12 Bound Residues of Nitrofen in Cereal Grain and Straw R. C. HONEYCUTT, J. P. WARGO, and I. L. ADLER
Bound and Conjugated Pesticide Residues Downloaded from pubs.acs.org by IMPERIAL COLLEGE LONDON on 04/06/19. For personal use only.
Rohm and Haas Co., Research Laboratories, Spring House, Pa. 19477
Nitrofen i s a selective herbicide marketed by Rohm and Haas Company and used to control annual grasses and broad-leafed weeds. The structural formula for nitrofen i s shown below.
2,4-dichloro-1-(4-nitrophenoxy) benzene *Site of C Labeling Investigations into the environmental fate of nitrofen- C applied pre- and postemergence to wheat and rice led to some interesting discoveries. We found that only 50% of the radioactive residue in the straw or grain of these 110-147 day old plants could be extracted by conventional organic solvent Soxhlet extraction. Thus, about 50% of the residue was considered "bound residue." During the course of this investigation, it was supposed that these "bound residues" may be naturally occurring plant structural or storage molecules. Thus, we set out to isolate starch from the grain of C nitrofen treated wheat or r i c e plants and lignin from the straw to determine if the C of nitrofen could be incorporated into these compounds. Figures 1 and 2 show the methods by which we isolated the starch and lignin from rice or wheat plants treated at 3-4 lb/acre with C nitrofen. Wheat or rice grain or straw was harvested at 110-147 days from treatment and worked into homogenous samples. Starch was extracted from wheat or rice grain with DMSO. The isolated starch was then hydrolyzed and the resulting C-glucose derivatized to the glucosazone with phenylhydrazine. The resulting osazone was recrystallized to constant specific radioactivity. Wheat or r i c e straw was Soxhlet extracted 18 hours with an ethanol-benzene mixture. Cellulose and lignin were then isolated from the remaining solids using hot sodium hydroxide under 14
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HONEYCUTT ET AL.
pressure. The l i g n i n was then p u r i f i e d to a constant s p e c i f i c radioactivity. Figure 1 Wheat G r a i n - ^ C Blend w i t h DMSO-centrifuge 1 Supernatant
Pellet
I Add EtOH J centrifuge Starch
i
Supernatant HCI Phenylhydrazine
^C-glucosazone luc ecrystallize I RRec y to purity Figure 2 Wheat straw
1 Solids
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Soxhlet Extraction 1 Extract
NaOH 160° 3 hours Filter Cellulose
Lignin ourify
Figure 3 shows the s p e c i f i c r a d i o a c t i v i t y o f glucosazones and l i g n i n i s o l a t e d from ^ C - n i t r o f e n t r e a t e d wheat g r a i n and straw r e s p e c t i v e l y and taken through 3 p u r i f i c a t i o n steps during a t y p i c a l experiment. We can e a s i l y see t h a t constant s p e c i f i c r a d i o a c t i v i t y can be obtained through repeated p u r i f i c a t i o n of both the C-glucosazones from wheat g r a i n and the ^ C - l i g n i n s from wheat straw. One can determine what percentage o f the t o t a l ^ C - n i t r o f e n residue at harvest i s i n s t a r c h o r l i g n i n by d i v i d i n g the s p e c i f i c r a d i o a c t i v i t y of the s t a r c h or l i g n i n by the s p e c i f i c r a d i o a c t i v i t y o f the o r i g i n a l wheat straw and m u l t i p l y i n g by the percent o f s t a r c h i n g r a i n o r the percent of l i g n i n i n straw. Such experiments and such c a l c u l a t i o n s o f the data obtained were c a r r i e d out on a v a r i e t y o f samples o f g r a i n and straw from wheat and r i c e p l a n t s t r e a t e d both preemergence and postemergence 1
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BOUND AND CONJUGATED PESTICIDE RESIDUES
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C - n i t r o f e n . F i g u r e 4 shows a summary o f such work. These data show that a s u b s t a n t i a l amount of the r a d i o a c t i v e residue found i n r i c e and wheat straw at harvest i s i n l i g n i n . A p p l i c a t i o n preemergence o r appears t o make no d i f f e r e n c e i n the amount o f C incorporated i n t o l i g n i n . Whether t h e x i n l i g n i n i s a l i g n i n - n i t r o f e n conjugate o r whether the C of n i t r o f e n has been incorporated i n t o the carbon s k e l e t o n of l i g n i n remains t o be e l u c i d a t e d . I t a l s o can be seen from t h i s f i g u r e that a great d e a l of the r a d i o a c t i v e residue i s i n t h e form o f s t a r c h . By d e r i v a t i z a t i o n o f the s t a r c h t o the glucosazone it has been proven that the C o f n i t r o f e n was reincorporated through metabolic processes i n t o glucose and f i n a l l y i n t o s t a r c h . W
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Figure 3 P u r i f i c a t i o n o f Glucosazones 14,O G l u c o s az ones
Specific Radioactivity dpm/g 122 147 133
1st R e c r y s t a l l i z a t i o n 2nd R e c r y s t a l l i z a t i o n 3rd R e c r y s t a l l i z a t i o n
P u r i f i c a t i o n of L i g n i n Specific Radioactivity C-Lignin dpm/g Crude L i g n i n 3,129 3,834 1st R e p r e c i p i t a t i o n 3,670 2nd R e p r e c i p i t a t i o n 3,432 3rd R e p r e c i p i t a t i o n 1 4
Figure Sample R i c e Straw R i c e Straw Wheat Straw Rice Grain Wheat Grain
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% o f Radioactive Residue % o f Radioactive at Harvest i n L i g n i n Residue a t Harvest i n Starch 33 Preemergence 25 Postemergence 30 Preemergence 64 Preemergence 70 Preemergence
Treatment
