Controlled Release Pesticides 9780841203822, 9780841204409, 0-8412-0382-2

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Controlled Release Pesticides

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Controlled Release Pesticides Herbert B. Scher, EDITOR Stauffer Chemical Co.

A symposium sponsored by the Division of Pesticide Chemistry at the 173rd Meeting of the American Chemical Society, New Orleans, La., March 21-22, 1977.

ACS SYMPOSIUM SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C. 1977

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

53

Library of Congress CIP Data Controlled release pesticides. (ACS symopsium series; 53 ISSN 0097-6156) Includes bibliographical references and index. 1. Pesticides, controlled release—Congresses. I. Scher, Herbert B., 1937II. American Chemical Society. Division of Pesticide Chemistry. III. Title. IV. Series: American Chemical Society. ACS symposium series; 53. SB951.C648 1977 ISBN 0-8412-0382-2

668'.65

77-22339

Copyright © 1977 American Chemical Society All Rights Reserved. No part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. PRINTED IN T H E UNITED STATES O F A M E R I C A

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

ACS Symposium Series Robert F. Gould, Editor

Advisory

Board

D o n a l d G . Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A . Hofstader J o h n L. Margrave N i n a I. M c C l e l l a n d J o h n B . Pfeiffer Joseph V . R o d r k k s Alan

C. Sartorelli

Raymond B . Seymour R o y L. W h i s t l e r Aaron W o l d

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

FOREWORD The A C S S Y M P O S I U M SERIES was founded i n 1 9 7 4 to provide

a medium for publishing symposia quickly i n book form. The format of the SERIES parallels that of the continuing A D V A N C E S I N C H E M I S T R Y SERIES except that i n order to save time the papers are not typeset but are reproduced as they are submitted b y the authors i n camera-ready form. A s a further means of saving time, the papers are not edited or reviewed except b y the symposium chairman, who becomes editor of the book. Papers published i n the A C S S Y M P O S I U M SERIES are original contributions not published elsewhere i n whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PREFACE /Controlled release technology was

pioneered by

the

drug industry

^ approximately 25 years ago. The initial goal was to produce controlled release oral drug forms that could maintain an effective level of drug i n the body, thereby eliminating the side effects caused by administrating high doses of conventional drugs. More recently, the drug industry has become even more sophisticated and has introduced controlled release drug forms capable of being implanted at the site of action, which further reduces drug level Applying the same controlled release principles, pesticide scientists are now developing controlled release pesticide formulations capable of maintaining an effective level of pesticide in the soil or on foliage, thereby reducing pesticide application rates and minimizing pesticide levels i n the environment. In addition, controlled release pesticide formulations can reduce pesticide toxicity and extend pesticide residual activity. This volume is a compilation of information dealing with the structural and chemical factors governing the controlled release of pesticides from polymer systems. The first five papers deal w i t h controlled release concepts, controlled release theory, and the environmental and toxicological aspects of controlled release pesticides. The next seven papers describe polymer systems that control the release of pesticides—i.e., elastomers, biodegradable matrices, polymers containing pendant pesticides, and microcapsules. The final four papers include research on microencapsulated insecticides for field use, laminated insecticide tapes for home use, a variety of systems for controlling the release of gypsy moth pheromone, and a microcapsule system for controlling the release of an insect growth regulator. I would like to thank all the authors and J . J . Menn, J . P. Minyard, Jr., and G . G . Still of the Pesticide Division for their full cooperation during all phases of this symposium. Richmond, Calif.

H E R B E R T B. S C H E R

M a r c h 1977

ix

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1 Principles of Controlled Release Pesticides D. H. LEWIS and D. R. COWSAR Southern Research Institute, Birmingham,Ala.35205

The rapidly growing deman entific community with a operations i n both industrial a n d a g r i c u l t u r a l production is paramount. M e t h o d s and processes t h a t a f f o r d higher y i e l d s and b e t t e r q u a l i t y , r e q u i r e less t i m e a n d m o n e y , a n d do n o t pose a t h r e a t t o t h e e n v i r o n m e n t a r e b e i n g sought a t a n u n p a r a l l e l e d p a c e w h i c h undoubtedly w i l l i n t e n s i f y f u r t h e r i n t h e l a s t q u a r t e r o f t h i s c e n t u r y . T h e c o n t r o l o f pests, a b a t t l e fought f o r g e n e r a t i o n s , i s u n q u e s t i o n a b l y a crucial t a s k if our goals f o r t h e f u t u r e c o n c e r n i n g food and e n e r g y a r e t o b e a c h i e v e d . R e c e n t e s t i m a t e s suggest t h a t losses due t o i n e f f i c i e n t p e s t - c o n t r o l t e c h n i q u e s a m o u n t t o b e t w e e n $10 and 30 billion e a c h y e a r (1). Losses o f cotton alone t o i n s e c t s e x c e e d $500 million p e r a n n u m . (2) In India, rodents a r e r e p o r t e d (3) t o destroy a fourth of t h e harvested grain crop annually. The astounding losses due t o pests a r e n o t limited t o food supplies a l o n e . T h e f o u l i n g o f s h i p hulls c o s t s t h e U . S . N a v y a n a d d i t i o n a l $150 m i l l i o n / y e a r i n f u e l (4), $15 m i l l i o n / y e a r i n labor a n d m a t e r i a l s f o r r e p a i n t i n g ships w i t h a n t i f o u l a n t s , and a p p r o x i m a t e l y $200 million e a c h y e a r f o r r e p l a c e m e n t o f b i o l o g i c a l l y d e t e r i o r a t e d m a r i n e p i l i n g s (5). T h e i m p o r t a n c e o f p e s t i c i d e s is e v i d e n c e d by t h e e s t i m a t e d sale o f $2.5 billion o f p e s t i c i d e s e a c h y e a r i n t h e U . S . alone (6). A l t h o u g h t h e reality o f i n c r e a s i n g danger t o m a n from persistent pesticides is recognized, the frightening fact remains that if terrestrial h e r b i c i d e s alone w e r e b a n n e d , s t a r v a t i o n w o u l d b e c o m e m o r e p r e v a l e n t i n t h e w o r l d p o p u l a t i o n i n short o r d e r . Historically, s c i e n t i s t s h a v e d e a l t w i t h t h e p r o b l e m o f pest c o n t r o l by designing new, .more potent a g e n t s . H o w e v e r , use o f these agents t o produce t h e d e s i r e d b i o l o g i c a l response is o f t e n i n e f f i c i e n t , p r i m a r i l y because o f i n a b i l i t i e s t o d e l i v e r t h e agents t o t h e i r t a r g e t s a t t h e p r e c i s e t i m e and i n t h e o p t i m u m q u a n t i t i e s r e q u i r e d . E n o r m o u s a m o u n t s o f funds are r e q u i r e d f o r t h e d e v e l o p m e n t o f a n e w b i o c i d e . R e c e n t e s t i m a t e s p l a c e t h e d e v e l o p m e n t costs f o r a new p e s t i c i d e a t about $8 million (6). R e c o g n i z i n g t h e c o s t a n d limitations i n t h e design o f n e w p e s t i c i d e s , s c i e n t i s t s began t o t u r n i n t h e 1960s t o a n alternative a p p r o a c h , t h a t o f i m p r o v i n g t h e d e l i v e r y o f t h e a g e n t s , b o t h n e w e r agents and o l d . In today's t e r m i n o l o g y , a c o n t r o l l e d - r e l e a s e f o r m u l a t i o n o r d e l i v e r y s y s t e m i s d e f i n e d as a c o m b i n a t i o n o f b i o l o g i c a l l y a c t i v e agent and e x -

1

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

CONTROLLED

RELEASE

PESTICIDES

c i p i e n t , usually a p o l y m e r , a r r a n g e d t o a l l o w d e l i v e r y of t h e agent t o the t a r g e t at c o n t r o l l e d r a t e s o v e r a s p e c i f i e d p e r i o d . The r a p i d e m e r g e n c e of c o n t r o l l e d r e l e a s e as an e s t a b l i s h e d s c i e n t i f i c f i e l d is e v i d e n c e d by the g r o w i n g n u m b e r of r e l a t e d p u b l i c a t i o n s a p p e a r i n g i n t h e l i t e r a t u r e and the i n c r e a s i n g n u m b e r of s y m p o s i a on t h e subject e a c h y e a r . A s r e c e n t as 1973, for e x a m p l e , only one s y m p o s i u m was d e v o t e d t o c o n t r o l l e d r e l e a s e , w h i l e d u r i n g 1976 s e v e r a l major m e e t i n g s addressed t h e subject i n d e p t h . F e w areas of r e s e a r c h have a c t i v a t e d t h e i n t e r e s t and a t t e n t i o n of s u c h a m u l t i d i s c i p l i n a r y group of p r o f e s s i o n a l s . A t t e n d e e s at w o r k s h o p s , c o n f e r e n c e s , and s y m p o s i a on c o n t r o l l e d r e l e a s e t y p i c a l l y i n c l u d e b i o l o g i s t s , chemists, engineers, pharmacologists, agronomists, entomologists, vete r i n a r i a n s , d e n t i s t s , and p h y s i c i a n s . It is now a w e l l r e c o g n i z e d f a c t t h a t t h e t e c h n o l o g y or c o n t r o l l e d r e l e a s e c a n c o n t r i b u t e p o s i t i v e l y t o man's f i g h t against disease and hunger. C o n t r o l l e d release a b e c o m i n g the subject o f e r t i l i z e r s w e r e k n o w n at l e a s t 30 years ago, m o s t of the s i g n i f i c a n t a d v a n c e s have c o m e i n t h e l a s t 10 y e a r s . O b v i o u s l y , i n a f i e l d e x p a n d i n g so r a p i d l y , a c o m p l e t e r e v i e w of t h e l i t e r a t u r e c a n n o t be g i v e n h e r e . H o w e v e r , a n u m b e r of e x c e l l e n t p u b l i c a t i o n s are a v a i l a b l e w h i c h o f f e r m o r e d e t a i l e d t r e a t m e n t s on f u n d a m e n t a l s of c o n t r o l l e d r e l e a s e and discussions of c o n t r o l l e d - r e l e a s e p e s t i c i d e f o r m u l a t i o n s (7-12). C a r d a r e l l i (1), a pioneer i n t h e f i e l d , has a u t h o r e d an e x c e l l e n t c o m p r e h e n s i v e r e v i e w of c o n t r o l l e d - r e l e a s e p e s t i c i d e f o r m u l a t i o n s . T h i s c h a p t e r is i n t e n d e d to i n t r o d u c e the n e w c o m e r t o the f i e l d , and for t h e e x p e r i e n c e d r e s e a r c h e r , t o m a k e t h e papers t h a t f o l l o w m o r e c o h e s i v e . F i r s t , a b r i e f d i s c u s s i o n of t h e s h o r t c o m i n g s of c o n v e n t i o n a l methods of d e l i v e r y w i l l be g i v e n , t h e n an o v e r v i e w of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s , and f i n a l l y a f e w of t h e c u r r e n t a p p l i c a t i o n s of c o n t r o l l e d r e l e a s e . A d v a n t a g e s of C o n t r o l l e d R e l e a s e The p r i n c i p a l a d v a n t a g e of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s is t h a t t h e y a l l o w m u c h less p e s t i c i d e t o be used for the s a m e p e r i o d of a c t i v i t y . M o r e o v e r , w h e n t h e n o r m a l h a l f - l i f e of a potent p e s t i c i d e is s h o r t , the r e l e a s e f o r m u l a t i o n s are e s p e c i a l l y advantageous i n c o m p a r i s o n t o c o n v e n t i o n a l methods of a p p l i c a t i o n . T o f u l l y u n d e r s t a n d t h i s b e n e f i t , one m u s t f i r s t u n d e r s t a n d the m a g n i t u d e of t h e e n v i r o n m e n t a l f o r c e s t h a t a c t t o r e m o v e excesses of p e s t i c i d e s f r o m t h e i r s i t e s of a p p l i c a t i o n . When a p p l i e d by c o n v e n t i o n a l m e t h o d s , p e s t i c i d e s are i n v a r i a b l y subject t o l e a c h i n g , e v a p o r a t i o n , and d e g r a d a t i o n ( p h o t o l y t i c , h y d r o l y t i c , and m i c r o b i a l ) , a l l of w h i c h r e m o v e t h e a c t i v e m a t e r i a l s f r o m t h e i r t a r g e t b e f o r e they c a n p e r f o r m t h e i r f u n c t i o n . In m o s t c a s e s , t h e r a t e of r e m o v a l f o l l o w s f i r s t - o r d e r k i n e t i c s , i . e . , t h e r a t e of r e m o v a l a t any t i m e is d i r e c t l y p r o p o r t i o n a l t o the a m o u n t (or c o n c e n t r a t i o n of t h e p e s t i c i d e present i n t h e e n v i r o n m e n t at t h a t t i m e . A m a t h e m a t i c a l e x p r e s s i o n of t h e f i r s t - o r d e r r a t e l a w is g i v e n by E q u a t i o n 1, (1)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

LEWIS

AND

COWSAR

Principles

of Controlled

Release

Pesticides

3

w h e r e dM/dt is t h e r a t e of r e m o v a l , k is t h e r a t e c o n s t a n t , and M is t h e a m o u n t of p e s t i c i d e present at any f i m e t . The i n t e g r a t e d s o l u t i o n t o E q u a t i o n 1 is M 1 η (

Ί5Γ

)

=

- ν

(2)

00

where M The r a t e expressed order rate œ

is t h e a m o u n t present at t = 0; M is thus t h e a m o u n t a p p l i e d . of r e m o v a l of a p e s t i c i d e f r o m t h e e n v i r o n m e n t is o f t e n as t h e agent's h a l f - l i f e , ty. The h a l f - l i f e is r e l a t e d t o the f i r s t c o n s t a n t f o r r e m o v a l , k , as f o l l o w s : œ

In 2 = - k t r Vz f/

or,

(3)

k

If M is the m i n i m u m e f f e c t i v e l e v e l of p e s t i c i d e and M is t h e a m o u n t on crosslinking the xanthate, the other polymers are entrapped along with the active agents. Another modification e a s i l y made which can modify release properties provides products which are doubly encapsulated. This i s achieved on addition of more starch xanthate, either alone or containing another polymer, after the i n i t i a l crosslinking reaction has been effected and then adding additional crosslinking agent. The starch xanthate used f o r encapsulation i s prepared under ambient conditions by treating a water suspension of starch with carbon d i s u l f i d e and an a l k a l i metal hydroxide. Typically about 701 of the carbon d i s u l f i d e i s converted to xanthate within 30 minutes with l i t t l e or no additional conversion occurring on prolonged standing. Although the theoretical number of xanthate groups possible for each anhydroglucose repeating u n i t of starch i s 3 [degree of substitution (DS) of 3 ] , we f i n d that a DS of 0 . 1 to 0 . 3 5 i s s u f f i c i e n t . V i s c o s i t y of xanthate solutions increases proportionally with DS and starch xanthate concentration. When whole unmodified starch (regular pearl starch) i s used as the starting material, a starch xanthate concentration of near 151 i s about the maximum that can be handled for the encapsulation process. Higher concentrations, usable i n t h i s process, of up to nearly 601 can be achieved, i f the starting starch i s reduced i n molecular size by hydrolysis of some of the glucopyranosyl linkages with acids or enzymes.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

76

C O N T R O L L E D R E L E A S E PESTICIDES

Such modifications are conventional commercial procedures designed to provide degraded starch products for a variety of i n d u s t r i a l uses. Use of the more concentrated starch xanthate solutions has an obvious advantage i n cost for drying the particulate encapsulated product. However, there are c e r t a i n l i m i t a t i o n s on using the highly concentrated solutions. The amount of active agent that can be e f f e c t i v e l y encapsulated within the crosslinked starch xanthate matrix i s inversely proportional to starch xanthate concentration. For example, when starch xanthate of 1 4 1 concentration i s used, a f i n a l product i s obtained which contains a maximum of 471 of a l i q u i d thiocarbamate. When 501 xanthate i s employed the maximum i s reduced to 1 3 1 . The values conceivabl might with th natur f the chemical to be encapsulated the active agent was butylate (S-ethy diisobutylthiocarbamate) At the highest l e v e l , where the particulate product consists of nearly 501 of the highly v o l a t i l e l i q u i d butylate, the p a r t i c l e s have a wetted appearance and are not completely free flowing. At about 401 or l e s s , they appear dry and give a free-flowing product. Although various methods have been employed for crosslinking the xanthate with apparently s i m i l a r r e s u l t s , we have worked mostly with the oxidative method and have used either nitrous acid or hydrogen peroxide as the selected oxidant. Both oxidants e f f e c t i v e l y crosslink the xanthate S S to xanthide (starch-O-C-S-S-C-0-starch) at a pH of 4 to 5. Since the xanthate i s made under a l k a l i n e conditions, the pH must be lowered to allow crosslinking. For pesticides, which are l a b i l e to a l k a l i , the pH can be adjusted to near n e u t r a l i t y before addition of the active agent. For the nitrous acid system, sodium n i t r i t e i s added to the alkaline xanthate solution and becomes the active oxidant when the pH i s lowered to 4-5. When peroxide i s used, i t i s added to a neutralized xanthate and then pH i s lowered further. Only s l i g h t l y more than stoichiometric amounts of oxidant are required, and since the oxidation proceeds to completion rapidly, even active agents which are susceptible to oxidation are not l i k e l y to be oxidized during encapsulation. Although * This paper reports the r e s u l t s of research only. Mention of a pesticide i n t h i s paper does not constitute a reconmendation for use by the U.S. Department of Agriculture nor does i t imply r e g i s t r a t i o n under FIFRA as amended. Also, mention of f i r m names does not constitute an endorsement by the U.S. Department of Agriculture over other firms not mentioned.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DO A N E E T A L .

Encapsulation

within a Starch

Matrix

77

both oxidants appear to work equally w e l l i n crosslinking the xanthate, encapsulated products are quite different i n appearance and i n release properties of the active agent. Nitrous acid crosslinked products contain numerous microscopic openings i n the matrix, due apparently to small amounts of nitrous oxide gas generated during the reaction. These openings result i n a r e l a t i v e l y rapid rate o f release as w i l l be described l a t e r . The peroxide-coupled products are without v i s i b l e openings and provide much slower release of active agent. Shelf l i f e of the starch-encapsulated pesticides i s good, and there i s no appreciable loss on storage i n closed containers during 1 year. When placed i n open containers for several days, loss of v o l a t i l e agent i s n e g l i g i b l e However, when products ar active agent i s then release simple laboratory screening test for comparing release properties of thiocarbamate- containing products to assist i n selection of formulations f o r subsequent bioassay. The test consists of placing several 1-gram portions of a product i n watch glasses placed i n a hood and applying to each 2-ml of water. The water slowly evaporates during a 24-hour period i n the hood. Then water i s again added and the wetted product again allowed to stand f o r 24 hours. This repeated wetting and drying i s continued for the duration o f the test with entire 1-gram samples being removed p e r i o d i c a l l y and analyzed f o r t o t a l nitrogen content i n those instances where the active agent contains nitrogen. Table I shows the release characteristics f o r four different formulations containing butylate. Table I Release Properties of Butylate Formulations Loss of butylate, % Xanthate b a s e

1 day

a

A c i d - m o d i f i e d flour* Acid-modified flours t a r c h mixture Starch S t a r c h + 201 l a t e x None ( c o n t r o l )

3

2 days

8 days

29

58

68

20 0 0 68

36 0 0 98

48 8 37 100

^ Xanthate DS was 0.35 and double encapsulation was used f o r each. NalC^ used f o r oxidation. E,0~ used f o r oxidation.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICrDES

78

I t would appear that either the protein component i n the f l o u r or the lower molecular weight of the starch component of the f l o u r contributes to a faster release of butylate; however, t h i s remains to be confirmed. Other preliminary tests indicate that DS of xanthate, e.g., crosslink density of the matrix, may play a s i g n i f i c a n t role i n controlling release of active agent, and studies to confirm t h i s are underway. Depending on the amount of shear placed on the p a r t i c u l a t e product before drying, a range of p a r t i c l e sizes can r e s u l t . With simple hand mixing, a p a r t i c l e size of 14 mesh or larger i s t y p i c a l l y obtained. For small laboratory preparations, we shear the wet product i n a Waring Blendor for a few seconds to produce smaller p a r t i c l e sizes. We have not as ye enough to pass 100 mesh products can y i e l d f i n e powders but considerable amounts of pesticide are l o s t , especially i f they are highly v o l a t i l e ones. Whereas shearing of the wet product results mostly i n breaking up the agglomerates composed of several smaller p a r t i c l e s , grinding or m i l l i n g of dry products disrupts the matrix encapsulating the pesticide. A product prepared from starch xanthate of DS 0.175 and crosslinked with r^C^ i n the presence of EPTC (S-ethyl dipropyl thiocarbamate) was dried and separated into four fractions by sieving. The four fractions were analyzed for active agent content and loss of agent a f t e r treatment with water for 2 days. Results are shown i n Table I I . Table I I Properties of Starch Xanthide-EPTC Formulations as Related to P a r t i c l e Size

Mesh size

ξ of Total

>60 30-60 14-30

*»

to 35 Η

.3 3s *3> V.

to S to 35^

a:i to 35

si • ^ to *C to

ε

C

gI 35 35

ο

ι

to **>

Is

5

to 35

κ ο to 3>

•s to «•Λ

"δCO

1 35

it! 3

S

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

Polymers

HARRIS E T A L .

with Pendant

Herbicides

109

90% o f the amount o r i g i n a l l y present. As can be seen from the F i g u r e , the r a t e o f h y d r o l y s i s increased during the f i r s t few days o f the study and then remained r e l a t i v e l y c o n s t a n t . Since the c o n c e n t r a t i o n o f e s t e r linkages decreases as the polymer i s h y d r o l y z e d , the r a t e constant f o r the h y d r o l y s i s must c o n t i n u a l l y increase. T h i s behavior, i n e f f e c t , provides a z e r o - o r d e r r a t e o f r e l e a s e , which i s i d e a l l y s u i t e d f o r c o n t r o l l e d - r e l e a s e applications. The increase i n the r a t e constant as the h y d r o l y s i s p r o ceeds may a l s o be due to i n t r a m o l e c u l a r c a t a l y s i s . Infrared data i n d i c a t e s t h a t amine acylimides have a reasonance s t a b i l i z e d s t r u c t u r e as shown (17). Hence, i t i s p o s s i b l e that the

R'

R

R

aminimide group acts as a c a t a l y s t i n the same manner as d e s c r i b e d f o r the carboxyl group. The mechanism by which c o polymer Va undergoes h y d r o l y s i s i s c u r r e n t l y being i n v e s t i g a t e d . Experimental U l t r a v i o l e t s p e c t r a were obtained with a Gary Model 14 spectrophotometer. Infrared spectra were obtained on t h i n f i l m s with a Perkin-Elmer Model 457 spectrophotometer. Viscosities were determined with a Cannon Number 75 viscometer. The aminimide monomer was furnished by Ashland Chemicals, Columbus, Ohio. General S o l u t i o n Copolymerization Procedure. Herbicide monomer, comonomer, 2-butanone (4 ml/g o f monomers), and 0.05% AIBN were thoroughly mixed and slowly heated under n i t r o g e n to 75°. A f t e r heating at 75° f o r 3 h r , the mixture was c o o l e d , d i l u t e d with 2-butanone, and p r e c i p i t a t e d i n hexane. The copolymer was c o l l e c t e d by f i l t r a t i o n and d r i e d under vacuum at 60° f o r 3 h r . Hydrolysis Studies. The copolymers were e x t r a c t e d with ether f o r 18 hr to remove unreacted monomer, d r i e d under vacuum, and then ground and sieved to a p a r t i c l e s i z e o f 125-400y. Three 0 . 5 - g samples o f each copolymer were placed i n 500-ml erlenmeyer f l a s k s c o n t a i n i n g 300 ml o f a b o r i c acid-sodium hydroxide buffer (pH = 8 . 0 8 ) . The f l a s k s were maintained a t 30 + 0.1° i n a constant temperature bath. The amount o f h e r b i c i d e r e l e a s e d from each copolymer was determined p e r i o d i c a l l y by spectrophotometric a n a l y s i s at 198 nm.

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Acknowledgement Support o f t h i s research by the Department o f the Army, U.S. Army Engineer Waterways Experiment S t a t i o n under Contract DACW39-86-C-0016 (Neg.) i s g r a t e f u l l y acknowledged. Appreciation i s a l s o expressed to AmChem Products, Inc. f o r f u r n i s h i n g the h e r b i c i d e s and to Ashland Chemicals Company f o r f u r n i s h i n g the aminimides used i n t h i s study.

Literature Cited 1. 2.

3. 4. 5.

6.

7. 8. 9. 10. 11. 12. 13. 14.

Harris, Frank W., Norris, Steve O., and Post, Larry Κ., Weed Science, (1973), 21 (4), 318. Harris, Frank W. and Post, Larry K. in "Proceedings 1974 International Controlled Release Pesticide Symposium," Cardarelli, Nate F. 1974. Harris, Frank W., and Post, Larry Κ., Am. Chem. Soc., Polym. Div., Preprints, (1975), 16 (2), 622. Harris, Frank W. and Post, Larry K., J. Polym. Sci., Polymer Letters Ed., (1975), 13, 225. Harris, Frank W., Feld, William Α., and Bowen, Bonnie, in "Proceedings 1975 International Controlled Release Pesticide Symposium," p. 334 Harris, F.W., Ed., Wright State University, Dayton, Ohio, 1975. Harris, Frank W., Aulabaugh, Ann Ε., Case, Robert D., Dykes, Mary Κ., and Feld, William Α., "ACS Symposium Series, No. 33, Controlled-Release Polymeric Formulations," p. 222, Paul, D.R. and Harris, F.W., Ed., American Chemical Society, Washington, D.C., 1976. Morawetz, Η., "Macromolecules in Solution," pp. 422-426, Wiley, New York, 1965. Morawetz, H., and Zimmering, P.E., J. Phys. Chem., (1954), 58, 753. Gaetjens, E. and Morawetz, J. Amer. Chem. Soc., (1961), 83, 1738. Morawetz, Η., and Westhead, E.W., J . Polym. S c i . , (1955), 16, 273. VanBeylen, M.M. in "Stereochemistry of Macromolecules," Vol. 3, p. 335, Ketley, A.D., Ed., Marcel Dekker, New York, 1968. Smets, G. and Hesbain, A.M., J. Polym. S c i . , (1959), 40, 217. Sakurada, I. and Sakaguchi, Y., Kobunshi Kagaku, (1956), 13, 441; Chem. Abst., (1957), 51, 17365 g. Smets, G. and VanHumbeeck, W., J . Polym. S c i . , (1963), 1, 1227.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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15. Goodman, N. and Morawetz, H., J . Polym. S c i . , Part C, (1970), 31, 177. 16. Smets, G., and DeLoecker, W., J . Polym. S c i . , (1960), 45, 461. 17. McKillip, W.J., Sedor, E.A., Culbertson, B.M., and Wawzonek, S., Chem. Rev., (1973), 73, 255.

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11 Synthesis, Characterization, and Release Mechanisms of Polymers Containing Pendant Herbicides CHARLES L. McCORMICK and MICHAEL FOOLADI Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Miss. 39401

As the w o r l d ' s populatio faced with the demand f o r enhanced production u t i l i z i n g chemicals with l i t t l e or no detrimental e f f e c t on the surrounding e n v i r o n ­ ment. P e s t i c i d e leaching i n t o drainage waters and subsequent t r a n s p o r t i n t o non-target areas i s o f growing e c o l o g i c a l concern. The immensity o f the problem i s apparent when c o n s i d e r i n g the t o t a l a g r i c u l t u r a l p e s t i c i d e a p p l i c a t i o n and the annual r u n - o f f f o r drainage a r e a s . The M i s s i s s i p p i Watershed area alone covers 1,244,000 square miles i n c l u d i n g vast s t r e t c h e s o f c e n t r a l U.S. farmland. The annual water discharge a t the mouth o f the M i s s i s s i p p i has been estimated to 7.8 χ 1 0 y d s and 2,000,000 tons o f sediment are c a r r i e d i n t o the sea per day. The average annual r a i n f a l l over t h i s area i s about 30 i n c h e s , o f which about one-fourth t r a v e l s to the G u l f o f Mexico by way o f the M i s s i s s i p p i River ( 1 , 2 ) . In 1974, nearly 1.4 b i l l i o n pounds o f organic p e s t i c i d e s were s o l d by U.S. companies, representing a growth o f 12% over 1973. I n s e c t i c i d e s accounted f o r 50.4% o f the t o t a l volume with the balance c o n s i s t i n g o f h e r b i c i d e s , f u n g i c i d e s , and p l a n t hormones (3). With some p e s t i c i d e systems, 70 - 80% of the useful chemical a c t i v i t y i s l o s t by various mechanisms i n c l u d i n g i n t e r a c t i o n with non-target organisms. S c i e n t i s t s have measured the rates o f loss o f a c t i v i t y o f various chemicals i n terms o f "persistence" levels. P e r s i s t e n t p e s t i c i d e s have been attacked i n environmental studies due t o t h e i r usual migration to nont a r g e t areas. However, i t should be pointed out that some degree o f persistence i s necessary t o y i e l d weed, i n s e c t or fungus c o n t r o l f o r a reasonable period o f time i n the t a r g e t area. Often the most p e r s i s t e n t chemicals are a l s o the most effective. Several f a c t o r s are known t o determine p e r s i s t e n c e i n the soil. These include (a) uptake and degradation by microorgan­ isms, (b) l o s s through p h y s i c a l processes o f v o l a t i l i z a t i o n and l e a c h i n g , and (c) chemical changes such as photo-decomposition and chemical reactions (4). 11

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The Environmental P r o t e c t i o n Agency i s imposing s t r i n g e n t requirements on several e f f e c t i v e and p r e v i o u s l y widely used pesticides. The t y p e , amount a p p l i e d , s p e c i f i c i t y , and p e r s i s t e n c e o f each p e s t i c i d e w i l l be under continuing s c r u t i n y . The pest c o n t r o l agents must not merely c o n t r o l t a r g e t organisms but must be harmless to humans, l i v e s t o c k , c r o p s , f i s h , w i l d l i f e , b e n e f i c i a l i n s e c t s , s o i l microorganisms, e t c . Dramatic improvements i n a n a l y t i c a l instrumentation have allowed claims o f d e t e c t i o n o f t r a c e amounts of organic chemicals i n non-target areas i n the parts per b i l l i o n range. T h i s a d vance, i n conjunction with the controversy generated by adverse p u b l i c i t y on i n s e c t i c i d e s such as DDT and Mi rex, has led to a f l u r r y o f experiments on n e a r l y every chemical manufactured i n the U.S. P a r t i c u l a r emphasis has been placed on chemicals having p o t e n t i a l impact on the aquatic environment. For example, B u t l e r ( 5 - 1 2 ) has reporte use of p e s t i c i d e chemicals i s producing environmental changes or residues i n the food web that may cause reproductive f a i l u r e . . " Some organisms have been shown to accumulate or concentrate c e r t a i n p e r s i s t e n t p e s t i c i d e s at alarming r a t e s . The o y s t e r , f o r example, when continuously exposed to 0.1 ppb o f DDT, was r e ported to concentrate i n i t s t i s s u e s up to 7.0 ppm i n a month. It may be p r e d i c t e d that c h l o r i n a t e d h e r b i c i d e s w i l l soon come under attack ( 1 3 , 2 8 - 3 0 ) . S t r i n g e n t r u l e s and r e g u l a t i o n s (apparently subject to frequent m o d i f i c a t i o n ) have been imposed on a g r i c u l t u r a l chemical producers and consumers as a r e s u l t of environmental s t u d i e s . Many knowledgeable sources p r e d i c t an impending d i s a s t e r f o r the whole a g r i c u l t u r a l i n d u s t r y from the high costs o f l i c e n s i n g , r e g i s t r a t i o n , and production of new p e s t i c i d e s . In 1976, new p e s t i c i d e commercialization required an average of 2 . 5 years of research and development at a cost o f over $10,000,000.00. The a g r i c u l t u r a l i n d u s t r y has, i n g e n e r a l , responded to the e n v i r o n mental r e g u l a t i o n s by producing l e s s p e r s i s t a n t but often l e s s e f f e c t i v e p e s t i c i d e s , r e q u i r i n g more frequent a p p l i c a t i o n over an extended growing season. A more l o g i c a l and c e r t a i n l y more f r u i t f u l approach i s to attack the undesired " l e a c h i n g " or t r a n s p o r t of a given p e s t i c i d e r a t h e r than i t s " p e r s i s t e n c e . " A g r i c u l t u r a l chemical leaching and subsequent p e s t i c i d e t r a n s p o r t to non-target environments can be g r e a t l y reduced, p o s s i b l y e l i m i n a t e d , by c o n t r o l l e d - r e l e a s e systems based on macromolecules. Polymers can be synthesized which contain r e a c t i v e chemical bonds to common p e s t i c i d e s ; these bonds are subject to enzymatic or h y d r o l y t i c break-down at a c o n t r o l l a b l e rate. The macromolecular nature of these systems w i l l prevent d i s s o l u t i o n , leaching and t r a n s p o r t to non-target areas. Cont r o l l e d - r e l e a s e can a l s o reduce the number of a p p l i c a t i o n s and the q u a n t i t y of chemical required f o r pest c o n t r o l . A number of n a t u r a l l y o c c u r r i n g polymers ( 2 5 - 2 7 ) o f f e r e x c e l l e n t p o t e n t i a l as raw m a t e r i a l s f o r substrate preparation o f c o n t r o l l e d r e l e a s e systems. In a d d i t i o n , c e r t a i n polysaccharides decompose y i e l d i n g

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products b e n e f i c i a l to the s o i l . Development of a commercial h e r b i c i d e system must combine e f f e c t i v e n e s s , favorable economics, with l i t t l e adverse e n v i r o n ­ mental impact. The chemical must: (1) c o n t r o l weeds at reason­ able dosages, (2) s e l e c t i v e l y c o n t r o l target organisms o n l y , l e a v i n g b e n e f i c i a l i n s e c t s , p l a n t s , and humans unharmed, (3) p e r s i s t f o r a reasonable time, (4) be inexpensive f o r l a r g e s c a l e usage, and (5) and be e a s i l y a p p l i e d , (preferably with conventional equipment). Provided the above c r i t e r i a are met, p o t e n t i a l b e n e f i t s d e r i v e d from properly formulated c o n t r o l l e d - r e l e a s e systems include: (1) enhanced a g r i c u l t u r a l p r o d u c t i o n , (2) fewer a p p l i c a t i o n s , (3) l e s s environmental p o l l u t i o n and (4) reduced production costs to the farmer. Macromolecular

Design

Polymeric systems f o r c o n t r o l l e d - r e l e a s e of p e s t i c i d e s may be assigned to two broad c a t e g o r i e s . In the f i r s t , the p e s t i ­ c i d e i s p h y s i c a l l y d i s s o l v e d , entrapped, or dispersed i n a polymer matrix. Chemical release i s g e n e r a l l y based on d i f ­ f u s i o n phenomena (14-19, 34-39); however, chemical or b i o l o g i c a l e r o s i o n of the polymer matrix i s a l s o p o s s i b l e . In the second category, the p e s t i c i d e i s chemically bound (pendant) to the macromolecular backbone. Release i s then dependent on the r a t e o f chemical or b i o l o g i c a l break-down of the p o l y m e r - t o - p e s t i c i de (20-24, 31-39). Polymers c o n t a i n i n g pendant p e s t i c i d e s can be prepared by two s y n t h e t i c methods. The f i r s t involves bonding (via covalent o r i o n i c chemical bonds) of a p e s t i c i d e to a ρre-formed polymer. T h i s approach requires macromolecules with pendant f u n c t i o n a l groups capable of r e a c t i o n with p e s t i c i d e s or t h e i r d e r i v a t i v e s . The nature of the chemical bond may be v a r i e d to y i e l d bonds with q u i t e d i f f e r e n t rates of cleavage i n the environment. Ad­ vantages of t h i s method i n c l u d e : (a) a v a i l a b i l i t y of r e l a t i v e l y inexpensive polymers with b i o d e g r a d a b i l i t y such as c h i t i n , c e l l u l o s e , e t c . , and (b) use of commercially a v a i l a b l e p e s t i c i d e s as s t a r t i n g m a t e r i a l s i n polymer s y n t h e s i s . The second approach involves polymerization of monomeric pesticides. The major advantages of t h i s method l i e i n the a b i l i t y to c o n t r o l the molecular design of the polymer and the pesticide/polymer weight r a t i o . b

o

n

d

s

Experimental Preformed, hydroxy-containing polymers were s e l e c t e d f o r i n i t i a l study. Three polymers - p o l y v i n y l a l c o h o l , c h i t i n , and c e l l u l o s e were chose on the basis o f : (a) p o t e n t i a l biode­ g r a d a b i l i t y , (b) commercial a v a i l a b i l i t y , and (c) h y d r o p h i l i c i t y i n a d d i t i o n to having proper pendant f u n c t i o n a l i t y . The r e s u l t s o f the experiments on p o l y v i n y l alcohol are reported i n t h i s work

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Metribuzin was chosen as a model p e s t i c i d e based on: (a) a v a i l a b l e amine f u n c t i o n a l i t y , (b) high a c t i v i t y at r e l a t i v e l y low c o n c e n t r a t i o n s , (c) s e l e c t i v i t y , (d) lack o f p e r s i s t e n c e i n the environment, and (e) high m o b i l i t y . A s e r i e s of laboratory and commercial polymers o f p o l y v i n y l a l c o h o l (with varying r e s i d u a l amounts of unhydrolyzed v i n y l acetate) were c a r e f u l l y c h a r a c t e r i z e d . Isocyanate adducts of metribuzin were prepared and reacted with the pendant hydroxy! f u n c t i o n a l i t y o f the pre-formed polymers (Figure 1). It was p o s s i b l e to prepare copolymers with varying degrees o f s u b s t i ­ t u t i o n on l i n e a r and h i g h l y c r o s s - l i n k e d c h a i n s . The isocyanate to hydroxy1 r a t i o s were v a r i e d over a wide range to prepare solvent s w o l l e n , c r o s s - l i n k e d g e l s . These were converted to microporous s o l i d s by a g i t a t i o n of the product i n the presence of a non-solvent ( s e l e c t e d from s o l u b i l i t y parameter data). Rates o f Release of Metribuzin Polymers with pendant metribuzin (0.100 g) were placed i n an Erlenmeyer f l a s k . 500 ml o f d i s t i l l e d water was added. At designated i n t e r v a l s , samples were taken to determine the c o n ­ c e n t r a t i o n o f released m e t r i b u z i n . U l t r a v i o l e t Spectroscopic Method. A Gary 1756 Spectrophoto­ meter was used to determine released metribuzin l e v e l s i n water. A standard p l o t of absorbance v s . concentration was obtained using l e a s t squares a n a l y s i s . 3 ml samples were taken at d e s i g ­ nated i n t e r v a l s and placed i n standard quartz c e l l s . The ab­ sorbance at 293.5 nm was monitored i n two types o f t e s t s . The f i r s t measured t o t a l concentration of released metribuzin over a time p e r i o d . The second t e s t was conducted as f o l l o w s : (a) 0.100 g samples were placed i n 500 ml o f d i s t i l l e d water f o r a predetermined time; (b) the samples were f i l t e r e d , d r i e d and again placed i n a second Erlenmeyer f l a s k c o n t a i n i n g 500 ml o f d i s t i l l e d water; (c) concentrations were measured d i r e c t l y from the f i l t r a t e . Gas Chromatographic Method. 2yl of aqueous s o l u t i o n were removed and e x t r a c t e d with 5.0 ml o f benzene. 1 μΐ o f the benzene phase was then i n j e c t e d i n t o the gas chromatograph (Micro-Tek 220 with e l e c t r o n capture d e t e c t o r ) . S o i l M o b i l i t y Studies T h i n - l a y e r p l a t e s were prepared by spreading a s o i l s l u r r y onto 20 X 20 cm glass p l a t e s to a thickness of 1.0 mm. Plates were d i v i d e d i n t o three equal s e c t i o n s by s c r i b i n g the s o i l layer. Metribuzin was a p p l i e d to one p l a t e by s t r e a k i n g 500 λ o f a 100 g/ml s o l u t i o n onto each s e c t i o n o f the p l a t e 2 cm from the bottom. Polymers c o n t a i n i n g pendant metribuzin were embedded i n

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3

) C-

3

Ν

i-S-CH.

^Ν-ΝΗ2

Ν-ψ-Ç-N-R Η Ο Η

-S-CHΗ

- f C H ^ C H ^ C H ^ Ç H ^ -

3

(CH ) C3

Η

CH -S-i

Η Ο Η OCNR-N-C-N-N*

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Figure 1. Synthetic method for preparation of PVA copolymer containing pendant metribuzin

-R-NCO

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the s o i l l a y e r on other p l a t e s which were a l s o d i v i d e d i n t o three sections. The p l a t e s were e l u t e d to 10 cm with water, a i r d r i e d , and 1-cm zones were removed from one of the three s e c t i o n s of each p l a t e . The p l a t e s were returned to the chamber and again e l u t e d with 10 cm of water, and the second zone was removed i n 1-cm s e c t i o n s . T h i s procedure was repeated with the t h i r d s e c t i o n of s o i l . The s o i l removed i n t h i s manner was e x t r a c t e d with 5 ml of hexane: acetone (3:1) by shaking. E x t r a c t was analyzed by gas chromatography. Residual P h y t o t o x i c i t y Of Metribuzin From Polymers The polymers c o n t a i n i n g pendant metribuzin were added to the surface of a Bosket sandy loam s o i l contained i n 4" p l a s t i c pots i n a c o n t r o l 1ed-environment chamber. The a p p l i c a t i o n rates were 0, 0 . 1 , 0 . 2 , and 0.3 g l a t i o n of metribuzin was a p p l i e d to other pots at 0.5 and 1.0 ppmw, and thoroughly mixed i n t o the s o i l . The s o i l s were b i o a s sayed over a period of 112 days with a mixture of weeds which are normally s u s c e p t i b l e to the h e r b i c i d e ; a f t e r growing two weeks, the weeds were harvested and f i r s t weights recorded. Results And Discussion Five polymers c o n t a i n i n g pendant metribuzin were chosen f o r study: 22-S, 23-S, 41-S, 45-S, and 50-S. 23-S, 4 5 - S , and 50-S were e s s e n t i a l l y l i n e a r polymers prepared from 99% hydrolyzed polyvinyl alcohol. 22-S and 41-S were h i g h l y c r o s s - l i n k e d m i c r o porous s o l i d s . These system r e q u i r e both h y d r o l y s i s of the urea bond and d i f f u s i o n from a water s w o l l e n , c r o s s - l i n k e d matrix f o r metribuzin r e l e a s e . P l o t s of s o l u t i o n concentration vs. time (Figures 2, 3) i n d i c a t e d that the l i n e a r polymers (23-S, 4 5 - S , and 50-S) r e leased h e r b i c i d e much more r a p i d l y than the c r o s s - l i n k e d systems. The 23-S, 45-S, and 50-S were c h a r a c t e r i z e d by a r a p i d i n i t i a l r e l e a s e i n the f i r s t few hours followed by a more gradual r a t e l a s t i n g several days. The c r o s s - l i n k e d systems 22-S and 41-S (Figure 4) had much lower r e l e a s e rates with l i t t l e i n i t i a l r e lease. T h i s could be p r e d i c t e d by the time required f o r s w e l l i n g o f the h y d r o p h i l i c polymer so that h y d r o l y s i s and d i f f u s i o n could occur. A f t e r s w e l l i n g , s l i g h t concentration increases were noted. The u.v. s p e c t r o s c o p i c data and the gas chromatographic data were i n t e r n a l l y c o n s i s t e n t . It should be noted that the u l t r a v i o l e t technique requires no e x t r a c t i o n and, t h e r e f o r e , o f f e r s less chance f o r e r r o r at small concentrations of metribuzin. S o i l t h i n - l a y e r chromatographic techniques showed metribuzin (Figure 5) moved as a normal chromatogram peak with each s u c c e s s i v e e l u t i o n moving the peak nearer the 10-cm zone. The chromatograms from 23-S (Figure 6) and 45-S (Figure 7) showed " s t r e a k i n g " continuously along the p l a t e i n d i c a t i n g a sustained r e l e a s e mechanism.· The c r o s s - l i n k e d f o r m u l a t i o n s , 22-S and 45-S,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

w

C/3

ο

a Figure 2. Metribuzin release from polymers in water (ultraviolet spectroscopy)

V)

W

*U

W

1

ο r r w α w w r w •

ζ

H-* h-»

00

ο ο

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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Figure 3. Metribuzin re­ lease from linear (23S) and cross-linked (22S) polymers

60 (hours)

L

0.4

0.3

0.2

0.1

V

40 TIME

60 (hours)

—ι Figure 4. Metribuzin release 80 from linear (45S) and crosslinked (41S) polymers

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

120

CONTROLLED

DISTANCE

Figure 5.

0

(cm)

Soil thin layer chromatography (TLC) of metribuzin

I 0

RELEASE

! 2

£

£

*

*_

4

6

8

10

DISTANCE

Figure 6.

(cm)

Soil TLC of metribuzin released from 2SS

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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0

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with Pendant

4

6

DISTANCE

121

Herbicides

8

(cm)

Figure 7. Soil TLC of metribuzin released from 45S

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10

g

en

η

W

Figure 8. Phytotoxicity of metribuzin from polymer formulations as a function of time

W

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M

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s

r

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did not r e l e a s e enough metribuzin f o r a measurable rate i n these studies. Residual p h o t o t o x i c i t y of the four polymeric systems i s i l l u s t r a t e d i n Figure 8. Metribuzin at 1.0 ppmw had d i s s i p a t e d to a l e v e l which was e s s e n t i a l l y n o n - t o x i c a f t e r 78 days. Likew i s e , p h y t o t o x i c i t y from 41-S had diminished to a large extent by t h i s time. A r e l a t i v e l y low l e v e l of p h y t o x i c i t y was observed f o r 22-S i n i t i a l l y ; however, t h i s same l e v e l was maintained f o r over 78 days, then r a p i d l y decreased. The highest l e v e l of p h y t o t o x i c i t y was observed with 23-S and 45-S. These m a t e r i a l s were s t i l l showing p h y t o t o x i c i t y at our l a s t t e s t date of 112 days. It must be noted that p h y t o t o x i c i t y comparison t e s t s of polymeric c o n t r o l l e d - r e l e a s e formulations and commercially formulated h e r b i c i d e s must be i n t e r p r e t e d with c a r e . In the pendant polymeric systems bond cleavage has occurred. For t h i s reason the t o t a l h e r b i c i d e e v e n t u a l l y a v a i l a b l e i n the polymer cannot be compared to t h a t immediately a v a i l a b l e i n a commercial f o r m u l a t i o n . Conclusions Polymeric systems f o r c o n t r o l l e d release of metribuzin have been prepared using biodegradable s u b s t r a t e s . Properly s e l e c t e d macromolecular substrates were reacted with p e s t i c i d e adducts to y i e l d systems with l a b i l e p e s t i c i de-to-polymer bonds s u s c e p t i b l e to chemical or enzymatic h y d r o l y s i s . The metribuzin/polyviny1 alcohol system i n t h i s work i s adaptable f o r formation of a range of products with d i f f e r e n t degrees of c r o s s - l i n k i n g and, t h e r e f o r e , d i f f e r e n t rates of herbicide release. P h y t o t o x i c i t y , s o i l t h i n - l a y e r chromatography, u l t r a v i o l e t spectroscopy, and gas chromatography t e s t s showed sustained r e l e a s e c a p a b i l i t i e s of the polymeric systems. The p r e l i m i n a r y r e s u l t s of t h i s research p o i n t to the immense p o t e n t i a l of polymeric systems f o r c o n t r o l l e d - r e l e a s e of s e l e c t i v e h e r b i c i d e s which can: (1) reduce environmental p o l l u t i o n i n non-target areas by reducing p e s t i c i d e m o b i l i t y , (2) r e q u i r e fewer a p p l i c a t i o n s during the growing season, and (3) r e s u l t i n enhanced a g r i c u l t u r a l production a t , perhaps, lower c o s t to the farmer. Acknowledgements The authors would l i k e to express t h e i r thanks f o r the generous support of research conducted at the U n i v e r s i t y of Southern M i s s i s s i p p i Polymer Science Laboratories provided by Hopkins A g r i c u l t u r a l Chemical Company of Madison, Wisconsin. Research support was a l s o obtained from the USDA Weed Science Laboratories at S t o n e v i l l e , M i s s i s s i p p i , and from the M i s s i s s i p p i Alabama Sea Grant Program. The s o i l studies were conducted by

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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PESTICIDES

Κ. E. Savage, Southern Weed Science L a b . , ARS, USDA, S t o n e v i l l e , MS, 38776.

Abstract Recently, there has been a growing interest in developing pesticide controlled release technology. Much of the impetus has resulted from demands for enhanced agricultural production at lower levels of environmental risk. Most of the activity has been directed toward formulations in which the pesticide is physically dissolved or dispersed in a polymer matrix. Polymers have been prepared in our laboratories which contain labile polymer to pesticide covalent bonds. These linkages are susceptible to aqueous and/or bacterial break-down, resulting in long-term release. Theoretically, the rate of herbicide release can be controlled by changin by altering the cross-link density of the polymer. The synthe­ sized systems have been characterized by IR, NMR, U.V., GPC, etc. Release studies have been conducted in aqueous media using U.V. and gas chromatography. In addition, soil mobility and phyto­ toxicity studies are in progress. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Barrett, Β. Β., Louisiana Wildlife and Fisheries Commission Report, Cooperative Gulf of Mexico Estuarine Inventory and Study, Hydrology, p. 115, 1971. Christmas, J.Y., Ed., Cooperative Gulf of Mexico Estuarine Inventory and Study, Mississippi, Publishers: Gulf Coast Research Laboratory, p. 12, 1973. Chemical and Engineering News, July 28, 1975, pp. 18-31. Kearney, R.C. and Kaufman, D.D., Herbicides, Chemistry, Degradation, and Mode of Action, 2nd Edition, Marcel Dekker, Inc., 1975. Butler, P.A., Pesticide Monitoring Journal, Vol. 6(4) 238, 1973. Butler, P.Α., "Pesticides in the Estuary," Proc. of Marsh and Estuary Management Symposium (July 1967), Baton Rouge, LA, pp. 120-124, 1968. Butler, P.A., Proc. of National Symposium on Estuarine Pollution, (August, 1967) Stanford University, p. 107, 1968. Butler, P.Α., "Significance of DDT Residue in Estuarine Fauna," Chemical Fallout, Chapter 9, pp. 205-220, 1969. "Pesticides in the Marine Environment," Journal Appl. Ecology 3, (Supplement) pp. 253-259, 1966. "Problems of Pesticides in Estuaries," American Fish Soc., SPE Public No. 3, pp. 110-115, 1966. Firth, F.E., Ed., "Pesticides in the Sea," Encyclopedia of Marine Resources, pp. 513-516. Butler, P.Α., "Pesticides," U.S. Bureau of Commercial Fisheries Report: Contract No. 85, 1967.

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13. Andus, L.J., Ed., The Physiology and Biochemistry of Herbicides, Academic Press, New York, 1964. 14. U.S. Patent #3,074,845. 15. U.S. Patent #3,318,769. 16. U.S. Patent #3,737,521. 17. U.S. Patent #3,127,752. 18. U.S. Patent #3,400,093. 19. U.S. Patent #3,343,941. 20. Allan, G.C., et al. Nature, 234, 349 (1971). 21. Neogi, A.N., Ph.D., Thesis University of Washington, Seattle, Washington, (1970). 22. Jakube, H.D., Busch, E., F. Chem, 13 (3), p. 105 (1973). 23. Allan, G.C., et al. Int. Pest Control, 14 (2), p. 15 (1972). 24. Harris, F.W. and Post, L.K., Polymer Preprints, 16 (1), pp. 622-627, (1975). 25. Pariser, E.R. and Block, S., Chitin and Chitin Derivatives, Report No. MITSG 73-2, October 15, 1972, (A bibliography with 593 references). 26. Davidson, R.L. and Sittig, Marshall, Eds., Water-Soluble Resins, Van Nonstrand Reinhold Co., New York, 1968. 27. Bikales, N.M., Water-Soluble Polymers, Plenum Press, New York, 1973. 28. O'Brien, R.D., Insecticides, Action and Metabolism, Academic Press, New York, 1967. 29. White-Stevens, R., Pesticides in the Environment, Marcel Dekker, 1973. 30. Chemical Engineering, January 19, 1976. 31. Allan, G.C., Canadian Patent #846785. 32. Allan, G.C., Canadian Patent #863310. 33. Allan, G.C., Canadian Patent #855181. 34. Chemical and Engineering News, June 28, 1976. 35. Controlled Release Pesticide Symposium, The University of Akron, September, 1974. 36. Proceedings 1975 International Controlled Release Pesticide Symposium, Wright State University, September, 1975. 37. Proceedings 1976 Controlled Release Pesticide Symposium, The University of Akron, September, 1976. 38. Cardarelli, N., Controlled Release Pesticides Formulations, CRC Press, Cleveland, Ohio, 1976. 39. Paul, D.R. and Harris, F.W., Eds., Controlled Release Polymeric Formulations, ACS Symposium Series; 33, 1976.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12 Microencapsulated Pesticides HERBERT B. SCHER Formulations Section, Chemical Research Department, Stauffer Chemical Co., 1200 So. 47th St., Richmond, Calif. 94804

Microcapsules are 1 or l i q u i d core surrounde polymeric i n nature (Figure 1) and c o n s t i t u t e s 5-25 percent o f the microcapsule by weight. The wall i s o l a t e s and protects the core material i n storage but i s designed to r e l e a s e the core m a t e r i a l i n a c o n t r o l l e d fashion when the microcapsules are e x posed t o the environment. The core material can be released from the microcapsules by crushing the w a l l , breaking the wall by pressure from w i t h i n , d i s s o l v i n g the w a l l , hydrolyzing the wall o r by d i f f u s i n g through the w a l l . Controlled release of pesticides ( i n s e c t i c i d e s , herbicides, f u n g i c i d e s , fumigants, j u v e n i l e hormone mimics, i n s e c t sex a t t r a c t a n t s and animal health compounds) can be achieved by microencapsulation. P e s t i c i d e microcapsule systems can be designed t o : 1. Reduce mammalian t o x i c i t y and extend a c t i v i t y . 2. Reduce evaporative l o s s e s . 3. Reduce p h y t o t o x i c i t y . 4. Protect p e s t i c i d e s from environmental degradation. 5. Reduce l e a c h i n g . 6. Reduce p e s t i c i d e l e v e l s i n the environment. An aqueous d i s p e r s i o n o f p e s t i c i d e microcapsules i s a p a r t i c u l a r l y useful c o n t r o l l e d r e l e a s e p e s t i c i d e formulation because: 1. It i s composed o f d i s c r e t e microcapsules as opposed to aggregates. 2. I t can be d i l u t e d with water or l i q u i d f e r t i l i z e r s and sprayed using conventional equipment. Uniform f i e l d coverage o f p e s t i c i d e i s p o s s i b l e . 3. I t requires l e s s polymeric component per pound o f p e s t i c i d e than m o n o l i t h i c d e v i c e s . 4. I t i s capable o f e s t a b l i s h i n g a constant p e s t i c i d e r e l e a s e rate (See Figures 2 and 3 ) .

126

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127

Pesticides

Gelatin

Polyethers

Gum A r a b i c

Polyesters

Starch

Polyamides

Sugar Ethyl

Polybutadiene

Cellulose

Carboxymethyl

Cellulose

Polysiloxanes

Paraffin Polyvinyl

Polyisoprene

alcohol

Polyurethanes

Polyethylene

Epoxy r e s i n s

Polypropylene

inorganic

silicates

Polystyrene Polyacrylamide Encyclopedia of Polymer Science and Technology

Figure 1. Common microcapsule wall materials

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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C O N T R O L L E D R E L E A S E PESTICIDES

0 * Diffusion Coefficient Κ » Distribution Coefficient DK * Permeability AC

s

Concentration Difference Across Wall

I n i t i a l high release due to migration of p e s t i c i d e

approaches exhaustion

Time Chemical Technology Figure 2.

Pesticide release rate from microcapsule (2)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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(SLAB GEOMETRY)

Dissolved P e s t i c i d e dM dt

dM dt

2M„

Dispersed P e s t i c i d e 1/2

M

dM dt

π l t 2

f o r 0.4