Movement of Selected Pesticides and Herbicides through Columns of

16 Movement of Selected Pesticides and Herbicides through Columns of Sandy Loam 1

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Viorica Lopez-Avila , Pat Hirata , Susan Kraska , Michael Flanagan , John H . Taylor, Jr. , Stephen C. Hern , Sue Melancon , and Jim Pollard 1

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Downloaded by IOWA STATE UNIV on April 13, 2017 | http://pubs.acs.org Publication Date: July 17, 1986 | doi: 10.1021/bk-1986-0315.ch016

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Acurex Corporation, Mountain View, C A 94039 U.S. Environmental Protection Agency, Las Vegas, NV 89114

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University of Nevada, Las Vegas, NV 89114

The mobility of chemicals through soils following landfill disposal or agricultural application is of concern whenever there is potential threat to contaminate the groundwater by leaching. This movement is evaluated by simulation modeling. Several models, including the Pesticide Root Zone Model (1) and the Seasonal Soil Compartment Model (2) are available, and are currently being evaluated by the Environmental Protection Agency-Las Vegas. The evaluation study consists of conducting a laboratory experiment in which lysimeter columns containing test chemicals at levels corresponding to agricultural application rates are irrigated with water at a constant rate for 30 days. Leachate samples collected daily from the lysimeter columns and soil cores obtained at the completion of the experiment are analyzed for the test chemicals. The observed concentrations are compared with the model predictions to establish how well the model can simulate the actual situation. Prior to the initiation of such an experiment (5 lysimeter columns 60 cm ID by 200 cm h e i g h t ) , a s m a l l - s c a l e experiment (3 columns 4.8 cm ID by 50 cm h e i g h t ) was performed t o e s t a b l i s h : breakthrough volumes o f the t e s t c h e m i c a l s , whether or n o t the s e l e c t i o n o f the t e s t c h e m i c a l s was a p p r o p r i a t e , and t o determine i f the a n a l y t i c a l m e t h o d o l o g i e s were adequate. The purpose o f t h i s paper i s t o summarize the r e s u l t s o f the s m a l l - s c a l e e x p e r i m e n t . The s i x t e s t c h e m i c a l s s e l e c t e d f o r i n v e s t i g a t i o n were: dicaraba, 2,4-D, a t r a z i n e , d i a z i n o n , pentachlorοphenol, and l i n d a n e . Their p h y s i c o - c h e m i c a l p r o p e r t i e s are p r e s e n t e d i n Table I . Dicamba and 2,4-D were chosen f o r t h i s s t u d y because o f t h e i r r e l a t i v e l y h i g h water s o l u b i l i t y . C o n s e q u e n t l y , they were e x p e c t e d t o move q u i c k l y t h r o u g h the s o i l column and be the f i r s t c h e m i c a l s t o appear i n the leachate. D e s p i t e the f a c t t h a t 2,4-D was known t o degrade q u i c k l y i n the s o i l , i t was f e l t t h a t due t o i t s h i g h water s o l u b i l i t y , 2,4-D would a l s o l e a c h q u i c k l y from the s o i l column and w i l l p r o b a b l y b r e a k t h r o u g h i m m e d i a t e l y f o l l o w i n g dicamba. The o t h e r c h e m i c a l s e x p e c t e d t o l e a c h from the s o i l column were a t r a z i n e and d i a z i n o n and b o t h were p r o b a b l y o f i n t e r m e d i a t e m o b i l i t y . 0097-6156/ 86/ 0315-0311 $06.00/ 0 © 1986 American Chemical Society

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


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P e n t a c h l o r ο phenol and l i n d a n e were s e l e c t e d p r i m a r i l y because they were r e p o r t e d t o be the l e a s t m o b i l e c h e m i c a l s ; i n f a c t , based on t h e i r o c t a n o l / w a t e r p a r t i t i o n c o e f f i c i e n t s , i t was e x p e c t e d t h a t these c h e m i c a l s would n o t l e a c h a t a l l . These c h e m i c a l s were s p i k e d i n t o the s o i l a t 16.2 ppm and were l e a c h e d f o r 30 days w i t h o r g a n i c s - f r e e water a t a r a t e o f 55.8 mL/day. R e s u l t s a r e p r e s e n t e d as amount l e a c h e d v e r s u s time and c o n c e n t r a t i o n o f c h e m i c a l i n s o i l at v a r i o u s depths i n s o i l column. F u r t h e r m o r e , mass b a l a n c e s a r e p r e s e n t e d f o r e a c h c h e m i c a l . Subsequent s e c t i o n s p r e s e n t the e x p e r i m e n t a l d e t a i l s and the r e s u l t s o f t h i s e x p e r i m e n t .


Experimental Leaching Experiment. Three p o l y e t h y l e n e columns (4.8 cm ID by 50 cm h e i g h t ) were employed t o i n v e s t i g a t e the m o b i l i t y o f dicamba, 2,4-D, a t r a z i n e , d i a z i n o n , pentachlorοphenol, and l i n d a n e . Each column was packed w i t h 1,080g o f f r e s h s o i l t o a depth o f 40 cm (sandy loam s o i l from S o i l s I n c o r p o r a t e d , P u y a l l u p , Washington: pH 5.9 t o 6.0; 89 p e r c e n t sand; 7 p e r c e n t s i l t ; 4 p e r c e n t c l a y ; c a t i o n exchange c a p a c i t y 7.5 raeq/lOOg). Each column was i r r i g a t e d from the bottom w i t h HPLC grade water (Baker A n a l y z e d Reagent) and a l l o w e d t o d r a i n f o r 1 hour. To remove r e s i d u a l s a l t , two pore volumes (500 mL) o f HPLC grade water were s l o w l y d r i p p e d t h r o u g h e a c h column. Next, 100g o f s o i l , s p i k e d w i t h 1.62 mg e a c h o f dicamba, 2,4-D, a t r a z i n e , d i a z i n o n , p e n t a c h l o r o p h e n o l , and l i n d a n e , t o s i m u l a t e an a p p l i c a t i o n r a t e o f 8 l b / a c r e , were l o a d e d onto e a c h column. The contaminated s o i l was packed on t o p o f e a c h s o i l column t o a depth o f 3.7 cm r e s u l t i n g i n a t o t a l column depth o f 43.7 cm. To t h i s , 32g o f f r e s h sandy loam s o i l were added t o b r i n g the t o t a l s o i l column h e i g h t t o 45 cm. The c o n t a m i n a t e d s o i l was p r e p a r e d as follows: 162-yL a l i q u o t s o f s i x s t o c k s o l u t i o n s o f e a c h c h e m i c a l ( c o n c e n t r a t i o n 10 mg/mL; dicamba, 2,4-D, and p e n t a c h l o r o p h e n o l s t o c k s o l u t i o n s were i n acetone; the r e s t i n methanol) were c o m p o s i t e d . Acetone (100 yL) was added t o the composite s o l u t i o n t o b r i n g the volume t o 1,072 y L . The composite s o l u t i o n was added t o 20 mL HPLC grade water which was then mixed w i t h 100g o f f r e s h s o i l . The p u r i t y o f the c h e m i c a l s used f o r t h i s experiment was g r e a t e r than 99 p e r c e n t . C h e m i c a l s were l e a c h e d from the s o i l column by a p p l y i n g w a t e r , twice d a i l y , a t a r a t e o f 55.8 mL per d a y , per column, f o r 30 d a y s . The i r r i g a t i o n water (27.9 mL per a p p l i c a t i o n ) was a p p l i e d a t 8 a.m. and 2 p.m., each day, f o r 30 d a y s . L e a c h a t e s from the s m a l l columns were c a p t u r e d d a i l y and s t o r e d i n the dark a t 4°C u n t i l a n a l y z e d (column I l e a c h a t e s were a n a l y z e d w i t h i n 3 days a f t e r c o l l e c t i o n ; column I I and I I I l e a c h a t e s were s t o r e d f o r almost 30 days p r i o r t o extraction). A f t e r the 30-day e x p e r i m e n t , each column was c r o s s s e c t i o n e d i n t o n i n e d i s c r e t e segments (5 cm i n d e p t h ) . P r i o r t o segmenting, the s o i l columns were f r o z e n a t -10°C f o r 8 hours t o facilitate sectioning. A l l s o i l samples were kept f r o z e n a t - 1 0 ° C u n t i l a n a l y s i s was p e r f o r m e d . The three s o i l columns were kept c o v e r e d w i t h aluminum f o i l t h r o u g h o u t the 30-day e x p e r i m e n t . A n a l y s e s were performed by gas


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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


chromatography/mass s p e c t r o m e t r y (GC/MS) f o l l o w i n g the e x t r a c t i o n procedure o u t l i n e d below.

sample

A d s o r p t i o n Study. The a d s o r p t i o n of the t e s t compounds by the sandy loam s o i l ( p a r t i c l e s i z e l e s s than 35 mesh) was determined by measuring the d i f f e r e n c e i n the c o n c e n t r a t i o n of an aqueous s o l u t i o n of e a c h c h e m i c a l , b e f o r e and a f t e r e q u i l i b r a t i o n w i t h s o i l . Four t o f i v e c o n c e n t r a t i o n s per c h e m i c a l were t e s t e d and t h r e e r e p l i c a t e measurements were performed at e a c h c o n c e n t r a t i o n . W a t e r - t o - s o i l r a t i o s of 2:1 to 10:1 were employed i n a l l e x p e r i m e n t s . The time r e q u i r e d to r e a c h e q u i l i b r i u m was determined s e p a r a t e l y f o r e a c h c h e m i c a l at one c o n c e n t r a t i o n and a s p e c i f i c w a t e r - t o - s o i l r a t i o . F o l l o w i n g e q u i l i b r a t i o n w i t h s o i l , the aqueous s o l u t i o n was s e p a r a t e d by c e n t r i f u g a t i o n at 2,800 rpm and was a n a l y z e d d i r e c t l y by h i g h - p r e s s u r e l i q u i d chromatography (HPLC). The e x p e r i m e n t a l c o n d i t i o n s f o r HPLC a n a l y s i s are g i v e n i n Reference 21. Attempts to a n a l y z e l i n d a n e i n the aqueous phase by HPLC w i t h u l t r a v i o l e t d e t e c t i o n , w i t h o u t p r e c o n c e n t r a t i o n , were u n s u c c e s s f u l . Lindane was a n a l y z e d by gas chromatography w i t h e l e c t r o n c a p t u r e d e t e c t i o n f o l l o w i n g p r e c o n c e n t r a t i o n on C^g-reverse phase r e s i n and e l u t i o n w i t h t e t r a h y d r o f u r a n . Other d e t a i l s can be found i n Reference 21. S o i l D e g r a d a t i o n Study. One hundred and f o r t y - f o u r amber j a r s (500 mL) were l o a d e d w i t h 50-g f r e s h sandy loam s o i l and d i v i d e d i n t o two g r o u p s . Seventy-two of them were a d j u s t e d a t 14 p e r c e n t m o i s t u r e (group I ) . The o t h e r 72 were a d j u s t e d at 22 p e r c e n t m o i s t u r e (group I I ) . The 72 samples i n group I were f u r t h e r d i v i d e d as f o l l o w s : 36 o f them were s p i k e d w i t h dicamba, 2,4-D, and p e n t a c h l o r o p h e n o l a t 1 yg/g; the o t h e r 36 s p i k e d w i t h l i n d a n e , a t r a z i n e , and d i a z i n o n at 1 yg/g. S p i k i n g was performed a f t e r the s o i l was a d j u s t e d at 14 p e r c e n t or 22 p e r c e n t m o i s t u r e . The s p i k e was added i n a c o n c e n t r a t e d s o l u t i o n to the s o i l (100 yL of a 0.5 rag/raL s t o c k s o l u t i o n ) and was mixed t h o r o u g h l y w i t h the s o i l . A l l samples from group I I were t r e a t e d s i m i l a r l y . The s p i k e d samples were i n c u b a t e d i n an oven at 85°F, i n d a r k , and i n open system; c o t t o n p l u g s were used to prevent dust from e n t e r i n g the f l a s k s . The experiment was s e t up f o r 90 days. The sampling times were 0.04; 0.67; 1.67; 4; 10 or 12; 20; 32; 61 and 93 days from the i n i t i a t i o n o f the e x p e r i m e n t . Three r e p l i c a t e s were a n a l y z e d at e a c h time i n t e r v a l f o r the t e s t compounds. Soil m o i s t u r e was m a i n t a i n e d at 14 p e r c e n t and 22 p e r c e n t by a d d i t i o n o f o r g a n i c s - f r e e water and was v e r i f i e d twice a week d u r i n g the experiment. Other d e t a i l s can be found i n Reference 21. Analytical

Methodologies

Dicamba and 2,4-D A n a l y s i s . A F i n n i g a n 1020 quadrupole mass s p e c t r o m e t e r c o u p l e d to a P e r k i n - E l m e r Sigma 1 gas chromatograph and an Incos 2300 d a t a system was used f o r a l l measurements r e p o r t e d here. C a l i b r a t i o n s t a n d a r d s and sample e x t r a c t s were i n j e c t e d manually. Compound s e p a r a t i o n s were performed on a 6 - f t g l a s s column packed w i t h U l t r a b o n d 20M, temperature programmed from 150°C (1 min) t o 240°C at 15°C/min; c a r r i e r gas He; f l o w r a t e 45 raL/min; i n j e c t o r temperature 220°C.; t r a n s f e r l i n e temperature 250°C. The mass spectrometer o p e r a t i n g c o n d i t i o n s i n c l u d e d : e l e c t r o n e n e r g y


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70 eV; and s e l e c t e d i o n m o n i t o r i n g mode f o r i o n s at m/z 188, 203, 206, 400, and 403 i n a t o t a l scan time of 0.65 s e c . Other d e t a i l s of the gas chromatographic/mass s p e c t r o m e t r i c a n a l y s e s can be found elsewhere ( 2 1 ) . A t r a z i n e , D i a z i n o n , Pentachlorοphenol, and Lindane Analy_sis_» ^ F i n n i g a n 4021 quadrupole mass spectrometer coupled to a F i n n i g a n 9610 gas chromatograph and an Incos 2300 d a t a system was used f o r a l l measurements r e p o r t e d h e r e . C a l i b r a t i o n s t a n d a r d s and sample e x t r a c t s were i n j e c t e d a u t o m a t i c a l l y by a V a r i a n a u t o s a m p l e r . Compound s e p a r a t i o n s were performed on a f u s e d s i l i c a c a p i l l a r y column 30ra χ 0.25 ram ID DB-5 (J&W S c i e n t i f i c , 0.25-ym f i l m t h i c k n e s s ) ; s p l i t l e s s i n j e c t i o n at 50°C f o l l o w e d by temperature programming to 300°C at 15°C/min; i n j e c t o r temperature 260°C.; t r a n s f e r l i n e temperature 280°C.; c a r r i e r gas He at 10 p s i p r e s s u r e . The mass spectrometer o p e r a t i n g c o n d i t i o n s were i o n source temperature 300°C.; e l e c t r o n e n e r g y 70 eV; s e l e c t e d i o n m o n i t o r i n g mode f o r i o n s at m/z 188, 200, 205, 181, 224, 304, 314, 266, and 272 i n a t o t a l scan time of 0.69 s e c . Other d e t a i l s of the gas chromatographic/mass s p e c t r o m e t r i c a n a l y s e s can be found elsewhere (21-22). Reagents and Standard Compounds. A n a l y t i c a l r e f e r e n c e s t a n d a r d s of dicamba, 2,4-D, a t r a z i n e , d i a z i n o n , pentachlorοphenol, and l i n d a n e were o b t a i n e d from the U.S. EPA P e s t i c i d e s and I n d u s t r i a l C h e m i c a l s R e p o s i t o r y (MD-8), R e s e a r c h T r i a n g l e P a r k , NC 27711. Stock s o l u t i o n s were prepared i n p e s t i c i d e grade methanol or acetone (Baker r e s i - a n a l y z e d ) and s t o r e d at -10°C. S t a b l e - l a b e l e d i s o t o p e s — dicamba-d3, 2,4-D-d3, a t r a z i n e - d 5 , d i a z i n o n - d j Q , and l i n d a n e - d ^ — were s y n t h e s i z e d by P a t h f i n d e r Laboratories, St. Louis, M i s s o u r i . Pentachlorophenol-^c^ was o b t a i n e d from MSD-isotopes, D i v i s i o n of Merck F r o s t Canada I n c . , M o n t r e a l , Canada. The d e u t e r a t e d compounds and the ^ C - l a b e l e d pentachlorοphenol were s p i k e d i n t o e v e r y sample at known c o n c e n t r a t i o n and were used to q u a n t i t a t e the n a t u r a l l y abundant compounds by s t a b l e - i s o t o p e d i l u t i o n p r o c e d u r e s (23-24). Leachate E x t r a c t i o n . Known volumes of l e a c h a t e samples ("-50 mL) were s p i k e d w i t h the s t a b l e - l a b e l e d i s o t o p e s at 80 ug/L and were e x t r a c t e d at t h e i r o r i g i n a l pH (6 to 6.5) by v i g o r o u s l y shaking f o r 2 min, i n a 250-mL s e p a r a t o r y f u n n e l w i t h 50 mL methylene c h l o r i d e . E x t r a c t i o n was performed three c o n s e c u t i v e t i m e s , e a c h time u s i n g f r e s h 50-mL a l i q u o t s of methylene c h l o r i d e . The e x t r a c t s were combined, moisture was removed by p a s s i n g the e x t r a c t through a column of anhydrous sodium s u l f a t e , and the e x t r a c t was then c o n c e n t r a t e d to 4 to 6 mL i n a Kuderna-Danish e v a p o r a t o r . Further c o n c e n t r a t i o n to 1 mL was performed u s i n g n i t r o g e n blowdown evaporation. F o l l o w i n g e x t r a c t i o n at pH 6 to 6.5, the aqueous phase was a c i d i f i e d at pH 1 and was e x t r a c t e d three c o n s e c u t i v e times w i t h 50-mL a l i q u o t s of methylene c h l o r i d e . The a c i d i c e x t r a c t s were combined and were c o n c e n t r a t e d to 10 mL u s i n g a Kuderna-Danish evaporator. P r i o r to a n a l y s i s , the a c i d i c e x t r a c t was d e r i v a t i z e d w i t h p e n t a f l u o r o b e n z y l bromide a c c o r d i n g to procedures d e s c r i b e d i n Reference 19.



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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

S o i l E x t r a c t l o g . S o i l samples were thawed at room temperature f o r 2 hours and were e x t r a c t e d as f o l l o w s : 50-g a l i q u o t s of the f r e s h sandy loam s o i l were s l u r r i e d w i t h 10 mL of o r g a n i c s - f r e e water and s p i k e d w i t h known amounts of s t a b l e - l a b e l e d i s o t o p e s . The s p i k e was added i n 100 t o 400-yL methanol a l i q u o t s to the wet s o l i and was a l l o w e d to e q u i l i b r a t e w i t h the s o i l f o r 1 hour. Two separate a l i q u o t s were e x t r a c t e d f o r e a c h sample. One a l i q u o t was e x t r a c t e d at n e u t r a l pH to s e p a r a t e a t r a z i n e , l i n d a n e , and d i a z i n o n . The o t h e r a l i q u o t was e x t r a c t e d at a c i d i c pH to s e p a r a t e dicamba, 2,4-D, and pentachlorophenol. The a l i q u o t d e s i g n a t e d f o r e x t r a c t i o n at n e u t r a l pH was e x t r a c t e d t h r e e t i m e s , w i t h f r e s h 100-mL acetone/hexane ( 5 0 / 5 0 ) . An u l t r a s o n i c c e l l d i s r u p t o r , i n p u l s e d mode at 50 p e r c e n t duty c y c l e , was employed to enhance the c o n t a c t between the e x t r a c t i o n s o l v e n t and s o i l . F o l l o w i n g e a c h e x t r a c t i o n , the s o i l was a l l o w e d to s e t t l e , the s o l v e n t d e c a n t e d , and the combined s u p e r n a t a n t s from the n e u t r a l pH e x t r a c t i o n were d r i e d t h r o u g h a column of anhydrous sodium s u l f a t e (5-cm bed h e i g h t ; 3-cm d i a m e t e r ) . Concentration of the e x t r a c t was performed u s i n g a Kuderna-Danish e v a p o r a t o r . Final volume was a d j u s t e d t o 1 mL u s i n g n i t r o g e n blowdown e v a p o r a t i o n . The e x t r a c t i o n at a c i d i c pH was performed as f o l l o w s : 50-g a l i q u o t s of the s o i l sample were s l u r r i e d w i t h 10 mL o f o r g a n i c s - f r e e water and s p i k e d w i t h the s t a b l e - l a b e l e d i s o t o p e s . F o l l o w i n g e q u i l i b r a t i o n , the s o i l s l u r r y was a d j u s t e d to pH

Movement of Selected Pesticides and Herbicides through Columns of

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