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Fate of Fenitrothion in Shaded and Unshaded Ponds 1
GREG P. MALIS and DEREK C. G. MUIR Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba, R3T 2N6, Canada
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Fenitrothion ( C-ring-labelled) was applied to two outdoor ponds (3.6 m water volume) at a rate of 165 g/ha on two consecutive years. One pond was shaded from direct sunlight with black polyethylene for the first 17 days of the experiment to simulate a forest pond. I n i t i a l concentrations of the insecticide in water were about 70 μg/L. Half-lives (t 1/2's) of fenitrothion were 1.0 and 1.6 days under unshaded and shaded conditions, respectively, indicating the importance of photolysis in the degradation of the compound in water. Τ 1/2's of the major degradation product, 3-methyl-4-nitrophenol were similar under shaded and unshaded conditions. Concentrations of fenitrothion in air above the ponds, at 10 cm height, averaged 0.020 and 0.098 μg/m over the shaded and unshaded water, respectively, during the first 24 hours after application (Year 1). Levels in air represented a flux estimated to be 5.5 μg/m hour in the unshaded pond or less than 1% of the insecticide applied. Aquatic macrophytes (Lemna and Typha species) and fish accumulated 3 to 6% of added ( C)-fenitrothion by two days post-treatment. Levels of C-fenitrothion in sediment (0-3 cm depth) reached a maximum after 5 days and were higher in unshaded conditions (27% of added 14C) than under shaded conditions (8.5%) during both years of the study. Greater than 90% of the radioactivity could be accounted for at 2 days post-treatment, however, by 21 days overall accountibility was reduced to .)). A bloom of filamentous green algae (Spirogyra sp.) occurred i n the unshaded pond during Year 2. Fathead minnows (Pimephales promelas) were added to the ponds one week p r i o r to the study each year. The shaded and unshaded ponds were each t r e a t e d on two consecutive years ( J u l y , 1979 and again i n June, 1980) w i t h f e n i t r o t h i o n at a r a t e of approximately 165 g/ha s i m i l a r to commonly used rates of a e r i a l a p p l i c a t i o n ( 1 ) . The f o r m u l a t i o n c o n s i s t e d of f e n i t r o t h i o n (175 mg Year 1 and 163.4 mg Year 2; t e c h n i c a l grade), C - f e n i t r o t h i o n (100 μΟί Year 1; 90 μ01 Year 2), 33 mg Aerotex 3470 (Texaco Canada Ltd.) and 34 mg A t l o x ( A t l a s Chemical Co.) i n 500 mL water. The f o r m u l a t i o n was s t i r r e d i n t o the upper 10 cm of the water column w i t h a metal rod. Water (0-30 cm depth), sediment (0-3 cm depth c o r e s ) , f i s h , duckweed, algae, and c a t t a i l shoots ( p o r t i o n of the plant above sediment) were c o l l e c t e d once pre-treatment each year and at various time i n t e r v a l s up to 77 days post-treatment. A l l samples except water were stored at -50°C i n sealed containers u n t i l analysis.
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Table I . Water chemistry parameters and l i g h t i n t e n s i t y i n outdoor ponds f o l l o w i n g f e n i t r o t h i o n treatment - Year 1.
Pond
a
Time (days)
pH
TSS Chloro Susp. C (mg/L) fog/L) (mg/L)
Shaded Unshaded Control
1
n.s 8.06 7.52
8 10 28
32.0 97.0 208.0
3.5 8.0 17.1
Shaded Unshaded
14
—
—
—
—
—
—
—
—
Shaded Unshaded Control
35
8.02 8.80 7.94
8 16 9
15.1 11.2 37.8
1.4 3.4 4.89
Light. Intensity (μΕ/m^ s e c ) +4 cm -15 cm !
45 1450 —
b
20 775 —
30 1700
14 800
1300 1550
750 800
——
—
a - TSS = T o t a l suspended s o l i d s ; Chloro = c h l o r o p h y l l a; Susp. < = suspended carbon, b - L i g h t i n t e n s i t y measured w i t h a quantum sensor. The s h e l t e r over the unshaded pond was removed on day 17.
A n a l y t i c a l methods, a. Water. Depth i n t e g r a t e d water samples (0.9 L d u p l i c a t e s ) were c o l l e c t e d by a t t a c h i n g a screw-cap w i t h i n l e t (6mm i . d . g l a s s ) and o u t l e t nozzles (6 mm i . d . U-tube) to
Garner and Harvey; Chemical and Biological Controls in Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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CHEMICAL AND BIOLOGICAL CONTROLS IN FORESTRY
each sample j a r and lowering the c o n t a i n e r s l o w l y through the water column (0-30 cm depth). Dichloromethane (DCM)(10mL) was added to the sample immediately a f t e r c o l l e c t i o n and the sample was s t o r e d at 4 C u n t i l analysed. Water samples were a c i d i f i e d (pH 2.0) and e x t r a c t e d w i t h DCM (150, 75, 75 mL). P o r t i o n s of the e x t r a c t were analysed by l i q u i d s c i n t i l l a t i o n counting (LSC) and by gas chromatography (GLC). The e x t r a c t s were a l s o assayed by t h i n - l a y e r chromatography (TLC) and r a d i o a c t i v i t y was detected by autoradiography. b. Sediment. A p o r t i o n of each sediment sample (0.5 g t r i p l i c a t e s ) was combusted on a Packard 306 o x i d i z e r (Packard Instruments, Chicago) and the C02 analysed by LSC. Samples (20 g wet wt) were r e f l u x e d w i t h 150 mL a c e t o n i t r i l e - w a t e r (9:1) f o r 17 hours. The mixture was f i l t e r e d , the f i l t r a t e evaporated t o 10 mL and t r a n s f e r r e d to a separatory funnel w i t h water. The aqueous phase was e x t r a c t e d w i t h DCM and the organic phase was evaporated to s m a l l volume. A l i q u o t s of the DCM e x t r a c t were assayed by LSC t o determine t o t a l e x t r a c t a b l e r a d i o a c t i v i t y . P o r t i o n s of the e x t r a c t were d i s s o l v e d i n methanol-water (9:1) and cleaned up by reverse phase chromatography on C18 Sep-Pak (Waters A s s o c i a t e s , M i s s i s s a u g a , Ont.) and then analysed by HPLC. Unextractable r a d i o a c t i v i t y i n sediment was determined by combustion of a s m a l l p o r t i o n of the residuum. Selected samples were a l s o r e - e x t r a c t e d by r e f l u x i n g w i t h IN HC1 (17 h r s ) and the a c i d i c e x t r a c t p a r t i t i o n e d w i t h DCM to recover a d d i t i o n a l r a d i o a c t i v i t y . Recoveries of ( C ) - f e n i t r o t h i o n from 4 pre-treatment sediment samples spiked at 0.75 ng/g averaged 90.2 ± 18.7% using the 17 hour r e f l u x w i t h a c e t o n i t r i l e - w a t e r . c. Aquatic p l a n t s and f i s h . Duckweed, c a t t a i l and f i s h samples were combusted (0.5 g ) ( d u p l i c a t e s Year 1, t r i p l i c a t e s Year 2) and the C02 assayed by LSC. Whole f i s h (average wt 3 g) were i n i t i a l l y ground and sub-sampled. Dry weight of p l a n t s was determined by a i r - d r y i n g to constant weight. Duckweed samples (20 g wet wt) were e x t r a c t e d by blending w i t h methanol (10 min). The e x t r a c t was then evaporated to remove most of the methanol. The residue was p a r t i t i o n e d w i t h DCM and cleaned up on C18 Sep-Paks as described f o r sediment. d. A i r . Polyurethane foam plugs (50 mm d i a . ) were prepared f o r use by e x t r a c t i o n w i t h hexane:acetone (1:1) f o r 84 hours (9). The foam plugs were placed i n g l a s s tubes located above the center of each pond. The tubes were located 10 cm above each pond (Year 1) or a t 2, 5 and 10 cm heights (Year 2 ) . A i r - f l o w s were maintained at 10L/min. Foam plugs were changed every 24 hours (days 1-3) and then every 2-3 days f o r the next 18 days post-treatment. The foams were placed i n wide-mouth g l a s s j a r s and hexane was added immediately. Further e x t r a c t i o n was c a r r i e d out on a Soxhlet apparatus and the e x t r a c t s were assayed by LSC and GLC. e. GLC, TLC and HPLC c o n d i t i o n s : GLC was c a r r i e d out w i t h e i t h e r a Tracor 560 or P e r k i n Elmer 900, both equipped w i t h
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llf
ll+
ll+
Garner and Harvey; Chemical and Biological Controls in Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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19.
MALIS AND MUIR
Fate of Fenitrothion in Ponds
281
nitrogen-phosphorus d e t e c t o r s . Columns (2 mm i . d . χ 1.8 m) c o n t a i n i n g 3% OV-17 on Chromosorb W-HP (80/100 mesh) were operated at 200°C f o r a n a l y s i s of f e n i t r o t h i o n and AF. MNP was chromatographed on a column of 1% SP-1240 DA on Supelcoport 100/120 mesh at 190°C. HPLC separations were c a r r i e d out w i t h a reverse-phase column ^Bondapak C-18) using methanol-water (45:55) at 1.8 mL/min f o r 13.5 min followed by methanol-water (60:40) f o r 20 min. A Waters 6000A pump, Model 440 UV absorption detector and a f r a c t i o n c o l l e c t o r (LKB M u l t i r a c ) were used. F r a c t i o n s e l u t i n g from the column were c o l l e c t e d and assayed by LSC. Retention times of f e n i t r o t h i o n , AF, and MNP under these c o n d i t i o n s were 27.0, 11.0, and 7.5 minutes, r e s p e c t i v e l y . TLC separations were performed on s i l i c a - g e l p l a t e s u s i n g two solvent systems: I . Toluene:ethyl formate:formic a c i d (5:7:1)(10) and I I . CCl^:DCM:methanol (5:7:1). Autoradiography was c a r r i e d out by exposing TLC p l a t e s to X-ray f i l m (Kodak NS-2T) f o r up to one month. R a d i o a c t i v e spots were scraped and e x t r a c t e d w i t h methanol to e s t a b l i s h the q u a n t i t y of each degradation product. Rf's ( f e n i t r o t h i o n = 1.0) of AF, MNP, F0 and SMF were 0.22, 0.76, 0.53 and 0.73 on System I and 0.83, 0.66, 0.77 and 0.60 on System I I . R e s u l t s and D i s c u s s i o n Water. F e n i t r o t h i o n disappeared r a p i d l y from unshaded ponds decreasing to
