Pesticide and Xenobiotic Metabolism in Aquatic Organisms - American

10 Metabolism of Insect Growth Regulators in Aquatic

Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on July 22, 2018 at 10:21:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Organisms DAVID A. SCHOOLEY and GARY R. QUISTAD Biochemistry Department, Zoecon Corporation, 975 California Avenue, Palo Alto, CA 94304 Insect growth regulators (IGRs), a new class of indirect insecticides which act by subtly misdirecting normal developmental processes, include compounds which mimic the juvenile hormone of insects as well as compounds which interfere with chitin biosynthesis. Chemicals with either mode of action have much greater specificity than earlier insecticides and have substantial advantages in certain applications. Since representatives of both classes of IGR are useful as mosquito larvicides, their fate in the aquatic environment has been investigated in some detail. This paper will review the degradation of several IGRs in water and aquatic organisms. Diflubenzuron Diflubenzuron (Dimilin®, TH-6040) is an IGR which inhibits the normal deposition of chitin. The metabolic fate of diflubenzuron has been studied in sheep (1, 2), cattle (1), rats (1, 3), house flies (4, 5), stable flies (5), chickens (6), swine (6), boll weevils (7), plants (8, 9), and soil (2, 8, 10). Since good reviews of diflubenzuron metabolism have been given by Ivie (11) and Verloop and Ferrell (9), we will present only a tabular summary of the degradation of diflubenzuron in nonaquatic systems for comparative purposes (Table I). The remaining discussion will focus on diflubenzuron degradation in the aquatic environment. H y d r o l y s i s . Schaefer and Dupras (12) i n v e s t i g a t e d the h y d r o l y t i c s t a b i l i t y o f d i f l u b e n z u r o n as a 0.1 ppm aqueous s o l u t i o n . At pH 7.7 d i f l u b e n z u r o n i s s t a b l e a t 10-24°, but g r a d u a l l y decomposes a t 38°. A t pH 10 i t i s s t a b l e a t 10°, but degrades slowly a t temperatures g r e a t e r than 24°. Photodegradation. The photochemical degradation products o f diflubenzuron i n s t r i c t l y aqueous s o l u t i o n are unreported, perhaps because o f the compound's r e f r a c t o r y s o l u b i l i t y . Exposure of t h i n f i l m s on g l a s s o r a 0.1 ppm aqueous s o l u t i o n t o s u n l i g h t 0-8412-0489-6/79/47-099-161$05.00/0 © 1979 American Chemical Society Khan et al.; Pesticide and Xenobiotic Metabolism in Aquatic Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

Khan et al.; Pesticide and Xenobiotic Metabolism in Aquatic Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

=P

=P

=

3

2

5

2

H

2

"3

*

*

*

***

Sheep

*

*

***

***

Cow

* * *

* * *

***

***

Rat

***

Soil

***

P l a n t s (5 species)

* = d e t e c t a b l e , but 10%

5

R =H

5

R =C0CH

3

o

R =C0NH

R

4

R =NH

4

R =NHCH C0 H

R =0H 4

I

2

2

=

R =OH

R

1

3

3

R = H ,

R

R =OH

2

»2

R =R =H,

R

=

=H

2 3

F

R^OH,

1

«1

R

F Q Q

Table I. Nonaquatic Degradation o f Diflubenzuron (5 species)

* * *

***

Insects

10.

S C H O O L E Y A N D QuisTAD

Insect Growth

163

Regulators

r e s u l t e d i n minimal photodecomposition ( 1 2 ) . M e t c a l f et al. (2) and Ruzo e t a l . (13) i r r a d i a t e d methanolic s o l u t i o n s o f d i f l u b e n zuron with a r t i f i c i a l l i g h t as p r e d i c t i v e models f o r environmental photodegradation (Table I I ) . Metcalf e t a l . (2) a l s o detected t r a c e amounts o f 4 - c h l o r o a n i l i n e and a n i l i n e from d i f l u b e n z u r o n a f t e r i r r a d i a t i o n f o r 4 h r (254 nm) i n aqueous dioxane while Ruzo et al. (13) found t r a c e s o f 4-chlorophenyl isocyanate i n methanol upon i l l u m i n a t i o n a t 300 nm. Table I I .

Photoproducts o f Diflubenzuron i n Methanolic S o l u t i o n % Yield Metcalf et al. (2)

^^-NC0 CH 2

CI-^-NC0 CH 2

Ruzo et al. (13)

18

3

45

trace

3

4

0 CNH

Table I I I .

68

2

49

M e t a b o l i t e s o f Diflubenzuron from B a c t e r i a and Bluegreen Algae, Booth and F e r r e l l ( 1 4 ) . 14 % Extractable C Bacteria Blue-green Algae

(Pseudomonas) (10 days) CI-Q-NCNH

2

C I - ^ - N H

5

2

5

unmetabolized diflubenzuron

(4 days) 53

u

2

C0 H

{Plectonema)

trace

36

5

Microorganisms. Diflubenzuron was s t a b l e t o degradation by u n c h a r a c t e r i z e d microorganisms from a sewage lagoon ( 1 2 ) . Pseudomonas putida ( s o i l microbe) a l s o was unable t o metabolize diflubenzuron upon i n c u b a t i o n o f pure c u l t u r e s (2). Using Pseudomonas sp. from aquatic Utah s o i l Booth and F e r r e l l (14) followed the metabolic f a t e o f d i f l u b e n z u r o n f o r twelve days


164

PESTICIDE AND XENOBIOTIC

METABOLISM

I N AQUATIC

ORGANISMS

(Table I I I ) . Pseudomonas was capable o f using diflubenzuron as a sole carbon source, but b a c t e r i a l growth was g r e a t l y a c c e l e r a t e d when the medium was supplemented with acetate. Booth and F e r r e l l (14) found t h a t blue-green algae, Plectonema boryanum, were voracious degraders o f diflubenzuron (Table I I I ) . J u s t 5 mg o f algae c e l l s could metabolize almost 80% o f the a p p l i e d diflubenzuron i n j u s t 1 hr. C u r i o u s l y , t h i s pace was not sustained s i n c e 45 mg o f algae could degrade only 95% o f the a p p l i e d dose a f t e r four days. Aquatic Ecosystem and F i s h . Metcalf e t al. (2) studied the f a t e o f d i f l u b e n z u r o n ( r a d i o l a b e l e d s e p a r a t e l y i n three d i f f e r e n t p o s i t i o n s ) i n t h e i r model ecosystem. Diflubenzuron was dubbed "moderately p e r s i s t e n t " i n algae, s n a i l s , s a l t marsh c a t e r p i l l a r s , and mosquito l a r v a e as evidenced by l i m i t e d b i o d e g r a d a b i l i t y (Table IV). However, d i f l u b e n z u r o n and i t s nonpolar metabolites were not prone t o e c o l o g i c a l m a g n i f i c a t i o n i n Gambusia f i s h . The lack o f bioaccumulation o f diflubenzuron residues i n f i s h was s u b s t a n t i a t e d by Booth and ' F e r r e l l (14) who used the channel c a t f i s h , Ictalurus, i n a simulated lake ecosystem. They t r e a t e d separate s o i l samples a t 0.007 and 0.55 ppm, r e s p e c t i v e l y . Table IV.

Degradation o f Diflubenzuron Model Ecosystem.

Water diflubenzuron

24-31

i n the Metcalf e t a l . (2)

% Extractable Radiolabel i n Mosquito Snail Alga Culex Oedogonium Physa 46-74

73-96

Fish

Gambusia

84-98

6-8

0-CO H

3-10

2

^ - C O N H

CI-^^-NH

2

11

2

0 CI-^^-NCCH

3

CI-^^-NCNH

2

CI-^-N(CH ) 3

10

2

5

5-17

12


10.


Insect Growth

Regulators

165

The s o i l was aged a e r o b i c a l l y f o r two weeks, then submerged under water f o r two weeks. F i n a l l y , a d d i t i o n a l water and c a t f i s h were added with monitoring o f residues f o r twenty-eight days. For s o i l t r e a t e d a t 0.55 ppm, 64% o f the i n i t i a l dose was r e l e a s e d from the s o i l , but only 2.3% o f the a p p l i e d r a d i o l a b e l was found i n the water upon termination o f the study. Water residues c o n s i s t e d mostly (>93%) o f 4-chlorophenylurea, accompanied by d i f l u o r o b e n z o i c a c i d (3-5%), 4 - c h l o r o a n i l i n e (0-1%), and diflubenzuron (0.4-1.5%). An average o f 66% o f the s o i l residues were e x t r a c t a b l e with methanol, c o n s i s t i n g predominantly o f unmetabolized d i f l u b e n z u r o n (74-84%) and 4 - c h l o r o a n i l i n e (11-17%). F o r s o i l t r e a t e d a t 0.55 ppm, f i s h residues q u i c k l y reached a p l a t e a u a f t e r three days a t about 4 and 10 ppb f o r muscle and v i s c e r a , r e s p e c t i v e l y . Hence, Booth and F e r r e l l (1£) concluded t h a t bioaccumulation o f d i f l u benzuron residues from marsh a p p l i c a t i o n s should be minimal. R-20458 An impressive l i s t o f degradative s t u d i e s has been performed with S t a u f f e r * s R-20458 i n c l u d i n g metabolism by e i g h t i n s e c t species (15_, 16) , r a t s (15, 17) , s t e e r s (18, 19) , mice (20) and mammalian enzymes (15, 20, 21). I t i s evident t h a t most p u b l i s h e d i n v e s t i g a t i o n s have concentrated on metabolism by mammals and insects. Insect metabolism o f R-20458 has been reviewed (22) and a summary o f nonaquatic metabolism i s given i n Table V. Several a d d i t i o n a l hydroxylated metabolites were i d e n t i f i e d by Hoffman e t a l . (17) from r a t s . 1

Photodegradation. C a s i d a s group (15, 20) has s t u d i e d the photodecomposition o f R-20458 on s i l i c a g e l and i n water. The major aqueous photoproducts are summarized i n F i g u r e 1. The predominant photoproduct i n aqueous s o l u t i o n r e s u l t e d from epoxide hydration t o the corresponding d i o l . The photoproducts on s i l i c a were q u i t e s i m i l a r t o aqueous products with an enhanced y i e l d o f diepoxide and diminished y i e l d o f d i o l . P h o t o s e n s i t i z e r dyes had l i t t l e e f f e c t on R-20458 photodegradation. Algae. G i l l et al. (20) studied the metabolic f a t e o f R-20458 i n the algae Chlorella and Chlamydomonas. Both algae e f f i c i e n t l y metabolized R-20458 with Chlorella demonstrating a higher metabolic c a p a c i t y . In Chlamydomonas, the main metabolite r e s u l t e d from hydration o f the parent epoxide t o the d i o l . After 48 h r , 78% o f the R-20458 was degraded by Chlorella, the metabol i t e s c o n s i s t i n g mainly o f d i o l s (Figure 2 ) . Epifenonane D e t a i l e d r e p o r t s o f the degradation o f t h i s Hoffman-LaRoche compound are l i m i t e d . Compared t o s e v e r a l other IGRs, epifenonane (Ro 10-3108) was r e l a t i v e l y s t a b l e a t pH 4 i n the dark (23).


PESTICIDE AND XENOBIOTIC M E T A B O L I S M I N AQUATIC ORGANISMS

166

I

ι

0.5 ppm 50%

METABOLISM

I^HJ methoprene

7% 3dq

^

3%

X» > recovered methoprene 6%

Cc]methoprene ^J!2!i_» ~ ° > ^ A A

60%

4

0

H

29% Figure 5.

Metabolism of methoprene by soil and aquatic microorganism (26, 27)


10.


Insect

Growth

173

Regulators

In summary, photodecomposition o f methoprene i s f a c i l e and leads t o a m u l t i p l i c i t y o f products. The lower p h o t o s t a b i l i t y i n s u n l i g h t o f methoprene compared t o epifenonane has been mentioned p r e v i o u s l y . Because o f i t s photochemical l a b i l i t y and i t s ready m i c r o b i a l degradation (see below), methoprene i s microencapsul a t e d f o r aquatic use as a mosquito l a r v i c i d e . Microorganisms. Outdoor incubation o f 0.42 ppm o f [10- H]methoprene with unknown aquatic microorganisms f o r three days l e d t o production o f the hydroxy e s t e r (7.0%), the methoxy a c i d (5.7%), and the hydroxy a c i d (2.6%). Recovered methoprene (60%) contained about 7% o f the analogous e t h y l e s t e r , while the hydroxy i s o p r o p y l e s t e r metabolite contained about 15% o f the analogous e t h y l e s t e r (Figure 5). The genesis o f these e t h y l e s t e r s i s u n c e r t a i n , but b e l i e v e d t o a r i s e from ethanol used t o dose the incubations ( f i n a l concentration only 0.08% ethanol i n water), with p o s s i b l e enzymic c a t a l y s i s . Outdoor i n c u b a t i o n o f [5- C]methoprene a t 0.65 ppm f o r t h i r t e e n days w i t h water from the same source, but c o l l e c t e d during August i n s t e a d o f February, l e d t o i s o l a t i o n o f a s i n g l e major metabolite i n 29% y i e l d . The metabolite, 7 - m e t h o x y c i t r o n e l l i c a c i d , i s a l s o known as a photoproduct. However, a simultaneous autoclaved c o n t r o l showed a lower y i e l d o f t h i s product. A l s o , 98% o f the r a d i o a c t i v i t y was recovered from the autoclaved c o n t r o l vs. 48% from the microb i a l l y - a c t i v e water. Since C - l o f 7 - m e t h o x y c i t r o n e l l i c a c i d i s the l a b e l e d p o s i t i o n , f u r t h e r m i c r o b i a l degradation o f 7-methoxyc i t r o n e l l i c a c i d t o [ C ] a c e t a t e and C02 can be i n f e r r e d . F a l l has studied the c a p a b i l i t y o f fourteen species o f microorganisms t o grow on methoprene as sole carbon source. One of these organisms, Cladosporium resinae, was able t o u t i l i z e methoprene as s o l e carbon source, while another, Pseudomonas citronellolis, was s i m i l a r l y able t o u t i l i z e 7 - m e t h o x y c i t r o n e l l i c a c i d . (41). S o i l microorganisms degrade methoprene r a p i d l y and extens i v e l y (27). The hydroxy e s t e r was i s o l a t e d as a minor metabolite; over 50% o f the a p p l i e d dose was evolved as C0z. R a d i o a c t i v i t y from [5- **c]methoprene incorporated i n t o the humic a c i d , f u l v i c a c i d , and humin f r a c t i o n s o f s o i l . 3

1

li+

1!|

lk

1

F i s h and Ecosystem Studies. When b l u e g i l l s u n f i s h are exposed t o a constant l e v e l o f methoprene i n a dynamic flowthrough system, they accumulate radiocarbon u n t i l a p l a t e a u i s reached a f t e r 7-14 days (33) . While l e v e l s o f methoprene i n f i s h were about lOOOx that i n water a t the p l a t e a u , t r e a t e d b l u e g i l l p l a c e d i n t o uncontaminated water showed a 93-95% radiocarbon r e d u c t i o n i n 14-21 days. A n a l y s i s o f f i s h t i s s u e s a t p l a t e a u l e v e l s revealed t h a t ^90% o f the radiocarbon was unmetabolized parent, 1% was the hydroxy e s t e r , while the remainder was p o l a r conjugates.


174

PESTICIDE A N D XENOBIOTIC M E T A B O L I S M

I N AQUATIC ORGANISMS

The f a t e o f methoprene was a l s o s t u d i e d i n an aquatic ecosystem designed t o simulate environmental exposure o f f i s h t o a mosquito l a r v i c i d e . B l u e g i l l f i s h were maintained i n two meter diameter pools c o n t a i n i n g m i c r o b i a l l y - a c t i v e water, s o i l , and bear rush p l a n t s . The p o o l was t r e a t e d three times a t weekly i n t e r v a l s with [5- **C]methoprene s u f f i c i e n t t o give 0.011 ppm s o l u t i o n . Radioassay o f samples revealed a r a t h e r general d i s t r i b u t i o n o f r a d i o a c t i v i t y throughout the system. We analyzed f i s h t i s s u e s two and four weeks a f t e r the l a s t treatment. While radioassay revealed an apparent concentration o f 2-3 ppm equivalents o f methoprene i n b l u e g i l l , e x t r a c t i o n and d e t a i l e d a n a l y s i s revealed t h a t l e s s than 0.1% o f the radiocarbon was methoprene and i t s known primary metabolites. R a d i o a c t i v i t y i n nonpolar e x t r a c t a b l e f r a c t i o n s was c h a r a c t e r i z e d as t r i g l y c e r i d e s , d i g l y c e r i d e s , c h o l e s t e r o l , and f r e e f a t t y a c i d s (14, 0.2, 1, and 3% o f the t o t a l r e s i d u e , r e s p e c t i v e l y ) a t two weeks posttreatment. Over 50% o f the radiocarbon was unextractable, but enzymatically s o l u b i l i z e d r a d i o a c t i v i t y was presumed t o be amino a c i d s based on s o l u b i l i t y (33). T h i s study provides a t e l l i n g c r i t i c i s m o f ecosystem s t u d i e s , when performed on r e a d i l y degraded m a t e r i a l s , and/or when not accompanied by cautious a n a l y s i s o f samples. The f a t e o f methoprene was i n v e s t i g a t e d i n the Metcalf ecosystem (42) before the environmental l a b i l i t y o f [5- *C]methoprene was documented. I t seems l i k e l y that the l i m i t e d data presented i n t h a t work gave s p u r i o u s l y high residue l e v e l s due t o formation of nonmetabolite residues which i n t e r f e r e with the simple t i c analyses performed. 1

1

Summary Insect growth r e g u l a t o r s c o n s i s t o f d i v e r s e chemical s t r u c t u r a l types, but appear t o share a common f e a t u r e : quick degradation i n the aquatic environment.

Literature Cited 1 Ivie, G.W., J. Agric. Food Chem., (1978), 26, 81. 2 Metcalf, R.L., Lu, P.-Y., and Bowlus, S., J. Agric. Food Chem., (1975), 23, 359. 3 Post, L.C. and Willems, A.G.M., paper in preparation, cited in ref. 9 below. 4 Chang, S.C., J. Econ. Entomol., (1978), 71, 31. 5 Ivie, G.W. and Wright, J.E., J. Agric. Food Chem., (1978), 26, 90. 6 Opdycke, J.C., Miller, R.W., and Menzer, R.E., Toxicol. Applied Pharmacol., (1976), 37, 96. 7 Still, G.G. and Leopold, R.A., Abstr. Pap., 170th Meet., Amer. Chem. Soc., (1975), PEST 5. 8 Bull, D.L. and Ivie, G.W., J. Agric. Food Chem., (1978), 26, 515.


10.

SCHOOLEY

AND

QUISTAD

Insect

Growth

Regulators

175

9 Verloop, A. and Ferrell, C.D., in "Pesticide Chemistry in the 20th Century", (J.R. Plimmer, ed.), ACS Symposium Series, 37, (1977), pp 237-270. 10 Verloop, A. Nimmo, W.B., and DeWilde, P.C., submitted to Pestic. Sci. 11 Ivie, G.W., in "Fate of Pesticides in Large Animals", (G.W. Ivie and H.W. Dorough, eds.), Academic Press, New York, (1977), pp 111-125. 12 Schaefer, C.H. and Dupras, E.F., Jr., J. Agric. Food Chem., (1976), 24, 733. 13 Ruzo, L.O., Zabik, M.J. and Schuetz, R.D., J. Agric. Food Chem., (1974), 22, 1106. 14 Booth, G.M. and Ferrell, D., in "Pesticides in Aquatic Environments", (M.A.Q. Khan ed.), Plenum Press, New York, (1977), pp 221-243. 15 Gill, S.S., Hammock, B.D., Yamamoto, I., Casida, J.E., in "Insect Juvenile Hormones: Chemistry and Action", (J.J. Menn and M. Beroza, eds.), Academic Press, New York, (1972), pp 177-189. 16 Hammock, B.D., Gill, S.S., Casida, J.E., Pestic. Biochem. Physiol., (1974), 4, 393. 17 Hoffman, L.J., Ross, J.H., Menn, J.J., J. Agric. Food Chem., (1973), 21, 156. 18 Ivie, G.W., Wright, J.E., and Smalley, H.E., J. Agric. Food Chem., (1976), 24, 222. 19 Ivie, G.W., Science, (1976), 191, 959. 20 Gill, S.S., Hammock, B.D., and Casida, J.E., J. Agric. Food Chem., (1974), 22, 386. 21 Hammock, B.D., Gill, S.S., Stamoudis, V., and Gilbert, L.I., Comp. Biochem. Physiol., (1976), 53B, 263. 22 Hammock, B.D. andQuistad,G.B., in "The Juvenile Hormones", (L.I. Gilbert, ed.), Plenum Press, New York, (1976),p374. 23 Hangartner, W.W., Suchý, Μ., Wipf, H.-K., and Zurflüh, R.C., J. Agric. Food Chem., (1976), 24, 169. 24 Dorn, S., Oesterhelt, G., Suchý, M., Trautmann, K.H., and Wipf, H.-K., J. Agric. Food Chem., (1976), 24, 637. 25 Quistad, G.B., Staiger, L.E., and Schooley, D.A., J. Agric. Food Chem., (1974), 22, 582. 26 Schooley, D.A., Bergot, B.J., Dunham, L.L., and Siddall, J.B., J. Agric. Food Chem., (1975), 23, 293. 27 Schooley, D.A., Creswell, K.M., Staiger, L.E., and Quistad, G.B., J. Agric. Food Chem., (1975), 23, 369. 28 Quistad, G.B., Staiger, L.E., and Schooley, D.A., Pestic. Biochem. Physiol., (1975), 5, 233. 29 Hammock, B.D., Mumby, S.M., and Lee, P.W., Pestic. Biochem. Physiol., (1977),7,261. 30 Quistad, G.B., Staiger, L.E., Bergot, B.J., and Schooley, D.A., J. Agric. Food Chem., (1975), 23, 743. 31 Quistad, G.B., Staiger, L.E., and Schooley, D.A., J. Agric. Food Chem., (1975), 23, 750.


176

PESTICIDE AND XENOBIOTIC METABOLISM IN AQUATIC ORGANISMS

32 Quistad, G.B., Staiger, L.E., and Schooley, D.A., J. Agric. Food Chem., (1976), 24, 644. 33 Quistad, G.B., Schooley, D.A., Staiger, L.E., Bergot, B.J., Sleight, B.H., and Macek, K.J., Pestic. Biochem. Physiol., (1976), 6, 523. 34 Chamberlain, W.F., Hunt, L.M., Hopkins, D.E., Gingrich, A.R., Miller, J.A., and Gilbert, B.N., J. Agric. Food Chem., (1975), 22, 736. 35 Davison, K.L., J. Agric. Food Chem., (1976), 24, 641. 36 Tokiwa, T., Uda, F., Uemura, J., and Nakazawa, Μ., Oyo Yakuri, (1975), 10, 471. 37 Hawkins, D.R., Weston, K.T., Chasseaud, L.F., and Franklin, E.R., J. Agric. Food Chem., (1977),25,398. 38 Quistad, G.B., Staiger, L.E., and Schooley, D.A., Life Sci., (1974), 15, 1797. 39 Schaefer, C.H. and Dupras, E.F., J. Econ. Entomol., (1973), 66, 923. 40 Quistad, G.B., Staiger, L.E., and Schooley, D.A., J Agric. Food Chem., (1975), 23, 299. 41 Fall, R.R., University of Colorado, personal communication, (1977). 42 Metcalf, R.L. and Sanborn, J.R., Ill. Nat. Hist. Surv. Bull., (1975), 31, 393. RECEIVED

January 2, 1979.


Pesticide and Xenobiotic Metabolism in Aquatic Organisms - American

Recommend Documents