Environmental Aspects of Controlled Release Pesticide Formulations

4 Environmental Aspects of Controlled Release Pesticide Formulations GUNTER ZWEIG

Downloaded by PURDUE UNIVERSITY on August 5, 2013 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0053.ch004

Environmental Protection Agency, Office of Pesticide Programs, Washington, D.C. 20460

During the past 10 years many persistent pesticides (e.g. chlorinated hydrocarbons) have been phased out because of environmental and toxicological problems. In their place, less persistent, but sometimes more acutely toxic pesticides have been substituted and created other problems: (a) greater chances for accidental, high exposure to operators and farm workers; and (b) a need for multiple applications because of lower persistence. Controlled-release (CR) formulations of these pesticides appear to offer an ideal solution to these problems. To cite another consideration, the insect growth regulator methoprene, for example, is so unstable in the aquatic environment that its practical application could only be effected as a controlled release formulation. Newly developed pesticides may never reach the market unless they can be stablized long enough to effect control through controlled-release formulations. Economic and environmental advantages might also be gained by the release of constant but lower concentrations of toxicants than may be possible with conventional type formulations. The technology of microencapsulation and other controlled release systems, as will be discussed during this Symposium, have been developed to the point of making controlled release pesticide formulations a r e a l i t y . Yet, there appears to be no satisfactory explanation why this f i e l d has not advanced more rapidly. One popular explanation might be that Government regulations for toxicological and environmental testing have become so cumbersome that they discourage further development of these formulations. In this paper, some personal reflections may help to alleviate these concerns, and i t may become apparent that the proposed tests are probably no more stringent than those required for conventional pesticide formulations. Asterisked terms throughout this paper indicate trademark products. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Environmental Protection Agency. 37

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

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PESTICIDES

F e a s i b l e CR P e s t i c i d e Formulations


Although the number o f commercial 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 products on the market may be few compared to the more than 3 0 , 0 0 0 other r e g i s t e r e d products, i t appears f e a s i b l e that a l l c l a s s e s of p e s t i c i d e chemicals are amenable to formulation as c o n t r o l l e d - r e l e a s e products. In a number o f cases, as i n the case o f methoprene, the CR formulation i s the method o f choice and e n hances the e f f i c a c y o f the p e s t i c i d e , a l b e i t , makes i t f e a s i b l e to be used as an e f f e c t i v e pest c o n t r o l agent. Table I i s a l i s t of these p e s t i c i d e c l a s s e s followed by a few words o f e x p l a n a t i o n . TABLE I CLASSES OF PESTICIDES FORMULATED AS CONTROLLED-RELEASE PRODUCTS Anti-Foulants Molluscicides Insecticides Herbicides Fungicides

Rodenticides Nematicides Algicides Predator Control Repellents

Devices

Anti-foulants. A n t i - f o u l i n g paints are composed o f a t o x i c a n t , f o r example, cuprous oxide which i s held w i t h i n a polymeric v e h i c l e such as p o l y a c r y l a t e , polyamide, p o l y e s t e r , c h l o r i n a t e d p o l y i s o p r e n e , polyurethane, e t c . Other t o x i c a n t s that have been s u c c e s s f u l l y incorporated i n t o a n t i - f o u l a n t paints include organot i n compounds ( e . g . , t r i butyl t i n ) and organoleads ( e . g . , t r i phenyl l e a d ) . These a n t i - f o u l i n g coatings have been shown to be b i o l o g i c a l l y e f f i c a c i o u s and long l a s t i n g (up to 9 years) (1_). The unresolved environmental problems with these products are (a) the p o s s i b l e long-term e f f e c t on aquatic organisms of low concentrations of t o x i c a n t s , and (b) the c h a r a c t e r i z a t i o n o f the released material which may have undergone chemical o r b i o l o g i c a l changes during i t s r e l e a s e . Molluscicides. M o l l u s c i c i d e s are used to c o n t r o l s n a i l s and slugs and are extremely important i n t r o p i c a l areas where a major d i s e a s e , S c h i s t o s o m i a s i s , i s transmitted by members o f the Schistosoma s n a i l family i n h a b i t i n g r i v e r s , streams and l a k e s . N.F. C a r d a r e l l i , Professor o f Chemistry, U n i v e r s i t y o f Akron, Ohio, has been a pioneer i n the development o f CR m o l l u s c i c i d e s . T r i butyl t i n oxide (TBTO) and t r i butyl t i n f l u o r i d e , niclosamide (ethanolamine s a l t o f 2 , 5 - d i c h l o r o - 4 ' - n i t r o s a l i c y l a n i l i d e ) , and copper s u l f a t e have been incorporated i n t o various elastomeric materials. The toxicants are released over a p e r i o d of many months f o l l o w i n g immersion i n t o i n f e c t e d waters. Although the t i n compounds are t o x i c to f i s h , when used as CR f o r m u l a t i o n s , however, the adverse e f f e c t on f i s h appears minimal. Most v a s c u l a r species o f plants are unaffected by t r i butyl t i n o x i d e ,


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although some adverse e f f e c t s on algae have been observed. Other nontarget aquatic organisms appear to be t o l e r a n t to TBTO at the concentration of the CR f o r m u l a t i o n s . The environmental fate of organotins i s not f u l l y understood, but t i n does not seem to bioaccumulate i n higher organisms and, as a matter of f a c t , i s an e s s e n t i a l trace element i n mammalian n u t r i t i o n . Another CR technique f o r s n a i l c o n t r o l i s the use of CR baits. In t h i s technique, the t o x i c a n t [niclosamide or t r i f e n morph ( N - t r i t y l m o r p h o l i n e ) ] and an a t t r a c t a n t are incorporated i n t o an i n s o l u b l e binding matrix ( e . g . , p o l y a c r y l a t e s c r o s s - l i n k e d with Z n or C a ) . S n a i l s are a t t r a c t e d by a g e n u s - s p e c i f i c a t t r a c t a n t and i n g e s t the polymers c o n t a i n i n g the t o x i c a n t . The use of CR m o l l u s c i c i d e s , although of minor importance i n the United S t a t e s , i l l u s t r a t e s that a t o x i c a n t can be used at lower concentrations than those required by d i r e c t a p p l i c a t i o n and provides greater environmental s a f e t y . + +


Aspects

+ +

Insecticides. In t h i s category are included (a) conventional t a r g e t i n s e c t i c i d e s and i n s e c t growth r e g u l a t o r s which are formul a t e d to produce c o n t r o l l e d r e l e a s e , and (b) pheromones and other a t t r a c t a n t s which are incorporated i n t o b a i t s c o n t a i n i n g convent i o n a l i n s e c t i c i d e s f o r the k i l l . One of the f i r s t types of a commercial CR formulation i s Penncap-M*, microencapsulated methyl parathion. The microencapsulation process i s based on forming a polycondensation polymer s h e l l ( c r o s s - l i n k e d polyamide) around the material to be encapsulated. The i n s e c t growth r e g u l a t o r methoprene i s incorporated i n t o a polyurethane foam providing some degree of p r o t e c t i o n from e n v i ronmental degradation. This product i s s o l d commercially as A l t s o s i d SR-10*. C h l o r p y r i f o s (TA) has been incorporated i n t o p o l y v i n y l c h l o r i d e , polyurethane foam, and polyamide and provides e x c e l l e n t c o n t r o l of mosquito larvae over a 2 2 to 24-week p e r i o d , as compared with 1 to 2 weeks using c h l o r p y r i f o s emulsion ( 2 ) . Even longer c o n t r o l was e f f e c t e d with polyethylene or p o l y v i n y l c h l o r i d e CR pellets ( 3 ) . Encapsulated Rabon* [(Gardona* - - 2 - c h l o r o - l - ( 2 , 4 , 5 - t r i c h l o r o p h e n y l ) v i n y l dimethyl phosphate] has been shown to provide l a r v a l feed-through c o n t r o l i n the manure of p o u l t r y and c a t t l e

(4, 5 ) . The second category of CR i n s e c t c o n t r o l agents are pheromones and a t t r a c t a n t s which have been reviewed r e c e n t l y (6). For example, d i s p a r l u r e has been formulated i n t o g e l a t i n capsules {7) or laminated p l a s t i c dispensers (8, £ ) ; grandiure has been formulated i n t o laminated p l a s t i c s (10); and encapsulated t r i m e d l u r e has been combined with methyl parathion or malathion (11). A l l of these formulations have the advantage of prolonging the l i f e of the environmentally l a b i l e and v o l a t i l e pheromones.



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

At t h i s time, pheromones have been i d e n t i f i e d f o r at l e a s t 40 economically important i n s e c t species (8), and a l a r g e r number of pheromone/toxicant or pheromone/trap systems may be expected to be developed on a commercial s c a l e i n the f u t u r e . Another type of CR i n s e c t i c i d e formulation i s represented by an a n t i - c o c k r o a c h p a i n t c o n t a i n i n g c h l o r p y r i f o s (12) and the Hereon* p l a s t i c i n s e c t i c i d e dispenser i n c o r p o r a t i n g c h l o r p y r i f o s , Baygon* ( o-isopropoxypheny1 N-methyl carbamate), or d i a z i n o n [ 0 , 0 - d i e t h y l 0 - ( 2 - i s o p r o p y l - 6 - m e t h y l - 4 - p y r i m i d i n y l ) phosphorot h i o a t e ] i n a 3 - l a y e r laminated p o l y v i n y l c o n s t r u c t i o n (13). DDVP ( d i c h l o r v o s - - 2 , 2 - d i c h l o r o v i n y l dimethylphosphate), widely used as a CR formulation under the trade name of No-Pest* s t r i p , i s i n corporated i n t o p o l y v i n y l c h l o r i d e and montan wax. The c h i t i n s y n t h e s i s i n h i b i t o r d i m i l i n [1 - ( 4 - c h l o r o p h e n y 1 ) - 3 - ( 2 , 6 - d i f 1 u o r o benzoyl)urea] has been experimentally incorporated i n t o c a s t o r wax and a s i l i c a t e to produce a CR formulation (14). Castor wax hydrolyzes to r i c i n o l e i c a c i d and g l y c e r o l with no apparent e n v i ronmental consequences. Herbicides. CR formulations o f h e r b i c i d e s may be c l a s s i f i e d as a q u a t i c / p l a s t i c , a q u a t i c / e l a s t o m e r i c , and a g r i c u l t u r a l . Aquatic h e r b i c i d e s (phenoxy e s t e r s , e n d o t h a l l , d i c h l o b e n i l ) have been incorporated i n t o polyamide, p o l y v i n y l (15, 16), and p o l y ethylene r e s i n matrices (17) to provide long-term c o n t r o l of Eurasian w a t e r m i l f o i l (18"]7 Long-term aquatic weed c o n t r o l i s c l e a r l y p o s s i b l e by h e r b i c i d e r e l e a s e from p l a s t i c matrices (19). Another experimental approach has been to incorporate hydrol y z a b l e phenoxy h e r b i c i d e moieties i n t o a polymerized v i n y l p o l y mer (20, 2 χ ) . Other CR m a t e r i a l s which have been tested i n c l u d e rubber-based compounds as s i n k i n g p e l l e t s slowly r e l e a s i n g the h e r b i c i d e (22, 23) with no detectable f i s h t o x i c i t y (18). During t h i s work the phenomenon of c h r o n i c i t y was d i s c o v e r e d , which w i l l be discussed i n greater d e t a i l l a t e r i n the paper. Although the use of aquatic h e r b i c i d e s as c o n t r o l l e d r e l e a s e formulations may r e c e i v e wider acceptance, there are r e l a t i v e l y few CR formulated commercial a g r i c u l t u r a l h e r b i c i d e s . Fungicides. F u n g i c i d a l r e s i n s f o r paints can be made by the polycondensation of g l y c o l , chlorophenol e s t e r , and benzene carboxylic acid. Seed p r o t e c t i o n can be afforded by the use o f CR formulations o f fungicides added to rubber l a t e x or as an encapsu l a t e d m a t e r i a l , e . g . , B e n l a t e * , for use on onion seeds. Rodenticides. Encapsulation of anticoagulants appears to e n hance b a i t acceptance (24), presumably masking the b i t t e r t a s t e o f , f o r example, norbormide (25). However, although encapsulation improves rodent i n g e s t i o n o f the a n t i c o a g u l a n t , i t does not im prove the e f f i c a c y (26) p o s s i b l y because of the competition between d e t o x i c a t i o n and slower r e l e a s e .


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Nematicides. Ethoprop (0-ethyl S , S - d i p r o p y l phosphorodithi o a t e ) , incorporated i n t o natural rubber and an e t h y l e n e - p r o p y l enediene terpolymer (27), has been shown to have an e f f e c t i v e r e l e a s e of three months. Dibromodichloropropane (DBCP) has been encapsulated with a w a t e r - s e n s i t i v e , biodegradable wall material (27A); t h i s formulation may p e r s i s t during dry periods u n t i l s u f f i c i e n t s o i l moisture ruptures the capsule membrane. The basic problem of processing nematicides by press cures of elastomers or hot melt e x t r u s i o n of p l a s t i c s i s the low b o i l i n g p o i n t of most fumigant-nematicides. Algicides. Most copper s a l t s have a short l i f e i n water and must be a p p l i e d p e r i o d i c a l l y to c o n t r o l the growth of a l g a e . Thus, CR formulations of C u ions would be h i g h l y d e s i r a b l e . Copper s u l f a t e has been incorporated i n t o a microporous polymer (Envirocap*). Another CR f o r m u l a t i o n , Incracide E-51* granules, has been shown e f f e c t i v e against blue-green algae f o r as long a period as 54 days a f t e r a p p l i c a t i o n . No published information on the composition of these CR matrices i s a v a i l a b l e (28). Experimental copper r e l e a s i n g thermoplastic m a t e r i a l s have been shown to r e l e a s e the metal ion f o r several months (29, 30, 31). Inc r e a s i n g e f f o r t i n t h i s f i e l d should y i e l d p r a c t i c a l a l g a l control methods by CR technology. + +

Predator Control Devices. A method that might be included i n t h i s b r i e f survey of CR p e s t i c i d e formulation i s the cyanide c o l l a r attached to a s a c r i f i c i a l lamb, which, upon attack by a coyote, i s punctured and releases the deadly poison. Many o b j e c t i o n s have been r a i s e d by c o n s e r v a t i o n i s t s and members of humane s o c i e t i e s that t h i s type of predatory c o n t r o l c o n s t i t u t e s a s i n g u l a r l y c r u e l method, and EPA has made no d e c i s i o n at t h i s time to allow the use of these d e v i c e s . Repellents. Diethyl-m-toiuamide (DEET) can be incorporated i n t o sprayable polymeric m a t e r i a l s (32) l i k e p o l y a c r y l i c s and polyurethane (unpublished data by N.F. C a r d a r e l l i ) . These formulations have been shown to r e l e a s e DEET on window screens f o r several months, while DEET alone i s r a p i d l y degraded i n sunlight. Specific

Products

Table II 1 i s t s some of the CR p e s t i c i d e formulations which have been r e g i s t e r e d by the EPA and are commercially a v a i l a b l e . In the study funded by EPA and r e c e n t l y completed (EPA Contract No. 68-01-1922), C a r d a r e l l i and Walker found references i n the open, patent, and company l i t e r a t u r e of 141 p e s t i c i d e chemicals which are p r a c t i c a l or have been t r i e d as CR f o r m u l a t i o n s . Thus, t h i s 1 i s t i n Table II seems 1 i m i t e d , and i t i s expected that a d d i t i o n a l CR products w i l l be on the market i n the f u t u r e .


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CONTROLLED RELEASE

TABLE

PESTICIDES

II

CONTROLLED RELEASE PESTICIDES


Product Altosid* Biomet* CAP-CYC* CBL-9B Herbicide 14 ACE-B1 Hereon* roach tape Incracide*

E-51

Killmaster* Nofoul* No-Pest* S t r i p Penncap-M* Staph-Chek*

Pesticide Action J u v e n i l e Hormone Mimic Molluscicide Plant Growth Regulator Molluscide Herbicide Insecticide Molluscide Algicide Herbicide Insecticide Anti-foulant Insecticide Insecticide Bacteriostat

A l t o s i d * i s the CR formulation of the i n s e c t growth methoprene.

regulator

Biomet* i s an organotin m o l l u s c i c i d e . CAP-CYC* i s 3M*s encapsulated chlormequat ( 2 - c h l o r o e t h y l t r i me thy 1 ammo ni urn c h l o r i d e ) , a p l a n t growth r e g u l a t o r . The composit i o n of the encapsulant and a d d i t i v e s are not p u b l i c information. CBL-9B i s a natural rubber matrix c o n t a i n i n g t r i butyl t i n f l u o r i d e as a c t i v e m o l l u s c i c i d e . Herbicide 14 ACE-B1 i s the 2,4-D butoxyethanol e s t e r formul a t e d with natural rubber; t h i s has been prepared as f l o a t i n g or s i n k i n g p e l l e t s and suspending s t r a n d s , depending on the nature of the v u l c a n i z e d elastomers. Hereon* roach tape u t i l i z e s the Hereon dispenser constructed from laminar s t r i p s c o n t a i n i n g an i n s e c t i c i d e i n a p l a s t i c r e s e r voir. Hereon* roach tape containing Baygon* i s e f f e c t i v e as a s t a t i o n a r y i n s e c t i c i d e dispenser e s p e c i a l l y useful against cockroaches around human h a b i t a t i o n . I n c r a c i d e * E-51 i s a terpolymer CR formulation of copper s u l f a t e intended as a m o l l u s c i c i d e , a l g i c i d e , and s e l e c t i v e herbicide. K i l l m a s t e r * i s a p a i n t a b l e or sprayable taining chlorpyrifos.

CR formulation c o n -


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Nofoul* i s an a n t i - f o u l i n g rubber, the p r i n c i p l e of which r e s t s on d i f f u s i o n - d i s s o l u t i o n . The i n g r e d i e n t s are p r o p r i e t a r y information.


No-Pest* S t r i p i s probably the best known CR formulation and i s composed of d i c h l o r v o s i n a s t a b i l i z e d p o l y v i n y l c h l o r i d e base. Penncap-M* i s a widely used CR i n s e c t i c i d e and i s polyamideencapsulated methyl p a r a t h i o n . At 25%-cross linkage of the polymer w a l l , the e f f i c a c y of Penncap-M* against the bollworm and b o l l w e e v i l was extended from one day to about 10 days when compared with conventional e m u l s i f i a b l e concentrate (EC) formulations (33). Comparative t o x i c i t y data i n d i c a t e that Penncap-M* i s approximately 50 times l e s s t o x i c to r a b b i t s by s k i n a b s o r p t i o n , 8 to 10 times l e s s t o x i c to white mice, and 4 to 7 times l e s s t o x i c to rats by i n g e s t i o n than the corresponding EC f o r m u l a t i o n . An unexpected hazard of Penncap-M* to the bee population has been discovered r e c e n t l y (34). The microcapsules, which are a p p r o x i mately the same s i z e as p o l l e n g r a i n s , adhere to the bee as i t f l i e s from sprayed flowers and returns the " p o l l e n " to the hive where i t contaminates the whole colony. Staph-Chek* i s a b a c t e r i o s t a t i c f a b r i c used i n h o s p i t a l s . Organotin or another b a c t e r i o c i d e ( s t a t ) i s incorporated i n t o PVC f i l m which i s laminated on a f a b r i c base. Other CR p e s t i c i d e products and commercial r e l e a s e systems are shown i n Table III. TABLE

III

CONTROLLED RELEASE PRODUCTS Polyethylene/chlorpyrifos Conrel* Hereon* Dispenser Microcapsule Dispenser Poroplastic* Sustrelle*

Blend 3714

Polyethylene - c h l o r p y r i f o s i s a CR mosquito l a r v i c i d e d e v e l oped by the U.S. Army Environmental Hygiene Agency; r e g i s t r a t i o n by the EPA has been a p p l i e d f o r . C o n r e l * i s a trademark f o r a wide range of f i b e r systems, e s p e c i a l l y s u i t a b l e f o r v o l a t i l e pheromones. C o n t r o l l e d vapor r e l e a s e rates can t a i l o r i n g the f i b e r s to s p e c i f i c diameters and The Hereon* Dispenser has been described

p r e c i s i o n hollow p e s t i c i d e s and be achieved by lengths.

previously.


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PESTICIDES

Microcapsule Dispenser. No information i s a v a i l a b l e about the composition o f the Microcapsule Dispenser produced by Cont r o l l e d Release Chemical C o r p o r a t i o n , Santa Fe, N. Mex. The dispenser i s useful for r e l e a s i n g pheromones and i n s e c t i c i d e s .


P o r o p l a s t i c * (sheets) and S u s t r e l l e * are trade names f o r gelled cellulose triacetate. The c o s t of these m a t e r i a l s i s r e l a t i v e l y high to make them p r a c t i c a l for use at t h i s time, but i n p r i n c i p l e , they should f u n c t i o n as a sustained and c o n t r o l l e d r e l e a s e system.

Environmental

Impact of

Polymers

Before c o n s i d e r i n g the environmental impact of f o r m u l a t i o n s , i t i s important to b r i e f l y review the m a t e r i a l s , or the s o - c a l l e d " i n e r t s , " which make up these types of f o r m u l a t i o n s . Table IV i s a l i s t of polymers that were chosen f o r c l o s e r i n v e s t i g a t i o n .

CR p e s t i c i d e polymeric the bulk of significant

TABLE IV CONTROLLED RELEASE MATERIALS Rubber Natural Synthetic Ethylene - Propylene Polymer C e l l u l o s i c Materials P o l y i s o b u t y l e n e - Butyl Rubber Styrene - Butadiene Copolymer P o l y a c r y l o n i t r i 1 es Polyacrylates Polyesters Polyamides

Polyethylene Polyvinyl Chloride Chloroprene Polymer Polyurethanes Ci s Polybutadiene Acetal Copolymer Others: S i l i c o n Rubber Polyacrylamides Hydrin Rubber Microporous P l a s t i c

Sheet

A d i r e c t quotation by C a r d a r e l l i and Walker i n t h e i r f i n a l r e p o r t to the EPA on the Development of R e g i s t r a t i o n C r i t e r i a f o r CR P e s t i c i d e Formulations, sums up t h e i r views on the e n v i r o n mental impact from the use of CR p e s t i c i d e products : " I t should be recognized that the polymeric material must degrade i n some fashion before there can be any environmental impact i n the c h e m i c a l , biochemical or b i o l o g i c a l sense. With reference to s o i l or the beds of watercourses, i t i s c o n c e i v a b l e , though b a r e l y , that the a d d i t i o n of a polymer to the ambient environment w i l l r e s u l t i n p h y s i c a l changes. It i s well known that the a p p l i c a t i o n of an i n e r t m a t e r i a l to s o i l a i d s i n a e r a t i o n . Thus, a non-



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Aspects

degraded polymer plowed i n t o s o i l w i l l enhance soil aeration. Since the authors cannot v i s u a l i z e more than a few hundred pounds per acre of a given polymer being a p p l i e d annually (a few pounds per acre being much more 1 i k e l y ) , and s i n c e the weight of an a c r e - f o o t of s o i l i s i n excess of a m i l l i o n pounds, the environmental impact a f t e r d i l u t i o n would appear to be n i l . I f polymers f o r use i n c o n t r o l l e d r e l e a s e were completely i n e r t or t h e i r degradation r a t e was measured i n geologic time - as occurs with g l a s s , the cumulative aspect would be a matter of concern. However, al 1 organic polymers degrade upon exposure to outdoor e n v i r o n ment, and with few exceptions t h e i r nature i s comp l e t e l y o b l i t e r a t e d a f t e r a number o f decades." Degradation of polymers occurs by one or a l l mechanisms: 1. 2. 3. 4. 5.

Solar radiation (especially Heat Hydrolysis Oxidation (oxygen or ozone) B i o l o g i c a l degradation

of the

following

ultraviolet)

In conventional polymer technology, i t i s u s u a l l y the i n t e n t to prevent environmental degradation by modifying the polymeric s t r u c t u r e or to add s t a b i l i z e r s . There appears ample l i t e r a t u r e on the degradation o f polymers i n order to improve the f i n a l product. A number of p l a s t i c s and polymers appear as food-contact m a t e r i a l s i n packaging or c l o s u r e s and have been exempted from a t o l e r a n c e by the EPA under s e c t i o n 40 CFR 180.1001. Yet i t i s prudent to r a i s e questions on the environmental impact, e s p e c i a l l y i n 1ight of the c u r r e n t i n t e r e s t on the s o - c a l l e d " i n e r t s " i n p e s t i c i d e products. Natural Rubber degrades r a p i d l y upon environmental exposure through m i c r o b i a l , o x i d a t i v e , and photochemical a c t i o n . Normally, a n t i - o x i d a n t s and p r e s e r v a t i v e s are added to rubber to extend i t s 1 i f e , but rubber formulations can be t a i l o r e d to increase degradat i o n , i f this is desired. C h l o r i n a t e d natural rubber, now i n use i n a n t i - f o u l i n g c o a t i n g s , i s h i g h l y r e s i s t a n t to b i o l o g i c a l attack but may be t o x i c to microorganisms (Unpublished o b s e r v a t i o n s , N.F. C a r d a r e l l i ) . Ethylene-Propy1ene Polymers show r e l a t i v e l y l i t t l e degradat i o n caused by heat, humidity or u v - r a d i a t i o n , ozone a t t a c k , and oxidation. C e l l u l o s i c M a t e r i a l s g e n e r a l l y degrade under environmental c o n d i t i o n s when exposed to the atmosphere and s u n l i g h t . Bacterial


46



decay i n l o o s e , moist s o i l i s extremely r a p i d . Cellulose t r i a c e t a t e has been c l e a r e d f o r food contact usage. Carboxymethylc e l l u l o s e s are used i n foods as gel 1 ants and thickeners and are e s s e n t i a l l y nontoxic to man. P o l y i s o b u t y l e n e and Butyl Rubber. Compounded butyl rubber m a t e r i a l s are h i g h l y r e s i s t a n t to moisture and f a i r l y r e s i s t a n t to o x i d a t i o n . A d d i t i o n o f peroxides, however, w i l l a c c e l e r a t e t h e i r breakdown. The degree of environmental impact depends on the c u r i n g agent ( e . g . , s u l f u r or lead p e r o x i d e ) . Generally speaking, butyl rubber degradation by environmental f a c t o r s appears to proceed very s l o w l y . No information has been found on environmental breakdown products. Styrene - Butadiene Copolymers are very s u s c e p t i b l e to a t tack by oxygen, ozone, and u v - r a d i a t i o n . Compared to natural rubber, these compounds e x h i b i t a g r e a t e r r e s i s t a n c e to b a c t e r i a l attack. I d e n t i f i c a t i o n o f metabolism or breakdown products has not been found i n the l i t e r a t u r e surveyed. P o l y a c r y l o n i t r i 1 es tend to be r e s i s t a n t to m i c r o b i a l degradation, but ozone degrades these m a t e r i a l s r a p i d l y . P o l y a c r y l a t e s . Carboxylated a c r y l i c systems such as Carboset* are r e a d i l y degraded by microorganisms, e s p e c i a l l y f u n g i . Carbos e t * polymers are ingested by m o l l u s c s , i n s e c t s , and probably nematodes (personal o b s e r v a t i o n , N.F. C a r d a r e l l i ) . Carboset* 514 has been exempted by EPA from the requirements o f a tolerance when used i n a g r i c u l t u r e (CFR 40 S e c t . 180.1001). No information i s a v a i l a b l e on the t o x i c i t y o f Carboset* to f i s h or plants or any other segment o f the b i o t a ; no environmental f a t e studies have been conducted by the manufacturer. P o l y e s t e r s are known f o r t h e i r r e s i s t a n c e to chemical and r a d i a t i o n - i n d u c e d degradation. Breakdown products a t elevated temperatures i n c l u d e a l l y l a l c o h o l , acetaldehyde, carbon d i o x i d e , water, formic and a c e t i c a c i d s . No information on p o s s i b l e b i o degradation was found. Polyamides degrade under the i n f l u e n c e o f heat and r a d i a t i o n to simple hydrocarbons and cyclopentanone. Under ambient e n v i r o n mental c o n d i t i o n s , however, the degradation o f Nylon microcapsules i s expected to be very slow. No environmental s t u d i e s were found i n t h i s survey. Exemption has been granted by the EPA under CFR 40 S e c t . 180.1001. Polyethylene (PE). P o l y e t h y l e n e , c h l o r i n a t e d - and c h l o r o sulfonated PE*s have been used f o r CR matrices ( e . g . , c h l o r p y r i fos/PE, Table III) and are g e n e r a l l y r e s i s t a n t to environmental degradation and m i c r o b i a l a t t a c k .


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47

P o l y v i n y l C h l o r i d e i s degraded a t d i f f e r e n t rates depending on the p l a s t i c i z e r used: phthalate and phosphate p l a s t i c i z e r s s t a b l e ; a d i p a t e , a z e l a t e , and sebacate p l a s t i c i z e r s - - suscept i b l e to degradation. The p o s s i b i l i t y o f v i n y l c h l o r i d e monomer present i n the p l a s t i c or as a degradation product must be investigated.


Chloroprene polymers are h i g h l y r e s i s t a n t to m i c r o b i a l attack (35, 36). Polyurethanes are e s p e c i a l l y prone to fungal and b a c t e r i a l attack (35) but are r e s i s t a n t to chemical degradation. C i s Polybutadiene i s thermally s t a b l e , and although e n v i ronmental studies were not found i n t h i s survey, i t i s suspected t h a t these polymers behave s i m i l a r l y to natural rubber. Acetal Copolymers, used i n the C o n r e l * d e l i v e r y system (Table I I I ) , may degrade to formaldehyde and ethylene oxide i n s o i l and water, although no hard data could be found to v e r i f y t h i s hypothesis. Other M a t e r i a l s . Although s i l i c o n e rubber i s not p r e s e n t l y used i n CR p e s t i c i d e f o r m u l a t i o n s , i t has found usage i n CR drug d e l i v e r y , systems and thus may f i n d future a p p l i c a t i o n s i n p e s t i cide products. S i l i c o n e s are recognized as nontoxic and extremely i n e r t to b i o l o g i c a l a t t a c k . Polyacrylamides are not p r e s e n t l y used f o r p e s t i c i d e formulat i o n s ; these m a t e r i a l s degrade slowly under the i n f l u e n c e o f heat, and i t i s a n t i c i p a t e d that they w i l l g r a d u a l l y depolymerize to ammonia or ammonium ions depending on pH. Hydrin rubber r e p r e sents another CR matrix f o r p e s t i c i d e s ; i t i s the homopolymer o f epichlorohydrin. Hydrin rubber i s s t a b l e to heat and ozone but might be s u s c e p t i b l e to m i c r o b i a l a t t a c k . The Microporous P l a s t i c Sheet* i s made o f s i l i c a modified PVC or v i n y l c h l o r i d e v i n y l acetate copolymers. It i s a l i k e l y candidate f o r CR formul a t i o n s , but l i t t l e i s known about i t s environmental behavior. Polymer - A d d i t i v e s Space does not permit extensive d i s c u s s i o n o f the nature and environmental impact o f polymer a d d i t i v e s . These a d d i t i v e s are a variety of p l a s t i c i z e r s , antioxidants, release regulators, e t c . Many o f these compounds are exempt from tolerance (CFR 40, Sect. 180.1001), although some, l i k e the p h t h a l a t e s , have been shown to e x h i b i t t o x i c o l o g i c a l and environmental problems. However, one would have to assess t h e i r escape from the CR system to evaluate p o s s i b l e environmental and human exposure. For a more complete d e s c r i p t i o n o f these a d d i t i v e s and t o x i c o l o g i c a l e v a l u a t i o n , the reader i s r e f e r r e d to the EPA Report on CR P e s t i c i d e Formulations (EPA Contract No. 68-01-1922). American Chemical Society Library 1155 16th St., N.W. Washington. D £Release 2003S Pesticides; Scher, H.; In Controlled

ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

48

PESTICIDES


T o x i c o l o g i c a l and Environmental Testing Generally speaking, CR formulations of p e s t i c i d e s and the conventional e m u l s i f i a b l e concentrate or wettable powder formulat i o n s are not considered d i f f e r e n t e n t i t i e s under present p e s t i c i d e laws and r e g u l a t i o n s . The p e s t i c i d e law (FIFRA as amended i n 1972 and 1975) addresses i t s e l f to " p e s t i c i d e s " and i t s i n t e n t i s to r e g u l a t e each of the approximately 30,000 p e s t i c i d e products. The Gui d e l i n e s f o r R e g i s t e r i n g P e s t i c i d e s i n the United S t a t e s , which are p r e s e n t l y undergoing f i n a l r e v i s i o n s before p u b l i c a t i o n , c l e a r l y d i s t i n g u i s h between the " t e c h n i c a l c h e m i c a l , " which p e s t i c i d e s c i e n t i s t s have always considered to be synonomous with " p e s t i c i d e , " and " p e s t i c i d e f o r m u l a t i o n s , " which the l e g i s l a t o r s have termed " p e s t i c i d e s " . It i s doubtful that any regul a t i o n s now or i n the future w i l l r e q u i r e d e t a i l e d t o x i c o l o g i c a l and environmental t e s t i n g for each p e s t i c i d e f o r m u l a t i o n . D e t a i l e d t o x i c o l o g i c a l and environmental t e s t s w i l l have to be performed on the t e c h n i c a l material (or s o - c a l l e d " a c t i v e i n g r e d i e n t " ) , although some a t t e n t i o n w i l l be d i r e c t e d towards the s o - c a l l e d " i n e r t " i n g r e d i e n t s , which have been discussed i n d e t a i l above f o r 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 . It appears t h a t most matrices so f a r u t i l i z e d for CR p e s t i c i d e formulations may be covered by CFR 40 Section 180.1001 (exempt c a t e g o r y ) , although t h i s d e c i s i o n must be made on each i n d i v i d u a l b a s i s . The crux of the unresolved question might be phrased l i k e this: Does the a c t i v e i n g r e d i e n t placed i n t o a p l a s t i c capsule behave d i f f e r e n t l y t o x i c o l o g i c a l l y than i f i t were formulated more c o n v e n t i o n a l l y as an e m u l s i f i a b l e concentrate or a dust? Toxicological Testing. D e t a i l e d d i s c u s s i o n s on t h i s t o p i c w i l l be covered i n the chapter by J . D o u l l . The best example o f lower t o x i c i t y , which one would g e n e r a l l y expect from a c o n t r o l l e d - or s l o w - r e l e a s e f o r m u l a t i o n , i s the case of Penncap-M* compared to methyl parathion e m u l s i f i a b l e c o n c e n t r a t e . As d i s cussed above, the dermal and oral t o x i c i t y of the CR formulation was c o n s i d e r a b l y lower than that of the e m u l s i f i a b l e concentrate (33). Table V i s a l i s t i n g o f the major t o x i c o l o g i c a l t e s t s now r e q u i r e d by the EPA f o r r e g i s t r a t i o n purposes. TABLE V MAJOR TOXICOLOGICAL TESTS FOR REGISTRATION OF PESTICIDES Acute Oral Subacute Oral Chronic ( i n c l . cancer) Eye I r r i t a t i o n Dermal I r r i t a t i o n

Acute Dermal Subacute Dermal Acute Inhalation Teratogenicity Mutagenicity


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Aspects


If the complete t e s t s have been performed on the p e s t i c i d e chemical i t s e l f , i t appears reasonable that only the acute t e s t s may be required f o r the CR product. Environmental T e s t i n g . As has been discussed before, the lack of knowledge about the environmental f a t e of CR matrices makes i t d i f f i c u l t to reach a d e c i s i o n on which environmental t e s t s should be r e q u i r e d . Furthermore, the mechanism of c o n t r o l l e d r e l e a s e of smal1 concentrations o f a t o x i c a n t over an extended period of time may present environmental problems t h a t cannot be p r e d i c t e d . Two problems, those of " c h r o n i c i t y " and " r e s i s t a n c e " have been i d e n t i f i e d and w i l l be discussed below. Therefore, i t i s only p o s s i b l e to summarize environmental t e s t requirements and f o r each t e s t to pose the q u e s t i o n : "Is i t reasonable to assume that the CR formulation behaves d i f f e r e n t l y than, f o r example, an EC formulation?" Table VI i s a summary of the required environmental t e s t s proposed i n the EPA Gui d e l i n e s f o r R e g i s t e r i n g P e s t i c i d e s soon to be p u b l i s h e d . TABLE VI ENVIRONMENTAL TESTS Hydrolysis Photolysis

Field dissipation Terrestrial Aquatic Forest

Metabolism Aerobic s o i l Anaerobic s o i l Aerobic aquatic Anaerobic aquatic Microbial on p e s t i c i d e s on microbes a c t i v a t e d sludge Mobility Leaching Volatility Adsorption/desorption Water d i s p e r s a l

Accumulation Rotational crops F i s h accumulation Aquatic noncrop uses Reentry Dislodgeable residues Volatility Photodegradation Procedures storage

for d i s p o s a l

and

" C h r o n i c i t y " Phenomenon. Chronic i n t o x i c a t i o n requires much l e s s of the c o n t r o l agent than that necessary to produce acute e f fects. As the c o n c e n t r a t i o n of the agent i s decreased, the time to e f f e c t l e t h a l i t y does not increase l i n e a r l y . This phenomenon has been termed " c h r o n i c i t y " by C a r d a r e l l i (37) and has been demonstrated with a number of CR formulations of phenoxy h e r b i c i d e s , d i q u a t , and d i c h l o b e n i l to c o n t r o l aquatic weeds l i k e water l e t t u c e , Eurasian w a t e r m i l f o i l , El odea, Southern n a i a d , and water


50



hyacynth. " C h r o n i c i t y " has a l s o been demonstrated with a n t i f o u l ing agents, incorporated i n t o c e r t a i n rubbery m a t e r i a l s , and molluscicides. The butoxyethanol e s t e r o f 2 , 4 - D , compounded i n t o natural rubber, has been shown to y i e l d e f f e c t i v e c o n t r o l concent r a t i o n s f o r over 18 months. From the p o i n t of view o f e f f i c a c y , the " c h r o n i c i t y " phenomenon may be advantageous. On the other hand, whether the phenomenon poses an environmental hazard, f o r example to f i s h , remains to be r e s o l v e d . An example of " c h r o n i c i t y " i s i l l u s t r a t e d i n Table V I I , which shows the extended c o n t r o l o f w a t e r m i l f o i l by diquat over a 32-day period a t d i f f e r ent concentrations o f diquat tested (38). TABLE VII THE CONTROL OF EURASIAN WATERMILFOIL BY DIFFERENT CONCENTRATIONS OF DIQUAT CONCN. OF DIQUAT

a

LT 99

9

L l

(PPM)

(Days)

1.0 0.1 0.01 0.001

11 19 16 32

Time which 99% c o n t r o l i s

effected

The Resistance Problem. The use o f c o n t r o l 1ed-release p e s t i c i d e s ( l a r v i c i d e s ) may well enhance the r e s i s t a n c e problem. Subl e t h a l dosages o f i n s e c t i c i d e s tend to lead to the development of more r e s i s t a n t p o p u l a t i o n s . Since c o n t r o l l e d r e l e a s e l a r v i c i d e s w i l l be c o n c e p t u a l l y used i n very low c o n c e n t r a t i o n s , and l o n g term r e l e a s e w i l l be achieved f o r c o s t e f f e c t i v e n e s s , c o n s i d e r a b l e s u b l e t h a l dosing can be expected. This e f f e c t r e s u l t s i n many generations o f the same species i n the same l o c a l e exposed to the a c t i o n of the l a r v i c i d e . The problem o f enhanced t o l e r a n c e (or r e s i s t a n c e ) through the use o f c o n t r o l l e d methods has y e t to be investigated. Summary A survey o f the types o f c o n t r o l l e d - r e l e a s e formulations of d i f f e r e n t c l a s s e s of p e s t i c i d e s has been presented. Some CR p e s t i c i d e formulations have become commercial products, while others are s t i l l experimental and f e a s i b l e but have not been t e s t e d . A d i s c u s s i o n o f the various CR matrices has shown that the environmental f a t e o f many i n e r t s i s unknown and should be s t u d i e d before they are introduced i n t o the environment. At the


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present s t a t e o f knowledge there do not seem to be serious e n v i ronmental problems except f o r p o s s i b l e r e s i s t a n c e and t o x i c i t y to nontarget populations o f b e n e f i c i a l i n s e c t s . Acknowledgements


This paper i s l a r g e l y based on a study funded by EPA, Contract No. 68-01-1922, Development of R e g i s t r a t i o n C r i t e r i a f o r C o n t r o l l e d Release P e s t i c i d e s , and s p e c i a l thanks are due to the authors o f t h i s r e p o r t , N.F. C a r d a r e l l i , K . E . Walker, and M. Beroza. General

References

C a r d a r e l l i , N.F. C o n t r o l l e d Release P e s t i c i d e Formulations. CRC Press, C l e v e l a n d , Ohio, 210 pp. (1976). Proc. C o n t r o l l e d Release P e s t i c i d e Symposium, Univ. o f Akron, Ohio. (1974, 1976). Proc. C o n t r o l l e d Release P e s t i c i d e Symposium, Wright State U n i v . , Dayton, 0. (1975).

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Wuerzer, D.R., Senderling, R . L . , and Cardarelli, N.F. Rubber World, (Nov. 1967) 157 (2), 77. Nelson, L.L., Barnes, W.W., Harris, F.W. and Lawson, M.A., J . Econ. Entomol. (1970) 63, 1870. M i l l e r , T . A . , Nelson, L.L., Young, W.W., Roberts, L.W., Roberts, D.R. and Wilkinson, R . N . , Mosq. News, (1973) 33 148. Nelson, L.L., M i l l e r , T . A . , Whitlaw, J.T., Young, W.W., and Lawson, M.A., Mosq. News, (1973) 33, 403. Wasti, S.S., Shaw, F.R. and Smith, C . T . , J. Econ. Entomol. (1970) 63, 1355. M i l l e r , R.W., Drazek, P . Α . , Martin, M.S. and Gordon, C.H., Rep. No. 169, Ann. Mtng. Amer. Dairy S c i . Assoc., Gainesville, Fla. DCRB 70-8, (June 1970). Inscoe, M.N. and Beroza, M. in Pest Management with Insect Sex Attractants, (pp. 145-181), M. Beroza, e d . , ACS Symposium Series 23, Amer., Chem. Soc., Wash., D.C. (1976). Cameron, E . A . , Schwalbe, C.P., Stevens, L.J. and Beroza, M . , J . Econ. Entomol., (1975) 68, 158. B i e r l , B.A. and DeVilbiss, D . , Proc. Controlled Release Pesticide Symp., 230, Wright State University, Dayton, OH, (September 8-10, 1975). Beroza, M . , Paszek, E . C . , DeVilbiss, D . , B i e r l , B.A. and Tardif, J . G . R . , Environ. Entomol., (1975) 4, 712. Hardee, D.C., McKibben, G.H. and Huddleston, P . M . , J. Econ. Entomol., (1975) 68, 477.


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27.

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Cardarelli, N.F. and Feldmesser, J., Proc. Controlled Release Pesticide Symp., 386, Wright State University, Dayton, OH (September 8-10, 1975). 27A. Feldmesser, J . Progress Report on Controlled Release of a Nematicide. Rep. No. 32, Proc. Controlled Release Pest. Symp. Akron, OH (Sept. 16-18, 1974). 28. Cardarelli, N . F . , Evaluation of Incracide E-51 Against Select Aquatic Weeds and Algae, Rep. Creative Biology Lab., Proj. 104 to International Copper Research Assoc., New York, N.Y. (April 5, 1975). 29. Cardarelli, N.F. and B i l l e , S.M., Evaluation of Environ mental Chemicals, Inc. Controlled Release Copper Sulfate, Rep. 1, Proj. 121, Creative Biology Lab., Barberton, OH, (March 1, 1976). 30. Hesketh, Β . , McKechnie Chemicals L t d . , Widnes, U . K . , corre spondence to Cardarelli, Ν . , University of Akron, Akron, OH (13 February 1976). 31. Anon., Envirocap C . , Chem. Eng. News (1972) 50 (23), 68. 32. Cardarelli, N . F . , Dermal Protective Films, U.S. Patent 3,749,772 (1973). 33. Ivy, E.E., J. Econ. Entomol., (1972) 65, 473. 34. Selkirk, J., Envir. Action Bulletin, 3 (Oct. 2, 1976). 35. Hep, W.M. and Morrell, S . H . , J. Appl. Chem., (1968) 18 (7), 189. 36. MacLachlin, J., Heap, W.M. and P a c i t t i , J., Monograph, Soc. Chemistry Industry, (1966) 23, 185. 37. Cardarelli, N . F . , Weeds, Trees & Turf, (1972) 11 (5), 16 38. Janes, G . A . , B i l l e , S.M. and Cardarelli, N . F . , Development and Evaluation of Controlled Release Herbicides, Quart. Rep. U.S. Army Corps Engineers Contract No. DACW 39-76-C-0029 (Oct. 1 - Dec. 31, 1975).


Environmental Aspects of Controlled Release Pesticide Formulations

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