Biological Unavailability of Bound Paraquat Residues in Soil - ACS

22 Biological Unavailability of Bound Paraquat Residues in Soil D. RILEY and W. WILKINSON

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

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.

301

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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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 .



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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




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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)



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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


306


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 .


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



-

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



308


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 .


RILEY E T A L .



22.


310



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


RILEY

ET


AL.

311


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


312

BOUND

A N D C O N J U G A T E D PESTICDDE

RESIDUES

T A B L E II


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


1400 1200 1600 1600 400 1800 1400 1400 1000 1400 1200 75 50

22.

RILEY ET AL.


313


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. >


300 450 1350 1500 1050 450 1350 450 600 600 1500


314


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



22.

RILEY

E T A L .

315


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


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


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 -



22.

RILEY

E T AL.


PARAQUAT IN SOLUTION (HQ/ml)

Figure 7.

Paraquat adsorption isotherms on Frensham soil


317



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. .

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


i

η

>

!

8

co to to


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.



324


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. 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



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


3266

7600

Paraquat 'Loosely Bound' C a p a c i t y


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



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 .


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


22.

RILEY

E T AL.

329


TABLE

X


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.


O.74 1.1

O.08 1.0 7.0 O.00 O.00 O.07 O.07 -

330


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.


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.


22.

331


RILEY ET AL.

T A B L E

XI

1

COMPARISON OF 'STRONG ADSORPTION AND TIGHTLY BOUND CAPACITIES OF SOILS


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



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.



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



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


22.

RILEY ET AL.


T A B L E

335

XIV


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




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 .



22.

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E T A L .


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 .



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


22.

339


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.)


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



340


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

!


342

BOUND AND

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 +

+


+

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.



22.

RILEY

E T A L .


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 .



344


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


22.

345


RILEY ET AL.

T A B L E

XLX

PARAQUAT SOIL RESIDUES IN OUTDOOR POT EXPERIMENT


(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


17.0

346

BOUND AND

CONJUGATED PESTICIDE

RESIDUES


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 (

Biological Unavailability of Bound Paraquat Residues in Soil - ACS

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