virginia  22161

                                                  March 1979
                     Kenneth W. Brown
   Monitoring Systems Research and Development Division
     Environmental Monitoring and Support Laboratory
                      P. 0. Box 15027
                 Las Vegas, Nevada  89114
                LAS VEGAS, NEVADA  89114

     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.

     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
                            Environmental Monito-ring and Support Laboratory
                                               Las Vegas

     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

     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.

     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.

     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

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),
      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

      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

 by  its  solubility and also  by the  numerous chemical reactions which occur in

     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
                            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

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

                                            CHAPIN WATERING LINE
                                                f ^MICROSORBAN
                                                «T      FILTER

                        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.

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.
      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

 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-

      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

     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

     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.

  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.

     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

     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.

     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

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

   Harvesting Period     	Plant Species	
 (Days After Planting)
                          Alfalfa   Radish	Rye	Wheat   Tomato




o  1 00-

 Alfalfa  •——-

Tomato ^~

           l          l

         75       113

         Time (Days)
Figure 2.  Concentration of americium-241 in the stem and leaf tissues of

         alfalfa and tomato plants.



g   10-

                                        • Rye

                                 ^—A Wheat
0        38      75      113      150
                           Time (Days)
Figure 3.  Concentration of americium-241 in the stem and leaf tissues of

         rye and wheat grass.

      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.


    Growing Time    	Americium-241 pCi/g  (dry)
(Days) Stem
52 20
149 383
164 267
and Leaves
Percentage Composition (%)

     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).


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Research Series.  EPA 600/3-77-052.  Ecological Research Series.
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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
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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
                                                           3. RECIPIENT'S ACCESSION NO.
 Plutonium-239 and Americium-241 Uptake By Plants  from
             5. REPORT DATE
                March 1979
Kenneth W.  Brown
Environmental Monitoring and  Support Laboratory
Office  of Research and Development
U.S.  Environmental Protection Agency
Las Vegas,  NV  89114
             10. PROGRAM ELEMENT NO.

             11. CONTRACT/GRANT NO.
U.S. Environmental Protection Agency—Las Vegas, NV
Office  of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, NV  89114
     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
                                KEY WORDS AND DOCUMENT ANALYSIS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                             COSATI Field/Group
  Plant Growth
Uptake  from Soil
                                              19. SECURITY CLASS (ThisReport)
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20. SECURITY CLASS (Thispage}
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