Effects of simulated radioactive fallout decay on growth and yield of cabbage, maize, peas and radish

Reldiation Botany, 1969, Vol. 9, pp. 77 to 92. Pergamon Press. Printed in Great Britain.

EFFECTS OF SIMULATED R A D I O A C T I V E F A L L O U T DECAY ON G R O W T H AND YIELD OF CABBAGE, MAIZE, PEAS AND RADISH* A. H. S P A R R O W mad LEANNE PUGLIELLI Biology Department, Brookhaven National Laboratory, Upton, New York 11973

(Received 1 August 1968) A b s t r a c t - - A n apparatus designed to simulate the decay of radioactive fallout from nuclear detonations is briefly described and data are reported from experiments undertaken to determine the relative effectiveness of similar total exposures of 187Cs gamma radiation given at uniform exposure rates vs. simulated fallout decay. Seedlings of pea, maize, cabbage and radish were given three different treatments (16-hr and 36-hr uniform dose-rate exposures, and a 36-hr simulated fallout decay exposure with changing dose rates). Seedlings were exposed to 13~Cs y-radiation and transplanted to the field (maize and cabbage) or moved to a greenhouse for observation (radish and pea). Data on plant survival, gross vegetative growth, crop yield and pollen abortion are reported from scorings made weekly for up to about three months. Comparisons were made among the three radiation treatments for the survival end points (LD10, LD60, LD,0 and gD100) and the 50 per cent reduction in fresh weight and crop yield. I n all experiments the simulated fallout decay gamma exposure produced more deleterious effects than an equivalent total exposure delivered at uniform rates. (The 16-hr exposure produced more severe effects than similar exposures delivered in 36 hr.) When the results of 36-hr uniform exposures were compared to those from the 36-hr simulated fallout decay, the average increase in effectiveness varied from a factor of 1.79 to a factor of 2.04, with the average for all end points being 1.93 (almost a factor of 2 greater). Exposures which gave reductions of 50 per cent in fresh weight and crop yield for the same two radiation treatments varied by a factor of 1.59 to a factor of 2" I 1 with an average increase in effectiveness for all end points of 1"80 for the simulated fallout exposures. Predicted LD58Sfor 16-hr uniform and 36-hr FDS exposures based on measured interphase chromosome volumes are given for 49 varieties of economic plants. R ~ s m m & - O n d6crit bri&vement un appareil destin6 h simuler le d6cours des retomb6es radio-actives provenant d'une explosion nucl~aire. O n rapporte les donn6es d'exp6riences r~alis*es en rue de d6terminer l'efficacit6 relative de relies expositions totales aux rayons gamma du ls~Cs ~tdes d6bits de dose uniformes en comparaison avec des d6bits simulant une retombde. Des plantules de pois, de mais, de choux et de radis ont 6t6 trait6es de trois fa~ons diff~rentes (16 hr et 36 hr de d~bits de dose uniformes et 36 hr d'exposition simulant une retomb*e doses variables). Les plantules ont 6t6 expos~es aux rayons gamma du nTC,s e t transplant6e en champ (mais et choux) ou en serre pour observation (radis et pois). O n rapporte diff6rentes donn~es sur la survie des plantes, la eroissance v6g6tative, le rendement et la d6g6n*rescence pollinique, provenant de relev~s hebdomadaires effectu~s pendant une p6riode d'environ 3 mois. O n compare la survie finale obtenue apr~s les 3 traitements (DLt0, DLs0, DL,0 et DL100) ainsi que la r6duction de 50 ~o du rendement. Au cours de toutes les experiences, l'exposition anx * Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission and the Office of Civil Defence, Department of the Army, Washington, D.C., under Task Order No. 3130(68). 77

78

A. H. SPARROW and LEANNE P U G L I E L L I rayons gamma simulant une retomb& radio-active produit plus d'effets dfildt&es qu'une dose totale, dquivalentc, donn~e ~ des ddbits uniformes. (L'exposition de 16 hr produit des effets plus s&~res que des expositions similaires de 36 hr). Lorsque l'on compare les rdsultats d'expositions uniformes de 36 hr ~ celles o~ la retomb6e est simul6e, l'accroissement moyen d'efficacitd varie d'un facteur 1,79 ~ un facteur 2,04, avec pour chaque effet terminal une moyenne de 1,93 (presqu'un facteur 2). Des expositions qui ont produit une rdduction de 50 % de poids frais ainsi que de rendement pour les deux irradiations varient par un facteur 1,59 ~t un facteur 2,11 avec un accroissement moyen d'efficacit~ pour chaque effet terminal de 1,80 pour les retomb&s simuldes. La DLs0 prddite (sur la base des mesures de volumes chromosomiques en interphase) pour une exposition uniforme de 16 hr et une exposition de 36 hr simulant une retomb&, est donnde pour 49 vari&& de plantes d'int~r~t ficonomique.

Zusamumenfassung--Eine Vorrichtung, konstruiert, um den Zerfall radioaktiven Niederschlags aus einer Kernexplosion zu simulieren, wird kurz beschrieben, und Ergebnisse yon Versuchen werden ertirtert, die unternommen wurden, um die relative Wirksamkeit/ihnlicher Gesamtdosen einer x37Cs Gammastrahlung zu bestimmen, die bei einheitlichen Raten bzw. im Vergleich dazu bei der Simulierung radioaktiven Niederschlags verabreicht wurde. Keimlinge yon Erbsen, Mais, Kohl und Rettich wurden 3 verschiedenen Behandlungen unterzogen (16 Std., 36 Std. einer Bestrahlung bei einheitlichen Dosis-Raten und 36 Std. einet Bestrahlung bei simuliertem Zerfall radioaktiven Niederschlags unter wechselnden Dosis-Raten). Die Keimlinge wurden einer laTCs Gamma-Strahlung ausgesetzt und auf das offene Feld verp- ° flanzt (Mais und Kohl) oder in ein Treibhaus zur Beobachtung gebracht (Rettich und Erbsen). Ergebnisse tiber die ¢,]berlebensrate der Pflanzen, tiber das vegetative Brutto-Wachstum, den Ernteertrag und das Absterben des Pollens werden er6rtert auf Grund yon Z/ihlungen, die ungefiihr 3 Monate lang w6chentlich vorgenommen wurden. Vergleiche wurden gezogen zwischen den 3 Arten der Bestrahlung hinsichtlich der Uberlebenden-Endwerte (LDlo, LDSO,LD9ound LD100)und der 50%igen Verminderung an Frischgewicht und Ernteertrag. Bei allen Versuchen ftihrte die Gammastrahlung bei Simulierung radioaktiven Niederschlags zu mehr sch~idlichen Wirkungen als eine entsprechende Gesamtstrahlung, die bei einheitlichen Raten verabreicht wurde. (Die 16-Std. Bestrahlung riefmehr starke Sch~idigungen hervor, als/ihnliche Dosen, die wfihrend 36 Std. gegeben wurden). Beim Vergleich der Befunde, die sich nach 36-stiindiger Bestrahlung unter Verwendung einheit]icher Raten ergaben und derjenigen Ergebnisse, die auf der 36-sttindigen Bestrahlung unter Bedingungen des simulierten Zerfalls radioaktiven Niederschlags basierten, variierte die durchschnittliche Zunahme der Wirksamkeit zwischen einem Faktor yon 1,79 und einem Faktor yon 2,04, wobei der Durchschnitt aller Endwerte 1,93 betrug (also fast um den Faktor 2 gr6sser). Dosen, die zu 50%igen Verminderungen im Frischgewicht und Ernteertrag bei diesen beiden Behandlungsmethoden fiihrten, schwankten zwischen einem Faktor yon 1,59 und 2,11, n i t einer durchschnittlichen Zunahme in der Wirksamkeit ftir alle Endwerte yon 1,80 fi~r die Dosen, die unter den Bedingungen des simulierten Zerfalls yon radioaktivem Niederschlag gegeben wurden. Ffir 49 Variet~iten yon Nutzpflanzen werden aufGrund yon gemessenen Interphasen-Chromosomen-Volumina vorausberechnete LD~0-Werte gegeben, und zwar for die 16-Std.-Bestrahlung bei einheitlichen Dosen und ftir die 36-Std. bei simulierung radioaktiven Niederschlags.

INTRODUCTION EVALUATION of the possible h a z a r d of fallout r a d i a t i o n resulting in direct i n j u r y to crops growing in the field (i.e., not i n c l u d i n g the p r o b l e m of c o n t a m i n a t i o n ) in a n i m m e d i a t e p o s t - n u c l e a r - a t t a c k p e r i o d involves m a n y variables. Some of the factors which must be con-

sidered are (1) the a c t u a l exposure rate, d u r a t i o n of exposure, a n d k i n d a n d a m o u n t of r a d i a tion; (s) (2) the n a t u r e of crop or crops c o n c e r n e d , i.e., w h e t h e r root, leaf, fruit, or seed crop, or some c o m b i n a t i o n such as broccoli; (3) the relative radiosensitivity of different p l a n t species or varieties;C3, e, 7) (4) the age, size a n d condition

EFFECTS OF SIMULATED RADIOACTIVE FALLOUT DECAY of the crop plants during exposure;(n,12,14, TM 3~,371 (5) the climatic or enviromnental conditions(13,16,20) such as temperature, day length, season,(2'q) growth rate, etc; and (6) the usability of the harvested crop, i.e., its wholesomeness and acceptability as food. Several of these factors are considered in this report. Much is already known about the sensitivity of growing plants to both chronic (for references see(24)) and acute radiation exposures,( 1°, 2~) but this information has generally been based on uniform exposure rates and only a few Of these(2,4, 5) are concerned with hazards of fallout(IS, ~9,35) or simulated fallout radiation to economic plants.(4, 5) When considering the variable exposure rates characteristic of fallout fi'om nuclear detonations, questions arise concerning (1) the extent of the difference, if any, in the effects on plants of decaying-dose-rate exposures as compared with uniform-dose-rate exposures where the total exposure is approximately equivalent, and therefore (2) the validity of trying to extrapolate from the already available acute and chronic data to the effects of estimated decaying exposure rates of fallout from nuclear detonations. The data reported here are from a series of experiments undertaken to establish the degree of difference in effects between equivalent total exposures given with simulated fallout decay compared with uniform exposure rates. In these preliminary experiments, it was considered desirable to hold other variables to a minimum, hence all plants were irradiated as young seedlings, although one root crop, one leaf crop, and two seed crops were used as the test plants. Observations were concerned primarily with percentage survival and reduced vegetative growth.

79

golden bantam; and cabbage, Brassica oleracea var. capitata H V ferrys round dutch) were also used in this experiment. The seeds were germinated in 2-in. peat pots in the greenhouse. At the seedling stage (2-3 weeks after germination), they were divided into three groups and exposed to aaTCs y-radiation in the following manner: (1) a 16-hr acute exposure (uniform exposure rate) ; (2) a 36-hr acute exposure (uniform exposure rate); and (3) a 36-hr simulated fallout decay exposure (changing exposure rates). A total of 16 exposures using 25 plants per exposure were used in each of the three irradiations. The exposure series was obtained by placing the plants in concentric arcs at various measured distances from the source during the radiation period. After irradiation the plants were transplanted either to the field (maize and cabbage) or to 4-in. pots and maintained under greenhouse conditions (radish and pea). Weekly scorings were continued until there were no more deaths due to radiation. At the time of irradiation, 25 control seedlings were weighed and the average fresh weight of the seedlings recorded. When the plants were harvested, this initial fresh weight was subtracted from the final weight of the plants to indicate the amount of growth after irradiation. When possible, pollen abortion and yield data were also collected. The end points used w e r e L D I o , L D s 0 , L D g 0 , LD100 (the exposures required to reduce survival to 90, 50, I0 and 0 per cent respectively, expressed in per cent of control) and 50 per cent reduction in fresh weight, crop yield and/or pollen abortion expressed as per cent of control. Except for the LD100, which was the actual value, the end points were determined by interpolation from the survival curves fitted by probit approximation on a CDC 6600 computer.

MATERIALS A N D M E T H O D S

A pilot experiment using radish (Rapham~s sativus H V cherry belle) was undertaken. Seedlings were exposed to 137Cs y-radiation during a 16-hr acute exposure (uniform exposure rates) and a 36-hr simulated fallout decay exposure (changing exposure rates). A thirty-six hour acute exposure (uniform exposure rate) was added as a third treatment in later experiments. Three other species of economic plants (pea, Pisum salivum H V alaska; maize, Zea mays H V

FaUout decaysimulator (FDS) In 1964, a facility designed to sinmlate fallout decay was installed at Brookhaven National Laboratory. This facility containing approximately 400 Ci of 137Cs is located in an open pit inside the outer fence of the g a m m a field (see Fig. la). A new fallout decay simulator (FDS) containing 12,000 Ci of X'~TCs(see Fig. lb) was installed in 1965 in the Controlled Environment Radiation Facility (CERF) built as an integral

A. H. SPARROW and LEANNE PUGLIELLI

80

readings were corrected for temperature, pressure, and the chamber correction factors for 1~7Cs as supplied by the National Bureau of Standards. Dosimetry for the C E R F fallout simulator was performed by R. Woodley, using lithium fluoride dosimeters. Measurements were made at 0.4, 1, 2, and 4 m from the source, and the dosimetry readings in rads were converted to roentgens by the use of the conversion factor 0.96. In order to simplify the calculations, it was assumed that fallout arrived at H + 1 (I hr after detonation) and that deposition was complete at that moment. T h e total exposure accumulated from fallout decay can then be related to a reference exposure rate using the

part of the new radiobotany wing at Brookhaven.(24) These simulators were designed to permit the exposure of biological material to decreasing intensities of radiation in order to simulate the exposure to fallout radiation which decays according to the T -~'2 law. The reduction of radiation intensities is accomplished by lowering, at appropriate times, a series of five concentric stainless steel shields around the source during the exposure period. Each shield tlfickness was machined to reduce the radiation intensity by approximately one-half using the absorption coefficient of iron. These configurations vary from no shield to a shield thickness equal to approximately 5 half-value layers (Table 1). The shields can be lowered automatically at predetermined times (Table 1) to

Table I. Physical parameters of the shields and exposure times usedfor the FDS (CERFfacility)

Thickness of added shield, cm

Shield configuration

No. of shields in use

1

0

0

2 3 4 5 6

1 2 3 4 5

2.95 2.30 2.00 1.90 1.90

simulate the decay rate of fallout from various hypothetical nuclear detonations.i°) It is thus possible to compare the radiation effect produced by decreasing exposure rates with that obtained from the same total exposure produced at a uniform exposure rate. Dosimetry Dosimetry was performed in the outside fallout decay simulator by C. Flood of the Instrumentation and Health Physics Department using Victoreen R chambers (0"25 R, 2.5 R, and 25 R) with the Victoreen electronic charger Model 570. Measurements were made at 0.5, 1, 2, and 4 m from the source, and the chambers were irradiated at the source height which is about 5 in. above the ground. All

Total thickness, cm 0

2.95 5.25 7.25 9.15 11.05

Exposure time, hr 1.5 1.5 4.0 8.0 12.0 9.0

following equation :C9) D = 5 R1 (ta -0"2 -- tb-0"2)

(l)

where D = the exposure received between times ta and tb (in this case, the exposure received between ta -~ 1 hr and tb = 36 hr during a 36-hr simulated fallout decay exposure). R 1 = the exposure rate at H + 1 (unit-time reference exposure rate). This reference exposure rate can be used to determine the exposure rate at any time b by the use of the relation: Re = R1 T -1"2 (2) where Re = the exposure rate at any time T after detonation. Values of D were obtained through measurements at 0.4, 1, 2, and 4 m for the C E R F facility

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F1o. I. (a) The 400 Ci FDS field facility at Brookhaven National Laboratory; (d) The 12,000 Ci FDS CERF facility located in a shielded room below ground Level; (c) A representative FDS exposure series of pea; (d) Comparison of the effects of the three different radiation treatments on pea.

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,.,v,,,,,v,.~ FIo. 7. Representative plants of irradiated maize (a-c) and radish (d) demonstrating the difference in effect of the 16-hr uniform and FDS tleatments. (a) control; (b) 16-hr uniform; (c) FDS; (d) 16-hr plants on the left in each group of two, FDS plants on the right.

EFFECTS OF SIMULATED RADIOACTIVE FALLOUT DECAY and at 0.5, 1, 2, and 4 m for the outside facility. The reference exposure rates were calculated from equation (1) and were used in equation (2) to calculate the corresponding decay curves shown as the smooth curves in Fig. 2. T h e stepped curves show the exposure rate delivered in the simulator employing the shields and the exposure times required to approximate the T -1"~ exposure. The exposure rates in R/hr

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A. H. SPARROW and LEANNE P U G L I E L L I

82

Table 2. Exposure rates (kR/hr) at various distances (m) from the 13~Cs source (CERF FDS) with the various shield configurations (see text)

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1.050 0.298 0.139 0.067 0.035 0.016

0.269 0.077 0.038 0.018 0.010 0-005

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Fie. 3. Accumulated exposures in the FDS (CERF facility) during a 36-hr exposure at 1 meter from the source and the total accumulated exposures expected during the same period from a T -1"2 decay cm've.

T h e p l a n t s were i r r a d i a t e d in the outside s i m u l a t o r for 35 hr. D u r i n g t h a t time, the plants received 50 p e r cent of the total fallout exposure they w o u l d n o r m a l l y receive b e t w e e n H -F 1 a n d infinity, a n d 75 p e r cent o f the total fallout exposure they w o u l d receive b e t w e e n H 4- 1 hr a n d H + 2 weeks. Plants were i r r a d i a t e d in the C E R F facility for 36 hr. D u r i n g t h a t time, they received 51 p e r cent of the total fallout exposure between H + 1 a n d infinity a n d 74 p e r cent o f the total fallout received b e t w e e n H + 1 h r a n d H 4- 2 weeks. Therefore, even though the exposure p e r i o d for the F D S was 36 hr, the plants a c t u a l l y received a large

EFFECTS OF S I M U L A T E D R A D I O A C T I V E F A L L O U T DECAY p r o p o r t i o n of the total fallout they w o u l d receive u n d e r n a t u r a l conditions. T a b l e 3 shows the c o m p a r i s o n b e t w e e n the a c t u a l a c c u m u l a t e d exposure in the F D S (the exposures for each o f the six shield configurations are also given) a n d the c a l c u l a t e d expected value.

83

F D S , the a v e r a g e increase in effectiveness for all the end points v a r i e d from a factor of 1.79 to a factor of 2.04, w i t h the average of all end points being 1.93 (almost a factor of 2 greater). D a t a on o t h e r end points m o r e closely related to yield are shown in Fig. 6. T h e exposures

Table 3. Comparison between the actual accumulated exposure (kR) in the FDS and the calculated expectedvalue (exposuresfor each of the six shield configurations are also given) Exposure in kR for shield configurations Distance, m

1

2

3

4

5

0"4 1'0 2"0 4-0

30.20 5.58 1.58 0.40

9.79 1.83 0.45 0.12

10.40 1.91 0.56 0.15

9-20 1.93 0.53 0.15

6.61 1.39 0.41 0.12

6

Actual simulator total*

Expected fallout total]"

2.21 0.44 0.15 0.05

68.41 13.08 3-68 0.99

68.42 13.08 3.67 0.98

* Total exposure delivered in the fallout simulator at the various distances. ]. Total calculated exposure between H + 1 hr and H + 36 hr based on the T -1"2 law (see text). R E S U L T S A N D DISCUSSION

T h e survival curves for the four species are shown in Fig. 5. LD10, LDs0, a n d LDg0 exposures o b t a i n e d b y p r o b i t analysis of the survival curves i n d i c a t e that, w i t h i n each species, the s i m u l a t e d fallout d e c a y g a m m a exposures produce m u c h m o r e deleterious effects t h a n a n equal a m o u n t of r a d i a t i o n delivered at u n i f o r m exposure rates. T a b l e 4 s u m m a r i z e s the exposures for each o f the survival end points studied. I n general, those p l a n t s exposed to the c h a n g i n g exposure rates of the 36-hr s i m u l a t e d fallout d e c a y t o l e r a t e d m u c h lower exposures t h a n those plants exposed either to the 16-hr or the 36-hr uniform exposures for the same end p o i n t (see Figs. l c - d a n d 7). C o m p a r i s o n s were m a d e a m o n g the three different exposures, a n d the ratios are shown in T a b l e 5. W h e n the 36 h r was c o m p a r e d to the 16 hr, the a v e r a g e difference a m o n g the end points r a n g e d from a factor of 1.42 to a factor of 1"68, with the a v e r a g e for all end points b e i n g 1.50. W h e n the 16 hr was c o m p a r e d to the F D S , the a v e r a g e difference a m o n g the e n d points r a n g e d from a factor of 1.21 to a factor of 1"53, with the a v e r a g e difference of all end points b e i n g 1.36. H o w e v c r , w h e n the 36-hr uniform was c o m p a r e d to the 36-hr

Table 4. Lethality end points in kR for the FDS (CERF) 16-hr uniform and 36-hr uniform exposure rates for four crop plants Species* Cabbage

Pea

End point LD10 LDs0 LDg0 LD100 LDI0 LDs0 LD90 LDIo 0

Radish

Maize

LDlo LD50 LDg0 LDI00 LD10 LDs0 LD90 LDIo 0

FDS

16 hr

36 hr

8'55 11 "23 13"90 15"00 1"33 2"22 3" 11 3-00 9.50 12"90 16"31 20"00 2"96 3.76 4"56 5"00

12.75 15'48 18.21 21.00 2"33 2.94 3"55 4.00 16.29 18.97 21 "65 22"00 3'48 4.55 5"62 5"00

18.69 22"29 25"89 28'83 2"50 3.34 4"41 6'00 ----6"04 7.75 9'47 "10'86

*The cabbage, peas, radishes, and maize were irradiated 2-6 October 1967, 21-31 January 1968, 18-20 September 1967, 3-14 August 1967 and were harvested 13, 10, 9 and 7 weeks postirradiation respectively.

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so •

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P;sum $alivum (PEAl

8rcl||Jca olorocea ¥or. ¢apil(lla (CABBAGE)

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12

I

I

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I

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26

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Fro. 5. Probit plot of the per cent smwival against exposure (kR) for four species of economic plants after the three treatments.

85

EFFECTS OF SIMULATED RADIOACTIVE FALLOUT DECAY

compared to the 36-hr FDS data, the ratios ranged from 1.59 to 2"11, with an average increase for all end points of 1.80. As found above for lethal effects, the simulated fallout Avg. of decay exposure produced much more deleterious all end effects than the equivalent total exposure LDgo LDI0 0 points Ratio Crop LD 10 LDso delivered at uniform rates. Some qualitative observations were noted 36 hr Cabbage 1 . 4 7 1 . 4 4 1.42 1.37 during the course of the experiments, the first 16hr Pea 1.07 1 . 1 3 1 . 2 4 1.50 of which was the difference in survival time of Maize 1.74 1 . 7 0 1.68 2"17 plants which succumbed to radiation injury. Avg. 1.43 1.42 1 . 4 5 1 . 6 8 1.50 In all cases deaths due to radiation occurred 16 hr Cabbage 1 . 4 9 1 . 3 8 1.31 1.40 earlier in those plants exposed to the FDS and FDS Pea 1.75 1.32 1 . 1 4 1-33 later in the 16-hr and 36-hr exposure groups. Radish 1.71 1 . 4 7 1 . 3 3 1.I0 Deaths began in the 16-hr experiment approxiMaize 1.18 1.21 1 . 2 3 1.00 mately a week after the plants fi'om the FDS Avg. 1.53 1 . 3 5 1-25 1.21 1"36 started dying, and deaths in the 36-hr experi36 hr Cabbage 2.19 1 . 9 9 1 . 8 6 1.92 ment started approximately two weeks after FDS Pea 1.88 1 . 5 0 1.42 2.00 the FDS plants (see Fig. 8). Maize 2"04 2.06 2-08 2.17 Avg. 2.04 1.85 1.79 2 . 0 3 1.93 Tiller formation in the maize was evident at the higher exposures in all irradiations (see Fig. 9). However, when the average number of required to reduce yield or weight of peas to tillers per plant was calculated, those plants 50 per cent of controls for the three treatments exposed to the FDS had larger percentages of and the ratios of the relative effectiveness of the tillers. When the apical meristem of the pea seedlings treatments are given in Table 6. The 36-hr compared to the 16-hr exposure yielded a are badly inhibited or killed, lateral buds range 1-18-1-56 for all the end points, with an send out shoots. The number of these lateral average of 1.33. When the 16 hr was compared shoots increased with exposure, the number to the FDS, the difference for all end points usually reaching a peak at approximately the ranged from a factor of 1.13 to a factor of 1.66 same exposure as the LDI0 of the plants (see with the average for all end points of 1-37. Fig. 10). At the time of scoring, the lateral When the 36-hr uniform exposure rate data were shoots were divided into two groups, those

Table 5. Ratios of the relative effectiveness of different treatments for the various crops compared at four lethality end points

Table 6. Exposures (kR) requiredto reduceyield or weight of pea seedlings to 50% of controls for the three treatments. Ratios of relative effectiveness of the treatments are also given End points observed

Plant fresh wt.* No. of pods/plant No. of peas/plant Wt.]pea Avg. pea wt.]plant

Exposure required for a 50% reduction (LDs0), kR

Ratios of relative effectiveness 36 hr 16 hr 36 hr

FDS

16 hr

36 hr

16 hr

FDS

FDS

1.15 1.28 1.13 1.20 0.88

1.55 1.73 1.55 1.35 1.45

1-83 2.35 1.95 2.10 1.85

1.18 i.36 1.26 1.56 1.28 1.33

1.35 1.35 1.38 1.13 1.66 1.37

1.59 1.84 1.73 1.75 2.11 1.80

Avg. * Plants cup offat soil level.

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EXPOSURE ( WRI

Fio. 6. Semi-log plot of various end points (e×pressed as per cent of control) for maize (A) and pea (B-F) for the three treatments.

arising from the cotyledonary node below the soil level, and those arising from buds above the soil level. In those plants exposed to the FDS, the percentage of underground shoots was much higher and the percentage of aboveground shoots was lower than those found in the other experiments. A delay in flowering and pod production was also noted in the peas (see Table 7). There was a general trend in all experiments for the delay to

Table 7. Delay, (weeks) in appearance of the first flowers and pods for peas at 1.5 kR for the three treatments

Treatments 36 hr Flowering Pod production

5 7

" --16 hr 6 8

i~DS 7 9

EFFECTS O F S I M U L A T E D R A D I O A C T I V E F A L L O U T DECAY 35

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Fro. 8. Plant deaths (pea) as per cent of control vs. time (weeks postirradiation) for the three treatments. increase with increasing exposure, b u t there was also a difference b e t w e e n t r e a t m e n t s in d e l a y p r o d u c e d b y the s a m e exposure. F o r e x a m p l e , at 1.5 k R the 36-hr plants flowered at the same time as the controls, the 16-hr plants flowered a week later, a n d the F D S p l a n t s were d e l a y e d by at least two weeks. S i m i l a r delays can be expected in most crops receiving exposures in the sublethal r a n g e a n d could have serious e c o n o m i c consequences in some cases. A n o t h e r factor b r o u g h t out b y these experi-

ments c o n c e r n e d the usability of those crops harvested from p l a n t s exposed to fallout. Peas p r o d u c e d at the h i g h e r exposures were too small to be e c o n o m i c a l l y practical. T h e small size was due to the d e l a y in flowering as the peas p r o d u c e d at the higher exposures were not m a t u r e at time o f harvest. I n areas with a limited g r o w i n g season such a d e l a y could be serious in c e r t a i n circumstances. I n a taste test, radishes from sublethal exposures were found to be edible b u t h a d a d i s a g r e e a b l e taste a n d

A. H. SPARROW and LEANNE PUGLIELLI

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very rough texture. In such cases, although the plants survived, they would have little value for h u m a n consumption except under very adverse circumstances. Further studies on the palatability to both man and animals of irradiated crops would seem desirable. The greater effectiveness of the FDS treatments as opposed to uniform exposure rate experiments is presumably due to the very high initial exposures necessary in the FDS treatments. This is in accord with well established radiobiological concepts, i.e., that for a given exposure, higher dose rates are generally more effective. Appropriate experiments could be designed to determine the exposure-rate effect over a wide range for various economic plants. From such data it should be possible to predict the expected modifying effect of FDS treatments with a wide range of m a x i m u m exposure rates, i.e., comparable to various size,detonations or various times after H + 1. While it is probable that effectiveness per roentgen of fallout radiation m a y decrease as the m a x i m u m exposure rates decrease, it seems less likely that the difference in effectiveness between uniform exposure rates and decaying exposure rates will change dramatically. Both the quantitative and qualitative results reported here have indicated that the effects on plants of the changing dose rates of simulated fallout decay are more deleterious than effects of uniform dose-rate exposures if total exposures are about the same. It m a y be possible to use the existing uniform dose-rate information already available for m a n y species to predict the effects of fallout radiation on plants. Several previous publications from this laboratory have been concerned with developing models for predicting radiation responses of previously unirradiated species from characteristics of their nuclei and chromosomes,(2t-~s,~-~a,a°-a~,s4, 35) and these models could be expanded to predict radiation responses to nuclear fallout as well. As indicative of what can be done along these lines, we have made LX%0predictions for various species of economic plants from the regression relating LDs0 and interphase chromosome volume.(l) These data have been further modified using the differences shown in this report between 16-hr uniform exposure rates and 36-hr

EFFECTS OF SIMULATED RADIOACTIVE FALLOUT DECAY

89

Table 8. Predicted gamma exposuresrequired* to produce an rDsofOr a 16-hr uniform dose rate exposure and a 36-hr simulated fallout decay exposurefor 18field crops

Interphase chromosome Common Name Alfalfa (yellow-flowered) Alfalfa (vernal) Barley Beet, sugar Buckwheat Cane, sugar Cotton Flax Hops Maize (hybrid) Oats Peanut Rice Rye, winter Sorghum Soybean Tobacco Wheat

Species Medicago sativa Medicago sativa Hordeum vulgare HV himalaya Beta vulgaris Fagopyrum sagittatum Saccharum o~cinarum (P.O.J. 2725) Gossypium hirsutum HV acala Linum usitatissimum Humulus lupulus Zea mars (B14Rfx B37Rf) Avena sativa HV cherokee Arachis hypogaea (NC2 breeder) Oryza sativa HV zenith Secale cereale HV abruzzi Sorghum vulgare Glycine max HV hawkeye aVicotiana tabacum Triticum aestivum HV marfed

Predicted LDs0 (kR) 4- SD

volume,

16-hr

36-hr

~t3

exposure

FDS

8.4 5-3 24.6 4.4 5-8 5.6 5.7 2.9 10.4 14.0 15.3 7.5 3.0 19.0 7.7 4.1 6.5 16.0

9.2±2.6 14-6±4-2 3"2t0"9 17-6t5.1 13"4t3.8 13"9t4.0 13'613.9 26'817.7 7-512-1 5.5±1.6 5"111.5 10"3t3-0 25"917.4 4.14-1.2 10.14-2.9 18"9t5.4 11"94-3.4 4.94-1.4

6"8±1-9 10"8t3"1 2"4t0-7 13"0t3"8 9"912"8 10"313"0 10"112"9 19"915"8 5"611'6 4"111"2 3"8ti-1 7"612"2 19"2t5"5 3"0t0"9 7"5t2'2 14.04-4.0 8.84-2.5 3.64-1.0

*Based on LDSOvs. ICV graph of Baetcke et al.Ct)

FDS treatments (an average factor for LDs0 for the four crops studied of 1.35, see Table 5). These predicted LDs0 values are shown in Tables 8 and 9. Similar predictions can now be made for other end points and more will be developed as additional data become available. Existing data already indicate that radiosensitivity of certain stages of meiosis is much higher than that generally found with irradiation of purely vegetative stages. This could lead to severe effects on seed yield for some of the more sensitive crops with exposures of a few hundred rads at critical stages of development. Predicted LD60Sfor about 200 species of woody plants have recently been published,(37) but since woody species behave somewhat differently from herbaceous species, C3z) it will be necessary to determine if the same difference between 16-hr uniform exposure rates and FDS treatments also holds for woody species. Relatively

dry seeds are much more resistant than growing plants of the same species. Here, too, rough predictions of expected sensitivities can be obtained by nuclear characteristics. C17) It seems appropriate to emphasize that predictions for radiation response of plants growing under field conditions cannot be expected to be highly accurate. In addition to the difficulty of predicting the exact amount of fallout radiation that will occur and be absorbed by various plant parts, much variability will also be introduced in the expected responses by variation in the age or morphological development and the environmental and cultural conditions of the crops in different areas, at different times during the year, and in different years. However, it seems obvious that an attempt at such predictions is worthwhile and that the accuracy of the predictions will increase with additional experience of the kind reported herein.

90

A . H . S P A R R O W and LEANNE P U G L I E L L I

Table 9 Predictedexposures required* to produce an LDnoJbr a 16-hr uniform dose rate exposure and a 36-hr simulatedfallout decay exposurefor 31 fruit and vegetable crops

Common Name Asparagus Bean, broad Bean. kidney

Species

Interphase chromosome volume, ~.3

Predicted LDso I" (kR) ,Sl~ 16-hr 36-hr exposure FDS

Maize

Asparagus oflicinalis HV mary washington 6.8 I 1.44- 3-3 Viciafaba HV sutton's prolific longpod 49"8 1.64- 0.4 Phaseolus vulgaris HV pencil pod 5.5 14.1 4- 4.0 black wax Beta vulgaris HV detroit dark red 5" 1 15"2, 4.4 Brassica oleracea var. italica 4.4 17.6 4- 5.1 HV waltham 29 Brassica oleracea var. gemmifera 3.6 21.6 4- 6.2 HV long island improved Brassica oleracea var. capitata 3f 12' 1 , 3.5 HV ferrys round dutch 6.4 L (15.5 4- 0.4.)1" Cucumis melo var. cantalupensis 4.9 15-8 ~ 4.5 HV golden gate Daucus carota var. sativa HV 4.0 19-4 4- 5-6 long imperator Brassica oleracea var. botrytis HV snowball 6.9 1 1 . 2 , 3.2 Apium graveolens var. dulce 6.7 11.6 4- 3"3 Cucumis sativus HV marketer 11.4 6 " 8 , 2"0 Solanum melongena HV foremost 5.0 1 5 . 5 , 4.4 Brassica oleracea var. acephala 5.8 1 3 . 4 , 3"8 HV louisiana sweet Alliumporrum HV broad london 37.6 2 . 1 , 0.6 Lactuca sativa HV great lakes 9.8 7"94- 2"3 5"2 4- 1.5 yea mays HV golden bantam 15.0 ( 4 . 6 , 0"2)I"

Okra Onion

Hibiscus esculentus HV emerald Allium cepa HV yellow sweet spanish

1.7 40.6

Pea

Pisum sativum HV alaska

22'4

Potato, Irish Potato, sweet

Solanum tuberosum HV katahdin Ipomoea batatas

4'6 3"2

Radish

Raphonus sativus HV cherry belle

5.6

Rhubarb Spinach

Rheum rhaponticum HV myatt's victoria Spinacia oleracea HV dark green bloomsdale Cucurbita pepo HV royal acorn Fragaria sp. HV northwest Beta cicla HV lucullus Lycopersicon esculentum HV rutgers Brassica rapa Citrullus vulgaris HV charleston gray

7.8 9"6

10.04- 2.9 8 . 1 , 2-3

1'63-0.5 5'9,1.~ 3.9,1.1 (3.8+0.08)I" 33"9"9.8 1.4,0.4 2-64-0.7 (2"2,0.07)t 12.5,3.6 18.0,5.2 10'34-3.0 (12"94-0'5)t 7.4,2.2 6'0+1.7

2.4 3.7 2.9 6"0 3"0 4.3

32.3, 21.0 + 26.8, 12.9425"9418.1 4-

23"94-6-9 15.64-4.5 19.9,5.8 9"64-2.8 19"24-5.5 13.44-3.9

Beet Broccoli Brussels sprouts Cabbage Cantaloupe Carrot Cauliflower Celery Cucumber Eggplant Kale Leek Lettuce

Squash. acorn Strawberry Swiss chard Tomato Turnip Watermelon

45.7 4-13.1 1 . 9 , 0.5 3.54- 1.0 (2.9 +0"04)I" 16.9424.3 413.94(19'0i

* Based on LDs0 VS. ICV graph ofBaetcke et al.(1) t Observed values are given in parenthesis for the four species studied in this report.

4.8 6.9 4.0 0"5)I

9.3 6-0 7.7 3.7 7.4 5"2

8.4,2.5 1.2,0.3 10-4~3.0 11'3~3.3 13.0,3.8 16.0,4.6 9-0 =I=2'6 (11'2 + 0 ' 3 ) t 11.7,3.4 14'~,4.2 8.3,2.4 8.6,2.5 5.0 ~ 1.5 11"54-3.3 9"9 4-2 "8

EFFECTS OF SIMULATED R A D I O A C T I V E F A L L O U T DECAY

Acknowledgements--The authors wish to thank Mr. CHARLES W. FLOOD and Mr. ROBERT G. WOODLEY for help with dosimetry and Mr. K. H. THOMPSON for statistical advice. The valuable assistance of Mr. E. ERIC KLUO in irradiating the plants and collecting data is also nmch appreciated.

REFERENCES 1. BAETCKEK. P., SPARRO~VA. H., NAUMANC. H. and SCHWEMMERS. S. (1967) The relationship of DNA content to nuclear and chromosome volumes and to radiosensitivity (LD50). Proc. Natl. Acad. Sci. (U.S.) 58, 533-540. 2. BELL IVI. C. and COLE C. V. (1967) Vulnerability of food crop and livestock production to fallout radiation. Agr. Rcs. Lab., AEC, Univ. Tennessee, Oak Ridge, Tenn., OCD Work Unit 3223A. 3. CAVAZZA L., GUERRIERI G,, PACUCC/ G. and SCARASCIA MUGNOZZA G. T. (1965) Radioscnsibilit~ di sei specic orticole. Genet. Agr. 19, 243-262. (Engl. summ.). 4. CLARKG. M., CHENO F., Roy R. M., S~..VEANEY W. P., BUNTmO W. R. and BAKER D. G. (1967) Effects of thermal stress and simulated fallout on conifer seeds. Radiation Botat~ 7, 167-175. 5. CLARK G. M., RoY R. M., BAKER D. G. and BUNTINO W. R. (1965) Simulated fallout studies in conifers--a preliminary report. Health Plus. 119 1627-1636. 6. DAVXESC. R. (1968) Effects ofgamma irradiation on growth and yield of agricultural crops--I. Spring sown wheat. Radiation Botany 8, 17-30. 7. DONINI B., SCARASCIA MUGNOZZA G. T. and D'AMATO F. (1964) Effects of chronic gamma irradiation in durum and bread wheats. Radiation Botany 4, 387-393. 8. Domm B., SPARROWA. H., SCHAIRERL. A. and SPARROW R. C. (1967) The relative biological efficiency of gamma rays and fission neutrons in plant species with different nuclear and chromosome volumes. Radiation Res. 32, 692-705. 9. GLASSTOr,mS. (ed.) (1962) The Effects of Nuclear Weapons. Revised ed., U.S. Atomic Energy Commission, U.S. Govt. Printing Office, Washington, D.C. 730 p. 10. GUNCKEL J. E. and SPARROW A. H. (1961) Ionizing radiations: biochemical, physiological and morphological aspects of their effects on plants. In Encycl. Plant Physiol. Vol. 16. (Edited by RUHLAND W.) pp. 556-611. Springer-Verlag, Berlin. 11. HERMELIN T. (1967) Effects of acute gamma irradiation in barley at different ontogenetic stages. Hereditas 57, 297-302.

91

12. KAWAI T. and INOSltlTA "F. (1965) Effects of gamma ray irradiation on growing rice plants-I. Irradiations at four main developmental stages. Radiation Botat@ 5, 233-255. 13. MCCORMICKJ. F. and MCJuNKIN R. E. (1965) Interactions of gamma radiation and other environmental stresses upon pine seeds and seedlings. Health Phys. I1, 1643-1652. 14. MAMEDOVT. G. and KUALISIF. (1965) Dynanfics of the growth of beans and peas aftcr a single y-irradiation. Radiobiology (USSR) 5 (5), 147-149 (Engl. transl.). Orig. pp. 730-731. 15. MmSCHEJ. P. (1965) Changes in radiosensitivity of root of Glycine max. (L.) Merril. during postdormant reactivation. Bull. Torrey Botan. Club

92, 1-6. 16. MmLER L. N. (1965) Changes in radiosensitivity of pine seedlings subjected to water stress during chronic gamma irradiation. Health Phys. 11, 1653-1662. 17. OSBORNE T. S. and LUNDEN A. O. (1965) Prediction of seed sensitivity from embryo structure. Radiation Botany 5 (Suppl.), 133-149. 18. PALUMBOR. F. (1962) Recovery of the land plants at Eniwetok Atoll following a nuclear detonation. Radiation Botany 1, 182-189. 19. SHIELDS L. M. and RmKARD W. H. (1961) A preliminary evaluation of radiation effects at the Nevada test site. In Recent Advances in Botany pp. 1387-1390. Univ. Toronto Press, Toronto. 20. SIIUL'GIN I. A. and PODOL'NYIV. Z. (1964) The effect of radiation intensity on thc dcvelopment and growth of plants as dependent on the length of photoperiod and temperature. Doklady Akad. Nauk SSSR 158, 1439-1442. 21. SPARROW A. H. (1963) The tolerance of plants to ionizing radiation: variations, modifications and predictions. Unpublished report. BNL 7435, Upton, N.Y. 42 pp. 22. SPARROW A. H. (1965) Comparisons of the tolerances of higher plant species to acute and chronic exposures of ionizing radiation. Japan.J. Genetics 40 (Suppl.), 12-37. 23. SPARROW A. H. (1965) Relationship between chromosome volume and radiation sensitivity in plant cells. In Cellular Radiation Biology pp. 199-218. Williams & Wilkins, Baltimore. 24. SPARROW A. H. (1966) Research uses of the gamma field and related radiation facilities at Brookhaven National Laboratory. Radiation Botany 6, 377-405. 25. SPARROWA. H., CUANYR. L., MIKSCHEJ. P. and SCHAIRER L. A. (1961) Some factors affecting the responses of plants to acute and chronic radiation exposures. Radiation Botany 1, 10-34.

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A. H. S P A R R O W and LEANNE P U G L I E L L I

26. SPARROWA. H. and EVANSH . J . (1961) Nuclear factors affecting radiosensitivity--I. The influence of nuclear size and structure, chromosome complement and DNA content. Brookhaven Syrnp. Biol. 14, 76-100. 27. SPARROWA. H., ROOERS A. F. and SCHWEMMZR S. S. (1968) Radiosensitivity studies with woody plants--I. Acute gamma irradiation survival data for 28 species and predictions for 190 species. Radiation Botany 8, 149-186. 28. SPARROW A. H., SCHAmER L. A. and SPARROW R. C. (1963) Relationship between nuclear volumes, chromosome numbers and relative radiosensitivities. Science 141, 163-166. 29. SPARROWA. H., SCHAIm~RL. A., SPARROWR. C. and CAMPBELLW. F. (1963) The radiosensitivity ofgymnosperms--I. The effect of dormancy on the response of Pinus strobus seedlings to acute gamma irradiation. Radiation Botany 3, 169-173. 30. SPARROW A. H., SPARROW R. C., THOMPSON K. H. and SCHAIRER L. A. (1965) The use of nuclear and chromosomal variables in determining and predicting radiosensitivities. Radiation Botany 5 (Suppl.), I01-132.

31. SPARROW A. H. and WOODW~.LL G. M. (1962) Prediction of the sensitivity of plants to chronic gamma irradiation. Radiation Botany 2, 9-26. 32. SPARROW R. C. and SPARROW A. H. (1964) Relative radiosensitivities of woody and herbaceous spermatophytic plants. Science 14/, 1449-1451. 33. WOODWELL G. M. (ed.) (1965) Ecological Effects of Nuclear War. Brookhaven Natl. Lab., Upton, N.Y. BNL 917(C-43). 72 p. 34. WOODW~LL G. M. (1967) Radiation and the patterns of nature. Science 156, 461--470. 35. WOODW~-LLG. M. and SPARROW A. H. (1963) Predicted and observed effects of chronic gamma radiation on a near-cllmax forest ecosystem. Radiation Botany 3, 231-238. 36. YAMASHITA A. (i964) Some aspects of radiosensitivity of crop plants under chronic exposure. In Gamma Field Syrup..No. 3 pp. 91-110. Inst. Radiation Breeding, Ohmiya-machi, Ibarakiken, Japan. 37. ZHuNusov R. S. (1964) Variations in the~protein and carbohydrate content of plants irradiated at different stages of ontogenesis. Radiobiology (USSR) 4 (4), 151-155 (Engl. transl.). Orig. pp. 599-602.