Evaluation of Pesticides in Ground Water - American Chemical Society

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Fate of Aldicarb in Wisconsin Ground Water John M . Harkin, Frank A . Jones, Riyadh N. Fathulla, E. Kudjo Dzantor, and David G. Kroll Department of Soil Science, University of Wisconsin-Madison, Madison, WI 53706

Small amounts of aldicarb sulfoxide and sulfone leach through sandy soils to shallow groundwater in Central Wisconsin fields where aldicarb is applied to irrigated potatoes. Leachate residue concentrations decrease with application rates and later application time. The pattern of leaching through soil and the levels detectable in groundwater are invariably highly erratic. Leaching occurs mainly during the late summer and fall of years of application; highest residue concentrations in groundwater occur later in a zone near the water table. These levels dissipate as this zone is overlain with uncontaminated leachate, but residues disappear at rates faster than can be ascribed to dilution and dispersion due to natural groundwater movement. The latter is complicated by water table fluctuations and flow perturbation caused by water extraction for irrigation. Residue attenuation is apparently accelerated by hydrolysis in the alkaline groundwater and degradation by a variety of groundwater-inhabiting bacteria. The groundwater alkalinity increases with depth and fluctuates seasonally, rising in summer with CO in the water, which dissolves dolomitic limestone in the aquifer sediments. Rates of breakdown presumably vary with the groundwater temperature, which ranges from 3-4°C in February-March to 20-21°C in August near the water table but remains at 12-14°C 10 m deep in the aquifer. This complex interplay of factors prevents accurate prediction of the fate of aldicarb residues in groundwater by mathematical modeling on the basis of available data. Sensitivity analysis indicates that degradation rates are the crucial determinant of occurrence and persistence in groundwater. 2

f

The i n t r o d u c t i o n i n t h e e a r l y 1 9 7 0 s o f t h e s o i l - i n c o r p o r a t e d , w a t e r - s o l u b l e s y s t e m i c i n s e c t i c i d e / n e m a t i c i d e a l d i c a r b was r e g a r d e d as a major advance i n t h e t e c h n o l o g y o f p e s t c o n t r o l . It eliminated t h e once p r e v a l e n t h a z a r d o f i n a d v e r t e n t exposure o f a p p l i c a tors or inhabitants o f nearby d w e l l i n g s , wildlife, and u s e f u l i n s e c t s to t o x i c chemicals during spraying or a e r i a l a p p l i c a t i o n o f pesticides. 0097-6156/86/0315-0219$10.25/0 © 1986 A m e r i c a n C h e m i c a l Society

Garner et al.; Evaluation of Pesticides in Ground Water ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


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E V A L U A T I O N O F PESTICIDES IN G R O U N D WATER

It was 1979 before i n t r u s i o n of a l d i c a r b residues into a d o m e s t i c w e l l l o c a t e d c l o s e to i r r i g a t e d p o t a t o f i e l d s i n S u f f o l k County on Long I s l a n d , New York was r e p o r t e d i n August, 1979 (1). T h i s d i s c o v e r y p r e c i p i t a t e d an e x t e n s i v e s u r v e y o f o t h e r w e l l s i n t h e v i c i n i t y (1_,2^ and r e g u l a t o r y a c t i o n s which e l i m i n a t e d the use o f the i n s e c t i c i d e on Long I s l a n d . A l d i c a r b was b e i n g used on a v a r i e t y of c r o p s i n s e v e r a l s t a t e s , and c o n c e r n a r o s e whether residues of the p e s t i c i d e might a l s o be encountered in other areas. On the b a s i s of i n f o r m a t i o n t h e n a v a i l a b l e , t h i s was deemed u n l i k e l y , because of the s p e c i a l c i r c u m s t a n c e s of a l d i c a r b use on Long I s l a n d . F i r s t , a p p l i c a t i o n r a t e s were h i g h : 5-7 pounds of a c t i v e i n g r e d i e n t per a c r e ( l b a . i . / A » 5.6-7.8 kg/ha) to e n s u r e adequate c o n t r o l of two major p o t a t o p e s t s , the C o l o r a d o p o t a t o beetle (Leptinotarsa deeemtineata) and the golden nematode (Hetevodeva rostoehiensis); i n other areas such as Wisconsin a p p l i c a t i o n r a t e s of o n l y 2-3 l b a . i . / A (2.2-3.4 kg/ha) were b e i n g used on p o t a t o e s . S e c o n d l y , on Long I s l a n d , p o t a t o e s are grown on irrigated sandy s o i l s over high water t a b l e s . While s i m i l a r c o n d i t i o n s e x i s t i n o t h e r a r e a s , such as the C e n t r a l Sands r e g i o n o f W i s c o n s i n , the a v e r a g e a n n u a l p r e c i p i t a t i o n r a t e i s much h i g h e r f o r Long I s l a n d (50 v e r s u s 30 i n c h e s 127 v. 76 cm per y e a r ) . T h i r d , the c o n t a m i n a t e d Long I s l a n d a q u i f e r i s l a r g e l y a s h a l l o w c o n f i n e d a q u i f e r , and the pH and a l k a l i n i t y of the water a r e low. In W i s c o n s i n , i n c o n t r a s t , much o f the uppermost a q u i f e r i n the p o t a t o - g r o w i n g a r e a i s c l o s e to d i s c h a r g e a r e a s , e i t h e r d r a i n a g e d i t c h e s or the W i s c o n s i n R i v e r and i t s t r i b u t a r i e s , and the pH and a l k a l i n i t y o f the water are h i g h · I t was known t h a t β

a l d i c a r b r e s i d u e s have o n l y b r i e f p e r s i s t e n c e i n s u r f a c e water, and a r e more s t a b l e under a c i d than a l k a l i n e c o n d i t i o n s . Indeed, on the b a s i s o f a g e o g r a p h i c s c a l e model ( c f . 6) p r o j e c t i o n s were made u s i n g a n u m e r i c a l r a t i n g system which a t the time ranked the Long Island aquifer first in sensitivity toward aldicarb residue c o n t a m i n a t i o n , W i s c o n s i n ' s C e n t r a l Sand P l a i n a d i s t a n t second, and all other areas of aldicarb use—especially those i n warmer southern states—as relatively safe, regardless of a p p l i c a t i o n rates. However, f o l l o w i n g p r e s s r e p o r t s c l a i m i n g t h a t e v i d e n c e f o r the o c c u r r e n c e of s e v e r a l p e s t i c i d e s , i n c l u d i n g a l d i c a r b , had been found by gas c h r o m a t o g r a p h i c a n a l y s i s o f s i x W i s c o n s i n groundwater samples, the m a n u f a c t u r e r and the S t a t e o f W i s c o n s i n examined f r e s h samples from the same w e l l s . The S t a t e t e s t s i n d i c a t e d no contam i n a t i o n by any of 70 p e s t i c i d e s f o r which a n a l y s e s were c o n d u c t e d . However a t the t i m e , no l a b o r a t o r y i n W i s c o n s i n had f a c i l i t i e s f o r conducting aldicarb residue analyses i n the p a r t s - p e r - b i l l i o n range. U n i o n C a r b i d e ' s a n a l y s e s i n d i c a t e d the p r e s e n c e of a l d i c a r b residues in one sample from a monitoring well at a potato processing p l a n t wastewater d i s p o s a l a r e a . This provoked the company to examine samples from s e v e r a l d o e m s t i c w e l l s , and to r e p o r t i n J a n u a r y 1981 t h a t a l d i c a r b r e s i d u e s had been found i n 12 samples. As more w e l l w a t e r samples were a n a l y z e d , f u r t h e r contam i n a t e d s i t e s were d e t e c t e d . O b v i o u s l y , the g e o g r a p h i c s c a l e model was i n a d e q u a t e to p r e d i c t p o l l u t i o n i n c i d e n t s f o r W i s c o n s i n . As a r e s u l t of the i n i t i a l p r e s s r e p o r t s , r e s e a r c h was begun by the U n i v e r s i t y of W i s c o n s i n i n the Central Sands a r e a of W i s c o n s i n t o examine groundwater f o r the p r e s e n c e of p e s t i c i d e



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residues. Because o f r e s t r i c t e d f u n d i n g , e f f o r t s were c o n c e n t r a t e d e x c l u s i v e l y on a l d i c a r b , as r e p r e s e n t i n g a w o r s t - c a s e s i t u a t i o n , because t h i s was t h e o n l y m a t e r i a l f o r which t h e p r e s e n c e o f residues at levels o f c o n c e r n had been c o n f i r m e d by r e l i a b l e analyses. The major g o a l o f t h e r e s e a r c h was t o determine which f a c t o r s a f f e c t e d t h e amount o f i n t r u s i o n o f p e s t i c i d e r e s i d u e s i n t o t h e groundwater and t h e i r p e r s i s t e n c e and d i s t r i b u t i o n i n t h e groundwater. Such i n f o r m a t i o n c o u l d e n a b l e t h e m a n u f a c t u r e r and s t a t e and f e d e r a l r e g u l a t o r y agencies t o d e c i d e whether the m a t e r i a l could be used safely, and i f s o , under what conditions i n Wisconsin. A f u r t h e r g o a l was t o p r e d i c t how l o n g t h e r e s i d u e concentrations a l r e a d y i n t h e water would remain a t l e v e l s o f c o n c e r n and whether t h e i r movement t o domestic w e l l s c o u l d be forecast. The f i r s t s t e p toward a t t a i n i n g these g o a l s was to c o l l e c t a l d i c a r b r e s i d u e c o n c e n t r a t i o n s and o t h e r water q u a l i t y p a r a m e t e r s f o r water samples withdrawn from v a r i o u s depths i n t h e a q u i f e r i n and around s e v e r a l f i e l d s i n which i r r i g a t e d p o t a t o e s had been t r e a t e d a t d i f f e r i n g times w i t h a l d i c a r b . The next s t e p was t o d e s c r i b e t h e mechanisms o f a l d i c a r b d i s p o s i t i o n f o l l o w i n g a p p l i c a t i o n and t o c a l i b r a t e and t e s t a model u s i n g d a t a f o r a l d i c a r b and other chemical s p e c i e s accumulated from t h e l i t e r a t u r e and from recent f i e l d analyses. I t was hoped t h i s approach would permit s a t i s f a c t o r y p r e d i c t i o n o f t h e d i s t r i b u t i o n and f a t e o f a l d i c a r b applied at a f i e l d - s i z e s c a l e , and t h e p o t e n t i a l f o r e n t e r i n g d o m e s t i c w e l l s w i t h i n 0.5-5 m i l e s (0.8-8.0 km) a t l e v e l s above t h e recommended s a f e t y l e v e l o f 10 yg/L. T y p i c a l 160-acre (65-ha) i r r i g a t e d p o t a t o f i e l d s i n W i s c o n s i n a r e square and have s i d e s 0.5 m i l e (0.8 km) l o n g , and p r i v a t e w e l l s s e r v i n g farmhouses o r r u r a l homes a r e o f t e n l o c a t e d i n t h e c o r n e r s o f o r i m m e d i a t e l y a d j a c e n t to such f i e l d s o r among a s e r i e s o f such f i e l d s . Procedures Site Selection. N i n e 160-acre (65-ha) i r r i g a t e d f i e l d s i n two o f the main potato-growing counties o f Wisconsin (Portage and Waushara, 6.4 and 2.2 m i l l i o n cwt. o r 3.2 and 1.1 m i l l i o n q u i n t a l s i n 1981) were s e l e c t e d f o r s t u d y . S o i l s i n each f i e l d were w e l l drained sands o r loamy sands, m a i n l y o f the P l a i n f i e l d s e r i e s ( T y p i c Udipsamments), c o n t a i n i n g 1-2% o r g a n i c matter i n the A horizon. Seven f i e l d s had p r e v i o u s l y been examined (5_,7_). The eighth f i e l d was l o c a t e d i m m e d i a t e l y southwest o f one f i e l d a l r e a d y b e i n g m o n i t o r e d i n Waushara County, t h e n i n t h f i e l d was d i r e c t l y northwest o f t h e e i g h t h f i e l d . A l l f i e l d s had known h i s t o r i e s o f a l d i c a r b t r e a t m e n t s ( T a b l e I ) . The d i r e c t i o n o f undisturbed groundwater f l o w i n t h e a r e a i s a p p r o x i m a t e l y westnorthwest and t h e r a t e i s a p p r o x i m a t e l y 1 f o o t (30 cm) p e r day (8,9_). When c e n t r a l - p i v o t i r r i g a t o r s a r e i n u s e , groundwater f l o w i s p e r t u r b e d by t h e cone o f d e p r e s s i o n c r e a t e d by water w i t h d r a w a l through h i g h - c a p a c i t y irrigation pumps (5J0L>2) · T N E C O N E O F d e p r e s s i o n does n o t extend t o the edge o f t h e f i e l d and r e c o v e r y i s r a p i d once pumping c e a s e s .



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Table I.

A p p l i c a t i o n r a t e i n pounds o f a c t i v e i n g r e d i e n t per a c r e (kg/ha) 3.0 (3.4) 3.0 (3.4) 2.4 (2.7) 2.5 (2.8) 2.7 (3.0) 3.0 (3.4) 3.0 (3.4)

Field 1 2 3


A l d i c a r b A p p l i c a t i o n Rates and 9 F i e l d s under Study

4

5

3.0 3.0 2.25 3.0 1.95 1.8 2.7 3.0

6 7

8 9

•Treated

at plant

(3.4) (3.4) (2.5) (3.4) (2.1) (2.0) (3.0) (3.4)

Frequencies i n

the

Years treated 1977, 1979, 1981 1976, 1978, 1980 1976, 1977 1978 1979 1980 30 rows west of center p i v o t , 1982 (5 a c r e s ) 1979 E a s t h a l f , 1980 1981* 1980 1982* 1984* 1978, 1980, 1981 1979, 1980

emergence; a l l o t h e r t r e a t m e n t s were a t

planting.

The f i e l d s were o r i g i n a l l y s e l e c t e d to a l l o w comparison o f aldicarb residue movement and persistence under the conditions pertinent to i t s p r e s c r i b e d ( l a b e l ) use and p r e - and post-1982 maximum a p p l i c a t i o n r a t e s [3 v e r s u s 2 l b a . i . / A (3.4 v. 2.2 kg/ha)]. At the s t a r t of the s t u d y : 1. 2. 3. 4. 5. 6.

F i e l d s 3, 8 and 9 had received a l d i c a r b a p p l i c a t i o n s at p l a n t i n g s e v e r a l y e a r s i n sequence; Fields 1 and 2 had received aldicarb applications at p l a n t i n g i n a l t e r n a t e years; F i e l d 5 had r e c e i v e d a l d i c a r b a t p l a n t i n g o n l y once; Field 4 had never been t r e a t e d w i t h a l d i c a r b and was downgradient i n the water t a b l e from a t r e a t e d f i e l d ; F i e l d 6 had been t r e a t e d o n l y once a t p l a n t emergence 1 y e a r before monitoring; F i e l d 7 had been t r e a t e d once at p l a n t i n g , then 2 y e a r s later at plant emergence during the first year of monitoring.

Well Installation. In seven fields, monitoring wells were i n s t a l l e d a t e i g h t o r more p o s i t i o n s around the p e r i m e t e r o f the f i e l d and one or more l o c a t i o n s c l o s e to the c e n t e r p i v o t . Only two p e r i m e t e r w e l l s i t e s were chosen i n the o t h e r two f i e l d s ( t o comply w i t h the owner's w i s h e s ) . The w e l l s were p l a c e d as c l o s e as p o s s i b l e to the t r e a t e d a r e a s . The w e l l c a s i n g s were Schedule 40 p o l y v i n y l c h l o r i d e (PVC) p i p e ; the w e l l p o i n t s were made of PVC w i t h 1 o r 3 f e e t (30 o r 91 cm) o f 0.006 i n c h (0.15 mm) s l i t s (Timco Mfg., Sauk C i t y , WT 53578). S h a l l o w w e l l s were i n s t a l l e d by handa u g e r i n g t h r o u g h the s o i l t o o r s l i g h t l y below the water t a b l e using a 4-inch (102 mm) diameter Soil Conservation Service



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s t a i n l e s s s t e e l bucket auger ( A r t ' s Machine Shop, American F a l l s , OR 83211)· The d r i l l i n g s were s t o r e d i n sequence on a s h e e t o f p l a s t i c a l o n g s i d e the h o l e . A d r i v i n g cap was p l a c e d i n t h e end o f the p i p e and t h e w e l l d r i v e n t o t h e d e s i r e d depth u s i n g a p o s t driver o r sledgehammer. The emergent p i p e was c u t o f f a t a s u i t a b l e e l e v a t i o n above ground and a r u b b e r vacuum pump hose inserted into the w e l l . Water pumped from t h e w e l l u s i n g a b a t t e r y - d r i v e n p e r i s t a l t i c pump (ISCO Model 1680 Wastewater Sampler Superspeed Pump, ISCO, L i n c o l n , NB 68528) was s q u i r t e d down the o u t s i d e o f t h e c a s i n g as t h e d r i l l i n g s from t h e h o l e were r e t u r n e d i n the r e v e r s e o f t h e sequence i n which they had been removed. This r e c o n s t i t u t e s the o r i g i n a l s o i l p r o f i l e without channeling o r arching. The t o p 1 m o f t h e d r i l l e d h o l e was s e a l e d w i t h d r y , p u l v e r i z e d b e n t o n i t e c l a y ( Q u i c k - J e l l , N.L. B a r o i d I n d u s t r i e s , P.O. Box 4350, Houston, TX 77210). A f t e r i n s t a l l a t i o n , t h e w e l l was d e v e l o p e d by pumping u n t i l t h e withdrawn water c o n t a i n e d no v i s i b l e s e d i m e n t s . Each w e l l was capped w i t h a screw-on t o p s e c u r e d w i t h a long-shank b i c y c l e p a d l o c k i n s e r t e d t h r o u g h h o l e s d r i l l e d d i a g o n a l l y t h r o u g h t h e cap and p i p e f i t t i n g . A commercial truck-mounted well d r i l l i n g r i g was used t o i n s t a l l deeper w e l l s . D r i l l i n g was performed u s i n g h o l l o w - s t e m c o n t i n u o u s f l i g h t a u g e r s , which were l e f t i n p l a c e w h i l e a p r e a s sembled PVC w e l l was d r i v e n by hand t o embed i t i n t h e a q u i f e r sediments a t t h e p r e s e l e c t e d d e p t h . The h o l l o w - s t e m auger was t h e n removed, t h e d r i l l i n g s washed i n as b e f o r e and t h e w e l l s e a l e d w i t h b e n t o n i t e a t t h e t o p and d e v e l o p e d by pumping. I n each f i e l d , a r a i n - g a u g e was a t t a c h e d t o one m o n i t o r i n g w e l l t o c o l l e c t r a i n f a l l and i r r i g a t i o n w a t e r . The l o c a t i o n o f t h e w e l l s and samplers i n F i e l d s 1-7 a r e shown i n F i g u r e s 1 and 2. M o n i t o r i n g w e l l s were a l s o p l a c e d i n f o u r t e s t p l o t s sown t o p o t a t o e s a t the U n i v e r s i t y o f W i s c o n s i n - M a d i s o n E x p e r i m e n t a l Farm, near Hancock, W i s c o n s i n . These p l o t s were t r e a t e d w i t h a l d i c a r b a t a r a t e o f 2 l b . a . i . / A (2.24 kg/ha) a t p l a n t i n g and a t p l a n t emergence. One s e t o f p l o t s was i r r i g a t e d a t a r a t e c o r r e s p o n d i n g t o the measured évapotranspiration r a t e f o r t h e r e g i o n , t h e second s e t a t 1.6 times t h e évapotranspiration r a t e ( 2 1 ) . M u l t i l e v e l Samplers. M u l t i l e v e l samplers (10) assembled i n the l a b o r a t o r y were i n s t a l l e d a t s e l e c t e d p o s i t i o n s i n f i v e f i e l d s . A b u n d l e o f 0 . 5 - i n c h (12.7 mm) o.d. h i g h - d e n s i t y l i n e a r p o l y e t h y l e n e tubes (Central Plastics Distributors, Madison, WI 53703) were c l u s t e r e d around a c e n t r a l 0 . 7 5 - i n c h (19.1 mm) d i a m e t e r PVC p i p e a t d i s t a n c e s 18 i n c h e s (45.7 cm) a p a r t . The ends o f each sampler were s u r r o u n d e d by a s c r e e n o f S t y l e 3401 Typar spunbonded p o l y p r o p y l e n e (DuPont de Nemours Chemicals Corp., W i l m i n g t o n , DE 19898) t a p e d t o the t u b i n g . The bundle o f tubes was s e c u r e d around t h e c e n t r a l PVC p i p e u s i n g duct tape and i n s t a l l e d t h r o u g h a h o l e d r i l l e d t o t h e d e s i r e d depth w i t h t h e d r i l l r i g . The bottom end o f t h e h o l l o w stem auger was c l o s e d w i t h a l a r g e r u b b e r s t o p p e r t o p r e v e n t sand from f i l l i n g t h e c e n t e r o f the auger d u r i n g d r i l l i n g . With the auger i n p l a c e a t a depth such t h a t t h e uppermost s a m p l i n g p o r t would be a t o r a l i t t l e below t h e water t a b l e , t h e i n s i d e o f t h e auger stem was f i l l e d w i t h water t o a l e v e l above t h e water table. The m u l t i l e v e l - s a m p l e r bundle was i n s e r t e d t h r o u g h the auger's h o l l o w stem and a l l o w e d t o s i t u n t i l t h e tubes had f i l l e d



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w i t h water. The r u b b e r s t o p p e r was then d i s l o d g e d from t h e end o f the auger by t a p p i n g s h a r p l y on t h e end o f t h e c e n t r a l PVC p i p e . Unless t h e auger stem i s f i l l e d w i t h water b e f o r e t h e rubber s t o p p e r i s d i s p l a c e d , sand i s swept up i n t o t h e h o l l o w stem when the s t o p p e r i s d i s l o d g e d . T h i s jams t h e m u l t i l e v e l sampler i n t h e h o l l o w - s t e m auger when i t i s removed from t h e h o l e . By f i l l i n g t h e h o l l o w stem w i t h water t h e auger c a n be withdrawn l e a v i n g the m u l t i l e v e l sampler i n p l a c e a t t h e d e s i r e d d e p t h . After positioni n g t h e s a m p l e r s , t h e d r i l l h o l e around t h e bundle was r e f i l l e d by washing i n removed m a t e r i a l and s e a l i n g t h e s u r f a c e w i t h b e n t o n i t e . Each sampler was d e v e l o p e d u s i n g t h e p e r i s t a l t i c pump u n t i l t h e water d e l i v e r e d c o n t a i n e d no sediment. The ends o f t h e tubes and c e n t r a l p i p e emerging from t h e ground were c o v e r e d w i t h a capped PVC p i p e which was l o c k e d t o t h e c e n t r a l PVC p i p e w i t h a b i c y c l e padlock. F i e l d Lysimeters. I n a d d i t i o n , p o t a t o e s were p l a n t e d i n each o f two f i e l d l y s i m e t e r s (11,12) and t r e a t e d w i t h a l d i c a r b a t p l a n t emergence a t a r a t e o f 3 (1982) and 2 (1983-5) l b a . i . / A (3.36 and 2.24 k g / h a ) . Each l y s i m e t e r was s p r a y - i r r i g a t e d w i t h 0.75 i n c h (19.3 mm) o f water t w i c e a week throughout t h e growing season. The s o i l i n each l y s i m e t e r was m a i n t a i n e d under a c o n s t a n t s u c t i o n u s i n g an e l e c t r i c pump ( G a s t , Benton Harbor, MI 49022) w i t h a bleed. D r a i n a g e from each l y s i m e t e r was passed t h r o u g h a s e p a r a t e water meter f i t t e d w i t h an a u t o m a t i c c o u n t e r and p r i n t e r t o measure incremental and c u m u l a t i v e f l o w . Portions o f d r a i n a g e were d i v e r t e d p e r i o d i c a l l y from each l y s i m e t e r t o a p l e x i g l a s s sampler in parallel t o t h e d r a i n a g e system and b o t t l e d and f r o z e n f o r future analysis. Sampling. Water samples were c o l l e c t e d p e r i o d i c a l l y from each m o n i t o r i n g w e l l , each s a m p l i n g tube on t h e m u l t i l e v e l s a m p l e r s , and from the i r r i g a t i o n w e l l s i n the f i e l d s under s t u d y . Before s a m p l i n g , water was pumped from each m o n i t o r i n g w e l l o r s a m p l i n g tube u n t i l a c l e a r sample c o u l d be o b t a i n e d o r u n t i l 3 t o 5 times the volume o f t h e w e l l had been removed, t o a s s u r e t h a t t h e sample came from t h e groundwater around the w e l l and not from s t a g n a n t water i n t h e w e l l . D u p l i c a t e o r t r i p l i c a t e samples were c o l l e c t e d i n new 500-ml Nalgene b o t t l e s o r 5 - l i t e r brown g l a s s b o t t l e s w i t h T e f l o n - l i n e d c a p s , each p r e v i o u s l y washed w i t h a c e t o n e , d i s t i l l e d water, and r i n s e d t h r e e times w i t h water from t h e w e l l o r sampler b e i n g sampled. The temperature o f each sample was measured t o t h e n e a r e s t 0.1°C and the pH measured w i t h a D i g i - S e n s e d i g i t a l pH meter ( C o l e - P a l m e r Instrument Co., C h i c a g o , I L 60648), p r e v i o u s l y c a l i b r a t e d i n the l a b o r a t o r y a g a i n s t a C o r n i n g Model 130 pH meter ( C o r n i n g M e d i c a l , M e d f i e l d , MA 02052). Each sample was c h i l l e d i n i c e water i n an i n s u l a t e d p i c n i c c o o l e r and l a t e r frozen u n t i l analysis. B e f o r e each m o n i t o r i n g w e l l was sampled, t h e e l e v a t i o n o f t h e groundwater t a b l e was measured u s i n g a "popper" ( a p l a s t i c c y l i n d e r w i t h a concave base which e m i t s a popping sound when i t impinges on a water s u r f a c e ) suspended a t the end o f a s t e e l measuring t a p e . T h i s d e v i c e gave a c c u r a t e measurements o f water t a b l e depths w i t h out c o n t a m i n a t i n g t h e w e l l w a t e r .



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I n A p r i l 1982, b e f o r e c r o p s were p l a n t e d , the d r i l l r i g was used to c o l l e c t water samples from s p o t s d i r e c t l y beneath the growing a r e a of F i e l d 5. A 30-cm m e t a l w e l l p o i n t w i t h s t a i n l e s s s t e e l s c r e e n welded to the end of a s e c t i o n o f h o l l o w - s t e m auger was d r i l l e d t o v a r i o u s depths below t r e a t e d a r e a s . Water samples were withdrawn t h r o u g h T e f l o n t u b i n g i n s e r t e d down the h o l l o w stem i n t o the p o i n t u s i n g the p e r i s t a l t i c pump. S e d i m e n t - f r e e samples were b o t t l e d and s t o r e d f o r a n a l y s i s as p r e v i o u s l y d e s c r i b e d . P e r i o d i c a l l y , b a t c h e s o f samples were removed from the f r e e z e r and thawed f o r a n a l y s i s . Parameters examined i n c l u d e d l a b o r a t o r y pH, conductivity, total a l k a l i n i t y , c a l c i u m , magnesium, sodium, p o t a s s i u m , n i t r a t e , c h l o r i d e , s u l f a t e , and a l d i c a r b r e s i d u e s . The pH was determined u s i n g a C o r n i n g Model 130 d i g i t a l pH meter; carbonate and bicarbonate a l k a l i n i t i e s were determined t i t r i m e t r i c a l l y , a c c o r d i n g to Method 403; n i t r a t e - n i t r i t e by the automated cadmium r e d u c t i o n method (Method 418 F) and s u l f a t e by the t u r b i d i m e t r i c method (Method 426c) of Standard Methods f o r the E x a m i n a t i o n o f Water and Wastewater ( 1 3 ) ; and c h l o r i d e u s i n g a B u c h l e r - C o t l o v e Model #4-2000 C h l o r i d o m e t e r t i t r a t o r ( 1 4 ) . Na and Κ were d e t e r m i n e d by flame photometry on a Coleman Model 21 i n s t r u ment a c c o r d i n g to Methods 322B and 325B ( 1 3 ) ; Mg and Ca were determined by atomic a b s o r p t i o n on a Perkin-Elmer Model 306 i n s t r u m e n t a c c o r d i n g t o Method 303A ( 1 3 ) . A l d i c a r b Residue A n a l y s i s . For a n a l y s i s o f a l d i c a r b r e s i d u e s , a 100-ml a l i q u o t o f each thawed sample was o x i d i z e d w i t h 1 ml of 40% p e r o x y a c e t i c a c i d , the e x c e s s a c i d n e u t r a l i z e d w i t h 25 ml of 10% sodium b i c a r b o n a t e , and the a l d i c a r b s u l f o n e produced by the oxidation extracted with two 100-ml portions of methylene chloride. The e x t r a c t was d r i e d over 100 g of sodium s u l f a t e , e v a p o r a t e d to d r y n e s s , r e d i s s o l v e d i n 1 ml o f a c e t o n e : e t h e r and chromatographed on a column 12.5 mm d i a m e t e r χ 10 cm of f l o r o s i l ( F l o r o d i n Co., B e r k e l y S p r i n g s , WV 25411) u s i n g 1:1 a c e t o n e : e t h e r as e l u e n t . The p u r i f i e d s u l f o n e f r a c t i o n was a g a i n e v a p o r a t e d to dryness, dissolved i n 1 ml of acetone and s u b j e c t e d to gas chromatography i n an H-P 5880 i n s t r u m e n t ( H e w l e t t - P a c k a r d , P a l o A l t o , CA 94304) on a 2 meter 2 mm i . d . column packed w i t h 10% SP1000 on 80-100 mesh S u p e l c o p o r t ( S c i e n t i f i c P r o d u c t s , McGraw Park, IL 60085) u s i n g a Tracor flame photometric detector (Tracor Instruments, Austin, TX 78721) o r an H-P nitrogen/phosphorus specific detector. The i n j e c t o r temperature was 260°C, the d e t e c t o r temperature 300°C. A n a l y s e s were r u n i s o t h e r m a l l y a t 180 o r 200°C u s i n g h e l i u m as c a r r i e r gas a t a f l o w r a t e of 25 ml/min. The hydrogen f l o w r a t e f o r the d e t e c t o r was 3 ml/min and the a i r f l o w r a t e 60 ml/min u s i n g an a t t e n u a t o r s e t t i n g of 2 . The l i m i t of d e t e c t i o n by this m e t h o d — a s s t a t i s t i c a l l y d e f i n e d by the American C h e m i c a l S o c i e t y ' s Committee on E n v i r o n m e n t a l Improvement ( 1 4 ) — w a s below 1 u g / l i t e r o r ppb but v a l u e s below 1 ppb p r i n t e d out by the i n s t r u m e n t p r o c e s s o r were r e p o r t e d as n o n - d e t e c t s (ND). For q u a l i t y c o n t r o l , s t a n d a r d s were a n a l y z e d f o l l o w i n g e v e r y t e n t h sample. Samples o f pure a l d i c a r b , a l d i c a r b s u l f o x i d e and a l d i c a r b s u l f o n e were donated by Union-Carbide Agricultural Products Company, Raleigh, NC. R e c o v e r i e s of over 90% were c o n s i s t e n t l y o b t a i n e d w i t h 1, 10, and 100 ppb l e v e l s o f the i n d i v i d u a l compounds o r m i x t u r e s of the pure



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s t a n d a r d s o l u t i o n s s p i k e d i n t o d i s t i l l e d o r Madison w e l l water or field samples and subjected to the extraction, cleanup and analysis. U n l e s s recommended c r i t e r i a f o r r e c o v e r i e s from f o r t i f i e d samples (16) and b l a n k s were met, d a t a were d i s c a r d e d and a l l reagents, solvents and p r o c e d u r e s were r e v i e w e d . As a further q u a l i t y c o n t r o l measure, some d u p l i c a t e samples were sent f r o z e n i n i n s u l a t e d c o n t a i n e r s to U n i o n C a r b i d e f o r a n a l y s i s f o r i n t e r l a b o r a t o r y comparison. Water samples from r u r a l r e s i d e n c e s c l o s e to the e x p e r i m e n t a l s i t e s were a l s o a n a l y z e d . Three s h a l l o w d o m e s t i c w e l l s c o n t a m i n a t e d by a l d i c a r b r e s i d u e s above the s u g g e s t e d no a d v e r s e r e s p o n s e l e v e l o f 10 ppb were deepened to examine whether the water q u a l i t y would be Improved. Bacterial Analysis. Groundwater and a q u i f e r sediments samples were c o l l e c t e d a s e p t i c a l l y f o r b a c t e r i a l a n a l y s i s ; the sediments were o b t a i n e d u s i n g h o l l o w - s t e m augers ( 1 7 ) . W i t h the augers i n p o s i t i o n i n the s o i l or groundwater a t a p r e s e l e c t e d d e p t h , samples were c o l l e c t e d i n s i d e a r i g i d , c l e a r p l a s t i c tube ( A c k e r D r i l l Co., S c r a n t o n , PE) p r e v i o u s l y s t e r i l i z e d u s i n g u l t r a v i o l e t l i g h t p a s s e d t h r o u g h the lumen. T h i s tube was inserted inside a split-spoon sampler sterilized by d o u s i n g w i t h e t h a n o l and flaming. The sampler was f e d t h r o u g h the h o l l o w stem w i t h an e x t e n d e r rod and f o r c e d i n t o the u n d i s t u r b e d s o i l / g r o u n d w a t e r below the bore h o l e . A f t e r removal from the s p l i t - s p o o n sampler, the ends of the p l a s t i c c y l i n d e r were c u t o f f w i t h a s t e r i l i z e d k n i f e and capped w i t h s t e r i l i z e d p l a s t i c caps. Subsamples removed under s t e r i l e l a b o r a tory conditions from the c e n t e r s of the s o i l c o r e s were examined for bacteria. Samples of [S-^^CH^] a l d i c a r b , a l d i c a r b s u l f o x i d e and a l d i c a r b sulfone were i n c u b a t e d w i t h samples of groundwater and aquifer s e d i m e n t s to examine the p o t e n t i a l f o r m i c r o b i a l degradation in situ i n groundwater. The [SCH3] a l d i c a r b was p r o v i d e d by U n i o n C a r b i d e A g r i c u l t u r a l P r o d u c t s Company; the l a b e l e d s u l f o x i d e was p r e p a r e d from t h i s by o x i d a t i o n w i t h hydrogen p e r o x i d e , the sulfone f r o m the aldicarb by oxidation with peroxyacetic a c i d . These oxidants afforded better y i e l d s of c l e a n e r p r o d u c t than t h e rrr c h l o r o p e r o x y b e n z o i c a c i d p r e v i o u s l y used ( 1 8 ) . 1

Results The r e s u l t s of the m o n i t o r i n g c l e a r l y i n d i c a t e t h a t regardless of a p p l i c a t i o n r a t e , t i m i n g and f r e q u e n c y , r e s i d u e s o f a l d i c a r b a r e l e a c h e d beyond the rooting zone of p o t a t o e s grown i n i r r i g a t e d sandy s o i l s i n t o u n d e r l y i n g groundwater. The water t a b l e d e p t h i s not the critical significant factor in restraining aldicarb leaching: r e s i d u e s were found where the water t a b l e was o n l y 3.9 feet (1.2 m) or as deep as 17.3 feet (5.3 m) below the soil surface. T h i s i s not s u r p r i s i n g , s i n c e n e i t h e r a l d i c a r b nor i t s sulfoxide or sulfone i s strongly absorbed by s o i l s , especially coarse-textured s o i l s (19,20). The groundwater t a b l e i n the a r e a is subject to s e a s o n a l and long-term f l u c t u a t i o n s . The water t a b l e s i n the f i e l d s s t u d i e d dropped by 2-4 f e e t (61-122 cm) d u r i n g the growing season due to water removal for irrigation but r e c o v e r e d to more o r l e s s the o r i g i n a l l e v e l by the s t a r t of the


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next season. The water t a b l e a t t h e U.W.-Madison E x p e r i m e n t a l Farm near Hancock, WI f l u c t u a t e d by ± 5 f e e t (152 cm) around a mean v a l u e d u r i n g t h e y e a r s 1951-1984. E r r a t i c Residue D i s t r i b u t i o n . However, t h e p a t t e r n o f a l d i c a r b r e s i d u e c o n c e n t r a t i o n s e n c o u n t e r e d were a s t o u n d i n g l y v a r i a b l e g i v e n a uniform a p p l i c a t i o n r a t e a c r o s s t h e 127-acre (51-ha) t r e a t e d c e n t r a l p o r t i o n o f each 160-acre (65-ha) f i e l d . The water l o a d i n g s from i r r i g a t i o n p l u s p r e c i p i t a t i o n may be assumed t o be u n i f o r m over t h i s r e l a t i v e l y s m a l l a r e a , and t h e s o i l s a r e r e l a t i v e l y uniform. Consequently, a l d i c a r b residue penetration t o the groundwater should be u n i f o r m . The s a n d - a n d - g r a v e l a q u i f e r i s r e l a t i v e l y homogeneous and l a r g e l y s t r a t i f i e d (8^9) > so t h a t m a i n l y l a t e r a l movement o f r e s i d u e s w i t h l i t t l e v e r t i c a l m i x i n g might be expected. I t was t h e r e f o r e s u r p r i s i n g t h a t i n each f i e l d no aldicarb residues were found i n some w e l l s downgradient from t r e a t e d a r e a s , low l e v e l s i n o t h e r s , and h i g h l e v e l s i n o t h e r s , a l l at approximately t h e same d e p t h (Table II). O c c u r r e n c e s and c o n c e n t r a t i o n s were a l s o e r r a t i c i n t h e m u l t i l e v e l samplers ( T a b l e III). Concentrations of a l d i c a r b r e s i d u e s i n the s o i l s o l u t i o n , i . e . v a l u e s based on the water c o n t e n t o f s o i l samples t a k e n from the vadose zone, were a l s o e r r a t i c ( T a b l e I V ) and c o n c e n t r a t i o n s i n l e a c h a t e from the l y s i m e t e r s a l s o v a r i e d w i d e l y over l a r g e ranges (Table V ) . Aldicarb residues apparently do n o t p e n e t r a t e t o groundwater by b l e e d i n g t h r o u g h t h e vadose zone a t a c o n s t a n t r a t e , but r a t h e r i n p u l s e s o f v a r y i n g c o n c e n t r a t i o n . Peak c o n c e n t r a t i o n s appear t o be a s s o c i a t e d w i t h minor w e t t i n g f r o n t s p a s s i n g t h r o u g h the s o i l . So f a r we have been u n a b l e t o d e t e r m i n e c l e a r l y whether h i g h e s t l o a d i n g s (volume χ c o n c e n t r a t i o n ) p e n e t r a t e w i t h sharp o r d i f f u s e w e t t i n g f r o n t s under c o n d i t i o n s o f u n s a t u r a t e d f l o w t h r o u g h t h e vadose zone, i . e . whether t h e l o a d i n g i s p r o p o r t i o n a l t o t h e flow. T a b l e I I r e c o r d s t h e c o n c e n t r a t i o n s o f a l d i c a r b r e s i d u e s found in water samples from m o n i t o r i n g wells which had d e t e c t a b l e residues present a t some time d u r i n g t h e s a m p l i n g p e r i o d . No s i g n i f i c a n t r e s i d u e s were d e t e c t e d a t any time i n any o t h e r w e l l s (12 more w e l l s i n F i e l d s 1 and 2, 13 i n F i e l d 3, 16 i n F i e l d s 4 and 5, 10 i n F i e l d 6, 11 i n F i e l d 7, and 1 i n each o f F i e l d s 8 and 9). Well depths i n t h e groundwater i n c r e a s e i n t h e sequence i n d i c a t e d by t h e d e s i g n a t i o n A, Β o r C a s s o c i a t e d w i t h t h e l o c a t i o n number f o r any f i e l d . The w e l l s which i n i t i a l l y c o n t a i n e d contam i n a t e d o r uncontaminated water i n any f i e l d were a t s i m i l a r d e p t h s i n t h e water t a b l e ; t h u s , t h e p a t t e r n o f r e s i d u e o c c u r r e n c e s cannot be a s c r i b e d t o i n a p p r o p r i a t e w e l l placement o r d e p t h . These d a t a g i v e some i d e a o f t h e e r r a t i c a r e a l d i s t r i b u t i o n o f a l d i c a r b residue contamination even w i t h i n a s i n g l e f i e l d . For example, on F i e l d 5, t r e a t e d i n i t s e n t i r e t y i n 1979 and i n t h e e a s t e r n h a l f i n 1980, s i g n i f i c a n t c o n c e n t r a t i o n s o f r e s i d u e s were i n i t i a l l y e n c o u n t e r e d o n l y a t two s p o t s — a t and d i r e c t l y n o r t h o f the c e n t e r p i v o t ( s i t e s 7 and 2, F i g . 1 ) . S u r p r i s i n g l y , no r e s i dues were i n i t i a l l y e n c o u n t e r e d i n water from w e l l s a t p o s i t i o n s 3, 4 o r 5, o r a t any time i n samples from t h e n e i g h b o r i n g F i e l d 4, a l l directly downgradient i n the a q u i f e r from the t r e a t e d area. R e s i d u e s (12 ppb) were found i n June 1981 i n water from t h e i r r i g a t i o n w e l l which was cased t o a depth o f 36 f e e t (11 m), o r 28 f e e t



541

13A

549

338

531

553

7B

9A

348

6A

7A

508

5B

6B

562

373

5A

4A

4B

365

399

3A

leld 3

526

1069

9C

1 OB

531

8A

270

427

7B

7C

206

295

338

323

40

128

131

292

427

28

2C

189

1 71

174

181

180

215

212

226

221

225

338

342

344

420

459

3

110

5

10

333

552

1052

7C

6

572

38

4A

ND

476

424

1072

2C

2

79

ND

12

150

69

47

22

15

ND

4

49

480

754

ND

2

549

195

12

1980

19

478

(cm)

table

water

Mean

77

171

191

22

35

2

116

ND

73

18

30

ND

3

1

83

142

103

30

17

30

1

26

11

1

70

4

86

140

7

16

69

4

157

ND

10

12

72

ND

3

9

ND

2

10

2

5

1981

5

2

18

26

21

66

150

86

153

ND

21

67

ND

10

10

ND

8

3

44

27

64

123

28

180

2

100

18

23

3

88

ND

69

68

12

2

ND

42

48

ND

4

1

11

1

78

8

1

83

39

39

1

82

Ζ

ND

1

13

6

53

40

8

18

ND

65

47

ND

2

6

3

23

1

ND

37

30

3

ND

6

37

55

6

9

ND

8

11

ND

30

7

6

7

3

8

13

ND

13

ND

88

ND

24

3

3

ND

21

ND

13

14

30

2

3

3

49

23

1

115

8

1

ND

28

ND

9

4

80

4

11

13

1

ND

15

2

3

24

35

1 1

7

ND

22

7

8

6

6

9

1982

1

8

19

ND

ND

3

6

7

7

121

10

1

ND

11

ND

6

3

39

10

6

17

3

ND

7

3

4

6

40

7

3

1

12

Date

4

2

ND

ND

3

ND

5

22

ND

ND

48

21

ND

4

116

39

9

11

ND

81

10

6

2

2

ND

ND

11

ND

6

24

ND

3

44

4

20

ND

ND

116

36

21

24

2

29

8

10

118

9

3

5

3

ND

ND

2

ND

5

7

ND

ND

38

2

33

13

ND

91

24

18

21

9

90

4

ND

63

12

( y e a r , month)

(15).

ND

ND

ND

ND

ND

2

7

ND

ND

5

5

8

3

2

70

24

8

6

36

3

4

58

11

6

8

7

ND

ND

ND

ND

ND

ND

7

ND

ND

8

1

18

ND

13

48

16

15

11

1

2

ND

ND

36

1983

In Water Samples from M o n i t o r i n g Wells (In

S t a t i s t i c a l l y Quantifiable

A l d i c a r b Residue C o n c e n t r a t i o n s (ppb)

23

l e l d s 1 ,2

(cm)

No.

F i e l d s 4, 5

c

depth

Wei 1

Wei 1

T a b l e II.

ND

ND

ND

ND

ND

ND

7

ND

7

ND

ND

ND

ND

16

48

18

32

20

6

ND

ND

1

11

17

8

ND

ND

ND

ND

ND

ND

11

ND

15

ND

ND

ND

ND

13

67

15

14

14

7

88

ND

4

13

24

9

ND

ND

ND

ND

ND

ND

24

ND

8

ND

ND

ND

ND

18

85

7

23

5

2

100

1

4

9

8

10

ND

ND

ND

ND

ND

ND

6

ND

2

2

6

2

9

72

6

14

13

3

64

1

13

2

21

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

5

9

55

7

17

10

3

51

ND

ND

ND

19

11 2

which Residues were


ND

ND

ND

ND

ND

ND

4

ND

1

ND

ND

2

5

14

40

7

19

18

3

25

ND

19

1

11

3

ND

ND

ND

ND

ND

1

3

ND

ND

2

-

ND

ND

9

33

4

8

ND

ND

5

ND

6

ND

5

5

1984

ND

ND

ND

ND

ND

ND

4

ND

1

1

ND

1

2

11

17

4

19

10

8

ND

ND

17

11

19

6

ND

ND

ND

ND

ND

ND

3

ND

ND

1

ND

2

2

13

10

8

29

15

6

7

1

28

6

16

7

ND

ND

ND

ND

ND

1

-

ND

-

-

_

ND

-

15

-

2

-

ND

ND

ND

16

9

1985

m το

i

Ζ ο Ο C

H Ο

-a m

δ ζ ο -η

c

HARKIN ET AL.

12.


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Evaluation of Pesticides in Ground Water - American Chemical Society

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