Degradation of Pesticides in Controlled Water-Soil Systems

4 Degradation of Pesticides in Controlled Water-Soil Systems

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 13, 2016 | http://pubs.acs.org Publication Date: August 15, 1984 | doi: 10.1021/bk-1984-0259.ch004

G. A. JUNK, J. J. RICHARD, and P. A. DAHM1 Ames Laboratory, Iowa State University, Ames, IA 50011

Atrazine, alachlor, 2,4-D ester, trifluralin, carbaryl, and parathion were added individually and as mixtures to 60 L of water and 15 kg of soil held in 110 L plastic garbage containers that were buried partially in open ground. Degradations from initial pesticide concentrations of 0.4 and 0.02 weight percent were investigated. Additional variables of aeration at 1 L/min and peptone nutrients at 0.1 weight percent, as possible aids to degradation, were also studied. Aliquots from 56 buried containers were taken for chemical analyses at regular intervals during a 68 week period. These samples were analyzed for the added pesticides and their hydrolysis products. Conclusions based on analytical results for the field experiment and supplementary laboratory experiments are: 1) soil and water in an inexpensive container provide for satisfactory containment of common pesticides so that chemical and biological degradations can occur; 2) soil is essential for containment and is a satisfactory source of microorganisms; 3) aeration and addition of buffers, nutrients and inoculants are of questionable value; 4) the half-life concept for degradation is not applicable; 5) sampling of disposal sites, even small controlled ones, is a problem; 6) degradations vary from rapid for hydrolysis of 2,4-D ester and carbaryl to unobservable for atrazine. Current address: Department of Entomology, Iowa State University, Ames, IA 50011

1

0097-6156/84/0259-0037$08.75/0 © 1984 American Chemical Society

Krueger and Seiber; Treatment and Disposal of Pesticide Wastes ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


38

T R E A T M E N T A N D DISPOSAL OF PESTICIDE WASTES

Studies were i n i t i a t e d at Iowa State U n i v e r s i t y i n 1977 to d e t e r mine i f p e s t i c i d e s would be contained and degraded when deposited i n w a t e r / s o i l systems. Although the a d d i t i o n of known amounts of the s e l e c t e d p e s t i c i d e s was c o n t r o l l e d , the p h y s i c a l environment was not; temperature, humidity, wind speed, e t c . were normal for the climate of Central Iowa. Four h e r b i c i d e s and two i n s e c t i c i d e s were chosen on the basis of three f a c t o r s . F i r s t l y , they represented s i x d i f f e r e n t f a m i l i e s of p e s t i c i d e s . The four h e r b i c i d e s , a l a c h l o r , a t r a z i n e , t r i f l u r a l i n , and 2,4-D e s t e r , represent the a c e t a n i l i d e s , t r i a z i n e s , d i n i t r o a n i l i n e s , and phenoxy acid h e r b i c i d e s , r e s p e c t i v e l y . The two i n s e c t i c i d e s , c a r b a r y l and parat h i o n , represent the carbamate and organophosphorus i n s e c t i c i d e s , respectively. Secondly, the p e s t i c i d e s were chosen on the b a s i s of current and projected use i n Iowa (1) and the Midwest. T h i r d l y , the chosen p e s t i c i d e s were ones for which a n a l y t i c a l methodology was a v a i l a b l e . Considerable information has been published concerning the degradation of these p e s t i c i d e s . A b r i e f summary of t h e i r degrada t i o n pathways and t h e i r expected persistence i n the environment i s presented here. Atrazine The major degradation of a t r a z i n e i n s o i l was i t s conversion to hydroxyatrazine by loss of the c h l o r i n e atom (2-5). Dealkylation also occurred with d e e t h y l a t i o n predominating over d e i s o p r o p y l a t i o n (5,6). Only small amounts of the r a d i o a c t i v i t y of the r i n g labeled a t r a z i n e was converted to COz by s o i l (6,8-10). G e l l e r (11) found that the percentages of C 0 evolved from C-labeled side chains were s i m i l a r for b i o l o g i c a l and n o n b i o l o g i c a l dealkyl a t i o n . No d i s t i n c t i o n could be made between the two processes so degradation was assumed to be i n i t i a t e d by a b i o t i c environmental f a c t o r s , such as low pH, mineral s a l t s , organic matter and photolysis. The ^ - t r i a z i n e s are one of the most r e c a l c i t r a n t groups of h e r b i c i d e s and p e r s i s t e n c e of over one year i n the s o i l was observed when a t r a z i n e was applied at the recommended rates (12). lk

llf

ilf

2

Alachlor Most a c e t a n i l i d e s are biodegraded r a p i d l y i n s o i l , but a l a c h l o r appears to be degraded by a mechanism d i f f e r e n t from that for other members of t h i s group of h e r b i c i d e s . The presence of e i t h e r the 2' , 6 ^ - d i a l k y l s u b s t i t u e n t s , the N-alkoxylmethyl s u b s t i t u e n t , or both, may preclude enzymatic h y d r o l y s i s of the carbonyl or


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amide linkages of a l a c h l o r (13). Hargrove and Merkle (14) r e p o r t ed that 2 - c h l o r o - 2 , 6 ' - d i e t h y l a n i l i d e was formed i n a l a c h l o r t r e a t e d , a i r - d r i e d s o i l incubated at 46°C. This degradation product was shown to r e s u l t from acid catalyzed h y d r o l y s i s on mineral s u r f a c e s . Beestman and Deming (15) found a h a l f - l i f e of 7.8 days for a l a c h l o r i n u n s t e r i l i z e d s o i l . The average p e r s i s t e n c e for recommended rates of a p p l i c a t i o n was 6-10 weeks ( 1 2 ) .


Trifluralin Both aerobic and anaerobic degradation pathways have been proposed for t r i f l u r a l i n (16) . D e a l k y l a t i o n i s the i n i t i a l aerobic degradation followed by sequential removal of the second a l k y l group to give the d e a l k y l a t e d product. Reduction of the two n i t r o groups e v e n t u a l l y leads to the formation of the 3,4,5-triamino-a,a,at r i f l u o r o t o l u e n e . Under anaerobic conditions the n i t r o groups are reduced f i r s t , followed by d e a l k y l a t i o n , with formation of the same 3 , 4 , 5 - t r i a m i n o - a , a , a - t r i f l u o r o t o l u e n e product. Degradation of t r i f l u r a l i n was more r a p i d and extensive i n substrate-amended s o i l under anaerobic conditions compared with well-aerated systems. The r e l a t i v e rates followed the order, moist anaerobic > flooded anaerobic > moist aerobic (17) . Degradation i n these environments a f t e r 20 days was 99, 45 and 15%, r e s p e c t i v e l y . Under f i e l d c o n d i t i o n s t r i f l u r a l i n has been p r e d i c t e d to degrade to nonphytotoxic l e v e l s w i t h i n a growing season when s o i l c o n d i t i o n s are moist and warm ( 1 2 ) . A f t e r three years, less than 1.5% of C - t r i f l u r a l i n was detected i n test p l o t s maintained under n a t u r a l c o n d i t i o n s (18). 1 I +

2,4-D

Ester

Evidence for the m i c r o b i o l o g i c a l degradation of 2,4-D ester i n s o i l s was based on the s t i m u l a t i o n by warm, moist conditions and organic matter (19); a c o r r e l a t i o n between degradation rate and the numbers of aerobic s o i l b a c t e r i a ( 2 0 ) ; and i n h i b i t i o n when the s o i l s were a i r - d r i e d and autoclaved ( 1 9 7 . L i t t l e information i s a v a i l a b l e , however, on the nature of the degradation products. The r e s u l t s of many studies of the degradation of phenoxyalkanoates using pure c u l t u r e s of microorganisms have been reported. The use of Arthrobacter i s o l a t e d by Loos (21) has been studied e s p e c i a l l y well . This organism was i s o l a t e d from s i l t loam and i t r a p i d l y o x i d i z e d 2,4-D. The f i r s t intermediate was 2 , 4 - d i c h l o rophenol. E v e n t u a l l y the aromatic r i n g of the 2,4-D was cleaved with a l l the bound c h l o r i n e converted to free c h l o r i n e .



40

T R E A T M E N T A N D DISPOSAL OF PESTICIDE WASTES

The r e s u l t s of Smith (22) suggested that the i s o p r o p y l and nb u t y l esters of 2,4-D are subject to rapid chemical h y d r o l y s i s i n soils; however the i s o o c t y l ester was more stable and p o s s i b l y undergoes some b i o l o g i c a l h y d r o l y s i s . B a i l e y et a l . (23) reported that the h y d r o l y s i s of the propylene g l y c o l b u t y l ester i n pond water was 90% complete i n 16-24 hours and 99% complete in 33-49 hours. Zepp et a l . (24) reported that the h a l f - l i f e for h y d r o l y s i s of various 2,4-D esters v a r i e d from 0.6 hour for the 2-butoxye t h y l ester to 37 hours for the 2-octyl e s t e r . Persistence of the e s t e r i n the s o i l environment was estimated to be less than one week. The degradation of the 2,4-D a c i d was also rapid (12) but slower than the h y d r o l y s i s of the e s t e r . Parathion Degradation of parathion i n s o i l was by h y d r o l y s i s to p - n i t r o phenol and d i e t h y l t h i o p h o s p h o r i c acid and reduction to aminoparathion (25,26). Chemical o x i d a t i o n of parathion i n s o i l s and waters was not prevalent, although o x i d a t i o n of the phosphoruss u l f u r bond has been shown to occur under u l t r a v i o l e t l i g h t and i n o x i d i z i n g environments (26). At ordinary l e v e l s of a p p l i c a t i o n to s o i l , parathion was degraded w i t h i n weeks i f m i c r o b i a l a c t i v i t y was a v a i l a b l e (27) . Accumulations even a f t e r repeated a p p l i c a tions were u n l i k e l y (28). When higher concentrations were a p p l i e d to s o i l , p e r s i s t e n c e increased. Simulated s p i l l s of concentrated parathion r e s u l t e d i n a 15% residue a f t e r f i v e years (29) and 0.1% a f t e r 16 years (30). Carbaryl Carbaryl degradation was p r i m a r i l y m i c r o b i o l o g i c a l as reported by a number of i n v e s t i g a t o r s (31-36). S o i l organisms transformed c a r b a r y l to many metabolites, i n c l u d i n g 1-naphthol, 1-naphthyl Nhydroxy methyl carbamate, 1-naphthyl carbamate, and 4 and 5hydroxy-1-naphthyl methyl carbamate. The degradation of 1-napht h o l also occurred m i c r o b i o l o g i c a l l y (32,35) by a pathway s i m i l a r to h y d r o x y l a t i o n with subsequent r i n g cleavage of naphthalene (37). Predicted p e r s i s t e n c e of c a r b a r y l i n the environment v a r i e d from one to s e v e r a l weeks (38). The degradation of 1-naphthol was p r e d i c t e d to be f a s t e r (34,35) than degradation of c a r b a r y l . EXPERIMENTAL D e s c r i p t i o n of System A t r a z i n e (Aatrex; 80W), a l a c h l o r (Lasso; E.C.) 2,4-D ester (Weedone LV4; E . C ) , t r i f l u r a l i n ( T r e f l a n ; E.C.), c a r b a r y l (Sevin; 50W) and parathion ( S e c u r i t y ; 15W) were blended, i n d i v i d u a l l y and as mixtures, with 60 L of water and 15 kg of sandy loam s o i l i n 110 L



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p l a s t i c garbage containers buried p a r t i a l l y i n the ground. A c r o s s - s e c t i o n a l view of one of these buried containers i s shown i n Figure 1. The i n d i v i d u a l p e s t i c i d e s were studied i n separate containers at the high and low concentrations of 0.4 and 0.02 weight percent a c t i v e i n g r e d i e n t . The mixtures were studied with a l l s i x p e s t i c i d e s each present at high and low concentrations i n separate c o n t a i n e r s . A d d i t i o n a l v a r i a b l e s of a e r a t i o n at 1 L/min and peptone n u t r i e n t s at 0.1% by weight r e s u l t e d i n a f a c t o r i a l experiment of 56 c o n t a i n e r s . The layout of these containers i n a 7x8 matrix, with dots showing the l o c a t i o n s , i s shown i n Figure 2. The high and low concentrations are i n d i c a t e d by IX and 0.05X, r e s p e c t i v e l y . Those systems under a e r a t i o n and with n u t r i e n t s are also i d e n t i f i e d . A l l 56 c o n t a i n e r s , for studying the degradations of these s i x p e s t i c i d e s , and the associated equipment were l a i d out i n a fenced area covering only 60 M . 2

Sampling A 100 g sample of the s o i l and l i q u i d contents of each container was taken for analyses at 1, 3, 4, 8, 12, 16, 20, 24, 28, 52 and 68 weeks a f t e r a d d i t i o n . The samples were obtained by slowly lowering and r a i s i n g a 100 mL b o t t l e , capped with a two-hole rubber stopper, through the s w i r l formed by vigorous mixing of the contents of the c o n t a i n e r . The mixing was accomplished using a p r o p e l l e r blade attached to a shaft d r i v e n by a v a r i a b l e speed drill. The amount of water necessary to adjust the volume to the o r i g i n a l 60 L was recorded before mixing and sample c o l l e c t i o n . E x t r a c t i o n Procedures The c o l l e c t e d sediment and water samples were c e n t r i f u g e d f o r 0.5 hour at 200 rpm. The water was decanted and the volume measured p r i o r to t r a n s f e r to a 250 mL separatory funnel where i t was ext r a c t e d four times with four 50 mL volumes of d i e t h y l ether for the high concentration samples and with 50 mL followed by two 25 mL volumes for the low concentration samples. The 2,4-D samples only were a c i d i f i e d to a pH of ~2 with H S0 to a i d i n the s o l v e n t extraction. For the four h e r b i c i d e s , the s o i l f r a c t i o n i n the sample b o t t l e was extracted by adding 50 mL of d i e t h y l ether followed by a g i t a t i o n for 15 minutes on a w r i s t - a c t i o n shaker. The d i e t h y l ether was decanted and the high concentration samples were ext r a c t e d three more times with 50 mL of d i e t h y l ether by hand shaking the capped b o t t l e s for 2 to 3 minutes. The low c o n c e n t r a t i o n samples were extracted two a d d i t i o n a l times with 25 mL of d i e t h y l ether. For the two i n s e c t i c i d e s , the s o i l was extracted with 75, 50 and 50 mL of an acetone :benzene:methanol (1:2:1 by v o l . ) mixture. The sample b o t t l e s were capped and a g i t a t e d for 60 minutes on a w r i s t - a c t i o n shaker for each e x t r a c t i o n . The contents of the bot2

1+



42

T R E A T M E N T A N D DISPOSAL O F PESTICIDE WASTES

Figure 1. C r o s s - s e c t i o n a l view o f a buried garbage can. A,D Tygon tube and d i f f u s e r used f o r a e r a t i o n ; B~ground l e v e l ; C—110L p l a s t i c garbage c o n t a i n e r . North

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Figure 2. Layout of the 7 χ 8 or 56 matrix of garbage cans containing 6 p e s t i c i d e s at two d i f f e r e n t concentrations and mixtures with and without a e r a t i o n and n u t r i e n t s .


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43

t i e s were then c e n t r i f u g e a for 15 minutes and the supernatant l i q u i d was decanted. The combined l i q u i d from the three e x t r a c t i o n s was reduced to about 25 mL under p a r t i a l vacuum. The l i q u i d was e x t r a c t e d i n a separatory funnel with three 50 mL p o r t i o n s of d i e t h y l ether. The combined d i e t h y l ether e x t r a c t s were f i l t e r e d through anhydrous Ν 3 8 0 ^ and the f i l t r a t e reduced to 50 mL under p a r t i a l vacuum. 2


Separation and

Analyses

A t r a z i n e , a l a c h l o r and t r i f l u r a l i n were determined i n the e x t r a c t s of the samples by gas chromatography using a N-P d e t e c t o r . An EC detector was used for the determination of parathion, 2,4-D e s t e r and the 2,4-D acid a f t e r e s t e r i f i c a t i o n with diazomethane. Carb a r y l and 1-naphthol were determined c o l o r i m e t r i c a l l y by the pro cedure of McDermott and DuVall (39). Recoveries f o r s o i l and water samples spiked i n d i v i d u a l l y with the s i x commercial formulations at the 0.4 and 0.02% l e v e l s were 96 and 97%, r e s p e c t i v e l y . Comparable recovery e f f i c i e n c i e s were obtained for mixures of the p e s t i c i d e s . In a d d i t i o n , the a b i l i t y to account for a l l the deposited p e s t i c i d e s i n the analyses of the samples taken from the containers p r i o r to any degradations was v a l i d a t i o n for the e f f e c t i v e n e s s of the e x t r a c t i o n procedures. RESULTS AND

DISCUSSION

S o i l and L i q u i d

Analyses

The a n a l y t i c a l data for the added p e s t i c i d e s and two of the h y d r o l y s i s products, 2,4-D acid and 1-naphthol, were used to formulate the degradation graphs shown i n Figures 3-14. Atrazine underwent no degradation e i t h e r alone or i n mixtures and a l a c h l o r and t r i f l u r a l i n underwent no degradation i n mixtures, so the graphs for these p e s t i c i d e s under these c o n d i t i o n s are not shown. For the sake of c l a r i t y , some of the a n a l y t i c a l data from 1, 3, and 4 weeks have been averaged and p l o t t e d as a s i n g l e r e s u l t at the four week i n t e r v a l . These graphs i n d i c a t e v i v i d l y which p e s t i c i d e s degrade and what f a c t o r s such as c o n c e n t r a t i o n , aera t i o n , mixtures, and n u t r i e n t s a f f e c t the rate of degradation. The graphs also i n d i c a t e the i n e v i t a b l e u n c e r t a i n t y i n the a n a l y t i c a l r e s u l t s , due to e r r o r s i n c o l l e c t i n g samples from a heterogeneous medium. The placement of the graphs show the e f f e c t of c o n c e n t r a t i o n , where s e v e r a l p e s t i c i d e s decay r e a d i l y at low l e v e l s but do not show measurable degradation when present at high c o n c e n t r a t i o n . The rate of degradation for an i n d i v i d u a l p e s t i c i d e when i t i s alone or i n mixtures can be compared by i n s p e c t i n g successive figures. For example, F i g u r e 3 shows the p l o t s f o r 2,4-D e s t e r when i t i s present alone at two d i f f e r e n t concentrations and under



NO

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NO NUTRIENTS

NO

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30

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15

3 0

WEEKS

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66

68 WEEKS

Figure 3. 2,4-D e s t e r degradation with time. s o i l and water; o , amount i n water.

· , amount i n


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J U N K ET A L .

NO


45


AERATION

WEEKS

NO

NUTRIENTS

FIVE

OTHER

PESTICIDES

WEEKS

Figure 4. 2,4-D e s t e r degradation with time in presence of f i v e other formulated p e s t i c i d e s . · , amount i n s o i l ; o , amount in water.




NO AERATION

NO NUTRIENTS

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WEEKS Figure

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4.

JUNK ET AL.

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Degradation of Pesticides in Controlled Water-Soil Systems

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