Chapter 18
Long-Term Controlled Release of Herbicides Root Growth Inhibition 1
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P. Van Voris , D. A. Cataldo , C. E. Cowan , N. R. Gordon , J. F. Cline , F. G. Burton , and W. E. Skeins Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 22, 2016 | http://pubs.acs.org Publication Date: June 24, 1988 | doi: 10.1021/bk-1988-0371.ch018
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1BattellePacific Northwest Laboratories, Battelle Boulevard, Richland, WA 99352 Battelle Columbus Division, Columbus, OH 43201 Optical Data, Inc, 9400 Gemini Drive, Beaverton, OR 97005 2
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Research on controlled-release o f pesticides has resulted i n products designed t o extend bioactivity f o r p e r i o d s o f s e v e r a l d a y s , months, o r a t most, s e v e r a l y e a r s . However, r e c e n t research directed t o w a r d solving problems a s s o c i a t e d w i t h plant-root p e n e t r a t i o n t h r o u g h caps and liners t h a t a r e designed t o minimize l e a c h i n g or movement o f b u r i e d nuclear and c h e m i c a l wastes has resulted in development o f a l o n g - t e r m controlled-release h e r b i c i d e delivery system designed t o stop r o o t growth f o r p e r i o d s o f up t o 100 y e a r s . Through the unique c o m b i n a t i o n o f polymers w i t h a herbicidally active dinitroaniline, a cylinderical pellet (9 mm long and 9 mm in diameter) was d e v e l o p e d t h a t c o n t i n u o u s l y r e l e a s e s a h e r b i c i d e f o r a period o f up t o 100 y e a r s . E q u i l i b r i u m c o n c e n t r a t i o n o f the herbicide in soil adjacent t o t h e pellet and t h e bioactive lifetime of t h e d e v i c e can be adjusted by changing t h e size o f the pellet; the type o f polymer; the type, quality, and quantity of carrier; a n d / o r t h e c o n c e n t r a t i o n and t y p e o f dinitroaniline used. Commercial p r o d u c t s t h a t have been d e v e l o p e d under a F e d e r a l Technology T r a n s f e r Program t h a t u t i l i z e t h i s t e c h n o l o g y i n c l u d e : 1) ROOT-SHIELD, a r o o t r e p e l l i n g sewer gasket f o r concrete, c l a y , and PVC sewer l i n e s , 2) BZOBARRIBR, a spun-bonded p o l y p r o p y l e n e g e o t e x t i l e f a b r i c developed t o prevent r o o t growth from i n v a d i n g s e p t i c t a n k s ; p e n e t r a t i n g under roadways, and a l o n g t h e edge o f s i d e w a l k s , a i r p o r t runways, and t e n n i s c o u r t s , and f o r landscaped a r e a s ; and 3) ROOT-GUARD, a p l a s t i c d r i p i r r i g a t i o n e m i t t e r designed t o p r o t e c t b u r i e d d r i p i r r i g a t i o n systems from b e i n g plugged by roots. 0097-6156/88/0371-0222$06.00/0 ° 1988 American Chemical Society
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
18. VAN v o w s ET AL.
Root Growth Inhibition
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The problem o f r e t a i n i n g n u c l e a r and c h e m i c a l wastes w i t h i n b u r i a l s i t e s has been the s u b j e c t o f r e s e a r c h f o r w e l l over two decades. For example, t h e r e are more than 90 m i l l i o n m e t r i c tons o f uranium m i l l t a i l i n g s which r e l e a s e r a d i o a c t i v e radon gas ( R n ) at -25 i n a c t i v e s i t e s throughout the U n i t e d States. The Uranium M i l l T a i l i n g s C o n t r o l A c t o f 1978 ( P u b l i c Law 95-604) d i r e c t e d the U . S . Department o f Energy (DOE) t o t a k e s t e p s t o p r o v i d e f o r "the s t a b i l i z a t i o n , d i s p o s a l , and c o n t r o l i n a safe and e n v i r o n m e n t a l l y sound manner o f such t a i l i n g s i n order t o prevent or minimize radon d i f f u s i o n i n t o the environment and t o prevent or minimize other environmental h a z a r d s from such t a i l i n g s . " I n i t i a l research efforts developed p h y s i c a l s e a l i n g techniques or " B a r r i e r s " for t a i l i n g s t o t r a p the radon gas. P h y s i c a l b a r r i e r s c o n s i s t e d o f m u l t i l a y e r c l a y / a g g r e g a t e m a t e r i a l (X), asphalt emulsions, (Z) and, more r e c e n t l y , t h i c k p o l y m e r i c covers ( e . g . , -10 m i l - t h i c k black polyethylene). In a l l cases the b a r r i e r s are covered w i t h compacted s o i l and p l a n t e d w i t h a grass or a n a t i v e p l a n t s p e c i e s . The compacted s o i l minimizes water i n f i l t r a t i o n i n t o t h e waste and p r o t e c t s t h e b a r r i e r from d e g r a d a t i o n by o x i d a t i o n and u l t r a v i o l e t r a d i a t i o n . The p l a n t s s e r v e as h y d r o l o g i c pumps, reducing water i n f i l t r a t i o n , and s t a b i l i z i n g t h e s o i l from wind-induced e r o s i o n . However, many o f these p h y s i c a l b a r r i e r s were breached by the r o o t s o f the p l a n t s growing i n the s o i l cover, c r e a t i n g a route f o r r e l e a s e o f the R n and f o r water i n f i l t r a t i o n and subsequent m o b i l i z a t i o n o f t h e waste. S i m i l a r problems e x i s t at l o w - l e v e l r a d i o a c t i v e waste b u r i a l s i t e s , w i t h t r a n s l o c a t i o n o f r a d i o a c t i v i t y by deep-rooted p l a n t s . Breaching of these p h y s i c a l b a r r i e r s i l l u s t r a t e d t h e need t o d e v e l o p an a l t e r n a t e method o f c o n t r o l l i n g root growth over p e r i o d s of 100 t o 300 y e a r s .
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P l a n t r o o t s a l s o p e n e t r a t e sewer l i n e s and s e p t i c d r a i n f i e l d s and damage s i d e w a l k s , s t r e e t s , t e n n i s c o u r t s , e t c . In 1984 the c i t y o f C h a r l o t t e , NC, which maintains over 1,800 m i l e s o f sewer l i n e s , spent i n excess o f $500,000 f o r r o o t c o n t r o l and system r e p a i r s caused by r o o t i n v a s i o n Q ) . In 1986 the c i t y o f Sunnyvale, CA, spent over $1,000,000 t o r e p a i r damage t o s t r e e t s and s i d e w a l k s caused by t r e e r o o t s (4.) . These problems are not i s o l a t e d t o c i t y - o w n e d sewers and s t r e e t s ; home owners a l s o experience i n t r u s i o n o f r o o t s i n t o sewer l i n e s or under driveways and s i d e w a l k s . Even w i t h the recent development of extremely t i g h t - f i t t i n g gasketed PVC p i p e t h e o n l y t r u l y e f f e c t i v e s o l u t i o n f o r sewer l i n e s t h a t have been p e n e t r a t e d by r o o t s i s t o p h y s i c a l l y remove them. However, p h y s i c a l r o o t - r e m o v a l i s o n l y a temporary s o l u t i o n . With PVC sewer p i p e , repeated r o o t removal w i l l e v e n t u a l l y damage the p i p e , making major r e p a i r s n e c e s s a r y . Existing methods f o r s t o p p i n g or c o n t r o l l i n g p l a n t r o o t s from c r a c k i n g , p u s h i n g up o r damaging s i d e w a l k s , s t r e e t s , d r i v e w a y s , and a i r p o r t runways are l i m i t e d . A f t e r the damage has begun t h e r e are o n l y two s o l u t i o n s a v a i l a b l e : p h y s i c a l l y removing the t r e e or p l a n t , o r t r e n c h i n g a l o n g the edge o f the invaded area t o cut the r o o t s . The l a t t e r o p t i o n t y p i c a l l y induces a d d i t i o n a l l a t e r a l r o o t growth, thus e x a c e r b a t i n g the p r o b l e m . When p l a n t i n g new t r e e s one can use p h y s i c a l s h i e l d s , t o attempt t o force the roots t o grow down.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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PESTICIDE FORMULATIONS: INNOVATIONS AND DEVELOPMENTS
The concept o f u s i n g h e r b i c i d e s t o r i d sewer systems o f i n v a d i n g r o o t s i s not new. P h y t o t o x i c c h e m i c a l s , such as copper s u l p h a t e , have been f l u s h e d through the sewer system or f o r c e d under pressure (U.S. patent 2,976,191) through the sewer pipe j o i n t i n t o the s o i l to k i l l r o o t s . The s o i l around the g a s k e t s o r the gasket i t s e l f has been t r e a t e d w i t h h e r b i c i d e s l i k e 2,4-D t o stop the p e n e t r a t i o n of roots (U.S. patent 3 , 2 3 1 , 3 9 8 ) . N e i t h e r approach has proven t o be v e r y e f f e c t i v e as evidenced by current l a c k of commercial use. A l s o , f l u s h i n g c h e m i c a l s through the system does not e l i m i n a t e the p h y s i c a l mass o f the r o o t s t h a t b l o c k the l i n e . Furthermore, chemicals can damage the aboveground v e g e t a t i o n as w e l l as the sewaged i g e s t i n g microorganisms. The second s o l u t i o n , namely the use of h e r b i c i d e s , w h i l e c o r r e c t i n concept, has been a problem i n t h e p a s t s i n c e t h e h e r b i c i d e s t h a t have been selected s i g n i f i c a n t l y damage o r k i l l the v e g e t a t i o n growing above the t r e a t e d sewer l i n e w h i l e not r e m a i n i n g a c t i v e f o r v e r y l o n g p e r i o d s o f t i m e . A t b e s t , a l l t h e s e methods t o t h i s a g e - o l d problem have been temporary, r e q u i r i n g r e p e a t e d t r e a t m e n t s r a t h e r than p r o v i d i n g a long-term s o l u t i o n . Methods f o r c o n t r o l l i n g p l a n t r o o t i n t r u s i o n i n t o waste b u r i a l s i t e s , sewer l i n e s , and under s i d e w a l k s , s t r e e t s and s i m i l a r areas have been the s u b j e c t o f r e s e a r c h a t B a t t e l l e ' s P a c i f i c Northwest L a b o r a t o r i e s s i n c e 1978. O r i g i n a l e f f o r t s f o r the U . S. Department o f Energy (DOE) were d i r e c t e d toward d e v e l o p i n g p l a n t " B i o b a r r i e r s " t h a t would prevent r o o t s from p e n e t r a t i n g waste r e p o s i t o r i e s (5-8) w i t h o u t k i l l i n g t h e aboveground p l a n t . Two b a s i c r e q u i r e m e n t s were imposed on development o f t h e b i o b a r r i e r system. F i r s t , the chemical r o o t - g r o w t h i n h i b i t o r ( i n t h i s case, t r i f l u r a l i n ) had t o be e n v i r o n m e n t a l l y safe and a c c e p t a b l e . Thus, i t had t o have a r e a s o n a b l y s h o r t environmental h a l f - l i f e , e x h i b i t l i t t l e s o i l m o b i l i t y (which would p r e v e n t any c o n t a m i n a t i o n o f s u r f a c e a n d / o r g r o u n d w a t e r s ) , and l i m i t p l a n t r o o t growth w i t h o u t a d v e r s e l y a f f e c t i n g t h e growth o f aboveground b i o m a s s . I n h e r e n t i n t h e s e c r i t e r i a was the requirement f o r a method t h a t would a l l o w f o r l o n g - t e r m c o n t r o l l e d d e l i v e r y o f a h e r b i c i d e from a r e s e r v o i r t h a t would p r o v i d e f o r i n h i b i t i n g root growth. Second, because a b u r i e d system was r e q u i r e d ( e . g . , 1 or more feet below the s u r f a c e ) , the cost o f placement d i c t a t e d t h a t t h e r o o t - g r o w t h - i n h i b i t i n g h e r b i c i d e remain b i o a c t i v e w i t h i n the r e s e r v o i r f o r an extended p e r i o d o f time (up t o 100 y e a r s ) . Since completing the r e s e a r c h f o r the DOE, a t t e n t i o n has been focused on t r a n s f e r r i n g t h i s technology t o i n d u s t r y and developing commercial products (9-14). B i o b a r r i e r t e c h n o l o g y b a s e d p r o d u c t s t h a t have been l a b o r a t o r y and f i e l d t e s t e d i n c l u d e a r o o t r e p e l l i n g sewer gasket (ROOT-SHIELD) f o r concrete, c l a y , and PVC sewer l i n e s , a spun-bonded p o l y p r o p y l e n e g e o t e x t i l e f a b r i c (BIOBARRIER) w i t h nodules or p e l l e t s e q u a l l y space over the g e o t e x t i l e developed t o p r e v e n t r o o t growth from i n v a d i n g s e p t i c t a n k s ; and f o r p e n e t r a t i n g under roadways, and a l o n g the edge o f s i d e w a l k s , a i r p o r t runways, and t e n n i s c o u r t s ; and i n t o landscaped a r e a s ; and an impregnated p l a s t i c d r i p i r r i g a t i o n e m i t t e r (ROOT-GUARD) d e s i g n e d t o p r o t e c t b u r i e d d r i p i r r i g a t i o n systems from b e i n g plugged by r o o t s . The l a c k o f environmental concerns r e l a t e d t o t h e s e a p p l i c a t i o n s has l e d t o t h e r a p i d a p p r o v a l o f an extended-use l a b e l f o r t e c h n i c a l - g r a d e t r i f l u r a l i n by the U . S . Environmental P r o t e c t i o n Agency.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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18.
Root Growth Inhibition
VAN VORIS ET AL.
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The B i o b a r r i e r Technology i s based on t h e p r i n c i p l e o f l o n g - t e r m c o n t r o l l e d - r e l e a s e by means o f a p o l y m e r i c d e l i v e r y system. The system a c t s as a r e s e r v o i r f o r t h e h e r b i c i d e , p r o t e c t i n g i t from p h o t o c h e m i c a l , c h e m i c a l , and b i o l o g i c a l degradation, w h i l e p r o v i d i n g a method f o r c o n t r o l l e d r e l e a s e . Thus the bioactive chemical is released slowly, i n a c o n t r o l l e d manner, t o the soil adjacent t o the device. T h i s p o l y m e r i c d e l i v e r y system maintains an e f f e c t i v e dose f o r a substantial length of time, i n contrast to s i n g l e a p p l i c a t i o n methods, which r e s u l t i n h i g h e r than necessary c o n c e n t r a t i o n s immediately a f t e r treatment f o l l o w e d by r a p i d degradation t o a l e v e l below the minimum e f f e c t i v e dose r e q u i r e d f o r c o n t r o l ( F i g u r e 1) . T h i s f i g u r e r e p r e s e n t s a t h e o r e t i c a l model o f 0-order c o n t r o l l e d - r e l e a s e from a polymeric r e s e r v o i r f o r which t h e r e i s 6 years of f i e l d t e s t data f o r v a l i d a t i o n purposes. MATERIALS
AND
METHODS
Trifluralin Pure t r i f l u r a l i n , which i s produced as a 95% t e c h n i c a l grade compound, i s a y e l l o w - o r a n g e c r y s t a l t h a t m e l t s a t 49°-50°C and t h e r m a l l y decomposes a t 275°C. It is readily s o l u b l e i n o r g a n i c s o l v e n t s , has low s o l u b i l i t y (0.3 ppm) i n w a t e r , and photodegrades r a p i d l y i f exposed t o u l t r a v i o l e t l i g h t (photochemical h a l f - l i f e i s approximately 2 hours) . The f a m i l y o f chemicals known as d i n i t r o a n i l i n e s , o f which t r i f l u r a l i n (trade name, TREFLAN) i s t h e most w i d e l y used, i n h i b i t s the d i v i s i o n o f c e l l s by i n h i b i t i n g s p i n d l e formation a t t h e end o f t h e r o o t t i p i n such a way t h a t t h e r o o t i s unable t o grow. I t i s e f f e c t i v e , through d i r e c t c o n t a c t and i n vapor phase w i t h i n s o i l s , on the r o o t s of b o t h g r a s s e s and broadleaf plants. I t i s not known t o bioaccumulate i n p l a n t s ( i . e . , i t i s not s y s t e m i c ) ; thus i t w i l l not be t r a n s p o r t e d through the food c h a i n t o w i l d l i f e , domestic animals, or humans. I n the a p p l i c a t i o n o f t r i f l u r a l i n f o r b i o b a r r i e r - b a s e d p r o d u c t s , t h e growth o f the aboveground p o r t i o n o f t r e e s , s h r u b s , o r g r a s s e s w i l l not be a d v e r s e l y a f f e c t e d except through the l i m i t i n g root mass. A l l d i n i t r o a n i l i n e s a f f e c t r o o t growth i n a s i m i l a r f a s h i o n , some more o r l e s s t h a n o t h e r s . However, t h e h e r b i c i d a l a c t i v i t y , p h y s i c a l and c h e m i c a l p r o p e r t i e s , and e n v i r o n m e n t a l c h a r a c t e r i s t i c s make t r i f l u r a l i n i d e a l f o r i n c o r p o r a t i o n i n t o p o l y m e r s f o r c o n t r o l l e d - r e l e a s e as a biobarrier. I n Table 1 the p h y s i c a l p r o p e r t i e s o f s e v e r a l d i n i t r o a n i l i n e - t y p e compounds m a r k e t e d as preemergence h e r b i c i d e s are compared. B i o b a r r i e r Device
Preparation
S p e c i a l p r e b l e n d s were p r e p a r e d (5-6) by t h e f o l l o w i n g t e c h n i q u e : p o l y e t h y l e n e powder (35 t o 50 mesh) was mixed thoroughly w i t h carbon b l a c k (18%) and the mixture warmed i n an oven t o 60-70°C. T r i f l u r a l i n was m e l t e d i n a beaker and heat« under a g i t a t i o n t o 100-110°C. T h i s m o l t e n t r i f l u r a l i n was the s l o w l y blended i n t o the warm p o l y e t h y l e n e - c a r b o n b l a c k mixture with constant mixing u n t i l cooled, producing a f r i a b l e black powder f o r use i n i n j e c t i o n molding.
Cross and Scher; Pesticide Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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F i g u r e 1.
Comparison o f S i n g l e A p p l i c a t i o n and C o n t r o l l e d Release Method.
Table 1. Physical Properties of D i n i t r o a n i l i n e Herbicides
Common Name
Trade Name
Melting Point l*C\
Vapor Pressure (mm H
