22 Biological Unavailability of Bound Paraquat Residues in Soil D. RILEY and W. WILKINSON
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ICI Plant Protection Division, Jealott's Hill Research Station, Bracknell Berkshire, U. K. Β. V. TUCKER Chevron Chemical Co., Ortho Division, Richmond, Calif. 94804
1.
INTRODUCTION
The herbicidal properties of paraquat [1, 1'-dimethyl-4,4'bipyridylium ion] were discovered at ICI's Jealott's H i l l Research Station, England, in 1955. Paraquat is now used commercially worldwide. It is normally manufactured as the dichloride salt.
Paraquat is a broad spectrum, rapidly acting contact herbi cide which is highly effective against grasses and most broad leaved species. A unique property of paraquat is its rapid and complete adsorption onto soil. Paraquat that reaches the soil is rendered unavailable to plant roots. It is used to k i l l emerged weeds anytime before planting a crop or before the crop emerges. Consequently, paraquat is widely used in agriculture for preplant and preemergence weed control and it has an im portant use in minimum tillage farming systems. It is also used for weed control between trees and as a directed spray in row crops. Due to its desiccating properties, it finds wide application as a harvest aid. The properties of paraquat have been reviewed by Calderbank (1) and Akhavein and Linscott (2). This paper summarizes studies on the biological unavailability of 'bound' paraquat r e s i dues in soil.
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Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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2.
N A T U R E AND
A M O U N T S OF P A R A Q U A T SOIL RESIDUES
P a r a q u a t is n o r m a l l y a p p l i e d as a s p r a y at r a t e s of O.1 to 2 k g / h a . * S o m e of the p a r a q u a t r e a c h e s the soil d i r e c t l y and is a d s o r b e d by c l a y m i n e r a l s o r o r g a n i c m a t t e r . The r e m a i n d e r is i n t e r c e p t e d by the t a r g e t w e e d s . P a r a q u a t a d s o r b e d on p l a n t s u r f a c e s is s u b j e c t to p h o t o c h e m i c a l d e c o m p o s i t i o n by s u n l i g h t . The m a i n p h o t o c h e m i c a l d e g r a d a t i o n p r o d u c t s a r e 4 - c a r b o x y - l m e t h y l p y r i d i n i u m c h l o r i d e and m e t h y l a m i n e h y d r o c h l o r i d e (3). The f o r m e r has a l o w t o x i c i t y and is r a p i d l y d e g r a d e d in soil and c u l t u r e s o l u t i o n s (1, 4, 5). M e t h y l a m i n e o c c u r s n a t u r a l l y and is r e a d i l y d e g r a d e d (5). P a r a q u a t a d s o r b e d on g l a s s s l i d e s o r t h i n - l a y e r s of soil is photoc h e m i c a l l y d e g r a d e d in s u n l i g h t o r u n d e r U V l a m p s (1). H o w e v e r , p h o t o c h e m i c a l d e g r a d a t i o n of s i g n i f i c a n t a m o u n t s on soil s u r f a c e s in the f i e l d has not b e e n c l e a r l y d e m o n s t r a t e d . The a m o u n t of p a r a q u a t e v e n t u a l l y r e a c h i n g the soil o b v i o u s l y depends on f a c t o r s s u c h as d e n s i t y of w e e d c o v e r and s u n l i g h t i n t e n s i t y to c a u s e p a r a q u a t p h o t o d e g r a d a t i o n on plant s u r f a c e s . A n a l y s i s of s o i l s f r o m o v e r 50 s i t e s has s h o w n that the a m o u n t of p a r a q u a t w h i c h r e a c h e s the soil c a n r a n g e f r o m 10 to a l m o s t 100% of that a p p l i e d . If 5 0 % of a 1 k g / h a a p p l i c a t i o n r e a c h e d the soil, t h i s w o u l d r e s u l t in O. 5 jug p a r a q u a t / g soil if the r e s i d u e s w e r e u n i f o r m l y i n c o r p o r a t e d into the top 15 c m . In f i e l d e x p e r i m e n t s , l a b e l l e d p a r a q u a t was s p r a y e d onto a g r a s s s w a r d , onto b a r e soil, o r i n c o r p o r a t e d into the soil. A f t e r 1 y e a r t h e r e was no s i g n i f i c a n t d e g r a d a t i o n of p a r a q u a t in the soil; at l e a s t 9 0 % of the labelled residues w e r e paraquat ( B . C . B a l d w i n - u n p u b l i s h e d data). B e c a u s e p a r a q u a t is f i r m l y bound to soil (see below) it is i m m o b i l e u n l e s s the a d s o r b e n t itself moves. P a r a q u a t i n i t i a l l y a d s o r b e d onto p l a n t d e b r i s i n c o r p o r a t e d into soil o r onto soil o r g a n i c m a t t e r t r a n s f e r s to c l a y m i n e r a l s w h i c h a d s o r b p a r a q u a t m u c h m o r e s t r o n g l y (1). In d i l u t e s u s p e n s i o n s the t r a n s f e r f r o m soil o r g a n i c m a t t e r to c l a y is r a p i d (6). A l s o w h e n m o n t m o r i l l o n i t e c l a y was m i x e d w i t h a m o i s t peat soil c o n t a i n i n g a v a i l a b l e p a r a q u a t r e s i d u e s the p a r a q u a t was r a p i d l y d e a c t i v a t e d (7). T h i s shows that in m o i s t s o i l s , as w e l l as s l u r r i e s , p a r a q u a t r a p i d l y t r a n s f e r s f r o m w e a k a d s o r p t i o n s i t e s on the c l a y m i n e r a l s . T h i s is not s u r p r i s i n g s i n c e m u c h of the soil o r g a n i c m a t t e r is c l o s e l y a s s o c i a t e d w i t h the c l a y s u r * Note:
T h r o u g h o u t t h i s p a p e r r a t e s and c o n c e n t r a t i o n s r e f e r to p a r a q u a t c a t i o n .
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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f a c e s . O n peat s o i l s c o n t a i n i n g o n l y s m a l l a m o u n t s of c l a y s e v e r a l w e e k s m a y be r e q u i r e d f o r the t r a n s f e r of p a r a q u a t f r o m o r g a n i c m a t t e r to the c l a y (8). The a d s o r p t i o n of p a r a q u a t o n s o i l s , c l a y s and o r g a n i c m a t t e r has b e e n e x t e n s i v e l y i n v e s t i g a t e d (j6, ], 9. to 27). C a l d e r b a n k (1) r e v i e w e d the n a t u r e of p a r a q u a t a d s o r p t i o n in soil. H a y e s et a l (26) and K h a n (27) r e v i e w e d the m e c h a n i s m of p a r a q u a t a d s o r p t i o n on c l a y s and o r g a n i c m a t t e r , r e s p e c t i v e l y . The q u a n t i t y of p a r a q u a t a d s o r b e d b y s o i l s is a l w a y s l e s s t h a n the b a s e exchange c a p a c i t y f o r i n o r g a n i c c a t i o n s , s u c h as a m m o n i u m i o n s . F u r t h e r m o r e , a l t h o u g h s o m e p a r a q u a t c a n be d i s p l a c e d by h i g h c o n c e n t r a t i o n s of a m m o n i u m ions w h e n the a d s o r p t i o n s i t e s of the soil a r e s a t u r a t e d w i t h p a r a q u a t , d i s p l a c e m e n t is n e v e r c o m p l e t e and a p o r t i o n of the p a r a q u a t is f i r m l y f i x e d to the soil. A s the quantity of a d s o r b e d p a r a q u a t d e c r e a s e s , d i s p l a c e m e n t b e c o m e s p r o g r e s s i v e l y m o r e d i f f i c u l t and m o r e c o n c e n t r a t e d s a l t s o l u t i o n s a r e r e q u i r e d . M a l q u o r i and R a d a e l l i (17) c o m p a r e d the r e l a t i v e e f f e c t i v e n e s s of N H , K + , C a , Mg^+ and Na+ f o r r e l e a s i n g p a r a q u a t p r e v i o u s l y a d s o r b e d on f i v e d i f f e r e n t c l a y m i n e r a l s at varying concentrations. K and N H w e r e , in g e n e r a l , m o r e e f f e c t i v e t h a n the o t h e r c a t i o n s s t u d i e d , but no p a r a q u a t was r e l e a s e d w h e n i t s c o n c e n t r a t i o n on the c l a y was b e l o w a c e r t a i n l i m i t , w h i c h v a r i e d c o n s i d e r a b l y w i t h the type of m i n e r a l . The o n l y e f f e c t i v e m e a n s of d i s p l a c i n g p a r a q u a t f r o m soil w h e n it is p r e s e n t in r e l a t i v e l y l o w c o n c e n t r a t i o n s , e v e n f r o m v e r y sandy s o i l s , is to r e f l u x the s a m p l e w i t h s t r o n g a c i d s , e.g. 18 N, s u l f u r i c a c i d . B o i l i n g w i t h s t r o n g s u l f u r i c a c i d r e p r e s e n t s m o r e t h a n e l u t i o n . T h e s t r u c t u r e of the c l a y is p a r t i a l l y d e s t r o y e d and the b i n d i n g s i t e s a r e thus e l i m i n a t e d . E v e n v e r y s m a l l a m o u n t s , b e l o w 1.0 /ug/g p a r a q u a t , c a n be q u a n t i t a t i v e l y r e c o v e r e d f r o m s o i l s w h e n t r e a t e d in t h i s way. O n a m o l e c u l a r s c a l e , the p h e n o m e n o n of f i r m a d s o r p t i o n is a s s o c i a t e d w i t h the shape and c h a r g e d i s t r i b u t i o n of the p a r a q u a t i o n . The two p y r i d i n e r i n g s of p a r a q u a t c a n r o t a t e about the int e r r i n g bond and r e a d i l y a s s u m e a c o p l a n a r s t r u c t u r e - a p r e r e q u i s i t e of h e r b i c i d a l a c t i v i t y . T h i s f l a t c o n f i g u r a t i o n undoubte d l y f a c i l i t a t e s t h e i r i n t e r a c t i o n w i t h the c l a y m i n e r a l s u r f a c e s . P a r a q u a t is h i g h l y p o l a r i z a b l e and i t s n o r m a l c h a r g e d i s t r i b u t i o n is d i s t o r t e d in the v i c i n i t y of the n e g a t i v e l y c h a r g e d c l a y s u r f a c e s thus c h a r g e t r a n s f e r c o m p l e x e s a r e f o r m e d (12), r e i n f o r c i n g the n o r m a l c o u l o m b i c a t t r a c t i o n f o r c e s . P a r a q u a t is r e a d i l y d i s p l a c e d q u a n t i t a t i v e l y f r o m c a t i o n exchange r e s i n s (28) as d i s t i n c t f r o m c l a y m i n e r a l s w h i c h f u r t h e r s u g g e s t s that o t h e r a d s o r p t i o n f o r c e s , in a d d i t i o n to c o u l o m b i c f o r c e s , a r e i n v o l v e d in the p a r a +
2 +
4
+
+
4
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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quat-clay system. P u b l i s h e d data and a l a r g e n u m b e r of u n p u b l i s h e d e x p e r i m e n t s c o n d u c t e d by I C I P l a n t P r o t e c t i o n D i v i s i o n in the U n i t e d K i n g d o m and the C h e v r o n C h e m i c a l C o m p a n y in the U.S.A. have s h o w n that the p a r a q u a t soil r e s i d u e s r e s u l t i n g f r o m n o r m a l a p p l i c a t i o n s of p a r a q u a t a r e f i r m l y bound. C l a y s c a n f i r m l y b i n d up to about 5 0 , 0 0 0 ^ i g p a r a q u a t / g c l a y (50 meq/100 g). The a m o u n t and s t r e n g t h of p a r a q u a t a d s o r p t i o n by soil depends on the a m o u n t and type of c l a y m i n e r a l s p r e s e n t . H o w e v e r , a l m o s t all a g r i c u l t u r a l s o i l s c o n t a i n s u f f i c i e n t c l a y to f i r m l y b i n d 50 to 5000 jug p a r a q u a t / g soil. The o n l y e x c e p t i o n s a r e v e r y sandy and peat s o i l s c o n t a i n i n g l e s s t h a n 5 % c l a y ; h o w e v e r , e v e n m a n y of t h e s e s o i l s w i l l f i r m l y b i n d at l e a s t 50/ug/g. P e a t s a d s o r b l a r g e a m o u n t s of p a r a q u a t but the a d s o r p t i o n is not as s t r o n g as w i t h c l a y s and m o s t of the p a r a q u a t is d e s o r b e d w i t h 5 M N H 4 C I (24). 3.
U N A V A I L A B I L I T Y OF B O U N D P A R A Q U A T S O I L R E S I D U E S TO P L A N T S
P a r a q u a t is an e x t r e m e l y a c t i v e h e r b i c i d e w h e n a p p l i e d to p l a n t r o o t s ( g r o w n in n u t r i e n t s o l u t i o n ) as w e l l as t h e i r l e a v e s . T h i s is i l l u s t r a t e d in F i g u r e 1. P u r e s o l u t i o n s of p a r a q u a t d i c h l o r i d e , w i t h and without H o a g l a n d and S n y d e r n u t r i e n t s o l u t i o n s (29), w e r e b i o a s s a y e d w i t h p r e g e r m i n a t e d w h e a t s e e d l i n g s ( T r i t i c u m a e s t i v i u m c u l t i v a r K o l i b r i ) . The r e s u l t s g i v e n in F i g u r e 1 a r e the m e a n of r e s u l t s f r o m t h r e e b i o a s s a y e x p e r i m e n t s c o n d u c t e d at d i f f e r e n t t i m e s ; at e a c h t i m e e a c h t r e a t m e n t was r e p l i c a t e d t h r e e t i m e s . The s e e d l i n g s f a i l e d to g r o w in s o l u t i o n s c o n t a i n i n g m o r e t h a n 1 jag p a r a q u a t / m l . In s o l u t i o n s b e l o w 1 jug/ml i n c r e a s i n g the p a r a q u a t c o n c e n t r a t i o n gave c o r r e s ponding r e d u c t i o n in the e l o n g a t i o n of both r o o t s and shoots. The e f f e c t was e s p e c i a l l y m a r k e d on the r o o t s , the a c t i v i t y - c o n c e n t r a t i o n c u r v e h a v i n g a m u c h s h a r p e r c u t - o f f at a s l i g h t l y l o w e r c o n c e n t r a t i o n t h a n w i t h the shoots. The s m a l l e r e f f e c t on shoot e l o n g a t i o n was p r o b a b l y due to p o o r t r a n s l o c a t i o n of p a r a q u a t ( B . C . B a l d w i n , u n p u b l i s h e d data). T h e r e was no c h l o r o s i s o r n e c r o s i s of the l e a v e s of t r e a t e d p l a n t s e x c e p t that w h e n p l a n t s w e r e e x t r e m e l y stunted (above O.1jug/ml) they t h e n b e c a m e c h l o r o t i c and d i e d . The e f f e c t as m e a s u r e d by r o o t and shoot e l o n g a t i o n was g r e a t e r t h a n the e f f e c t as m e a s u r e d by the d r y w e i g h t of the s e e d l i n g s . S u c c e s s i v e b i o a s s a y s on the s a m e p a r a q u a t s o l u t i o n s showed that the p a r a q u a t c o n c e n t r a t i o n in the s o l u t i o n s dec r e a s e d 2-3 f o l d d u r i n g e a c h b i o a s s a y . The l o w e s t c o n c e n t r a t i o n of p a r a q u a t w h i c h had a s t a t i s t i c a l l y s i g n i f i c a n t e f f e c t (p = O. 05)
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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on r o o t length r a n g e d f r o m O. 005 t oO.02 jug/ml a n d f o r shoots it r a n g e d f r o m O. 01 toO.1u g / m l . T h e c o n c e n t r a t i o n o f p a r a q u a t w h i c h r e s u l t e d in a 5 0 % r e d u c t i o n in the lengths o f r o o t s r a n g e d f r o m O. 005 t oO.04 μg/ml and f o r shoots r a n g e d f r o m O. 03 t o O.10 μg/ml. T h e v a l u e s depended o n g r o w t h c o n d i t i o n s a n d w h e t h e r o r not n u t r i e n t s w e r e added d u r i n g the b i o a s s a y . P l a n t r o o t s a r e in i n t i m a t e c o n t a c t w i t h soil p a r t i c l e s a s w e l l as w i t h the soil s o l u t i o n . T h e r e is e v i d e n c e f o r a b r i d g e o f " m u c i g e l " b e t w e e n the r o o t s a n d soil p a r t i c l e s (30), w h i c h m i g h t p r o v i d e a r o u t e b y w h i c h c h e m i c a l s a d s o r b e d o n soil s u r f a c e s c a n m o v e t o r o o t s w i t h o u t e n t e r i n g the soil s o l u t i o n . It has b e e n s u g g e s t e d that n u t r i e n t s s u c h a s p o t a s s i u m c a n be a d s o r b e d b y r o o t s d i r e c t l y f r o m a d s o r p t i o n s i t e s o n soil p a r t i c l e s (30, 31) a n d itisc o n c e i v a b l e that a d s o r b e d p e s t i c i d e s c a n a l s o be t a k e n u p b y d i r e c t c o n t a c t . H o w e v e r , it h a s b e e n s h o w n that s o m e h e r b i c i d e s , s u c h as a t r a z i n e , a r e s u p p l i e d to r o o t s m a i n l y v i a the soil s o l u t i o n (32). D u r i n g the p a s t 15 y e a r s p a r a q u a t has b e e n a p p l i e d to m i l l i o n s of h e c t a r e s throughout the w o r l d . T h e r e have b e e n a n i n s i g n i f i cant n u m b e r of r e p o r t s of p a r a q u a t h a v i n g a n y r e s i d u a l h e r b i c i d a l a c t i v i t y in the soil. T h e r e f o r e ,itm u s t be c o n c l u d e d that the p a r a q u a t soil r e s i d u e s a r e u n a v a i l a b l e t o p l a n t s . It h a s a l s o b e e n s h o w n in g l a s s h o u s e e x p e r i m e n t s that 'bound' p a r a q u a tisu n a v a i l a b l e t o p l a n t s (25). In m o s t s o i l s , p a r a q u a t has t o be a p p l i e d at s e v e r a l h u n d r e d t o s e v e r a l t h o u s a n d t i m e s the n o r m a l r a t e of a p p l i c a t i o n b e f o r e the r e s i d u e s have any e f f e c t on p l a n t s . A f t e r s u c h e x t r e m e l y h i g h r a t e s of a p p l i c a t i o n p a r a q u a t c a n be d e t e c t e d in the e q u i l i b r i u m soil s o l u t i o n (16). A l s o s o m e of the a d s o r b e d p a r a q u a t r e s i d u e s c a n be d e s o r b e d w i t h h i g h c o n c e n t r a t i o n s of i n o r g a n i c s a l t s o l u t i o n s , s u c h as 5 M a m m o n i u m c h l o r i d e (24). We have u s e d two d i f f e r e n t a p p r o a c h e s to c h a r a c t e r i z e the a v a i l a b i l i t y of p a r a q u a t r e s i d u e s t o p l a n t s :
A.
A
D e t e r m i n a t i o n of the c a p a c i t y of s o i l s to r e d u c e the c o n c e n t r a t i o n of p a r a q u a t in the e q u i l i b r i u m s o l u t i o n b e l o w phytotoxic levels.
Β
D e t e r m i n a t i o n of the c a p a c i t y of s o i l s t o b i n d p a r a q u a t s o t i g h t l y thatitisnot d e s o r b e d w i t h s a t u r a t e d (5M) a m m o nium chloride.
C a p a c i t y of S o i l s t o R e d u c e P a r a q u a t in the E q u i l i b r i u m Solution Below Phytotoxic Levels T h e s e e x p e r i m e n t s showed that any r e s i d u a l a c t i v i t y o f
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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BOUND AND CONJUGATED PESTICIDE RESIDUES
p a r a q u a t , r e s u l t i n g f r o m e x t r e m e l y h i g h r a t e s of a p p l i c a t i o n to soil, a r e due to uptake of p a r a q u a t f r o m the soil s o l u t i o n ; p a r a q u a t a d s o r b e d on soil p a r t i c l e s is not t a k e n u p by p l a n t s .
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D e t a i l s of 4 E n g l i s h s o i l s s t u d i e d a r e g i v e n in T a b l e I. P a r a q u a t a d s o r p t i o n i s o t h e r m s w e r e d e t e r m i n e d by s h a k i n g 10 g of soil w i t h 200 m l p a r a q u a t d i c h l o r i d e s o l u t i o n s in O. 01M C a C l 2 . T h e O.01M C a C l 2 s o l u t i o n was u s e d to s i m u l a t e the s a l t c o n c e n t r a t i o n o f t e n found in the soil s o l u t i o n (33). A f t e r s h a k i n g f o r 16 h o u r s , the s u s p e n s i o n s w e r e c e n t r i f u g e d and the s u p e r n a tant s o l u t i o n s a n a l y z e d c o l o r i m e t r i c a l l y a f t e r r e d u c t i o n w i t h a l k a l i n e d i t h i o n i t e s o l u t i o n (1). C o n c e n t r a t i o n s in the r a n g e O.01 to O.1 /ug/ml w e r e d e t e r m i n e d a f t e r the p a r a q u a t had b e e n c o n c e n t r a t e d 10 f o l d u s i n g Z e r o l i t 225 c a t i o n e x c h a n g e r e s i n . E q u i l i b r i u m soil s o l u t i o n s w e r e a l s o b i o a s s a y e d w i t h wheat s e e d l i n g s as d e s c r i b e d above, w i t h o u t any a d d i t i o n of n u t r i e n t s , o t h e r t h a n those e x t r a c t e d f r o m the soil.
Glasshouse Studies Soil b i o a s s a y s w e r e a l s o p e r f o r m e d on the 4 s o i l s g i v e n in T a b l e I. P a r a q u a t d i c h l o r i d e s o l u t i o n s (200 m l ) w e r e t h o r o u g h l y m i x e d w i t h 2 k g s a m p l e s of e a c h of the 4 s o i l s . E a c h t r e a t m e n t was r e p l i c a t e d 3 t i m e s . The s o i l s w e r e p l a c e d in p l a s t i c pots and a r r a n g e d in a r a n d o m i z e d b l o c k d e s i g n in the g l a s s h o u s e . A f t e r l e a c h i n g out e x c e s s c h l o r i d e s a l t s (there was n e g l i g i b l e l e a c h i n g of p a r a q u a t ) and the a d d i t i o n of n i t r o g e n , p h o s p h o r o u s and p o t a s s i u m n u t r i e n t s , the pots w e r e b i o a s s a y e d w i t h a s e r i e s of c r o p s . B e t w e e n e a c h c r o p the soil was a i r d r i e d and m i x e d . E a c h c r o p was g r o w n f o r about 6 w e e k s b e f o r e h a r v e s t . D r y w e i g h t s of shoots and in s o m e c a s e s l e n g t h and d r y w e i g h t of r o o t s (after w a s h i n g ) w e r e m e a s u r e d . The c r o p s g r o w n w e r e w h e a t ( T r i t i c u m a e s t i v u m , c u l t i v a r K o l i b r i ) , r a d i s h (Raphanus s a t i v a 8 . c u l t i v a r S u t t o n s c a r l e t G l o b e ) , peas ( P i s u m s a t i v u m c u l t i v a r M e t e o r ) and l e t t u c e ( L a c t u c a s a t i v a , c u l t i v a r Suttons Unrivalled). A f t e r t h e s e b i o a s s a y s had b e e n c o m p l e t e d s a m p l e s of e a c h t r e a t e d soil w e r e b i o a s s a y e d w i t h the a q u a t i c w e e d L e m n a p o l y r h i z a w h i c h has b e e n r e p o r t e d to be v e r y s e n s i t i v e to p a r a quat (34J, Soil s a m p l e s (10 g) w e r e m i x e d w i t h 100 m l d i s t i l l e d w a t e r p l u s 1 m l H o a g l a n d and S n y d e r n u t r i e n t s o l u t i o n (29). S a m p l e s of L e m n a w e r e f l o a t e d on the s u r f a c e of the m i x t u r e . The i n c r e a s e in the d r y o r f r e s h w e i g h t of the L e m n a was d e t e r m i n e d a f t e r 7 d a y s g r o w t h . S a m p l e s o f the t r e a t e d S a n d y H i l l s
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
-
65.0
-
-
42.3
7.3
Fen peat (Muck)
Methwold
27.8
31 48
21
4.8
7.8
Calcareous
Tarlton
10.0 65
4.5 18
m
Sand
17
loam
Sandy Loam
Broadricks
1.9
6.7
Sandy Loam 5.8
m
79
Silt
S2à-
Clay
Cation Exchange Capacity (meq/100g a t D H 7.0)
10
m
Organic M a t t e r
11
pH 1.7
Type
Sandy H i l l s
Name
AND DEACTIVATION STUDIES
PROPERTIES OF SOILS USED IN PARAQUAT ADSORPTION
TABLE I
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soil w e r e a l s o b i o a s s a y e d w i t h L e m n a in the p r e s e n c e of O. 05 and O.1 M C a C l 2 ; the L e m n a d i d not g r o w in the 0. LM C a C ^ . Pure s o l u t i o n s of p a r a q u a t d i c h l o r i d e p l u s n u t r i e n t s o l u t i o n w e r e s i m i l a r l y bioassayed. S a m p l e s (400 g) of the t r e a t e d Sandy H i l l s and M e t h w o l d s o i l s w e r e b i o a s s a y e d w i t h S23 P e r e n n i a l R y e g r a s s ( L o l i u m perenne) in the p r e s e n c e of 0, O.5 and O.25 M C a C l 2 . The C a C l 2 c o n c e n t r a t i o n in the soil s o l u t i o n was m o n i t o r e d and kept constant by p e r i o d i c a d d i t i o n s of C a C l 2 s o l u t i o n , to r e p l a c e C a C l 2 l e a c h e d f r o m the pots d u r i n g w a t e r i n g . F i g u r e 2 shows the a m o u n t of p a r a q u a t a d s o r b e d by the 4 s o i l s w h e n the c o n c e n t r a t i o n of p a r a q u a t in the e q u i l i b r i u m soil s o l u t i o n is in the r a n g e 1-20 u g / m l . F i g u r e 3 shows the a m o u n t of p a r a q u a t a d s o r b e d w i t h O. 005 to O. 2 jug/ml in the e q u i l i b r i u m s o l u t i o n . C l e a r l y the s o i l s have v e r y d i f f e r e n t a d s o r p t i o n i s o t h e r m s . F o r e x a m p l e , the peat (Methwold) a d s o r b s l a r g e r a m o u n t s of p a r a q u a t t h a n the B r o a d r i c k s and T a r l t o n s o i l s w h e n the c o n c e n t r a t i o n of p a r a q u a t in the e q u i l i b r i u m s o l u t i o n is 5/ug/ m l , but the peat (Methwold) a d s o r b s l o w e r a m o u n t s of p a r a q u a t t h a n the B r o a d r i c k s and T a r l t o n s o i l s w h e n the e q u i l i b r i u m s o l u t i o n c o n t a i n s l e s s t h a n O.1 u g / m l . R e s u l t s of the b i o a s s a y of the e q u i l i b r i u m s o l u t i o n s a r e g i v e n in F i g u r e 4. O n l y r e s u l t s f o r the r o o t g r o w t h a r e g i v e n b e c a u s e they w e r e a f f e c t e d m o r e t h a n shoots; as they w e r e in p u r e p a r a quat d i c h l o r i d e s o l u t i o n s . T y p i c a l r e s u l t s f o r the soil b i o a s s a y s a r e g i v e n in F i g u r e 5 ( f i r s t wheat c r o p on all s o i l s ) and F i g u r e 6 (wheat, pea, and l e t t u c e c r o p s on B r o a d r i c k s soil); all the soil b i o a s s a y r e s u l t s a r e s u m m a r i z e d in T a b l e II. The r e s i d u a l a c t i v i t y of the p a r a q u a t d e c r e a s e d s l i g h t l y d u r i n g the first few b i o a s s a y s . T h i s was p r o b a b l y due to a s l o w e q u i l i b r a t i o n of the p a r a q u a t w i t h the a d s o r p t i o n s i t e s . A n a l y s i s of the s o i l s showed it was not due to d e g r a d a t i o n of the p a r a q u a t . The r e s i d u a l a c t i v i t y of p a r a q u a t was v e r y s i m i l a r on all the plant s p e c i e s tested. The d i f f e r e n c e between the s e n s i t i v i t i e s of r o o t s and shoots to p a r a q u a t was not as g r e a t in the soil b i o a s s a y as in the s o l u t i o n b i o a s s a y . T h i s was p r o b a b l y b e c a u s e the e m e r g i n g shoots as w e l l as r o o t s w e r e in contact w i t h the r e s i d u a l p a r a q u a t in the soil b i o a s s a y , but not in the s o l u t i o n b i o a s s a y . A l s o , in s o l u t i o n c u l t u r e s s e v e r e l y stunted r o o t s c a n m a i n t a i n n o r m a l shoot g r o w t h , w h i l e in the m o r e a u s t e r e soil e n v i r o n m e n t the stunted r o o t s m a y not be able to s u p p l y the shoots w i t h s u f f i c i e n t w a t e r and n u t r i e n t s .
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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0
0O5 0-1 015 PARAQUAT IN SOLUTION ( j i ^ m l )
Figure 3.
Ο
200
400
0*2
Paraquatsoiladsorption isotherms
BOO
Θ
SANDY HILLS
+
BROADRICKS
800
1000
120O
PARAQUAT CONCENTRATIONS IN EXTRACTED SON. */Q>
Figure 4. Wheat bioassay of equilibrium solutions from soils treated with paraquat
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
RILEY
ET
Bound Paraquat Residues
AL.
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Θ SANDY HILLS
Ο
400
800
BROADRICKS
À
TARLTON
120O
PARAQUAT IN SOIL
Figure 5.
+
1600
2000
iy^g)
Wheat bioassay of soih treated with paraquat (first crop)
Δ WHEAT 3rd crop
Ο PEA •
Ο
Figure 6.
200
400 600
8 0 0 100O 1400 PARAQUAT IN SOtLQi^g)
LETTUCE
1800
Bioassay of Broadrickssoiltreated with paraquat
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
312
BOUND
A N D C O N J U G A T E D PESTICDDE
RESIDUES
T A B L E II
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CAPACITIES OF SOILS TO DEACTIVATE PARAQUAT
Date of Bioassay
Soil
Bioassay
Sandy
Soil treated Wheat 1st crop
March 1971 A p r i l 1971
Wheat 2nd crop
June 1971
Wheat 3rd crop
July 1971
Wheat 4th crop Wheat 5th crop
Sept.1971 Jan. 1972
Radish 1st crop Radish 2nd crop
Mar.1972 May 1972
Lemna Lemna (+O.05MCaClo) Ryegrass
July 1972 July 1972 June 1973
Ryegrass (-K).05MCaCl ) June 1973 2
Ryegrass (+O.25MCaCl2)June 1973
Methwold
Soil treated Wheat 1st crop Wheat 2nd crop Radish
Dec. 1971 Feb. 1972 A p r i l 1972 June 1972
Lemna Pea
Aug.1972 Oct. 1972
Wheat 3rd crop
Feb. 1973
Lettuce
June 1973
Soil treated Wheat 1st crop
May 1972 June 1972
Observed effect of paraquat
Lowest concentration of paraquat which s i g n i ficantly (P=O.05) affected crop ()ug paraquat/g soili
Increased Decreased Increased Decreased Increased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased
300 dry wt.shoots 400 dry wt.shoots 300 dry wt.shoots > 450 dry wt.shoots 300 dry wt.roots > 450 dry wt.roots 300 length roots 500 dry wt.shoots 450 length roots 500 dry wt.shoots 550 dry wt.shoots .550 dry wt.roots 500 length roots > 700 dry wt.whole plant 600 fresh wt.whole plant 600 dry wt.whole plant 550 dry wt. 500 dry wt. 600 dry wt.shoots 550 length roots 600 dry wt.shoots 550 length roots 600 dry wt.shoobs length roots 450
Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased
dry wt.shoots dry wt.shoots fresh wt.whole plant dry wt.whole plant fresh wt. dry wt.shoots length roots dry wt.shoots length roots dry wt.shoots length roots
Decreased dry wt.shoots Decreased length roots
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
1400 1200 1600 1600 400 1800 1400 1400 1000 1400 1200 75 50
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T A B L E II. CAPACITIES OF SOILS TO DEACTIVATE PARAQUAT (CONT.)
Soil
Date o f Bioassay
Bioassay
Meth- Wheat 2nd crop wold (Cont.) Lemna Soil treated Wheat 3rd crop
Aug. 1972 Sept.1972 May 1972 Sept. 1972
Wheat 4th crop
Oct. 1972
Wheat 5th crop
Jan. 1973
Wheat 6th crop
Mar. 1973
Ryegrass
June 1973
Ryegrass(+O.05MCaCl )June 1973 2
Ryegrass(+O.25MCaCl2)June 1973 Tarlton
Soil treated Wheat 1st crop Wheat 2nd crop Radish
Aug. 1971 Mar. 1972 A p r i l 1972 Aug. 1972
Wheat 3rd crop
Oct. 1972
Wheat 4th crop
Dec. 1972
Wheat 5th crop
Jan. 1973
Lemna
Sept.1973
Observed e f f e c t of paraquat
Lowest concentration of paraquat which s i g n i ficantly (P-O.05) affected crop (pg paraquat/g soil)
Decreased dry wt.shoots Decreased length roots Decreased fresh wt.
75 50 200
Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased
dry wt .shoots length roots dry wt .shoots length root 8 dry wt .shoots length roots dry wt shoots length roots dry wt shoots length roots dry wt shoots length roots dry wt, shoots length roots
75 50 200 50 100 75 200 75 200 200 200 100 100 25
Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased Decreased
dry wt.shoots dry wt.shoots fresh wt.whole plant dry wt.whole plant > dry wt.shoots length roots dry wt.shoots length roots dry wt.shoots length roots fresh wt. >
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
300 450 1350 1500 1050 450 1350 450 600 600 1500
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C o m p a r i s o n of F i g u r e s 4 a n d 5 shows that the e f f e c t s of p a r a quat o n g r o w t h w e r e s i m i l a r in s e p a r a t e d e q u i l i b r i u m soil s o l u t i o n s a n d in the t o t a l s y s t e m of soil p l u s e q u i l i b r i u m s o l u t i o n . T h e r e f o r e , the p a r a q u a t bound to the soil w a s not a v a i l a b l e to the p l a n t s a n d the p h y t o t o x i c i t y o b s e r v e d w a s due t o f r e e p a r a q u a t in the soil s o l u t i o n . T h e c o n c e n t r a t i o n of bound p a r a q u a t in the soil w a s a p p r o x i m a t e l y 10,000 t i m e s g r e a t e r than the p a r a q u a t c o n c e n t r a t i o n in the soil s o l u t i o n w h e n p h y t o t o x i c i t y w a s first ob served. U n d e r o u r c o n d i t i o n s , the L e m n a b i o a s s a y h a d a s i m i l a r s e n s i t i v i t y t o that of the w h e a t b i o a s s a y ; O.02 μg/ml p a r a q u a t s e v e r e l y r e d u c e d g r o w t h . In the L e m n a b i o a s s a y of the s o i l s , r o o t s w e r e s u s p e n d e d in the e q u i l i b r i u m s o l u t i o n above the soil but c a m e into c o n t a c t w i t h the soil t o w a r d the e n d of the 7-day g r o w t h p e r i o d . R e s u l t s f o r the L e m n a b i o a s s a y w e r e s i m i l a r to t h o s e of the wheat b i o a s s a y s of b o t h s o i l s a n d e q u i l i b r i u m s o l u t i o n s ( T a b l e II). W h e n the c o n c e n t r a t i o n of p a r a q u a t in soil is v e r y h i g h it is p o s s i b l e to d i s p l a c e s o m e of the a d s o r b e d p a r a q u a t w i t h h i g h c o n c e n t r a t i o n s of i n o r g a n i c c a t i o n s (1). N e v e r t h e l e s s , the e f f e c t of soil r e s i d u e s o n the g r o w t h of L e m n a w a s not i n c r e a s e d in the p r e s e n c e of O.05 M C a C l 2 . L e m n a w o u l d not g r o w in the p r e s ence of h i g h e r c o n c e n t r a t i o n s of C a C ^ . O.05 a n d O.25 M C a C l 2 o n l y s l i g h t l y r e d u c e d the c a p a c i t i e s of Sandy H i l l s and M e t h w o l d (peat) s o i l s t o d e a c t i v a t e p a r a q u a t w i t h the e x c e p t i o n of O. 25 M C a C l 2 o n the M e t h w o l d peat; O.25M C a C l 2 i t s e l f r e d u c e d the g r o w t h of r y e g r a s s b y about h a l f . T h e O.25M c o n c e n t r a t i o n o f C a C l 2 is h i g h e r than the s a l t c o n c e n t r a t i o n found in m o s t soil s o l u t i o n s (33) a n d s u r r o u n d i n g f e r t i l i z e r bands (35). T h e r e f o r e , t h e r e is no d a n g e r of i n o r g a n i c c a t i o n s in s o i l s d i s p l a c i n g bound paraquat residues. T h e d e t e r m i n a t i o n of the c a p a c i t y of s o i l s to d e a c t i v a t e p a r a quat by b i o a s s a y i n g s o i l s t r e a t e d w i t h h i g h r a t e s of p a r a q u a t in l o w v o l u m e s of t r e a t m e n t s o l u t i o n is not p r a c t i c a l b e c a u s e it t a k e s at l e a s t s e v e r a l m o n t h s f o r the p a r a q u a t t o e q u i l i b r a t e in the soil. H o w e v e r , in d i l u t e s l u r r i e s e q u i l i b r a t i o n is c o m p l e t e a f t e r o v e r n i g h t s h a k i n g a n d the e q u i l i b r i u m s o l u t i o n c a n t h e n be a n a l y z e d p h o t o m e t r i c a l l y o r b i o a s s a y e d a s d e s c r i b e d above. The p a r a q u a t 'Strong A d s o r p t i o n ' c a p a c i t y of a soil d e t e r m i n e d by b i o a s s a y i n g e q u i l i b r i u m s o l u t i o n s w i t h wheat is d e f i n e d a s the c o n c e n t r a t i o n of soil-adsorbed p a r a q u a t w h e n the c o n c e n t r a t i o n of p a r a q u a t in the e q u i l i b r i u m s o l u t i o n is s u f f i c i e n t to r e d u c e the l e n g t h of 14-day o l d w h e a t r o o t s by 5 0 % ; t h i s s o l u t i o n c o n c e n t r a t i o n is about O.Oljug p a r a q u a t / m l ( T a b l e III). The c o n c e n t r a t i o n
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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Bound Paraquat Residues
TABLE
III
'STRONG ADSORPTION' CAPACITIES OF SOILS
'Strong Adsorption' C a p a c i t y (1) frig p a r a q u a t / g soil)
Soil Sandy H i l l s Tarlton Broadricks Methwold Pure paraquat dichloride solution
Paraquat c o n c e n t r a t i o n in soil s o l u t i o n which reduced length o f wheat r o o t s by 50% (jug paraquat /ml) O.05 O.01 O.02 O.004
400 300 800 40
O.005
1.
Mean o f 2 determinations
2.
Assuming a bulk d e n s i t y o f 1.2 g / c c
3.
Assuming a bulk d e n s i t y o f O.5 g / c c
kg paraquat/ha r e q u i r e d to saturate 'Strong Adsorption' C a p a c i t y o f top 15 cm soil 720 540 1440 30
(2) (2) (2) (3)
- O.04
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
316
RESIDUES
of p a r a q u a t w h i c h r e d u c e d r o o t l e n g t h b y 5 0 % is o n l y s l i g h t l y h i g h e r than that w h i c h first s i g n i f i c a n t l y a f f e c t s r o o t l e n g t h (see above), 5 0 % r e d u c t i o n of r o o t g r o w t h is u s e d t o m e a s u r e the S t r o n g A d s o r p t i o n c a p a c i t i e s of s o i l s b e c a u s e it c a n be e a s i l y d e t e r m i n e d by v i s u a l e x a m i n a t i o n of the data, w h e r e a s the first e f f e c t c o n c e n t r a t i o n depends v e r y m u c h o n the v a r i a b i l i t y of the e x p e r i m e n t and the data have t o be s t a t i s t i c a l l y a n a l y z e d . B i o a s s a y of the e q u i l i b r i u m s o l u t i o n s and thus 'Strong A d s o r p t i o n ' c a p a c i t y v a l u e s , g i v e s a good e s t i m a t e of the c a p a c i t y of s o i l s t o d e a c t i v a t e p a r a q u a t ( c o m p a r e T a b l e s II and III). If a n y t h i n g , t h e 'Strong A d s o r p t i o n ' c a p a c i t y v a l u e s tend t o u n d e r e s t i m a t e the c a p a c i t y of s o i l s t o d e a c t i v a t e paraquat. This s o l u t i o n b i o a s s a y technique has b e e n w i d e l y u s e d b y I C I P l a n t P r o t e c t i o n D i v i s i o n to d e t e r m i n e the c a p a c i t y of s o i l s t o d e a c t i vate paraquat. f
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B O U N D A N D C O N J U G A T E D PESTICIDE
1
Field Trials The r e l a t i o n s h i p b e t w e e n 'Strong A d s o r p t i o n ' c a p a c i t y v a l u e s and the c a p a c i t y of s o i l s to d e a c t i v a t e p a r a q u a t in the f i e l d has b e e n s t u d i e d . P a r a q u a t w a s a p p l i e d at r a t e s of 1/2, 1 a n d 4 t i m e s the 'Strong A d s o r p t i o n ' c a p a c i t y found by the e q u i l i b r i u m soil s o l u t i o n b i o a s s a y t e c h n i q u e . T h e effect of p a r a q u a t soil residues on crop growth and crop residues were a c c u r a t e l y pre d i c t e d ; r e s i d u e s b e l o w the 'Strong A d s o r p t i o n ' c a p a c i t y b e i n g un available to plants. One e x p e r i m e n t w a s c o n d u c t e d at F r e n s h a m in E n g l a n d . T h e l o a m y sand soil c o n t a i n s 9% c l a y , 8 % s i l t and 8 3 % sand and 2 . 0 % o r g a n i c m a t t e r ; it h a s a p H of 6. 6 and c a t i o n exchange c a p a c i t y of 5 meq/100 g at p H 7.O. T h e 'Strong A d s o r p t i o n ' c a p a c i t y of the soil is 120 u g p a r a q u a t / g soil. P a r a q u a t a d s o r p t i o n i s o t h e r m s , d e t e r m i n e d in d i l u t e s l u r r i e s as d e s c r i b e d above, a r e g i v e n in F i g u r e 7. The t r i a l w a s l a i d out in 3 b l o c k s . E a c h b l o c k w a s s p l i t into two h a l v e s a n d e a c h h a l f w a s s p l i t into 4 p l o t s , 40 m χ 5 m. F o u r p l o t s o f o n e - h a l f o f e a c h b l o c k w e r e t r e a t e d w i t h 0, 15, 33 and 120 k g / h a of p a r a q u a t ; t h i s w a s then l i g h t l y i n c o r p o r a t e d into the t o p 2 c m soil u s i n g a hand r a k e . T h e 4 p l o t s o n the o t h e r h a l f o f e a c h b l o c k w e r e t r e a t e d w i t h 0, 90, 198 a n d 720 k g / h a o f paraquat; t h i s w a s t h o r o u g h l y r o t o v a t e d into the top 15 c m . T h e p a r a q u a t w a s a p p l i e d in N o v e m b e r , 1971, a n d the p l o t s w e r e left u n d i s t u r b e d t h r o u g h the w i n t e r . In the s p r i n g , w e e d s w e r e c o n t r o l l e d by a n o v e r a l l s p r a y o fO.5 k g / h a paraquat. In M a r c h , 1972, the t r i a l a r e a w a s s e e d e d w i t h b a r l e y ( H o r d e u m v u l g a r e -
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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22.
RILEY
E T AL.
Bound Paraquat Residues
PARAQUAT IN SOLUTION (HQ/ml)
Figure 7.
Paraquat adsorption isotherms on Frensham soil
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
317
BOUND AND CONJUGATED PESTICIDE RESIDUES
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318
c u l t i v a r J u l i a ) by d i r e c t d r i l l i n g w i t h a t r i p l e d i s c d r i l l , i . e . , by z e r o t i l l a g e . In A u g u s t , w h e n the c r o p had r e a c h e d m a t u r i t y , s a m p l e s of g r a i n and s t r a w w e r e a n a l y z e d f o r p a r a q u a t r e s i d u e s . A s e c o n d c r o p of b a r l e y was s i m i l a r l y g r o w n in 1973. A l s o in 1973, l a r g e soil s a m p l e s w e r e t a k e n f r o m the top 15 c m of the deep i n c o r p o r a t e d t r e a t m e n t s . T h e s e soil s a m p l e s w e r e u s e d to g r o w c a r r o t s (Daucus c a r o t a - c u l t i v a r New M o d e l R e d C o r e ) o u t d o o r s in 20 c m d i a m e t e r , 20 c m deep pots. The c a r r o t s w e r e h a r v e s t e d 119 d a y s a f t e r s o w i n g , t h o r o u g h l y w a s h e d and a n a l y z e d for p a r a q u a t r e s i d u e s . In 1972, the 90 k g / h a i n c o r p o r a t e d and 15 and 33 k g / h a s u r f a c e t r e a t m e n t s o n l y s l i g h t l y a f f e c t e d e a r l y g r o w t h of b a r l e y and the c r o p q u i c k l y and c o m p l e t e l y r e c o v e r e d ( T a b l e IV). The 20 k g / h a s u r f a c e t r e a t m e n t and 198 k g / h a i n c o r p o r a t e d t r e a t m e n t had a s i g n i f i c a n t e f f e c t on b a r l e y g r o w t h and r e d u c e d the n u m b e r of p l a n t s . H o w e v e r , the r e m a i n i n g p l a n t s g r e w n o r m a l l y and a l t h o u g h g r a i n y i e l d s w e r e s l i g h t l y l e s s t h a n on the c o n t r o l p l o t s t h e r e was no s t a t i s t i c a l d i f f e r e n c e in the y i e l d at the 9 5 % c o n f i dence l e v e l . T h e r e was an a l m o s t c o m p l e t e c r o p f a i l u r e on the 720 k g / h a i n c o r p o r a t e d t r e a t m e n t . H o w e v e r , a few p l a n t s s u r v i v e d and they g r e w n o r m a l l y ; they w e r e h a r v e s t e d f o r r e s i d u e a n a l y s i s . The r e s i d u a l a c t i v i t y of the p a r a q u a t was l e s s in 1973 t h a n 1972. T h i s was due to a s l o w e q u i l i b r i u m of the l a r g e a m o u n t s of p a r a q u a t w i t h a d s o r p t i o n s i t e s ; t h e r e was no s i g n i f i cant d e g r a d a t i o n of p a r a q u a t d u r i n g the e x p e r i m e n t . In 1973, the 15 and 33 k g / h a s u r f a c e t r e a t m e n t s and 90 and 198 k g / h a i n c o r p o r a t e d t r e a t m e n t s had no s i g n i f i c a n t e f f e c t s on b a r l e y g r o w t h . The 120 k g / h a s u r f a c e t r e a t m e n t s l i g h t l y a f f e c t e d b a r l e y g r o w t h but d i d not s i g n i f i c a n t l y a f f e c t g r a i n y i e l d ( T a b l e IV). The 720 k g / ha i n c o r p o r a t e d t r e a t m e n t was a g a i n s e v e r e l y p h y t o t o x i c but m a n y m o r e p l a n t s s u r v i v e d and g r e w n o r m a l l y t h a n in 1972. R e s i d u e s in b a r l e y g r a i n and s t r a w w e r e n e g l i g i b l e , e x c e p t f o r the 720 k g / h a i n c o r p o r a t e d t r e a t m e n t (Table I V ) . T h i s c o u l d have b e e n due to c o n t a m i n a t i o n w i t h t r a c e s of soil c o n t a i n i n g l a r g e p a r a q u a t r e s i d u e s as w e l l as a d s o r p t i o n by the c r o p . R e s i dues in the c a r r o t s w e r e v e r y low, i . e . , O.04 (ug/g o r l e s s (Table IV) A f u r t h e r t r i a l was c o n d u c t e d on B r o a d r i c k s f i e l d at J e a l o t t ' s H i l l R e s e a r c h S t a t i o n . D e t a i l s of the soil a r e g i v e n in T a b l e I. It has a 'Strong A d s o r p t i o n c a p a c i t y of 800 jug p a r a q u a t / g soil. Two 6 χ 6 m p l o t s w e r e t r e a t e d w i t h 5 a n n u a l a p p l i c a t i o n s of 112 k g / h a p a r a q u a t ; t h i s r e s u l t e d in r e s i d u e s of 1000 μg/g in the top 2. 5 c m soil. S23 p e r e n n i a l r y e g r a s s s o w n in the top 2. 5 c m of soil f a i l e d to g e r m i n a t e o r was s e v e r e l y stunted. H o w e v e r , a f t e r f
1
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976. .
1973 Paraquat r e s i d u e s in c a r r o t r o o t s Qug/g f r e s h weight)
8000
Paraquat ' T i g h t l y Bound' Capacity(/ue/g) 80
Ocoee, Florida
112.7
3.3
pH
Cation Exchange CapaSoil c i t y meq./lOO g O r i g i n
CHEMICAL AND MECHANICAL ANALYSIS OF SOILS
TABLE V
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i
η
>
!
8
co to to
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
20 500 1000 2500
Loam
36 900 1800 4500
36 180 900 2160
9 45 450 1800
9 36 360 900 12 49 930 3603 1 34 328 901 0 222 648 1528
0 0 0 5 0 0 0 1 0 0 0 360
17 174 170 203
18 50 86 85
10 14 15 101
2 2 4 5
None Minor S t u n t i n g Eventual K i l l No germination
None Minor S t u n t i n g Eventual K i l l No germination
None None Stunted Partial germination
Minor S t u n t i n g Eventual K i l l No germination No germination
Gross P l a n t Symptoms
g / c c f o r m i n e r a l s o i l s and O.3 g / c c f o r muck.
3 15 159 181
0 0 16 200
• C a l c u l a t i o n s based on bulk d e n s i t i e s o f 1.2
20 100 500 1200
Loamy Sand
5 20 200 500
20 100 1000 4000
Type
fortification pg kg/ha Paraquat/g in top dry soil 15 cm
Soil
1
μ* P a r a q u a t / g dry soil •Loosely Bound* ' T i g h t l y Bound Leached w i t h residue extracted 'Unbound' saturated by r e f l u x i n g Leached ammonium 18 Ν s u l w i t h water chloride furic acid
DIFFERENT FORMS OF PARAQUAT IN SOIL ACCORDING TO STRENGTH OF ADSORPTION
Muck
Sand
Soil
T A B L E VI.
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324
BOUND AND CONJUGATED PESTICIDE RESIDUES
t y p e s . S i m i l a r s y m p t o m s w e r e o b s e r v e d w i t h 15 jug/g ' L o o s e l y Bound' p a r a q u a t in the sand and 600 ug/g ' L o o s e l y Bound' p a r a quat in the l o a m . B y c o m p a r i n g these b i o a s s a y r e s u l t s w i t h those g i v e ninS e c t i o n A above,itc a n be c o n c l u d e d that w h e n a soil c o n t a i n s ' L o o s e l y Bound' p a r a q u a t t h e r e a r e t r a c e s of p a r a quat (O.005 -O.05μg/ml)inthe e q u i l i b r i u m soil s o l u t i o n . The sand, l o a m y sand and m u c k w e r e t r e a t e d w i t h 14cm e t h y l p a r a q u a t at t h e i r l o w e s t t r e a t m e n t l e v e l in the u n l a b e l l e d p a r a q u a t e x p e r i m e n t . T h r e e w e e k s a f t e r p l a n t i n g , the p l a n t s g r o w n in the sand c o n t a i n e d O.02 t oO.05μg/g ^ C c a l c u l a t e d as p a r a q u a t . The c o r n and beans g r o w n in the l o a m y sand and m u c k c o n t a i n e dO.01 o r l e s s t h a n O. 01 μg/g p a r a q u a t ( T a b l e VII). T h u s , w h e n m o s t of the p a r a q u a t is ' T i g h t l y Bound' t h e r e is little o r no a v a i l a b i l i t y to plant uptake (25). Field Trials F i e l d t r i a l s w e r e p e r f o r m e d using e x c e s s i v e l y high paraquat soil t r e a t m e n t s to study the a v a i l a b i l i t y of bound p a r a q u a t r e s i dues. T r i a l s w e r e in M o o r e s t o w n , N e w J e r s e y , and F r e s n o , C a l i f o r n i a . The c h a r a c t e r i s t i c s of the s o i l s and t h e i r a d s o r p t i o n c a p a c i t i e s f o r p a r a q u a t a r e g i v e n in T a b l e VIII. B o t h s o i l s w e r e sandy l o a m s and the p a r a q u a t ' T i g h t l y Bound' c a p a c i t y was a p p r o x i m a t e l y 300 μg/g f o r the C a l i f o r n i a soil and 1000 μg/g f o r the New J e r s e y soil. T h i s w o u l d be e q u i v a l e n t to a p p r o x i m a t e l y 670 k g / h ainthe top 15 c m f o r the C a l i f o r n i a soil and 2240 kg/ha f o r a 15 c m depth f o r the New J e r s e y soil. P l o t s w e r e t r e a t e d at t h r e e d i f f e r e n t l e v e l s of p a r a q u a t at e a c h t e s t s i t e . The t r e a t m e n t r a t e s w e r e 1/2, 1-1/2 to 2 and 2-1/2 to 5 t i m e s the ' T i g h t l y Bound' c a p a c i t y . The t r e a t m e n t r a t e s in C a l i f o r n i a w e r e 336, 1400 and 3360 k g / h a f o r a 15 c m depth and in New J e r s e y w e r e 1120, 3360 and 5600 kg/ha f o r a 15 c m depth. The p l o t s w e r e r o t o t i l l e d r i g h t a f t e r t r e a t m e n t and s e v e r a l t i m e s a y e a r t h e r e a f t e r . C r o p s w e r e g r o w n 1 to 3 y e a r s a f t e r the soil w a s t r e a t e d . C r o p s g r o w n in soil t r e a t e d w i t h p a r a q u a t b e l o w the ' T i g h t l y Bound' c a p a c i t y d e v e l o p e d s i m i l a r to those g r o w ninu n t r e a t e d soil In soil t r e a t e d at 1-1/2 to 2 t i m e s the ' T i g h t l y Bound' c a p a c i t y , s o m e c r o p i n j u r y was o b s e r v e d . A t soil t r e a t m e n t s of 2-1/2 to 5 t i m e s the 'Tightly Bound' c a p a c i t y , g r o s s plant s y m p t o m s w e r e o b s e r v e d . V i s u a l e v a l u a t i o n s of c r o p s p l a n t e dinthe C a l i f o r n i a t r i a l one y e a r a f t e r soil t r e a t m e n t a r e g i v e n in T a b l e DC. A t 336 kg/hainthe t o p 15 c m , w h i c h was 1/2 of the ' T i g h t l y Bound' c a p a c i t y , no d e t e c t a b l e p h y t o t o x i c i t y was o b s e r v e d on rye, barley, alfalfa, white c l o v e r , turnip, dichondra, r a d i s h o r
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976. C PARAQUAT FROM TREATED SOILS*
**
*
O.01
L i m i t of d e t e c t i o n is O.01 p g / g . Background was 45 c o u n t s / m i n . C o m and bean p l a n t values are averages of t r i p l i c a t e a n a l y s e s . Bean pod values are averages of d u p l i c a t e a n a l y s e s . Not a n a l y z e d .
86
20
Loamy Sand
O.00
46
O.00
23
O.01
40
20
Muck
17
139
O.05
387
O.02
160
5
Sand
Type
Soil
1 4
VII
O.00
O.01
O.02
53
** *• O.01
31
**
**
O.00
E i g h t Weeks Afte; Flanting S i x Weeks A f t e r P l a n t i n g Three Weeks A f t e r P l a n t i n g Soil Be?n Pod Corn Bean Corn Bean Fortification Net pg/g Net pg/g Net pg/g Net u g / g Net μ g / g ug/g counts/m η Paraquat counts/min Paraquat c o u n t s / m i n Paraquat counts/min Paraquat counts/min Paraquat Paraquat
UPTAKE OF
TABLE
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Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
14
11
Fresno, California
% Clay
Moorestown, New J e r s e y
Test Location
36
12
% Silt
53
74
7o Sand
Sandy Loam
Sandy Loam
Soil Type
O.3
1.1
% Organic Matter
14
16
Cation Exchange Capacity (meq/100 g)
5.8
5.7
pH
338
1125
1
Paraquat 'Tightly Bound C a p a c i t y
CHARACTERISTICS OF SOILS FROM ftlGH RATE FIELD TRIALS
TABLE VIII
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3266
7600
Paraquat 'Loosely Bound' C a p a c i t y
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Barley
O.0 O.0 O.0 O.0
Control
*
Wht C l o v e r
Turnip
I N J U R Y (1)
4.5
2.0
4.8
1.8
9.3
10/29/71.
10 ,
A f t e r treatment
soil
Dichondra
-— —
O.0 3.0 O.0
1.5 7.5 O.0
4.5 O.0
to 15 cm d e p t h .
1.0
—
O.0
O.0
O.0
was r o t o t i l l e d
complete k i l l .
1.8
O.3
2.0
O.5
4.5
O.0 O.0
O.0
O.0
O.0 O.0
O.0
0 - no crop i n j u r y ,
7.8
treated 9/17/70.
Crops p l a n t e d
Soil
R a t i n g 0-10;
8.0
5.3
3360
2.3
2.8
O.8
1400
O.5
O.0
O.0
(1)
Alfalfa
>C R Ο Ρ Radish
O.0
5.8
1.0
O.0
U / 3 0 2/18 11/3^ 2/18 11/30 2/18 U / 3 0 2/18 11/30 2/18 II/30 2/18 11/30 2/18
Rve
336
Paraquat Soil Trpatment
CROP GROWTH IN PARAQUAT HIGH RATE SOIL TRIALS AT FRESNO, CALIFORNIA*
T A B L E IX
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BOUND AND CONJUGATED PESTICIDE RESIDUES
328
cabbage. A t 1400 kg /ha in the top 15 c m , w h i c h w a s 2 t i m e s the ' T i g h t l y B o u n d c a p a c i t y , p h y t o t o x i c i t y to a l f a l f a , c l o v e r , t u r n i p , d i c h o n d r a , r a d i s h and cabbage w e r e c o m m e r c i a l l y a c c e p t a b l e , but i n j u r y t o r y e and b a r l e y w a s not a c c e p t a b l e . A t 3360 k g / h a in the top 15 c m , w h i c h w a s 5 t i m e s the ' T i g h t l y Bound' c a p a c i t y , the c r o p i n j u r y w a s s e v e r e . T h r e e y e a r s a f t e r the soil w a s t r e a t e d , the c r o p g r o w t h at the d i f f e r e n t p a r a q u a t soil t r e a t m e n t s w a s s i m i l a r t o that o b s e r v e d at the 1 y e a r i n t e r v a l . P a r a q u a t r e s i d u e s found in the s a m p l e c r o p s a r e g i v e n in T a b l e X. C r o p s g r o w n in soil t r e a t e d at 1/2 the ' T i g h t l y B o u n d p a r a q u a t soil c a p a c i t y c o n t a i n e d l e s s than O. 01 to 3. 8 (ug/g p a r a quat. C r o p s g r o w n in soil t r e a t e d at 1-1/2 to 2 t i m e s the ' T i g h t l y Bound' p a r a q u a t soil c a p a c i t y c o n t a i n e d l e s s than O.01 t o 17 (ug/g p a r a q u a t . C r o p s g r o w n in soil t r e a t e d at 2-1/2 t o 5 t i m e s the ' T i g h t l y Bound' p a r a q u a t soil c a p a c i t y c o n t a i n e d O.07 t o 42 μg/g paraquat. T h e l o w e s t r e s i d u e s w e r e found in s h e l l e d soybeans and c o t t o n f u z z y s e e d w h i l e the h i g h e s t r e s i d u e s w e r e found in m a t u r e potato v i n e s . A p o r t i o n of the r e s i d u e f r o m the potato v i n e s c o u l d be due to soil c o n t a m i n a t i o n and not uptake. I n t e r p r e t a t i o n of c r o p r e s i d u e s f r o m f i e l d t r i a l s of e x c e s s i v e l y h i g h soil t r e a t m e n t s is d i f f i c u l t , s i n c e t r a c e soil c o n t a m i n a t i o n c a n c a u s e s i g n i f i c a n t c r o p r e s i d u e s . N e v e r t h e l e s s , the r e s i d u e data show that c r o p s g r o w n in soil t r e a t e d at e x c e s s i v e l y h i g h r a t e s of p a r a q u a t c o n t a i n s m a l l a m o u n t s , if any, of p a r a q u a t . T h a t is, p a r a q u a t is bound t o the soil a n d not a v a i l a b l e t o p l a n t s .
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1
1
C.
C o m p a r i s o n of 'Strong A d s o r p t i o n ' C a p a c i t y a n d ' T i g h t l y Bound' C a p a c i t y of S o i l s
The 'Strong A d s o r p t i o n ' c a p a c i t y p r o c e d u r e d e t e r m i n e s the a m o u n t of p a r a q u a t a d s o r b e d by a soil b e f o r e p h y t o t o x i c t r a c e a m o u n t s a r e p r e s e n t in the e q u i l i b r i u m s o l u t i o n (about O.01 p g paraquat/ml). The ' T i g h t l y Bound' c a p a c i t y p r o c e d u r e d e t e r m i n e s the c a p a c i t y of a soil to a d s o r b p a r a q u a t s o f i r m l y that it cannot be d e s o r b e d b y s a t u r a t e d (5M) a m m o n i u m c h l o r i d e ; it c a n o n l y be r e l e a s e d by r e f l u x i n g the soil w i t h 18 Ν s u l f u r i c a c i d . B o t h the 'Strong A d s o r p t i o n ' c a p a c i t y and the ' T i g h t l y Bound' c a p a c i t y of 4 s o i l s have b e e n d e t e r m i n e d . D e t a i l s of the s o i l s (Frensham, England; Moorestown, New Jersey; F r e s n o , C a l i f o r n i a ) a r e g i v e n above. The O c o e e soil w a s a sand ( a p p r o x i m a t e l y 9 8 % sand) f r o m F l o r i d a . T h e a d s o r p t i o n c a p a c i t i e s d e t e r m i n e d by the two m e t h o d s a r e g i v e n in T a b l e X I . T h e 'Strong A d s o r p t i o n ' a n d T i g h t l y Bound' c a p a c i t i e s f o r a g i v e n soil d i d not
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
22.
RILEY
E T AL.
329
Bound Paraquat Residues
TABLE
X
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PARAQUAT RESIDUES IN CROPS FROM HIGH RATE SOIL TRIALS
Test Location
Crop
13
Immature Vines
33
Mature Vines
34
Tubers
34
Volunteer Weeds
Foliage
33
Carrots
Tops
34
Roots
34
Volunteer Weeds
Foliage
33
Cotton
Fuzzy Seed
37
Leaves & Twigs
37
Potatoes
Fresno, California
Months After Soil Treatment
Shelled Beans
Soybeans
Moorestown, New Jersey
Crop Part Analyzed
Soil Treatment (kg/ha) in 15 cm Depth 1120 3360 5600 1120 3360 5600 1120 3360 5600 1120 3360 5600 1120 3360 5560 1120 3360 5600 1120 3360 5600 336 1400 3360 336 1400 3360 336 1400 3360
Paraquat Found in Crop (ug/g)* O.08 O.04 O.07 O.18 O.41 1.5 3.8 17 42 O.13 O.85 O.48 O.40 0^6 0Π.2 O.29 1.9
* Average of 2 determinations.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
O.74 1.1
O.08 1.0 7.0 O.00 O.00 O.07 O.07 -
330
BOUND AND CONJUGATED PESTICIDE RESIDUES
d i f f e r by a f a c t o r of m o r e than 2.
T h i s was e x p e c t e d
both v a l u e s a c c u r a t e l y p r e d i c t the c a p a c i t y of a soil to
because deactivate
paraquat. T h r o u g h o u t the r e m a i n d e r of t h i s r e p o r t the t e r m - bound p a r a q u a t soil r e s i d u e s - w i l l be u s e d to d e s c r i b e soil r e s i d u e s below the ' S t r o n g A d s o r p t i o n ' / ' T i g h t l y B o u n d ' c a p a c i t i e s of soil.
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4.
UNAVAILABILITY O F BOUND PARAQUAT SOIL RESIDUES T O E A R T H W O R M S
E x t e n s i v e f i e l d and l a b o r a t o r y studies h a v e shown that bound p a r a q u a t has no effect on w o r m s and it is not a b s o r b e d b y w o r m b o d i e s . V e r y l a r g e p a r a q u a t soil r e s i d u e s , w h i c h r e s u l t in ' f r e e ' p a r a q u a t in the e q u i l i b r i u m soil s o l u t i o n ( g r e a t e r than about O.01 jug/ml) c a n r e d u c e the n u m b e r of w o r m s . T h e r e d u c e d plant c o v e r is as l i k e l y to be the c a u s e of a r e d u c t i o n as d i r e c t p a r a quat t o x i c i t y . E a r t h w o r m s a m p l e s a r e o b t a i n e d by e x p e l l i n g t h e m f r o m a r e a s 60 c m s q u a r e w i t h 4 . 5 L of O. 2% f o r m a l d e h y d e s o l u t i o n o r o c c a s i o n a l l y by hand s o r t i n g of soil. T h e y have b e e n s a m p l e d on 12 s i t e s w h e r e p a r a q u a t has b e e n u s e d a p p l i e d at n o r m a l o r e x c e s s i v e r a t e s , but o n l y two a r e r e c o r d e d in this p a p e r . These a r e s i t e s o n w h i c h m u c h p a r a q u a t soil a d s o r p t i o n w o r k has b e e n d o n e , w h e r e the s o i l s have a m o d e r a t e and low c l a y content, and on w h i c h p a r a q u a t has b e e n a p p l i e d at g r o s s l y e x c e s s i v e r a t e s . One t r i a l was done o n B r o a d r i c k s f i e l d at J e a l o t t ' s H i l l R e s e a r c h S t a t i o n . D e t a i l s of the soil have a l r e a d y b e e n g i v e n . It has a ' S t r o n g A d s o r p t i o n c a p a c i t y of 800 u g p a r a q u a t / g soil. The field was c o v e r e d with a thin g r a s s s w a r d . The t r i a l was l a i d out in O c t o b e r 1964 as two r e p l i c a t e b l o c k s , c o n t a i n i n g 6 m s q u a r e plots s e p a r a t e d by 1. 5 m g u a r d r o w s . Three random plots o n e a c h b l o c k w e r e r o t o v a t e d and s p r a y e d 2 w e e k s l a t e r w i t h 0, 2 . 2 4 and 112 k g / h a p a r a q u a t . A f t e r a f u r t h e r w e e k , they were seeded with r y e g r a s s . T h r e e u n d i s t u r b e d plots o n e a c h b l o c k w e r e s p r a y e d w i t h the s a m e r a t e s of p a r a q u a t , and r y e g r a s s s o w n one w e e k l a t e r by d i r e c t d r i l l i n g ( z e r o t i l l a g e ) . In M a y 1965, the 112 k g / h a p l o t s w e r e r e s e e d e d as the g r a s s was t h i n and p a t c h y . 1
E a r t h w o r m s w e r e a s s e s s e d in O c t o b e r 1965, 12 m o n t h s a f t e r a p p l i c a t i o n , a n d the r e s u l t s a r e s h o w n in T a b l e X I I . O n l y two s a m p l e s p e r t r e a t m e n t w e r e t a k e n , so that c o n s i d e r a b l e v a r i a t i o n m i g h t be e x p e c t e d . N e v e r t h e l e s s , it is c l e a r that the p o p u l a t i o n h a s not b e e n a d v e r s e l y a f f e c t e d e v e n by the e x c e s s i v e r a t e of 112 kg/ha.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
22.
331
Bound Paraquat Residues
RILEY ET AL.
T A B L E
XI
1
COMPARISON OF 'STRONG ADSORPTION AND TIGHTLY BOUND CAPACITIES OF SOILS
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1
1
Strong Adsorption capacity (jug paraquat/g soil)
' T i g h t l y Bound capacity (pg paraquat/g
1
Soil
1500
1100
Frensham
120
200
Fresno
500
300
6
3
Moorestown
Ocoee
T A B L E
1
soil)
XII
EARTHWORMS FROM THE BROAD RICKS SITE 12 MONTHS AFTER PARAQUAT APPLICATION EXPRESSED AS NUMBER AND WEIGHT/M , EACH FIGURE DERIVED FROM THE TOTAL EXPELLED FROM TWO O.37 m AREAS 2
2
C u l t i v a t i o n Before Paraquat Rotovated Application
None 0
Paraquat a p p l i e d T o t a l number/m
(kg/ha)
2
2
T o t a l biomass (g/m )
0
2.24
2.24
112
1.12
44
83
40
20
40
24
81
43
100
35
29
73
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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332
BOUND AND
CONJUGATED PESTICIDE RESIDUES
A t the F r e n s h a m , E n g l a n d s i t e , a n o t h e r t r i a l was done; d e t a i l s of w h i c h have p r e v i o u s l y b e e n d e s c r i b e d . The e a r t h w o r m p o p u l a t i o n was a s s e s s e d in N o v e m b e r 1972, a y e a r a f t e r a p p l i c a t i o n of the p a r a q u a t and t h r e e m o n t h s a f t e r the b a r l e y h a r v e s t . The r e s u l t s w e r e s t a t i s t i c a l l y a n a l y z e d a f t e r l o g a r i t h m i c t r a n s f o r m a t i o n . The d e t r a n s f o r m e d m e a n s a r e g i v e n in T a b l e XIII. E x a m i n a t i o n of the e f f e c t s of c u l t i v a t i o n , a v e r a g e d o v e r the r a t e s , showed the n u m b e r s of A l l o l o b o p h o r a c a l i g i n o s a and A. c h l o r o t i c a to be h i g h l y s i g n i f i c a n t l y l o w e r ( P = O.01) on the p l o t s w h i c h had b e e n d e e p l y r o t o v a t e d . T h i s is t a k e n to be a r e s i d u a l e f f e c t of p h y s i c a l d a m a g e to n e a r - s u r f a c e s p e c i e s c a u s e d by t r i p l e rotovated. The c o m b i n e d s p e c i e s t o t a l showed a r e d u c t i o n of s i m i l a r s i g n i f i c a n c e , b e i n g w e i g h t e d l a r g e l y by A. c a l i g i n o s a . The s i g n i f i c a n c e of the b i o m a s s r e d u c t i o n u n d e r r o t o v a t i o n was l o w e r ( P = O.05). T h e r e was no s u c h d i f f e r e n c e in the s p e c i e s h a v i n g deep b u r r o w s , L u m b r i c u s t e r r e s t r i s and A. longa/nocturna, and it c o u l d be a r g u e d that they w e r e able to take refuge below r o t o v a t i o n depth. O t h e r w o r k e r s have a l s o found that the n u m b e r of w o r m s on u n c u l t i v a t e d soil, w h e r e p a r a q u a t has been u s e d to c o n t r o l w e e d s , tend to be g r e a t e r than w h e n the soil has been ploughed and c u l t i v a t e d (36). C a u t i o n m u s t be e x c e r c i s e d in i n t e r p r e t i n g r e s u l t s obtained by e x p u l s i o n m e t h o d s , as the soil structure can affect efficiency. It is l e s s e a s y to a s c r i b e c a u s e s to d i f f e r e n c e s o b s e r v e d on p l o t s of the t h r e e p a r a q u a t r a t e s w i t h i n the s a m e c u l t i v a t i o n type. The l o w e r n u m b e r s o c c u r r e d p r i n c i p a l l y on p l o t s w h e r e the exc e s s i v e l y h i g h r a t e s had b r o u g h t about l i g h t e r v e g e t a t i o n c o v e r . It is h a r d l y s u r p r i s i n g that the 720 k g / h a r a t e , b a r e f o r m u c h of the y e a r w i t h a c o n s e q u e n t r e d u c t i o n in o r g a n i c m a t e r i a l , s h o u l d have an i m p o v e r i s h e d e a r t h w o r m p o p u l a t i o n . The 198 and 120 kg r a t e s had a r e d u c e d c o v e r of both w e e d s and b a r l e y plants in the e a r l y p a r t of the y e a r . It is k n o w n that g r o u n d c o v e r and soil m o i s t u r e are important factors affecting e a r t h w o r m distribution, but d i r e c t t o x i c e f f e c t s of 'free' p a r a q u a t in the soil s o l u t i o n cannot be r u l e d out. The n u m e r i c a l l y d o m i n a n t i m m a t u r e A. c a l i g i n o s a p r e s e n t the c l e a r e s t p i c t u r e , c o r r e l a t i n g w i t h v e g e t a t i o n s p a r s e n e s s . The g r e a t e s t r e d u c t i o n , on the 720 kg r a t e , and that on the 120 kg r a t e , a r e h i g h l y s i g n i f c a n t ( P = O.01) and that on the 198 kg r a t e s i g n i f i c a n t ( P = O.05) c o m p a r e d w i t h t h e i r c o n t r o l s . N u m b e r s of A. c a l i g i n o s a a d u l t s and A. c h l o r o t i c a on the s a m e p l o t s a r e low, but s a m p l e d i s t r i b u t i o n is s u c h that t h e r e is no s t a t i s t i c a l s i g nificance.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
2
number
2
(g/m )
- O.05).
10* 21 32 29 21* 48
45
49
type (P
11** 31* 56 71 33**
111
119
103
* S i g n i f i c a n t l y d i f f e r e n t from untreated of Si Eune c u l t i v a t i o n * * H i g h l y s i g n i f i c a n t l y d i f f e r e n t (P=O.01) + A d u l t s too few f o r s t a t i s t i c a l a n a l y s i s and not i n c l u d e d . XMay i n c l u d e a few speciments of A . rosea ( S a v i g n y ) .
T o t a l biomaes
Total
0 1 5 3 2
15
9
6
43 51
23**
77
93
79
(imm.)X
A. caliginosa
A . c h l o r o t i c a (Savigny) (adult and immature)
1 8**
4 16*
1 2
3
o**
3
1**
6
1**
5
5
(Savigny)
1*
A. caliginosa (adult)
1*
0**
I* 6
4
5
1*
5
6
5
3
(immature)
Lumbricus t e r r e s t r i s
1 1
1
1
2
3
1
1
720
198
90
0
15. cm 120
33
15
cm
0
2
2
Allolobophora longa/ n o c t u m a (immature)*
(adult)
Lumbricus t e r r e s t r i e
(ke/ha)
Depth Paraquat Incorporated into Soil
Paraquat A p p l i e d
XIII
EARTHWORMS FROM THE FRENSflAM SITE 12 MONTHS AFTER APPLICATION OF PARAQUAT AND CULTIVATION, AND 7 MONTHS AFTER DIRECT DRILLING OF BARLEY SEED. EXPRESSED AS N O / M , CALCULATED FROM THE LOGARITHMICALLY TRANSFORMED MEANS OF SAMPLES FROM SIX O.36m AREAS
T A B L E
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334
BOUND
AND CONJUGATED
PESTICIDE
RESIDUES
N u m b e r s of L u m b r i c u s t e r r e s t r i s w e r e s m a l l , but the l o w c a t c h on the 720 and 120 k g p l o t s w a s found to be s t a t i s t i c a l l y s i g nificant. A l l o l o bopho r a long a and A . n o c t u r n a a r e o f t e n d i f f i c u l t to s e p a r a t e , and have b e e n t r e a t e d as one. It c a n be s e e n f r o m the t a l b e that the n u m b e r s of i m m a t u r e s f r o m all t r e a t e d p l o t s a r e all s i g n i f i c a n t l y l o w e r than t h e i r c o n t r o l s . O n the f a c e of it h e r e w o u l d s e e m to be a n effect of p a r a q u a t , but e x p e r i e n c e o n o t h e r s i t e s , w h e r e s u c h a n e f f e c t has not b e e n r e c o r d e d , l e a d s u s to c o n s i d e r t h i s v e r y u n l i k e l y . The n u m b e r s at F r e n s h a m a r e s m a l l ; t h e r e f o r e l e s s r e l i a b l e , and the few a d u l t longa/nocturna found w e r e e q u a l l y d i s t r i b u t e d b e t w e e n the 33 k g r a t e and i t s control. The c o m b i n e d t o t a l s f o l l o w the s a m e p a t t e r n of s i g n f i c a n c e as the i m m a t u r e A. c a l i g i n o s a . T h e bio m a s s r e d u c t i o n s a r e l e s s s t r o n g l y m a r k e d in both amount and s t a t i s t i c a l s i g n i f i c a n c e , b e i n g b e i n g i n f l u e n c e d by the h e a v i e r L. t e r r e s t r i s and A. l o n g a / nocturna. A s earthworms a r e an important means whereby a chemical c a n be t r a n s f e r r e d f r o m the soil to v e r t e b r a t e l i f e , t e s t s w e r e m a d e to d i s c o v e r w h e t h e r p a r a q u a t is c a r r i e d b y w o r m s and if so w h e r e it is s i t u a t e d and if it is a c c u m u l a t e d . P a r a q u a t r e s i d u e s in w o r m s w e r e d e t e r m i n e d at 8 t r i a l s i t e s . P a r a q u a t w a s a p p l i e d at the n o r m a l r a t e (1 o r 2 kg/ha) and at 112 k g / h a . C r o p s of g r a s s o r c e r e a l s w e r e g r o w n by d i r e c t d r i l l i n g ( z e r o t i l l a g e ) o r a f t e r the soil h a d b e e n r o t o v a t e d o r ploughed. W o r m s w e r e c o l l e c t e d by the f o r m a l d e h y d e m e t h o d , at i n t e r v a l s b e t w e e n 2-12 m o n t h s a f t e r p a r a q u a t a p p l i c a t i o n , and analyzed f o r p a r a q u a t r e s i d u e s . A t o t a l of 14 d i f f e r e n t a p p l i c a t i o n r a t e / c r o p / m e t h o d of c u l t i v a t i o n / t r i a l s i t e t r e a t m e n t s w e r e s t u d i e d . T y p i c a l w o r m r e s i d u e data, f o r the B r o a d r i c k s t r i a l , a r e g i v e n in T a b l e X I V . T y p i c a l soil r e s i d u e data a r e g i v e n in T a b l e X V . D e t a i l s of the B r o a d r i c k s t r i a l have a l r e a d y b e e n s t a t e d . In all t r i a l s , p a r a q u a t r e s i d u e s in w o r m s w e r e the s a m e , o r m o r e g e n e r a l l y m u c h l e s s , t h a n in the soil. T h u s , t h e r e is no t e n d e n c y f o r p a r a q u a t to a c c u m u l a t e in w o r m s . A f u r t h e r i n v e s t i g a t i o n w a s m a d e to d e t e r m i n e w h e t h e r the p a r a q u a t r e s i d u e s a c t u a l l y e n t e r the body of the w o r m o r w h e t h e r they r e m a i n bound to soil in the gut. L a r g e n u m b e r s of w o r m s w e r e c o l l e c t e d f r o m the two 112 k g / h a t r e a t m e n t s in the B r o a d r i c k s t r i a l and b u l k e d t o g e t h e r . T h e w o r m s , m o s t l y L u m b r i c u s t e r r e s t r i s , w e r e opened and the gut contents r e m o v e d b y a s t r o n g j e t of w a t e r . T h e gut contents and c l e a n e d w o r m b o d i e s w e r e a n a l y z e d f o r p a r a q u a t r e s i d u e s . The gut contents c o n t a i n e d
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
22.
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Bound Paraquat Residues
T A B L E
335
XIV
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PARAQUAT RESIDUES IN WORMS FROM THE BROADRICKS TRIAL
Cultivation Treatment Before Paraquat Application
Time After Paraquat Application (Months)
Paraquat Residues in Whole Worms (ug/g Fresh Weight)
2.24
None
12
O.60
2.24
Rotovated
12
O.83
112
None
12
62.9
112
Rotovated
5
90.8
112
Rotovated
12
28.7
Paraquat Applied
T A B L E
XV
PARAQUAT RESIDUES IN BROADRICKS SOIL (fG PARAQUAT/G SOIL); PARAQUAT WAS APPLIED OCTOBER 26, 1964
Paraquat Application Rate (kg/ha)
Cultivation Treatment Before Paraquat Application
Date Soil Sampled (Dav/Month/Year)
Soil Depth (cm) 0-2.5 2.5-5 5-7.5 7.5-10
2.24
Rotovated
12.3.65
5.7
1.1
O.1
O.1
2.24
Rotovated
10.2.66
4.2
1.5
O.7
O.2
2.24
None
12.3.65
6.6
O.4
O.3
O.3
2.24
None
1.3.66
3.5
1.2
O.8
O.3
112
Rotovated
12.3.65
268
42
6
2
112
Rotovated
10.2.66
192
90
34
9
112
None
12.3.65
356
14
7
2
112
None
1.3.66
206
45
20
7
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
BOUND AND CONJUGATED PESTICIDE RESIDUES
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336
111 μg p a r a q u a t / g w h i l e the c l e a n e d b o d i e s c o n t a i n e d o n l y O. 28 /ug p a r a q u a t / g f r e s h w e i g h t , and e v e n t h i s c o u l d have b e e n due to i m p e r f e c t w a s h i n g out of the gut. B o u n d p a r a q u a t is c l e a r l y not s i g n i f i c a n t l y a b s o r b e d by the w o r m b o d i e s . T h i s c o n c l u s i o n is s u p p o r t e d by e x p e r i m e n t s on the r a p i d e l i m i n a t i o n of p a r a q u a t f r o m living worms. Specimens were collected from a straw b e r r y f i e l d at F e r n h u r s t , E n g l a n d w h i c h had r e c e i v e d 5 a n n u a l 2 k g / h a a p p l i c a t i o n s , the l a s t dose h a v i n g b e e n about 3 m o n t h s b e f o r e . S o m e w h o l e w o r m s w e r e a n a l y z e d and found to c o n t a i n 1. 71 (ug/g f r e s h w e i g h t of p a r a q u a t . O t h e r l i v i n g w o r m s w e r e p l a c e d in u n t r e a t e d soil f o r 36 h o u r s , then r e c o v e r e d and ana l y z e d . T h e r e w e r e no d e t e c t a b l e r e s i d u e s (< O.1/ug/g) in the worms. It is c o n c l u d e d that bound p a r a q u a t soil r e s i d u e s a r e not ab s o r b e d by w o r m t i s s u e . A l s o , it is e x t r e m e l y u n l i k e l y that any s u c h p a r a q u a t i n g e s t e d by a w o r m p r e d a t o r c o u l d a f f e c t it in any way. 5.
U N A V A I L A B I L I T Y OF B O U N D P A R A Q U A T S O I L R E S I D U E S TO M I C R O A R T H R O P O D S
E l e v e n t r i a l s have shown that bound p a r a q u a t r e s i d u e s in s o i l s have no e f f e c t on m i c r o a r t h r o p o d s . V e r y l a r g e p a r a q u a t r e s i d u e s , w h i c h r e s u l t in 'free' p a r a q u a t in the e q u i l i b r i u m soil s o l u t i o n ( g r e a t e r than about O.01(ug/ml), c a n r e d u c e the n u m b e r of m i c r o a r t h r o p o d s , but the e f f e c t m a y be due to changes in v e g e t a t i o n c o v e r r a t h e r t h a n a d i r e c t t o x i c e f f e c t of the p a r a q u a t . A soil m i c r o a r t h r o p o d s a m p l e is n o r m a l l y o b t a i n e d by t a k i n g 4 soil c o r e s 25 m m d i a m e t e r χ 150 m m deep and b u l k i n g t h e m . T h i s is done in p r e f e r e n c e t o t a k i n g s i n g l e l a r g e c o r e s a s it r e d u c e d s a m p l i n g e r r o r c a u s e d by f a u n a l a g g r e g a t i o n s . The soil is s t o r e d at -15°C b e f o r e the m i c r o a r t h r o p o d s a r e e x t r a c t e d by a w a s h i n g , f l o t a t i o n and d i f f e r e n t i a l w e t t i n g t e c h n i q u e . M i t e s and s p r i n g t a i l s f o r m the b u l k of the s a m p l e s , and of t h e s e the M e s o s t i g m a t a , m a i n l y p r e d a t o r s , and the C r y p t o s t i g m a t a and C o l l e m b o l a , p r i n c i p a l l y d e t r i t u s and fungus f e e d e r s , a r e c u r r e n t l y c h o s e n f o r i d e n t i f i c a t i o n to s p e c i e s l e v e l . In s o m e of the e a r l y s t u d i e s the g r o u p s w e r e not so d e t a i l e d . Of the 11 s i t e s w h e r e soil m i c r o a r t h r o p o d o b s e r v a t i o n s on p a r a q u a t t r e a t e d p l o t s have b e e n m a d e , o n l y two a r e quoted h e r e . A s w i t h the e a r t h w o r m s t u d i e s , r e s u l t s f o r o n l y a few s a m p l i n g o c c a s i o n s a r e g i v e n . G r o u p s s e l e c t e d f o r the t a b l e s i n c l u d e some w h i c h are e x c l u s i v e l y euedaphic, p r i n c i p a l l y hemiedaphic, and those of m i x e d h a b i t s o r no k n o w n soil depth p r e f e r e n c e .
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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22.
RILEY
E T A L .
Bound Paraquat Residues
337
One of the s t u d i e s w a s done o n B r o a d r i c k s f i e l d at J e a l o t t ' s H i l l R e s e a r c h S t a t i o n . B r i e f d e t a i l s of the t r i a l have b e e n g i v e n in the e a r t h w o r m s e c t i o n . The c o n d e n s e d r e s u l t s of a s s e s s m e n t on t h r e e o c c a s i o n s d u r i n g the first y e a r a r e shown in T a b l e X V I . The two-month s a m p l i n g m a y be c o n s i d e r e d l e s s r e l i a b l e than later work, as single large cores were used for sampling, and the e x t r a c t i o n technique was s t i l l b e i n g d e v e l o p e d . The figures w e r e not s u b j e c t e d to s t a t i s t i c a l a n a l y s i s . The r e s u l t s show no m o r e v a r i a t i o n b e t w e e n t r e a t m e n t s than m i g h t be e x p e c t e d f r o m the s a m p l i n g r e g i m e and plot h i s t o r i e s . The n u m b e r of A s t i g m a t a ( T y r o p h a g u s spp. and S c h w i e b i a sp. ) on the n o n - c u l t i v a t e d 112 kg p l o t s a f t e r 12 m o n t h s is e x c e p t i o n a l l y h i g h , but t h i s g r o u p is n o t o r i o u s l y e r r a t i c in o c c u r r e n c e . A n o t h e r t r i a l , of w h i c h d e t a i l s have a l r e a d y b e e n g i v e n , w a s done at F r e n s h a m . M i c r o a r t h r o p o d s w e r e s a m p l e d at the s a m e t i m e as the e a r t h w o r m s , and the s a m e g e n e r a l r e m a r k s about the v e g e t a t i o n and p h y s i c a l e f f e c t s a p p l y . A l l M e s o s t i g m a t a , C r y p t o s t i g m a t a and C o l l e m b o l a w e r e i d e n t i f i e d to s p e c i e s , a n d o t h e r a n i m a l s to h i g h e r c a t e g o r i e s . F o r the p u r p o s e of t h i s p a p e r 9 s p e c i e s of d i f f e r e n t l i f e - f o r m s and h a b i t s have b e e n sel e c t e d , and 6 m a i n g r o u p s . A n a l y s i s of v a r i a n c e was done o n l o g a r i t h m i c a l l y t r a n s f o r m e d data. P o p u l a t i o n e s t i m a t e s b a s e d on the c o r r e c t e d m e a n s a r e shown in T a b l e X V I I . The e f f e c t of r o t o v a t i o n a v e r a g e d o v e r r a t e s is m u c h l e s s m a r k e d t h a n f o r the e a r t h w o r m s . In o n l y t h r e e g r o u p s (Rhodac a r u s r o s e u s , t o t a l M e s o s t i g m a t a and L e p i d o c y r t u s c y a n e u s ) w a s the s m a l l r e d u c t i o n in n u m b e r s found to be s t a t i s t i c a l l y s i g n i f i cant. It has b e e n d i s c o v e r e d in s o m e o t h e r t r i a l s that d i s t u r b a n ce of the h a b i t a t b y ploughing and c u l t i v a t i o n has an a p p r e c i a b l e effect on m a n y soil m i c r o a r t h r o p o d s . D i s t u r b a n c e e f f e c t s w o u l d be e x p e c t e d to be l e s s on the r e l a t i v e l y u n s t r a t i f i e d sandy soil at Frensham. The c o m b i n e d s p e c i e s of M e s o s t i g m a t a , a p r e d a t o r y g r o u p , show a c o n s i d e r a b l e and s i g n i f i c a n t r e d u c t i o n o n l y on the 720 k g r a t e . S e v e r a l i n d i v i d u a l s p e c i e s a r e a b s e n t o r p r e s e n t o n l y in s m a l l n u m b e r s on these p l o t s , but u n e v e n d i s t r i b u t i o n p r e c l u d e s s t a t i s t i c a l significance. Rhodacarellus s i l e s i a c u s presents some s o m e w h a t a n o m a l o u s r e s u l t s . The low n u m b e r s on the 120 k g r a t e a r e s t a t i s t i c a l l y s i g n i f i c a n t c o m p a r e d w i t h the u n t r e a t e d p l o t s of the s a m e c u l t i v a t i o n type. O n the 90 and 198 k g r a t e s the n u m b e r s a r e s i g n i f i c a n t l y h i g h e r than t h e i r c o n t r o l . A l i n k m i g h t e x i s t w i t h the n e m a t o d e s (not s a m p l e d ) on w h i c h t h i s euedaphic s p e c i e s is b e l i e v e d to f e e d .
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
Prostigmata
β
euedaphlc g r o u p s .
T o t a l Microarthropods+
T o t a l Collembola
Η
Œ
288 409
398
580
Heraiedaphic.
165
7 122
41 635
507
1
3
8 195
8
0 11
1
91
13
0
369
214
3
1
171 13
21 5
35 0
1
42 90
63 66
2 39
0
1
4
4
793 127 425
16 273
0
464
19
12 225 0 21
4
15 6
7 148
5
42 0
0 132
0
3 13 22 469
8
43 43
70 73
334 40
418 124 128
561 203 353
310 221 641
465 127 154
168 136
5 503
0
0 5
0 1
1
1 3
3
8
2 31
Β Μ
Ο
ι 413 553
Ο
Ο
8
ο
β
0
8
31
11
ι 14
35 20
22 7
25
12 51
112 6
46 ι
17 3
3 21
2
λ
3
3
53 65
10 28 50 63
33 34
26
33
5
31
40
12
2
2.24 6
12
0 6
12 47 49 79 40 6 5 14
8
2
5
53
357
48
25
56
0
II
112 6
2
R O T O V A T E D
+ i n c l u d e s remaining i n s e c t s and the m y r l a p o d s .
529
265
2
0
1
2
0
H Sminthuridae
5
1
3
3
0
H Entomobryidae
468
239
35 14
22
15
2
4
25
20
6 8
42 15
49 0
3
235
361
5
24
0
13
2
3 29
Isοtornidae
59 3
98 8
Ε Onychiuridae
Hypogas t r u r i d a e
Total
T o t a l Astigmata
43
12
52 49
77
2.24 6
NON Ε
90 110
6 26
30 51
61 58
18 28
T o t a l Mesostigmata
T o t a l Cryptostigmata
5
22
53
3
Ε Rhodacarldae
2
12
0 6
2
2
Months A f t e r A p p l i c a t i o n
Paraquat A p p l i e d (kg/ha)
C u l t i v a t i o n Before A p p l i c a t i o n
Ε
XVI
MICROARTHROPODS FROM THE BROADRICKS SITE ASSESSED AT INTERVALS UP TO A YEAR AFTER PARAQUAT APPLICATION. EXPRESSED AS HUNDREDS/m , CONVERTED FROM THE UNTRANSFORMED MEANS OF 6 SAMPLES PER TREATMENT, EACH FROM 4 SOIL CORES OR THEIR EQUIVALENT
T A B L E
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22.
339
Bound Paraquat Residues
RILEY ET AL.
T A B L E
XVII
MICROARTHROPODS FROM THE FRENSHAM SITE 12 MONTHS AFTER APPLICATION OF PARAQUAT AND CULTIVATION, AND 7 MONTHS AFTER DIRECT DRILLING OF BARLEY SEED. (EXPRESSED AS HUNDREDS/m , CALCULATED FROM THE LOGARITHMICALLY TRANSFORMED MEANS OF 6 SAMPLES PER TREATMENT, EACH SAMPLE FROM 4 SOIL CORES.)
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2
Depth Paraquat Incorporated i n t o Soil
15 cm
2 cm
Paraquat A p p l i e d (kg/ha)
0
15
33
120
90
198
720
Veigaia planicola
2
6
1
1
3
2
0
Hypoaspis a c u l e i f e r (Canestrini)
3
3
2
4
6
6
0
Ε Rhodacarus roseus Oudemans
13
16
19
24
12
24
10
Ε Rhodacerellus s i l e s i a c u s (Willmann
15
9
15
11*
18**
T o t a l Mesostigmata
77
70
85
68
46
56
76
1
1
0
1
2
0
0
0
85
58
(Berlese)
T o t a l Cryptostigmata
4*
2
208** 50
16
0 15*
T o t a l Astigmata
12
30
44
T o t a l Prostigmata
31
25
25
61
19
23
23
5
Ε T u l i b e r g i a spp
342
199
290
225
177
314
281
82*
H Cryptopygus thermophilus (Axelson)
147
74
109
38* 183
90
60
8**
9
7
4
13
15
14
19
4
24
30
29
8* 46
21
28
5**
8
8
7
7
7
3
0**
T o t a l Collembola
649
458
596
386* 676
569
461
116**
T o t a l microarthropods+
812
693
825
913
810
710
673
240**
Ε Isotomodes productus (Axelson Ε Folsomia Candida Willem H L e p i d o c y r t u s cyaneus Tuliberg
11
* S i g n i f i c a n t l y d i f f e r e n t from untreated o f same c u l t i v a t i o n type (P , O.05). * * H i g h l y s i g n i f i c a n t l y d i f f e r e n t from untreated o f same c u l t i v a t i o n type
(P = O.01). Ε = euedaphlc s p e c i e s . Η hemiedaphic. + = i n c l u d e s remaining i n s e c t s and the myriapods. 3
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T h e r e is a p a u c i t y of C r y p t o s t i g m a t a o n the s i t e , a n d num b e r s a r e too l o w a n d i r r e g u l a r to be m e a n i n g f u l . The A s t i g m a t a , often a s s o c i a t e d w i t h d e c a y i n g vegetable m a t t e r , a r e r e p r e s e n t e d at F r e n s h a m c h i e f l y by T y r o p h a g u s spp. The l a r g e p o p u l a t i o n o n the 120 kg /ha p l o t s is h i g h l y s i g n i f i c a n t l y g r e a t e r t h a n that on the c o n t r o l p l o t s . C o m p a r i s o n m a y be m a d e w i t h the l a r g e n u m b e r s on the 12 m o n t h d i r e c t d r i l l e d h i g h r a t e p l o t s at B r o a d r i c k s , but no d e f i n i t e e x p l a n a t i o n c a n be o f f e r e d . The P r o s t i g m a t a , of w h i c h P y e m o t i d a e is the d o m i n a n t f a m i l y h e r e , has l o w n u m b e r s on the 720 k g p l o t s , but not s i g n i f i c a n t l y l o w e r than o n the c o n t r o l p l o t s . A m o n g the euedaphic C o l l e m b o l a T u l l b e r g i a spp. have s i g n i f i c a n t l y l o w e r n u m b e r s on the 720 k g r a t e . A t t h i s p a r a q u a t r a t e Is otomode s p r o d u c t u s w a s l o w but not s i g n i f i c a n t l y l o w e r t h a n o n the c o n t r o l p l o t s . T h e e f f e c t w a s s t r o n g e r w i t h F o l s o m i a Can d i d a , w h e r e the r e d u c t i o n o n the 120 k g r a t e w a s s i g n i f i c a n t (P = O.05) a n d on the 720 k g r a t e h i g h l y s i g n i f i c a n t ( P = O.01). C r y p t o p y g u s t h e r m o p h i l u s , abundant at F r e n s h a m , is a s u r face-dwelling i s o t o m i d highly sensitive to vegetation cover. The v e r y g r e a t a n d h i g h l y s i g n i f i c a n t r e d u c t i o n s o n the a l m o s t b a r e 720 k g p l o t s w a s t h e r e f o r e p r e d i c t a b l e . T h e n u m b e r s w e r e a l s o low o n the 120 a n d the 198 k g r a t e s , though the l a t t e r w a s not s t a t i s t i c a l l y significant. Lepidocyrtus cyaneus, another surface s p e c i e s , but not c o m m o n in N o v e m b e r , w a s a b s e n t a l t o g e t h e r on the 720 k g p l o t s . T a k e n a s a w h o l e , the C o l l e m b o l a o n the 720 k g r a t e w e r e about a f i f t h of the c o n t r o l p l o t s p o p u l a t i o n , o n the 120 k g m o r e t h a n h a l f , a n d on the 198 k g r a t e m a r g i n a l l y but not s i g n i f i c a n t l y less. In c o n c l u s i o n , it m a y be s a i d that no c o n s i s t e n t e f f e c t s on soil m i c r o a r t h r o p o d s have b e e n detected at n o r m a l a p p l i c a t i o n r a t e s of p a r a q u a t in any of the 11 t r i a l s . S u c h changes as have been recorded are associated with regimes involving mechanical d i s t u r b a n c e o r e x c e s s i v e r a t e s c a u s i n g a l t e r a t i o n s in v e g e t a t i o n cover. 6. U N A V A I L A B I L I T Y O F B O U N D P A R A Q U A T S O I L RESIDUES TO MICROORGANISMS B o u n d p a r a q u a t r e s i d u e s in soil a r e u n a v a i l a b l e t o m i c r o o r g a n i s m s . M i c r o o r g a n i s m s d i f f e r g r e a t l y in t h e i r s e n s i t i v i t y to paraquat; the l o w e s t c o n c e n t r a t i o n w h i c h i n h i b i t s g r o w t h o r a c t i v i t y of m i c r o o r g a n i s m s in l i q u i d c u l t u r e s r a n g e s f r o m O.1 to 50,000 μ g / m l p a r a q u a t . I n s o i l s , r e s i d u e s up t o s e v e r a l h u n d r e d μg/g have no s i g n i f i c a n t e f f e c t s on m i c r o o r g a n i s m s , e v e n p a r a -
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quat s e n s i t i v e o r g a n i s m s s u c h as A z o t o b a c t e r spp. S o i l s c o n t a i n m i c r o o r g a n i s m s , p a r t i c u l a r l y L i p o m y c e s spp., w h i c h r a p i d l y degrade p a r a q u a t in l i q u i d c u l t u r e s . H o w e v e r , in soil bound p a r a q u a t is u n a v a i l a b l e to m i c r o o r g a n i s m s ; c o n s e q u e n t l y , these r e s i d u e s a r e d e g r a d e d e x t r e m e l y s l o w l y o r not at all. E f f e c t of P a r a q u a t o n M i c r o o r g a n i s m s The e f f e c t of p a r a q u a t on a w i d e range of m i c r o o r g a n i m s h a s b e e n e x t e n s i v e l y s t u d i e d in both l i q u i d c u l t u r e s a n d soil (37 t o 66). In l i q u i d c u l t u r e s the l o w e s t c o n c e n t r a t i o n w h i c h a f f e c t s m i c r o o r g a n i s m s r a n g e s f r o m about O.1 t o 50,000 p g / m l p a r a q u a t . F o r e x a m p l e , s o m e s t r a i n s of A z o t o b a c t e r a r e c o m p l e t e l y in h i b i t e d b y O.5 p g / m l (50), s o m e f u n g i w i l l g r o w in 1, 000 μg/ml (64) a n d C o r y n e b a c t e r i u m f a s c i a n s c a n be " t r a i n e d " to t o l e r a t e 50,000 μg/ml (6£). The e f f e c t of p a r a q u a t on the n u m b e r and a c t i v i t y of m i c r o o r g a n i s m s in soil is v e r y m u c h l e s s than in l i q u i d c u l t u r e s . F o r e x a m p l e , S z e g i (53) showed that the a c t i v i t y of 20 c e l l u l o l y t i c m i c r o s c o p i c f u n g i w e r e s e v e r e l y r e d u c e d b y 2-5 μg/τήί p a r a q u a t . H o w e v e r , in sand a n d C h e r n o z e m s o i l s the l o w e s t c o n c e n t r a t i o n of p a r a q u a t w h i c h s i g n i f i c a n t l y r e d u c e d d e c o m p o s i t i o n of c e l l u l o s e w a s 500 and 1000 μg/g p a r a q u a t , r e s p e c t i v e l y (53). T h e p u b l i s h e d data a l s o shows that s e v e r a l h u n d r e d Mg/g p a r a q u a t has to be a p p l i e d t o m o s t s o i l s b e f o r e it s i g n i f i c a n t l y a f f e c t s the n u m b e r a n d a c t i v i t y of soil m i c r o o r g a n i s m s . A n y e f f e c t s at l o w e r c o n c e n t r a t i o n s a r e s m a l l a n d t r a n s i t o r y . T h u s , it c a n be c o n c l u d e d that bound p a r a q u a t h a s no s i g n i f i c a n t e f f e c t s o n soil m i c r o o r g a n i s m s . E v e n w h e n t r a c e s of " f r e e " p a r a q u a t r e s i d u e s a r e p r e s e n t in the soil s o l u t i o n , e f f e c t s o n m i c r o o r g a n i s m s a r e often s m a l l . F o r e x a m p l e , at a f i e l d t r i a l s i t e at O c o e e , F l o r i d a the soil h a s e x c e p t i o n a l l y l o w T i g h t l y B o u n d and S t r o n g A d s o r p t i o n ' c a p a c i t y of 3 a n d 6 μg/g, r e s p e c t i v e l y ( T a b l e X I ) . How e v e r , a p p l i c a t i o n s of p a r a q u a t at 5. 6, 22.4 a n d 112 kg/ha h a d o n l y s m a l l e f f e c t s o n the n u m b e r s of a c t i n o m y c e t e , b a c t e r i a l and f u n g a l p r o p a g u l e s (37); these s m a l l e f f e c t s c o u l d have b e e n c a u s e d by r e d u c e d plant g r o w t h r a t h e r t h a n d i r e c t t o x i c e f f e c t s of paraquat. The l a c k of e f f e c t s of p a r a q u a t soil r e s i d u e s on m i c r o o r g a n i s m s is w e l l i l l u s t r a t e d b y s t u d i e s o n n i t r o g e n t r a n s f o r m a t i o n s in soil. T u and B o l l e n (55, 56) showed that a m m o n i f i c a t i o n of native soil o r g a n i c m a t t e r and added peptone w a s not a p p r e c i a b l y a f f e c t ed b y O.25, O.5, 2.5 o r 25 |ug/g p a r a q u a t in two s i l t l o a m s , a s i l t y c l a y l o a m a n d a sandy l o a m . 1
1
!
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CONJUGATED PESTICIDE
RESIDUES
In l i q u i d c u l t u r e s o l u t i o n s p a r a q u a t is h i g h l y i n h i b i t o r y of the o x i d a t i o n of N H 4 t o N O 2 " and N O 3 " by N i t r o s o m o n a s and N i t r o b a c t e r (39)* H o w e v e r , m a n y w o r k e r s have s h o w n that the c o n v e r s i o n of added N H 4 to N O 3 " and n i t r i f i c a t i o n of soil o r g a n i c m a t t e r is not s i g n i f i c a n t l y a f f e c t e d by p a r a q u a t r e s i d u e s . T u and B o l l e n (5j>, 56) s h o w e d that O.25 t o 25 (ag/g p a r a q u a t in the 4 s o i l s l i s t e d in the p r e v i o u s p a r a g r a p h d i d not s i g n i f i c a n t l y a f f e c t the c o n v e r s i o n of N H 4 to N O 3 " . D e b o n a and A u d u s (39) a l s o s h o w e d that 50 and 100 ug/g p a r a q u a t in a n u n c l a s s i f i e d soil d i d not s i g n i f i c a n t l y a f f e c t the c o n v e r s i o n of N H ^ * to N O 2 " by N i t r o s o m o n a s and NC>2~ to N O 3 " by N i t r o b a c t e r . 500 μg/g s l i g h t l y r e d u c e d n i t r i f i c a t i o n and 1000 |ug/g r e d u c e d n i t r i f i c a t i o n by about t w o - t h i r d s . N i t r i t e d i d not a c c u m u l a t e in the soil s u g g e s t i n g the r e d u c e d n i t r i f i c a t i o n w a s due to p a r a q u a t a f f e c t i n g N i t r o s o m o n a s r a t h e r t h a n N i t r o b a c t e r . A n d e r s o n and D r e w (65) s h o w e d that 4 and 40 pg/g p a r a q u a t in a c a l c a r e o u s l o a m had no s i g n i f i c a n t e f f e c t s on the c o n v e r s i o n of NH4"*" t o N O 2 " and N O 3 " . T h o r n e b u r g and T w e e d y (54) a l s o s h o w e d that 6 and 12 μg/g p a r a quat in a s i l t l o a m soil d i d not a f f e c t the c o n v e r s i o n s of NH4+ to +
+
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+
NO3-.
G i a r d i n a et„ a l (42) s t u d i e d the e f f e c t of p a r a q u a t on the u r e a s e a c t i v i t y of soil; u r e a s e is r e s p o n s i b l e f o r the c o n v e r s i o n of u r e a to N H 4 + . T h e y s h o w e d that 100, 200 and 400 μg/g para quat in a c l a y l o a m soil d i d not a f f e c t i t s u r e a s e a c t i v i t y . N i t r o g e n f i x i n g o r g a n i s m s v a r y w i d e l y in t h e i r s e n s i t i v i t y to p a r a q u a t in l i q u i d c u l t u r e s . The g r o w t h and Ν-fixing c a p a b i l i t i e s of s o m e s t r a i n s of A z o t o b a c t e r spp a r e s e v e r e l y i n h i b i t e d by as l o w as O.1 μ g / m l w h i l e m a n y s t r a i n s of R h i z o b i u m spp a r e not a f f e c t e d by 50 p g / m l a n d s o m e R h i z o b i u m spp w i l l t o l e r a t e m o r e t h a n 100 u g / m l (44, J>0, 52). In soil the e f f e c t of p a r a q u a t on n i t r o g e n f i x i n g o r g a n i s m s is m u c h l e s s t h a n in l i q u i d c u l t u r e s . S z e g i et. a l . (52) found that 1000 μg/g p a r a q u a t d i d not a f f e c t the n u m b e r s of A z o t o b a c t e r in c a l c a r e o u s sand and c h e r n o z e m s o i l s . A n d e r s o n and D r e w (65) s h o w e d that the a p p l i c a t i o n of 1.1 and 11 k g / h a p a r a q u a t to a g r a s s - c l o v e r s w a r d on a c a l c a r e o u s l o a m soil had o n l y s m a l l e f f e c t s on the n u m b e r of A z o b a c t e r spp in the soil. T h e y a t t r i b u t e d the s m a l l e f f e c t s to c h a n g e s in the v e g e t a t i o n c o v e r and c o n s e q u e n t c h a n g e s in soil m o i s t u r e r a t h e r t h a n a d i r e c t e f f e c t of p a r a q u a t . It is c o n c l u d e d that bound p a r a q u a t does not have any s i g n i f i c a n t e f f e c t s on n i t r o g e n t r a n s f o r m a t i o n s in soil.
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
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22.
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E T A L .
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343
E f f e c t of M i c r o o r g a n i s m on P a r a q u a t S o i l s c o n t a i n o r g a n i s m s c a p a b l e of d e g r a d i n g p a r a q u a t in n u t r i e n t c u l t u r e s ; f o r e x a m p l e , L i p o m y c e s spp (62), C o r y n e b a c t e r i u m f a s c i a n s (62), C l o s t r i d i u m p a s t e u r i a n u m (62) and a n u n i d e n t i f i e d b a c t e r i a l i s o l a t e (64). A l s o , it has b e e n r e p o r t e d that a c t i n o m y c e t a l i s o l a t e s d e g r a d e p a r a q u a t (67): h o w e v e r , we have b e e n unable to c o n f i r m t h i s . L i p o m y c es spp ( p r o b a b l y L i p o m y c es s t a r k e y i ) is p a r t i c u l a r l y e f f e c t i v e and r e a d i l y de g r a d e s p a r a q u a t u n d e r a w i d e range of t e m p e r a t u r e and p H v a l u e s (68). It w i l l g r o w and d e g r a d e p a r a q u a t in a w i d e range of n u t r i e n t b r o t h s and c a n u s e p a r a q u a t as its s o l e n i t r o g e n s o u r c e ; h o w e v e r , it r e q u i r e s a n a l t e r n a t i v e c a r b o n s o u r c e f o r s y n t h e s i s of the p a r a q u a t - c a t a b o l i z i n g s y s t e m (68). L i p o m y c es spp is w i d e l y d i s t r i b u t e d in s o i l s t h r o u g h o u t the w o r l d ( J . R. A n d e r s o n , I C I P l a n t P r o t e c t i o n D i v i s i o n u n p u b l i s h e d data). The p e r s i s t e n c e of p a r a q u a t in s o i l s has b e e n e x t e n s i v e l y s t u d i e d (25, and JQ to 75) p l u s v e r y e x t e n s i v e u n p u b l i s h e d I C I and C h e v r o n t r i a l s in both the l a b o r a t o r y and f i e l d w i t h both ^ C l a b e l l e d and u n l a b e l l e d p a r a q u a t ) . T h e s e t r i a l s show that bound p a r a q u a t is not d e g r a d e d , e v e n w h e n the s o i l s c o n t a i n o r g a n i s m s , s u c h as L i p o m y c es spp, c a p a b l e of d e g r a d i n g p a r a q u a t in c u l t u r e s o l u t i o n s . Itisc o n c l u d e d that bound r e s i d u e s a r e not a v a i l a b l e to m i c r o o r g a n i s m s . The f o l l o w i n g pot e x p e r i m e n t i l l u s t r a t e s t y p i c a l r e s u l t s of s t u d i e s on the p e r s i s t e n c e of bound p a r a q u a t r e s i d u e s in soil. F o u r s o i l s ( T a b l e X V I I I ) w e r e t r e a t e d w i t h p a r a q u a t and p l a c e d in 5 L p l a s t i c b u c k e t s w i t h d r a i n a g e h o l e s in the bottom. T h e s a m p l e s w e r e kept o u t s i d e u n p r o t e c t e d f r o m the w e a t h e r and r e c e i v e d a m i n i m u m of 7 c m of w a t e r p e r month. A t i n t e r v a l s , s a m p l e s w e r e e x t r a c t e d w i t h 18 Ν H 2 S O 4 and the p a r a q u a t m e a s u r e d c o l o r i m e t r i c a l l y a f t e r a r e s i n c l e a n u p and r e d u c t i o n w i t h a l k a l i n e d i t h i o n i t e (24). R e s u l t s a r e s u m m a r i z e d in T a b l e XLX. T h r e e of the 4 s o i l s t r e a t e d w i t h 4 to 50 μg/g p a r a q u a t showed no l o s s of p a r a q u a t a f t e r 4 1/2 y e a r s . One sand s a m p l e t r e a t e d at 18 μg/g p a r a q u a t s h o w e d a 2 5 % l o s s of p a r a q u a t a f t e r 4 1/2 y e a r s . H o w e v e r , l e a c h i n g data i n d i c a t e s the l o s s in the sand was p r o b a b l y due to l e a c h i n g . T w o o t h e r sand s a m p l e s t r e a t e d at 4 and 11 f i g / g p a r a q u a t d i d not show any l o s s in 4 1/2 y e a r s .
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T A B L E
XVIII
CHARACTERISTICS OF SOILS USED IN OUTDOOR POT EXPERIMENT
Soil Origin
Soil Type
% Clay
Florida
Sand
1
Florida
Muck
-
% Sand 97
% Silt 2
Cation Exchange Capacity (Meq/100 g Soil)
7. Organic Matter
PH
O.5
7.0
1.4
Approx.
3.3
112.7
100 Calif.
Loam A
16
47
37
1.3
6.5
33.2
Calif.
Loam Β
12
46
42
3.3
5.6
22.4
26
4
70
3.8
7.7
16.2
Hawaii
S i l t Loam
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XLX
PARAQUAT SOIL RESIDUES IN OUTDOOR POT EXPERIMENT
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(jug paraquat/g
3
soil)
MONTHS AFTER TREATMENT 0
Sample
1-2
3-4
7-9
12.9
11.7
11.3
14-16
22-24
38-40
11.7
10.2
13.0
53-55
(c) 1 (b) 2
Sand
11.2
4.41
3.83
4.10
4.01
4.77
4.08
4.15
(b)
Muck
(c) 4
Loam A
47.0
53.7
55.1
53.0
46.7
5
14.5
16.0
16.4
18.5
13.7
13.2
17.4
' 18.8
(c) 6
14.0
15.6
12.9
17.5
15.0
17.1
13.9
16.6
(c)
Loam Β
(b) 6.29 (b) 8
24.3
4.48
21.6
3.53
16.5
4.57
14.6
5.08
15.8
3.21
16.8
4.52
18.7
(b) 4.34
5.54
5.98
4.93
3.79
5.18
3.91
S i l t Loam (b) 10
19.4
18.2
(a)
Average of duplicate analyses.
(b)
Paraquat bis-methyl s u l f a t e .
(c)
Paraquat dichloride
16.8
15.4
14.3
18.3
Kaufman et al.; Bound and Conjugated Pesticide Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1976.
17.0
346
BOUND AND
CONJUGATED PESTICIDE
RESIDUES
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 11, 2017 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0029.ch022
7. L O N G T E R M C O N S E Q U E N C E S O F REPEATED PARAQUAT APPLICATIONS The long t e r m s a f e t y of the r e p e a t e d use of p a r a q u a t is w e l l i l l u s t r a t e d by a t r i a l c o n d u c t e d in S o u t h A f r i c a on an e x t r e m e l y sandy soil w h i c h c o n t a i n s o n l y 1% c l a y . In an eight y e a r p e r i o d o v e r 20 a p p l i c a t i o n s (total 15. 6 k g / h a p a r a q u a t ) have b e e n m a d e to c o n t r o l w e e d s in a c o m m e r c i a l v i n e y a r d . The soil r e s i d u e s have had no e f f e c t on the v i n e s o r b a r l e y and L e m n a t e s t c r o p s . The e x p e r i m e n t was s t a r t e d in 1965, to study m e t h o d s of c o n t r o l l i n g w e e d s in v i n e s . The t r e l l i s e d B a r l i n k a t a b l e g r a p e s , 27 y e a r s o l d in 1973, a r e i r r i g a t e d . A n a t u r a l w e e d c o v e r is a l l o w e d to d e v e l o p in the w i n t e r . P a r a q u a t is u s e d to c o n t r o l w e e d s in the s u m m e r ; o c c a s i o n a l l y the h e r b i c i d e diquat is a l s o a p p l i e d . B e t w e e n 2 and 4 a p p l i c a t i o n s of p a r a q u a t a r e u s e d e a c h s e a s o n ; r a t e s of a p p l i c a t i o n r a n g e d f r o m O.3 to 1.0 k g / h a . The soil c o n t a i n s 9 8 % sand, 1% c l a y and < 1% o r g a n i c m a t t e r and has a pH of 6. O. It has a 'Strong A d s o r p t i o n c a p a c i t y of 70 ug p a r a q u a t / g soil (O.08 meq/100 g soil) as d e t e r m i n e d by the b i o a s s a y of the soil e q u i l i b r i u m s o l u t i o n m e t h o d (see S e c t i o n 3). P a r a q u a t r e s i d u e s in the soil have b e e n m e a s u r e d at l e a s t once p e r y e a r . T w e n t y s a m p l e s w e r e t a k e n at r a n d o m , w i t h a 3. 8 c m d i a m e t e r c o r e r f r o m e a c h p l o t and the c o r e s d i v i d e d into O.25, 2.5-5, 5-10 and 10-15 c m deep h o r i z o n s . The s a m p l e s f r o m e a c h depth w e r e b u l k e d t o g e t h e r . A n n u a l a p p l i c a t i o n r a t e s and t o t a l a m o u n t p a r a q u a t r e s i d u e s in the top 15 c m soil a r e g i v e n in T a b l e X X . The c o n c e n t r a t i o n of p a r a q u a t r e s i d u e s in d i f f e r e n t soil h o r i z o n s a r e g i v e n in T a b l e XXI. The p a r a q u a t r e s i d u e s had no s i g n i f i c a n t e f f e c t s on the v i n e s o r g r a p e y i e l d s . S a m p l e s of l e a v e s , g r a p e s and t w i g s w e r e t a k e n in M a r c h , 1973. No p a r a q u a t r e s i d u e s w e r e d e t e c t e d (