- Email: [email protected]
Disinfestation of maize by irradiation
Radiat. Phys. Chem. 1977, Vol. 9, pp. 763-768.
Pergamon Press.
Printed in Great Britain.
DISINFESTATION OF MAIZE BY IRRADIATION* E s b a i d e Adem C h a h i n , R o b e r t o M. U r i b e R e n d 6 n , Anibal de la Piedad Benitez and Javier R e y e s Lu-
j~n**. Instituto de Fisica, Universidad NacionaI Autdnoma de M~xico, M~xico 20, D.F. ABSTRACT. A joint program between Institute de Fisica, UNAM a n d P r o g r a m a de Tecnologia, INEN h a s b e e n d e v e l o p e d s i n c e 197Z i n t h e f i e l d of disinfestation of maize by irradiation. Several experiences at laboratory scale were done in order to determine that a dose o f 25 k r a d e l i m i n a t e s t h e m o r e common s p e c i e s t h a t i n f e s t the maize in Mexico. A p i l o t p l a n t was b u i l t to treat i n b u l k up t o 2 t o n s p e r d a y . As i r r a d i a t o r i t i s u s e d a 2 . 0 Mev E l e c t r o n Van d e G r a a f f a c c e lerator. The i r r a d i a t i o n dose has been determined using as dosimeter LiF in powder inside capsules that are irradiated with the g r a i n b u l k . The e f f i c i e n c y of the treatment has been studied by means of long term storage observations of samples with one - particular or several s p e c i e s a t t h e same t i m e . Also, different bromatological studies have been done with tile maize disinfested by irradiation in order to be sure that the -treatment does not change its characteristics. Some c o m m e n t s a r e large scale using
presented for next step, a Dynamitron accelerator.
the
application
to
a
INTRODUCTION. D u r i n g many y e a r s t h e c o n s e r v a t i o n of stored grains has been done b y m e a n s o f t h e u s e o f p e s t i c i d e s . They have been used from the farmer to the great store plants. One p e s t i c i d e sustitute -* Work s u p p o r t e d b y C o n s e j o N a t i o n a l d e C i e n c i a y T e c n o l o g f a . ** P r o g r a m a d e T e c n o l o g i a , Institute Nacional de Energia Nuclear 763
RP(
764
periodically
g.
other
because
Adem
Ch.
, t, , ~ / .
of results
more effective
or feasible.
However, in last years, a critical situation a p p e a r e d due t o three factors: i ) The e c o l o g i c a l problem of contamination, exposed constantly by experts. They explain that the excessive use of pesticides could leave nocive residues for consumers. i i ) The e n e r g e t i c crisis and continously growing costs of chemicals. iii) The d e v e l o p m e n t o f r e s i s t a n c e by i n s e c t s to certain species, doing necessary t h e s e a r c h o f new f o r m u l a s a n d i n c r e a s i n g dosages for disinfestation. I n many c o u n t r i e s technologies for
t h e r e a r e g r o u p s l o o k i n g f o r new a n d b e t t e r grain and grain products conservation.
--
The p r o b l e m i n t h e f u t u r e w o u l d b e s t r e s s in those countries whe re weather conditions permit the proliferation of insects. Losses i n some c o u n t r i e s , due to infestation of stored grain is around10~ o f t h e t o t a l c r o p . Several years ago, in different countries, research was done in the field of irradiation of grain and its products, and in some, the food authorities aproved the human comsumption. However, until today any large scale application has not been reported. Irradiation technology, in both ways, electrons or gammas is already prepared for application and in certain circumstances is cheaper than normal fumigation. The main problem that seems -appear is that one country is waiting that another starts. In M6xico, maize is the basic grain; around 10 million of tons are cropped per year; 601 o£ this production is retained by the farmers for their own comsumption, amounts of one or two tons are kept in very poos sanitary conditions. Another 201 is trade by small and local commerce, and finally the rest is controlled by federal dependencies in order to maintain the appropiate reserves and for cost controls. Most common pesticides, like phosphine and malathion are used at any level. S i n c e 1972 a j o i n t r e s e a r c h p r o g r a m i n d i s i n f e s t a t i o n of maize by irradiation has been developed by Institute de F ~ s i c a , UNAM, a n d P r o g r a m a de T e c n o l o g ~ a , INEN. The f i r s t step included: i) Determination of dislnfestation d o s a g e s f o r t h e m o r e common insects in M~xico, using gumas and electrons. ii) Construction of a laboratory pilot plant for bulk irradiation with electrons. iii) Bromatological analysis of maize disinfested by irradiation. The p u r p o s e
of this
paper
is
to present
briefly
the
results
-
Disinfestation of maize by irradiation
765
obtained in this program and to explain some of the considera-tions for its future. EXPERIMENTAL. The s a m p l e s o f m a i z e hav~ b e e n o b t a i n e d f r o m l a r g e s t o r e d g r a i n u n i t s and p u b l i c m a r k e t s . U s u a l l y t h e s a m p l e s w e r e a l r e a d y i n f e s ted. There are six to eight species that usually are present inthe samples for experiments. In other cases the samples were in r e s t e d by a p a r t i c u l a r specie. Two gamma irradiators have been used to treat the samples: i) Gammabeam 650 (AECL) irradiating the samples in plastic bags at the panoramic and central areas to the appropriated dosages. Dose rates were 9.1 x 103 and 2.75 x 104 rad/hr. ii) Gammacell 200 (AECL), irradiating the samples in the same form with a dose rate of 2.5 x 103 rad/min. Dose rates were determined simeter as dosimeter.
by usual
techniques,
using Fricke do-
Electron irradiation were done with the pilot plant at the Van de Graaff accelerator. A calibration of the dose rate and the description of the plant appears later. Thermoluminescence TL analyzer.
readings were done with a Harshaw model
Determinations of protein content, done with standard techniques.
vitamins
and a m i n o a c i d s
With t h e p u r p o s e to s t u d y t h e e l e c t r o n treatment was b u i l t , whose d e s c r i p t i o n appears below. Pilot
a pilot
2000 were
plant
Plant(l)
The a c c e l e r a t o r , a Van de G r a a f f , HVEC m o d e l AN, p r o d u c e s e l e c - t r o n s i n t h e r a n g e up t o 1 . 5 MeV, w i t h beam c u r r e n t s b e t w e e n 10 and 100 ~A. F i g . 1 shows a c r o s s s e c t i o n o f t h e i n s t a l l a t i o n . At t h e t o p - appears the accelerator tank (A), inside which is located the h i g h v o l t a g e u n i t and t h e e l e c t r o n s o u r c e . The beam i s a c c e l e r a t e d i n s i d e a vacumm l i n e (B) a n d e m e r g e s f r o m t h e s c a n e x t e n s i o n t h r o u g h a 60 t i t a n i u m w i n d o w . The beam c o u l d be s c a n n e d by a - coils system along the extension with frequencies in the range 1 t o 50 Hz. The g r a i n c o n t a i n e r (1) i s l o c a t e d a t t h e u p p e r l e f t , where a f l o w r a t e v a l v e (2) w i t h h o l e s r e g u l a t e s the proper amount of -g r a i n t o t h e s c r e w c o n v e y o r (4) when v a l v e (3) i s o p e n . The g r a i n falls i n s i d e a p i p e (5) t o a r e g u l a t o r (6) w h i c h p r o d u c e s a t h i n flux. Then, the grain flux passes under the electron scanned -beam i n an i n c l i n e d i s p o s i t i v e . After irradiation, the grain - falls i n o t h e r p i p e (8) t o a c o n t a i n e r (9). Another valve allows
766
E. Adem Ch. e~ a~.
the evacuation of the irradiated grain. T h i s p l a n t i s c a p a b l e t o t r e a t up t o 200 K g / h r a t a d o s e i n t h e r a n g e up t o 25 g r a d . B a t c h e s o f 2 5 0 - 5 0 0 Kg a r e i r r a d i a t e d one time.
-at
Bulk operation is fixed and dose rate is given by the parameters ef the accelerator, i.e. energy, current and scanning conditions. One o~ the technical problems is related with the determination of these accelerator conditions in order to release the appro-priated dose to the grain in one pass. For this purpose, it was used lithium fluoride in powder (LIP) (Baker's 2381) irradiated in capsules that were moved with the bulk of grain through the electron beam. This design gives similar conditions in the irradiation of the grain and the capsules containing the powder. It was studied extensively the TL reading of this substance after irradiation and it was selected because it is a commercial substance cheaper than other powder dosime-ter, like TLD-100 from Harshaw, though it's a chemical grade substance used mainly for analytical work. It was first obtained the glow curve for LiP irradiated with -60Co gamma radiation and it was found the TL peaks temperature. It was also studied the time stability of those peaks and were determined its half life. The TL r e a d i n g a g a i n s t 60Co gamma r a d i a t i o n d o s e was s e t t i n g a s a calibration curve, relating t h e TL i n t e n s i t y and d o s e . Dose was d e t e r m i n e d by P r i c k e s o l u t i o n m e t h o d . Afterwards, t h e LiP p o w d e r was i r r a d i a t e d w i t h 1 . 0 MeV e l e c t r o n s and t h e g l o w c u r v e was f o u n d . The f i r s t calibration c u r v e was - u s e d i n o r d e r t o know t h e d o s a g e s a b s o r b e d b y t h e p o w d e r i r r a d i a ted in capsules jointly w i t h t h e g r a i n b u l k . I n t h i s way, s e v e - ral accelerator conditions were s e t t i n g v e r s u s d o s e ( 2 ) .
RESULTS AND DISCUSSION. A f t e r e n t o m o l o g i c a l e x p e r i m e n t s w i t h t h e common i n s e c t s , like Sitophilus sp., Tribolium sp., etc. that infest the maize in -M ~ x i c o , a d o s e i n t h e r a n g e 25 t o 30 Krad i s a p p r o p r i a t e d for disinfestation. Observation of irradiated s a m p l e s f r o m week up to months have permitted to evaluate the radiation effect in each specie or in mixtures of species. Irradiated samples sto-red in clean conditions f o r 4 y e a r s h a v e shown t h e f e a s i b i l i t y of the process. The p r e l i m i n a r y bromatological s t u d i e s show t h a t t h e c o n t e n t and quality of proteins, vitamins, and a m i n o a c i d s d o e s n o t c h a n g e w i t h d o s e g e s i n t h e r a n g e up t o 30 K r a d , u s e d f o r d i s i n f e s t a t i o n .
Disinfestation of maize by irradiation
767
Next step of the project is to built an industrial pilot plant, using an electron Dynamitron accelerator. The p l a n t w o u l d b e constructed in order to treat samples at fluxes of hundreds of tons per hr, and would be used for several types of grain. Basic i d e a s f o r t h e p l a n t h a v e b e e n p r o p o s e b y RDI. ACKNOWLEDGMENTS The a u t h o r s e x p r e s s t h e i r g r a t i t u d e t o C o n s e j o N a c i o n a l de C i e n ciay Tecnologia for financial support to the project, an to - staff of the mechanical shop of the Instituto de F i s i c a , UNAM f o r their help to built the pilot plant. REFERENCES 1) Adem E . , R e y e s L . J . , Ramos J . M . a n d V e l a z q u e z V . F . , " D e s i n - festaci6n de m a f z p o r i r r a d i a c i 6 n a escala piloto. IX.-Dise5o y construcci6n de u n a p l a n t a p i l o t o p a r a l a d e s i n f e s t a c i 6 n de mafz a granel con electrones" IFUNAM-74-408; P T - F - 7 4 - 1 6 (1974). 2) U r i b e R . M . , d e l a P i e d a d B . A . , Adem E. a n d R e y e s L . J . , "Dosimetry in a pilot plant for bulk disinfestation of grain by -electron irradiation. I.- Lithium fluoride in powder", - IFUNAM-TS-26 ( 1 9 7 5 ) .
E. Adem Ch. et a~.
768
2 3
D 5
I IO
Figure 1.- Side view diagram of the grain disinfestation plant at the Instituto de F i s i c a , UNAM. Number 1, i n d i c a t e s the grain container; Z, t h e t u b e w h i c h r e g u l a t e s t h e g r a i n f l o w ; 3, a v a l v e ; 4, a s c r e w c o n v e y o r ; 5, t h e t u b e t h r o u g h w h i c h t h e g r a i n - falls; 6, a b o x w i t h a r e g u l a t i o n v a l v e ; 7, t h e i r r a d i a t i o n chan n e l ; 8, t h e t u b e w h i c h s e n d s t h e i r r a d i a t e d grain to 9 the cont a i n e r a n d 10 t h e e x i t v a l v e .
Pergamon Press.
Printed in Great Britain.
DISINFESTATION OF MAIZE BY IRRADIATION* E s b a i d e Adem C h a h i n , R o b e r t o M. U r i b e R e n d 6 n , Anibal de la Piedad Benitez and Javier R e y e s Lu-
j~n**. Instituto de Fisica, Universidad NacionaI Autdnoma de M~xico, M~xico 20, D.F. ABSTRACT. A joint program between Institute de Fisica, UNAM a n d P r o g r a m a de Tecnologia, INEN h a s b e e n d e v e l o p e d s i n c e 197Z i n t h e f i e l d of disinfestation of maize by irradiation. Several experiences at laboratory scale were done in order to determine that a dose o f 25 k r a d e l i m i n a t e s t h e m o r e common s p e c i e s t h a t i n f e s t the maize in Mexico. A p i l o t p l a n t was b u i l t to treat i n b u l k up t o 2 t o n s p e r d a y . As i r r a d i a t o r i t i s u s e d a 2 . 0 Mev E l e c t r o n Van d e G r a a f f a c c e lerator. The i r r a d i a t i o n dose has been determined using as dosimeter LiF in powder inside capsules that are irradiated with the g r a i n b u l k . The e f f i c i e n c y of the treatment has been studied by means of long term storage observations of samples with one - particular or several s p e c i e s a t t h e same t i m e . Also, different bromatological studies have been done with tile maize disinfested by irradiation in order to be sure that the -treatment does not change its characteristics. Some c o m m e n t s a r e large scale using
presented for next step, a Dynamitron accelerator.
the
application
to
a
INTRODUCTION. D u r i n g many y e a r s t h e c o n s e r v a t i o n of stored grains has been done b y m e a n s o f t h e u s e o f p e s t i c i d e s . They have been used from the farmer to the great store plants. One p e s t i c i d e sustitute -* Work s u p p o r t e d b y C o n s e j o N a t i o n a l d e C i e n c i a y T e c n o l o g f a . ** P r o g r a m a d e T e c n o l o g i a , Institute Nacional de Energia Nuclear 763
RP(
764
periodically
g.
other
because
Adem
Ch.
, t, , ~ / .
of results
more effective
or feasible.
However, in last years, a critical situation a p p e a r e d due t o three factors: i ) The e c o l o g i c a l problem of contamination, exposed constantly by experts. They explain that the excessive use of pesticides could leave nocive residues for consumers. i i ) The e n e r g e t i c crisis and continously growing costs of chemicals. iii) The d e v e l o p m e n t o f r e s i s t a n c e by i n s e c t s to certain species, doing necessary t h e s e a r c h o f new f o r m u l a s a n d i n c r e a s i n g dosages for disinfestation. I n many c o u n t r i e s technologies for
t h e r e a r e g r o u p s l o o k i n g f o r new a n d b e t t e r grain and grain products conservation.
--
The p r o b l e m i n t h e f u t u r e w o u l d b e s t r e s s in those countries whe re weather conditions permit the proliferation of insects. Losses i n some c o u n t r i e s , due to infestation of stored grain is around10~ o f t h e t o t a l c r o p . Several years ago, in different countries, research was done in the field of irradiation of grain and its products, and in some, the food authorities aproved the human comsumption. However, until today any large scale application has not been reported. Irradiation technology, in both ways, electrons or gammas is already prepared for application and in certain circumstances is cheaper than normal fumigation. The main problem that seems -appear is that one country is waiting that another starts. In M6xico, maize is the basic grain; around 10 million of tons are cropped per year; 601 o£ this production is retained by the farmers for their own comsumption, amounts of one or two tons are kept in very poos sanitary conditions. Another 201 is trade by small and local commerce, and finally the rest is controlled by federal dependencies in order to maintain the appropiate reserves and for cost controls. Most common pesticides, like phosphine and malathion are used at any level. S i n c e 1972 a j o i n t r e s e a r c h p r o g r a m i n d i s i n f e s t a t i o n of maize by irradiation has been developed by Institute de F ~ s i c a , UNAM, a n d P r o g r a m a de T e c n o l o g ~ a , INEN. The f i r s t step included: i) Determination of dislnfestation d o s a g e s f o r t h e m o r e common insects in M~xico, using gumas and electrons. ii) Construction of a laboratory pilot plant for bulk irradiation with electrons. iii) Bromatological analysis of maize disinfested by irradiation. The p u r p o s e
of this
paper
is
to present
briefly
the
results
-
Disinfestation of maize by irradiation
765
obtained in this program and to explain some of the considera-tions for its future. EXPERIMENTAL. The s a m p l e s o f m a i z e hav~ b e e n o b t a i n e d f r o m l a r g e s t o r e d g r a i n u n i t s and p u b l i c m a r k e t s . U s u a l l y t h e s a m p l e s w e r e a l r e a d y i n f e s ted. There are six to eight species that usually are present inthe samples for experiments. In other cases the samples were in r e s t e d by a p a r t i c u l a r specie. Two gamma irradiators have been used to treat the samples: i) Gammabeam 650 (AECL) irradiating the samples in plastic bags at the panoramic and central areas to the appropriated dosages. Dose rates were 9.1 x 103 and 2.75 x 104 rad/hr. ii) Gammacell 200 (AECL), irradiating the samples in the same form with a dose rate of 2.5 x 103 rad/min. Dose rates were determined simeter as dosimeter.
by usual
techniques,
using Fricke do-
Electron irradiation were done with the pilot plant at the Van de Graaff accelerator. A calibration of the dose rate and the description of the plant appears later. Thermoluminescence TL analyzer.
readings were done with a Harshaw model
Determinations of protein content, done with standard techniques.
vitamins
and a m i n o a c i d s
With t h e p u r p o s e to s t u d y t h e e l e c t r o n treatment was b u i l t , whose d e s c r i p t i o n appears below. Pilot
a pilot
2000 were
plant
Plant(l)
The a c c e l e r a t o r , a Van de G r a a f f , HVEC m o d e l AN, p r o d u c e s e l e c - t r o n s i n t h e r a n g e up t o 1 . 5 MeV, w i t h beam c u r r e n t s b e t w e e n 10 and 100 ~A. F i g . 1 shows a c r o s s s e c t i o n o f t h e i n s t a l l a t i o n . At t h e t o p - appears the accelerator tank (A), inside which is located the h i g h v o l t a g e u n i t and t h e e l e c t r o n s o u r c e . The beam i s a c c e l e r a t e d i n s i d e a vacumm l i n e (B) a n d e m e r g e s f r o m t h e s c a n e x t e n s i o n t h r o u g h a 60 t i t a n i u m w i n d o w . The beam c o u l d be s c a n n e d by a - coils system along the extension with frequencies in the range 1 t o 50 Hz. The g r a i n c o n t a i n e r (1) i s l o c a t e d a t t h e u p p e r l e f t , where a f l o w r a t e v a l v e (2) w i t h h o l e s r e g u l a t e s the proper amount of -g r a i n t o t h e s c r e w c o n v e y o r (4) when v a l v e (3) i s o p e n . The g r a i n falls i n s i d e a p i p e (5) t o a r e g u l a t o r (6) w h i c h p r o d u c e s a t h i n flux. Then, the grain flux passes under the electron scanned -beam i n an i n c l i n e d i s p o s i t i v e . After irradiation, the grain - falls i n o t h e r p i p e (8) t o a c o n t a i n e r (9). Another valve allows
766
E. Adem Ch. e~ a~.
the evacuation of the irradiated grain. T h i s p l a n t i s c a p a b l e t o t r e a t up t o 200 K g / h r a t a d o s e i n t h e r a n g e up t o 25 g r a d . B a t c h e s o f 2 5 0 - 5 0 0 Kg a r e i r r a d i a t e d one time.
-at
Bulk operation is fixed and dose rate is given by the parameters ef the accelerator, i.e. energy, current and scanning conditions. One o~ the technical problems is related with the determination of these accelerator conditions in order to release the appro-priated dose to the grain in one pass. For this purpose, it was used lithium fluoride in powder (LIP) (Baker's 2381) irradiated in capsules that were moved with the bulk of grain through the electron beam. This design gives similar conditions in the irradiation of the grain and the capsules containing the powder. It was studied extensively the TL reading of this substance after irradiation and it was selected because it is a commercial substance cheaper than other powder dosime-ter, like TLD-100 from Harshaw, though it's a chemical grade substance used mainly for analytical work. It was first obtained the glow curve for LiP irradiated with -60Co gamma radiation and it was found the TL peaks temperature. It was also studied the time stability of those peaks and were determined its half life. The TL r e a d i n g a g a i n s t 60Co gamma r a d i a t i o n d o s e was s e t t i n g a s a calibration curve, relating t h e TL i n t e n s i t y and d o s e . Dose was d e t e r m i n e d by P r i c k e s o l u t i o n m e t h o d . Afterwards, t h e LiP p o w d e r was i r r a d i a t e d w i t h 1 . 0 MeV e l e c t r o n s and t h e g l o w c u r v e was f o u n d . The f i r s t calibration c u r v e was - u s e d i n o r d e r t o know t h e d o s a g e s a b s o r b e d b y t h e p o w d e r i r r a d i a ted in capsules jointly w i t h t h e g r a i n b u l k . I n t h i s way, s e v e - ral accelerator conditions were s e t t i n g v e r s u s d o s e ( 2 ) .
RESULTS AND DISCUSSION. A f t e r e n t o m o l o g i c a l e x p e r i m e n t s w i t h t h e common i n s e c t s , like Sitophilus sp., Tribolium sp., etc. that infest the maize in -M ~ x i c o , a d o s e i n t h e r a n g e 25 t o 30 Krad i s a p p r o p r i a t e d for disinfestation. Observation of irradiated s a m p l e s f r o m week up to months have permitted to evaluate the radiation effect in each specie or in mixtures of species. Irradiated samples sto-red in clean conditions f o r 4 y e a r s h a v e shown t h e f e a s i b i l i t y of the process. The p r e l i m i n a r y bromatological s t u d i e s show t h a t t h e c o n t e n t and quality of proteins, vitamins, and a m i n o a c i d s d o e s n o t c h a n g e w i t h d o s e g e s i n t h e r a n g e up t o 30 K r a d , u s e d f o r d i s i n f e s t a t i o n .
Disinfestation of maize by irradiation
767
Next step of the project is to built an industrial pilot plant, using an electron Dynamitron accelerator. The p l a n t w o u l d b e constructed in order to treat samples at fluxes of hundreds of tons per hr, and would be used for several types of grain. Basic i d e a s f o r t h e p l a n t h a v e b e e n p r o p o s e b y RDI. ACKNOWLEDGMENTS The a u t h o r s e x p r e s s t h e i r g r a t i t u d e t o C o n s e j o N a c i o n a l de C i e n ciay Tecnologia for financial support to the project, an to - staff of the mechanical shop of the Instituto de F i s i c a , UNAM f o r their help to built the pilot plant. REFERENCES 1) Adem E . , R e y e s L . J . , Ramos J . M . a n d V e l a z q u e z V . F . , " D e s i n - festaci6n de m a f z p o r i r r a d i a c i 6 n a escala piloto. IX.-Dise5o y construcci6n de u n a p l a n t a p i l o t o p a r a l a d e s i n f e s t a c i 6 n de mafz a granel con electrones" IFUNAM-74-408; P T - F - 7 4 - 1 6 (1974). 2) U r i b e R . M . , d e l a P i e d a d B . A . , Adem E. a n d R e y e s L . J . , "Dosimetry in a pilot plant for bulk disinfestation of grain by -electron irradiation. I.- Lithium fluoride in powder", - IFUNAM-TS-26 ( 1 9 7 5 ) .
E. Adem Ch. et a~.
768
2 3
D 5
I IO
Figure 1.- Side view diagram of the grain disinfestation plant at the Instituto de F i s i c a , UNAM. Number 1, i n d i c a t e s the grain container; Z, t h e t u b e w h i c h r e g u l a t e s t h e g r a i n f l o w ; 3, a v a l v e ; 4, a s c r e w c o n v e y o r ; 5, t h e t u b e t h r o u g h w h i c h t h e g r a i n - falls; 6, a b o x w i t h a r e g u l a t i o n v a l v e ; 7, t h e i r r a d i a t i o n chan n e l ; 8, t h e t u b e w h i c h s e n d s t h e i r r a d i a t e d grain to 9 the cont a i n e r a n d 10 t h e e x i t v a l v e .