H_::_______::____:.:_ m

 

THESE

fl

. ,

THE ABSORPTION AND DISTRIBUTION OF RADIOSTRONTIUM
(3:89) AND RADIORUTHENIUM (1111103) IN

CERTAIN VEGETABLE CROPS

By

Charles Glenn Iohns

AN ABSTRACT

Submitted to the School of Graduate Studies of Michigan

State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

 

Approved by

CHARLES GLENN JOHNS ABSTRACT

The effects of temperature, pH, and time interval between
treatment and harvest upon the absorption of Sr89 by the roots of beans,
tomatoes, corn, and radishwere studied. The plants were grown in nutrient
solutions in porcelain crocks (7 liter capacity) filled with Hoagland's nutrient
solution (1/2 strength) and adjusted to pH levels of either 4 or 6. 7° To
each container was added 10 microcuries of Sr89. Night temperatures of
50° F and 60° F were utilized.

89 to the nutrient cultures the

Following the addition of Sr
plants were harvested at intervals of 24, 72 and 168 hours, and the various
plant parts were dried, ashed, and assayed for radioactivity as cpm/mg
dry weight. Based on the criterion as shown in Table I, the movement of

Sr89

into stems and leaves following root absorption was in general less
for corn than for radish, tomato or bean. The effects of temperature on
the uptake and transport of radiostrnntium in the four crops were not
clearly defined. Generally, temperatures optimum for growth of each crop
resulted in greater accumulation (i. e. tomato at 60° F). As the time inter-
val between treatment and harvest increased there was a general increase
in radioactivity of leaves and stems, but an erratic pattern of radioactivity
accumulation was characteristic of the roots, the latter probably resulting

largely from direct surface adsorption. The effects of pH were most

apparent in the radioactivity of the roots, wherein a greater accumulation

occurred at a pH of 6. 7 again probably resulting from greater surface
absorption than at pH 4. 0. The pH effects on absorption and accumulation in
other plant parts were not clearly defined except in the case of beans grown at
60° F, wherein a pH 4. 0 favored accumulation in leaves and stems.

In studies of absorption of Rum3

by the roots of the tomato

the effects of time and the presence of iron in the nutrient solution were
evaluated. As in the strontium studies, porcelain crocks and Hoagland's
nutrient solution (1/2 strength) were utilized. Three levels of iron, 0,
1.25, and 3. 75 ppm as Fe203 supplied as 17 per cent in sequestrene (sodium
ferric ethylene diamine tet racetate monohydrate) were established. Radio-
ruthenium (Ru103) was added at the rate of 62. 5 microcuries per crock.
Seedling tomato plants were harvested 24, 48, 96, and 144 hours after

the 1111103

was added. Roots, stems, and leaves were assayed for radio-
activity and results expressed as counts per minute per milligram of

dry tissue. The accumulation of Ru103 by the roots, stems and leaves
was directly related to increasing time intervals between treatment and
harvest, and was inversely related to the amount of iron in the nutrient
cultures, and as with Sr89, adsorption directly on root surfaces likely
accounted for a large part of the extremely high radioactivity in the roots.
Leaves generally accumulated per unit dry weight, more radioactivity than
the stems.

The effects of pH of treating solutions and time of treatment

in terms of fruit maturity upon the absorption of Sr89 by the tomato fruit

following an overall spray applied to the above ground plant parts was
studied. Two groups of 15 tomato plants grown in 8-inch pots of soil
were utilized. The plants were trained to a single stern, and pruned to
allow only the first four fruits in the initial flower cluster to develop.
The first spray containing Sr89 (40 microcuries) was applied shortly
following fruit set when the fruits were 1 to 2 cms in diameter, and in
the second group of plants when the fruits were 5 to 8 cms in diameter,
but still green.

The accumulative absorption of the foliar applied Sr89 at
3 pH levels during the growth and maturation of the fruit was determined.
On the basis of the total radioactive contaminant sprayed on the plants
and that recovered in the flesh and seed of the tomato fruit after removal
of the epidermis of the ripe fruit, an expression in terms of per cent ab-
sorption and transport into the fruit was obtained. The pH of Sr89 sprays
did not influence its accumulation in the fruit. Radiostrontium accumu-
lat ed in fruit approaching maturity as well as during the initial stages of
fruit growth. Both the flesh and seed were found highly radioactive, and
as much as 4 per cent of the total radioactivity sprayed on the plants was
found to accumulate in the developing fruit.

Similar results have been obtained with Ruthenium (Ru103).
Whereas it, like radiostrontium, is relatively immobile in the plant with

little basipetal transport, it is absorbed by tomato fruit surfaces and con-

siderable quantities will accumulate in edible portions of plants following

foliar applications.

THE ABSORPTION AND DISTRIBUTION OF RADIOSTRONTIUM
(Sr39) AND RADIORUTHENIUM (Rum) IN

CERTAIN VEGETABLE CROPS

By

Charles Glenn Johns

A THESIS

Submitted to the School of Graduate Studies of Michigan
State University of Agriculture and Applied Science
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Horticulture

1955

ACKNOWLEDGEMENTS

My most sincere gratitude to Dr. Sylvan H. Wittwer for his excellent
judgement and accurate guidance throughout this study.
To Dr. F. G. Teubner for his willingness, enthusiasm, and valuable assist-

ance in many phases of the work, as well as to Dr. W. G. Long, who supplied

an: .a- 5 A .— __‘_____.‘__4_.._..‘_‘ -—-ZI'—'—:1——~—_...— 'L- . .. o,
-_ ._ W _.. -

much of the information needed for me to carry out the necessary analytical

work. To Martin J. Bukovac for sharing many of his ideas and much appreciated

.IA~.u.i..n.'_—x-

help whenever help was required.
And finally to the Biological and Medical Division of the United States Atomic
Energy Commission for supplying the radioactive isotopes and providing the

financial support (Contract AT-(ll—l)—159).

 

361669

TABLE OF CONTENTS

Page
Introduction ...................... 7. 1
Review of Literature . . ................ 2
The Problem for Investigation . . .. . ., w. .' ...... 5
Materials and Methods ................ . 6
Analytical Technic .................. 9
Results ................. ‘ ...... . . 12
Discussion ...................... . 22
Summary ....................... 24

Literature Cited .......... , ....... . . . 26

INTRODUCTION

The advent of nuclear weapons brought with it problems many of which are
not yet fully resolved. The logical approach of the biologist is to learn, if not
how to live with, these problems at least. to what extent they may influence our
future. Radiation "fall out" following an atomic blast poses a serious hazard as
a contaminant especially to vegetation and most especially to the plants on which
man and animals thrive. An attempt has been made in this paper to show the
extent to which some of the products of atomic fission present in "fall-out" are
absorbed by certain vegetable crops through the roots, foliage and fruit. A

. . 89 103
speCIal reference is given to Sr and Ru .

REVIEW OF LITERATURE

It has been demonstrated experimentally that strontium like calcium can be
incorporated into the tissues of plants as well as animals in large quantities. In
animals it behaves like calcium with respect to absorption and excretion (7), and
it has been used to mark the rate of growth of dentine (26). It has been claimed
that radiostrontium has therapeutic possibilities in the treatment of secondary
growths in bone (19). Strontium and calcium are believed to be closely allied in
biological behavior and it has been shown that plants and animals have a calcium/
strontium ratio of about 3/1 (7). Sacks (15) states that although these two elements
have the same general metabolic fate, there are considerable quantitative and
qualitative differences and he advises that it would not be good practice to trans-
fer the data of experiments with radiostrontium to interpretation of calcium metabo-
lism. Tweedy (20) found that 11 per cent of an interperitoneal injection of stron-
tium89 was excreted in the urine of rats in the first 24 hours. When the experi-

45

ment was repeated with calcium the total urinary excretion over a period of

66 hours was only about two per cent of the injected dose (21).

89 90 91, Srgz) are products of

Radioactive isotopes of strontium (Sr , Sr , Sr
atomic fission and constitute about 15 per cent of all fission products (19). They
are said to be the most hazardous of the fission products (23) (Table II). The
deposition in humans, based upon ingestion, inhaltion and parenteral is five to

80 per cent in bone varying with age and existing calcium levels (23) (Table I).

The maximum permissible amounts of strontium89 in the entire human body is

two microcuries (22). As regards the two elements (calcium and strontium) in
plant tissue it is reported (4) that calcium is one of the few essential elements
entering into the framework of the plant. Combining with pectic acid to form
calcium pectate, as a constituent of the middle lamella and no new cell walls are
laid down when calcium becomes limiting. Calcium does not appear to move freely
from older to the younger plant parts even though a large proportion (60 per cent)
in cabbage may be water soluble (24).

Strontium on the other hand is not reported to have any specific function.
However, it has been suggested (29) that a peach leaf chlorosis can be corrected
by strontium sprays. The correction was obtained only on the branches sprayed
indicating little or no strontium translocation to branches not sprayed. Neel
M (13) studied soil-plant-interrelationships on different soils artificially
contaminated with five fission products, Strontiumgo, Cesium 137, Rutheniummé,
Ceriuml44, and Yittriumgl, and reported that Strontium90 moves more readily
in plants than do the other products and suggested that this is due to strontium
being less strongely adsorbed on the soil colloid. All plants demonstrated the
highest activity in the leaves. The seeds, where studied, were the lowest.
Collander (2) reported that calcium and strontium behave in the salt absorption
of plants somewhat as identical ions or two isotopes of the same element.

Selders (17) reported that the maximum concentration of strontium in leaves and

stems of tomato plants occurred in about twenty days.

Strontium has a valence of two, a melting point of 800°C. a boiling pOint of
llSOOC (9). In the form of chlorides it is soluble in slightly acid solution, as the
nitrate it is easily water soluble.

Strontium89 is said to be the isotope best suited for tracer investigation (8).
It is presently the only available radioisotope of strontium which is exclusively a
beta emitter and can be almost completely absorbed by 700 mg. per cm -2

aluminum (11). St rontium89

has a half life of 53 days, a beta radiation of l. 5 m. e. v.
The critical organ in animals is bone.

Unlike strontium, ruthenium has not been associated with any element essen-
tial to plant or animal growth. The metabolism of this element is of interest
primarily because it is a fission product (3). Daily M (5) have shown that
over 3 mg/kg injected into the heart of mice gives chemical toxic effects.

105 injected (interperitoneal and intra-

Scott and Fischer (16) noted that ruthenium
muscular) into mice was not deposited in the skeleton as compared to other tissue
but showed high values in kidney and unusually low uptake in brain. The critical
organ in the animal body is the kidney (3). On the other hand, Walton and Brues (25)
reported higher concentrations in the liver and spleen. With respect to plant
studies, Neel M (13) observed the uptake of ruthenium106 and other products
mentioned above by barley, lettuce, carrot, bean, and radish and indicated that

6
the ruthenium was second only to strontium90

in rate and total uptake.
Ruthemum1°3 has a half life of 39. 8 days, beta radiations of 0.222 and o. 684

and a gamma of 0.494 m. e. v.

THE PROBLEM FOR INVESTIGATION

The purpose of this study was to ascertain the extent of contamination
possible in food crops by the adsorption and transport within plants of radioactive
"fission fall-out" materials. Radiostrontium (Sr89) and Ruthenium (Ru103) con-

stituted the isotopes used, and application to plants were made to the above ground

parts as well as to the roots.

MATERIALS AND METHODS

Four species of plants were used, tomato lLycopersicon esculentum, variety

 

 

Spartan Hybrid; corn, Zea mays, variety Golden Cross; bean, Phaseolus vglgaris,

variety Sweetheart; and radish, Raphanus sativus, variety Comet. Plants were

 

grown from seeds sown in flats containing vermiculite. When approximately
1-1/2 inches in height they were then transferred either to benches of quartz sand ,
water cultures or to clay pots of soil.

For the nutrient cultures the formula which follows was used and represents
a modification of Hoagland's solution as described by Curtis and Clark (4). The

solution was prepared in 400 liter batches at one-half its recommended strength.

Hoagland Solution (one-half strength)

 

Nutrient Concentration ppm Carrier
Nitrogen 105 Ca(NO3)2 KNO3
Phosphorous 15. 5 KHZ P04
Potassium 117. 5 KHZ P04 KNO3
Calcium 100 Ca(NO3)2
Magnesium 24 MgSO4
Sulfur ‘ 32 ' Mgso4

I Iron 1. 25 Na sequestrene
Boron . 25 H 3 BO3

Manganese .25 McClz 4H20
Zinc .025 zttso4 7H20
Copper . 01 CuSO4 SHZO
Molydenum . 005 HZMO O4 H20

The plants were grown in solution culture in two gallon glazed crocks accord-
ing to the method described by Asen, _e_t_. _a_I_1. (1). Each crock was supplied with
a 12" square masonite cover with enough holes to insert four plants and an air
supply. The plants were supported in the holes by styrofoam plugs fitted to pro-
per hole size. Air entered each crock by the use of tygon plastic tubing fitted on
the end with a porous air stone. Prior to addition of the isotope solution the pH
of the solutions was adjusted by the use of a pH 4. 0 Acetic acid-Sodium acetate
buffer and a pH 7. 0 Di—Mono potossium phosphate buffer as described by West
and Todd (27) and by means of a Beckman model H2 pH meter. After the solutions
were contaminated with radioactivity, color indicator paper was utilized. The pH
of the original solution varied from 4. 8 - 5. 8 and the amount of buffer needed to
reach the desired pH levels ranged from one drop to 2. 8 cc. Duplicate experi—
ments were run at both 500 and 60°F night temperatures. After the plants were
in the containers over night to equilibrate, the covers were lifted so the roots were
not in the solution and the radioactive materials were pippetted into each container.
The solutions were left to stand for ten minutes before replacing the plants. The
cultures were kept well aerated. The rate of air was adjusted by means of a
main needle valve plus an individual screw clamp fixed to the inlet of each con-

tainer.

Eight inch standard clay pots were utilized for growing tomato plants in soil.
The plants were pruned to the first cluster, staked and the first fruit cluster
grown to maturity. When radioisotopes were sprayed on the foliage the entire
pot was wrapped with polyethelene film to prevent soil contamination. All tests
were conducted in the greenhouse between September 1954 and May 1955 when

some degree of temperature control was possible.

ANALYTICAL TECHNIC

103 89

The radioactive isotopes, ruthenium , and strontium were secured from
the Atomic Energy Commission's pile reactor at Oak Ridge, Tennessee. The
first shipment of Sr89, received December 26, 1954, was in the form of carrier
free Sr Clz. A later shipment on March 24, 1955 was received as Sr(No3)2_

The two shipments of Ru103

came as carrier free Ru103Cl3 in l. 0 N HCl solution.
Following treatment, plants were harvested at different time intervals and separated
in some cases into root, stem, and leaf and in other instances stem, leaf, and
fruit. The three plant parts were separately dried in paper. bags. Following

24 hours in a 70°C oven, the plant material was weighed and ashed either in a
muffle furnace at 525°C or wet ashed, and taken up in concentrated nitric acid.
One ml. of the wet ashed sample was put into a stainless steel container and

dried. The dry ashed material was dissolved in two mls of water and trans-
ferred to stainless steel planchets and taken to dryness either by a thermostatically
controlled hot plate or 150 watt infra red heat lamps, the infra red lamps proving
to be more desirable. All samples in the stainless steel planchets were assayed
for radioactivity. The samples were counted with a Nuclear model number 172
scaler utilizing an end window counting tube in a lead shield. Half life corrections
were determined according to Jaffey (9). Since Scott and Fischer (16) had reported

high losses by volatilization of ruthenium over 3000C, all ruthenium samples were

wet ashed as described on a steam bath at temperatures not exceeding 215°C.

10

The samples were evaporated to dryness with heat lamps and the radioactivity
determined using proper conversions for total sample activity. Radioactivity
measurements are expressed as counts per minute per milligram dry weight and
the per cent uptake in each plant part is based upon the total initial radioactivity
applied.

Autoradiograms, (Figures 1 and 2) illustrating the uptake of radioruthenium .
and strontium by young tomato plants were prepared according to the methods
described by Wittwer and Lundahl (28). Eastman Kodak Medical X-Ray No-Screen
film eight by ten inch size and Liquid X-Ray film developer and fixer were used

for developing the autoradiograms.

Figure l. Autoradio ams showing the distribution of radio-
ruthenium (Rul 3') in the tomato plant following application
to the root medium.

Left: after 96 hours. Right: after 48 hours.

 

12

RESULTS
Experiment I

The effects of temperature, pH, and time interval between treatment and harvest
upon the absorption of Sr89 by the roots of the bean, tomato, corn, and radish
were studied. The plants were grown in nutrient solution in two gallon glazed
crocks. In each of the 36 containers (18 per temperature) were grown one of
each of the four species. After the plant roots were in the respective solutions
for 24 hours ten microcuries of Sr89 was pippetted into each container. The 18
containers in each house were divided into three groups of six and harvested at
24, 72, and 168 hours following treatment. The plant parts were harvested, ashed,
and assayed for radioactivity as cpm/mg dry weight.

As is shown in Table I, the movement of Sr89 into stems and leaves follow-
ing root absorption was in general less for corn than for radish, tomato or bean.

The effect of temperature on strontium89

absorption by the roots of the four crops
are not clearly defined. Generally temperatures approaching the optimum for
vegetative growth of each crop re sulted in greater accumulation (i. e. tomato at
60°F). As the time interval between treatment and harvest increased there was

a general increase in radioactivity of leaves and stems but an erratic pattern of

radioactivity accumulation was characteristic of the roots, the latter probably

resulting largely from direct surface adsorption. The effects of pH were most

l3

apparent in the radioactivity of the roots. Greater accumulations occurred at a
pH of 6. 7 probably resulting again from greater surface adsorption than at pH
4. 0. Ph 4.0 except in leaves and stems in the case of beans grown at 60°F

favored accumulation.
Experiment 11

The tomato, Lycopersicon esculentum, variety Spartan Hybrid, was utilized

for absorption studies of Ru103 by the roots. As is indicated in Table II, the

 

effects of time and the presence of iron in the nutrient solution were evaluated.
The nutrient solutions (Hoagland) were formulated at three levels of iron 0, l. 25,
and 3. 75 ppm with Fe203 supplied in a chelated form (sodium ferric ethylene
diamine tetracetate monohydrate). Seedling tomato plants grown in quartz sand
were transferred to nutrient solutions and allowed to equilibrate for 24 hours.
Radioruthenium (Ru103) was then added at the rate of 625 microcuries to each
crock. The plants were harvested after 24, 48, 96, and 144 hours and separated
into roots, stems, and leaves and dried. The dried tissue was then weighed,

one hundred mls of concentrated HNO3 added to each sample and digested over

a steam bath until all the tissue was completely digested and in solution. A one
ml aliquot of this solution was transferred to a stainless steel planchet and dried.
The samples were assayed for radioactivity and results were expressed as counts
per minute per milligram of dry tissue. Autoradiograms (Figure I) were taken

of plants at 48 and 96 hours after treatment.

14

The accumulation of Ru103 by the roots, stems, and leaves, as shown by
Figure I and Table II was directly related to increasing time intervals between
treatment and harvest. Accumulation was indirectly related to the amount of

iron in the nutrient cultures, and as with Sr89

adsorption directly on root sur-
faces likely accounted for the extremely high radioactivity in the roots. Leaves

generally accumulated, per unit dry wt. , more radioactivity than the stems.
Experiment III

Fruit absorption of radiostrontium (Sr89) sprayed on the entire tomato
plant at various stages of fruit size was next ascertained. As shown in Table III,
the variables consisted of pH of treating solution and time of treatment with
respect to size of fruit.

Tomatoes were grown in eight inch standard clay pots to a stage of maturity
where the lower cluster contained enough fruit where four young tomatoes could
be selected within a size range of between one and two centimeters in diameter.
Forty tomato plants were selected for this experiment from over three hundred
plants. Fifteen, five at each pH level, were sprayed when the fruit was one to
' two centimeters in diameter. A second fifteen plants were similarly treated when
the fruits were of a diameter of five to eight centimeters. The plants were sprayed
with one hundred mls (forty microcuries) of a solution of Sr89 by the use of a
"sure shot" pressure sprayer (two hundred ml capacity)l. To prevent contamina—

tion of the surrounding area, two 3 foot diameter fiber drums Were attached one

 

1. Sure Shot Sprayer Company, Milwaukee, Wisconsin.

Figure 2. Autoradio ams showing the distribution of radio-
strontium (Sr8§)Tin the tomato plant following application
to the root medium (24 hours after treatment).

 

16

 

 

 

 

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17

TABLE II

THE UPTAKE OF RADIORUTHENIUM (Ru103) BY THE ROOTS OF TOMATO AND
TRANSPORT TO STEMS AND LEAVES AS INFLUENCED BY THREE LEVELS OF)
IRON IN THE NUTRIENT CULTURES AND TIME INTERVAL BETWEEN TREAT-

MENT AND HARVEST

 

Levels of Plant Interval between treatment and harvest (hours)
Iron (ppm) , Part 24 48 96 144
(Counts per minute per milligram dry wt.

 

0 root 3, 169 4, 186 6, 000 22, 756
stem 23 45 130 178
leaf 31 45 256 266
l. 25 root 3, 230 2, 173 2,178 14, 629
stem 27. 4 31 70 161
leaf 24 38 156 204
3. 75 root 1, 789. 0 2, 020 2, 547 11, 378
stem 23 37 64 110
leaf 26 44 120 167

 

15

above the other. The pot was wrapped in a piece of polyethylene film tied on

the base of the stem. Both the plant and drum were placed in a pan with four inch
sides which was lined with water absorbent diaper paper.1 The plants were
sprayed from above and allowed to dry bebre moving to the bench, and removal
of the polyethylene film. When the fruit had matured and was fully ripe the
plants were harvested and each part dried, ashed and prior to assaying the

fruit the skins were carefully removed and the radioactivity of the pulp and seeds
determined. Table III shows no apparent difference in the incorporation Of radio-
activity into the fruit uptake as the result of the three pH levels. Radiostrontium
also accumulated in approximately the same amount in fruit sprayed at the two
stages of fruit maturity. Both flesh and seeds were found highly radioactive and
as much as four per cent of the total radioactivity sprayed on the plants was

recovered in the fruit after the skins were removed (Table III).
Experiment IV

Similar to experiment III with Sr89, the absorption of radioruthenium
(Ru103) by the tomato fruit from foliage sprays Of varying pH levels as related
to fruit size was studied. Experiment IV was a duplication Of experiment III with
respect to materials and methods. With radioruthenium (Ru103) pH played a

significant role in the accumulation Of radioactivity in tomato fruit. The dif-

ference between pH 2. 0 and pH 4. 0 was significant at a one per cent level as is

 

l. Kimball Paper Company, Kenosha, Wisconsin.

19

TABLE III

THE INCORPORATION OF RADIOSTRONTIUM (Sr89) FROM F OLIAR SPRAYS
INTO THE DEVELOPING TOMATO FRUIT AS INF LUENCED BY pH OF TREAT-

ING SOLUTIONS AND TIME OF TREATMENT AS RELATED TO FRUIT MATURITY

 

 

 

Maturity Total radioactivity Radioactivity % of
pH of fruit cms applied . . in fruit Total activity
2.0 1-2 32, 600 1, 304 4. 0
5-8 34,197 1,041 3.0
4.0 1-2 32, 741 310. 6 1.0
5-8 41, 017 l, 640 4.0
6.0 1-2 33,500 884 2.6
5—8 36, 440 l, 214 3 3

20

Shown in Table IV but no significant difference was noted between pH 4. 0
and 6. 0. The time of treatment as related to fruit size was significant at
the one per cent level irrespective of pH. The plants treated when the fruit
was one to two centimeters in diameter accumulated four times as much
radioactivity as compared with spraying the plants when the fruit was five

to eight centimeters in diameter.

21

TABLE IV

THE INCORPORATION OF RADIORUTHENIUM (Ru103) FROM FOLIAGE SPRAYS
INTO THE DEVELOPING OF THE TOMATO FRUIT AS INFLUENCED BY THE pH
OF TREATING SOLUTION AND TIME OF TREATMENT AS RELATED TO FRUIT

SIZE

 

 

Per cent radioactivity
applied to above ground
parts recovered in fruit

 

 

pH (Fruit size in centimeters) Mean
1;: 1;?
2.0 2. 3 0.9 1.6
4. O 1.3 0.2 0 8
6. 0 __l_._0_ Q_._2 0.6
Mean 1. 6 0.4
L. S. D. 0.3 L.S.D.

for fruit size for pH 0.4

 

22

DISCUSSION

The absorption of radioruthenium (Ru103) and radiostrontium (Sr89) by
various plant parts has been studied. Rediske and Selders (14), Martin (12), and
Neel at; £03) have found that strontium can be accumulated in plants in rather
large amounts. Neel i al. (13) also studied an isotope Of ruthenium, (Ru106)
and found that it too is taken up by plants although Comar(3) states that ruthenium
does not ordinarily Occur in plants. That is, it is not chemically detectable by
present means of chemical analyses. Experiment I, therefore, substantiates what
has been thus far reported and gives additional information with respect to effects
of pH of the growing medium and temperature on strontium (Sr89) absorption.

Experiments III and IV are somewhat different in that the foliage of the
tomato plant was sprayed by solutions of the two radioactive "fall-out" materials
in an attempt to "Simulate" actual conditions when crops might be contaminated
following an atomic blast. It was found that both radiostrontium (Sr89) and
radioruthenium (Ru103) can be incorporated into the edible portion Of an economic-
ally important Vegetable crop. Removal of the Skin or peeling the fruit did not
eliminate the hazard. Rediske and Selders (14) state that the emphasis in the
study of the absorption of fission products by plants is in being able to estimate
the degree Of absorption Of the element by a plant from its natural environment
Whether a plant in its natural environment would be introduced to the products

of atomic fission in such quantities as it experiment III and IV has not been

23

ascertained but would appear very likely. However, it is feasible that a relation-
ship can be set up for each isotope to determine what portion based on percentage
falling on a plant will enter a plant after it has been Offered a certain concentra-
tion. These experiments it would seem, could serve as a basis for field
experiments with no great difficulty.

In experiment II an attempt was made to determine whether an essential
element such as iron, could influence the accumulation Of a chemically allied
substance, ruthenium. This was found to be the case. To run field experiments
with ruthenium and iron, however, would not seem practical since it would be
more difficult to maintain exact levels due to the minute amounts of these elements
that would normally be applied. A small change on the soil complex would
undoubtedly influence their availability. Information thus far gathered on the
absorption and distribution of radiostrontium (Sr89) and ruthenium (Ruloz) in
plants herein reported should be of value as a basis for futher Studies on the

incorporation of these materials in living organisms following atomic fission.

24

SUMMARY

The effects of temperature, pH, and time interval between treatment and
harvest upon the absorption of Sr89 by the roots of beans, tomatoes, corn, and
radish were studied.

The movement of Sr89

into stems and leaves following root absorption was
in general less for corn than for radish, tomato or bean. The effects of temperature
on the uptake and transport Of radiostrontium in the four crops are not clearly
defined. Generally temperatures Optimum for grth of each crop resulted in
greater accumulation (i. e. tomato at 60°F). As the time interval between treat-
ment and harvest increased there was a general increase in radioactivity of
leaves and stems but an erratic pattern of radioactivity accumulation was character-
istic of the roots, the latter probably resulting largely from direct surface adsorp-
tion. The effects of pH were most apparent in the radioactivity of the roots,
wherein a greater accumulation occurred at a pH Of 6. 7 again probably resulting
from greater surface absorption than at pH 4.0. Pb effects on absorption and
accumulation in other plant parts were not clearly defined except in the case of
beans grown at 60°F wherein a pH 4. 0 favored accumulation in leaves and stems.
The accumulation of Ru103 by the roots, stems and leaves was directly related
to increasing time intervals between treatment and harvest. The accumulation

was inversely related to the amount Of iron in the nutrient cultures, and as with

Sr89, adsorption directly on root surfaces likely accounted for a large part Of

25

of the extremely high radioactivity in the roots. Leaves generally accumulated,
per unit dry wt , more radioactivity than the stems.

The effects Of pH Of treating solutions and time of treatment in terms of
fruit maturity upon the absorption of Sr89 by the tomato fruit following an overall
foliage spray applied to the above ground plant parts was studied. Ph of Sr89
sprays did not influence its accumulation by the fruit. Radiostrontium likewise
accumulated in fruit approaching maturity as well as during the initial stages of
fruit growth. Both the flesh and seed were found highly radioactive and as much
as four per cent of the total radioactivity sprayed on the plants was found to in-
corporate intO the developing fruit even after removal of the Skin.

Similar results were obtained with Ruthenium (Ru103). Like radiostrontium,
it was relatively immobile in the plant with little basipetal transport. It was
absorbed by tomato fruit surfaces and considerable quantities accumulated in
edible portions of plants following foliar applications. The accumulation in the

ripe fruit was greatest when the treating solutions had a pH of two and when the

fruits were treated while small in Size.

10.

ll.

12.

26

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