18 Potential Pesticide Contamination of Groundwater from Agricultural Uses S.Z.COHEN andS.M.CREEGER—Office of Pesticide Programs, TS-769c, Environmental Protection Agency, Washington,DC20460
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R.F.CARSEL—Environmental Research Laboratories, Environmental Protection Agency, Athens,GA30613 C.G.ENFIELD—Environmental Research Laboratories, Environmental Protection Agency, Ada,OK74820 EPA began to emphasize work on ground water contamination by pesticides i n 1979. Much monitoring has been done i n this area since 1979, mostly by state agencies and, to a lesser extent, pesticide registrants, university s c i e n t i s t s , and EPA. To date, as a result of agricultural use, a total of 12 different pesticides have been found i n the ground water of 18 different states. The 12 chemicals represent seven different chemical classes. Despite significant limitations i n the laboratory and f i e l d data, some generalizations about the key environmental fate parameters and f i e l d conditions are made which aid i n predicting which compounds w i l l leach to ground water. Use of p e s t i c i d e s i n the production o f U.S. a g r i c u l t u r a l commodities is widespread; 370,455 m e t r i c tons of a c t i v e i n g r e d i e n t s , which corresponds t o 70.3% of the total poundage of p e s t i c i d e a c t i v e i n g r e d i e n t s used i n the U.S., were a p p l i e d to a g r i c u l t u r a l land i n 1982 ( 1 ) . With the worldwide i n c r e a s e in need f o r food and fiber ( 2 ) , use of p e s t i c i d e s is expected to i n c r e a s e ( 3 ) . Since n e a r l y h a l f of the U.S. p o p u l a t i o n relies on ground water as t h e i r source of d r i n k i n g water ( 4 ) , p o t e n t i a l f o r contamination of ground water due t o p e s t i c i d e use must be considered in the r e g i s t r a t i o n process. In t h i s paper, the environmental f a t e c h a r a c t e r i s t i c s o f those p e s t i c i d e s found t o date in ground water as a r e s u l t of a g r i c u l t u r a l use are summarized. M o n i t o r i n g data are a l s o summarized. From those summaries, and i n f o r m a t i o n on the s i t e s of ground water contamination, it can be concluded which combinat i o n of p e s t i c i d e chemical c h a r a c t e r i s t i c s and use s i t e s r e p r e sent a h i g h p o t e n t i a l f o r ground water contamination. Other aspects of a s s e s s i n g p o t e n t i a l f o r ground water contamination, such as study design and modeling, as w e l l as i n t e r p r e t a t i o n s of s o r p t i o n , volatility, and p h o t o l y s i s data are a l s o d i s c u s s e d . This chapter not subject to U.S. copyright. Published 1984, American Chemical Society
In Treatment and Disposal of Pesticide Wastes; Krueger, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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TREATMENT AND
DISPOSAL OF PESTICIDE WASTES
The EPA began to emphasize work on ground water contaminat i o n by p e s t i c i d e s i n 1979. The impetus f o r t h i s e f f o r t was the f i n d i n g of l,2-dibromo-3-chloropropane (DBCP) and a l d i c a r b ( c h i e f l y as the s u l f o x i d e and sulfone m e t a b o l i t e s ) i n ground water i n various s t a t e s (5-9). P r i o r to 1979, water monitoring studies had g e n e r a l l y not focused on p e s t i c i d e s i n ground water per se. The reasons are t h a t : (1) monitoring had generally focused on urban rather than on r u r a l , a g r i c u l t u r a l areas; (2) analyses were o f t e n f o r v o l a t i l e / p u r g e a b l e organics, and many p e s t i c i d e s are of low v o l a t i l i t y and (3) reports of p o s i t i v e f i n d i n g s of organics i n d r i n k i n g water have not always d i s t i n guished between surface water and ground water systems. Another concern has been an i n c r e a s e i n use of p e s t i c i d e s with higher water s o l u b i l i t i e s i n recent y e a r s . O v e r a l l , there have been many f i n d i n g s of p e s t i c i d e s i n ground water. This paper presents the r e s u l t s of work done i n t h i s area over the l a s t few years by s t a t e governments, p e s t i cide r e g i s t r a n t s , u n i v e r s i t y s c i e n t i s t s , and the EPA. The r e s u l t s discussed here g e n e r a l l y p e r t a i n to normal a g r i c u l t u r a l use, as opposed to waste dump s i t e s , although some comments are made i n the s e c t i o n on Chemical C h a r a c t e r i s t i c s , as w e l l as i n the Conclusions, on p e s t i c i d e l e a c h i n g from d i s p o s a l s i t e s . Chemical C h a r a c t e r i s t i c s & M o n i t o r i n g Data In t h i s s e c t i o n , two types of data are b r i e f l y summarized: 1) environmental transport and p e r s i s t e n c e , and (2) m o n i t o r i n g . The d i s c u s s i o n i s chemical s p e c i f i c . Some i n t e r e s t i n g concepts r e l e v a n t to some of the chemical c h a r a c t e r i s t i c s are developed l a t e r i n the D i s c u s s i o n s e c t i o n . Results from t h i s s e c t i o n are a l s o used i n the Conclusion s e c t i o n to derive some g e n e r a l i z a t i o n s about p e s t i c i d e s l e a c h i n g to ground water. A l l data presented i n t h i s s e c t i o n were e i t h e r generated under ambient c o n d i t i o n s (pH 6 to 8, 15°-30°C) or extrapolated to ambient c o n d i t i o n s , unless noted otherwise. In some cases, data was a v a i l a b l e only under c o n d i t i o n s u n l i k e l y to be found i n the environment. D e f i n i t i o n s of terms are as follows: = soil/water d i s t r i b u t i o n c o e f f i c i e n t ; K = divided by the s o i l organic carbon f r a c t i o n ; m o b i l i t y c l a s s e s , given f o r three p e s t i c i d e s , are taken from H e l l i n g ' s work (10) which e v a l uates the movement of 40 p e s t i c i d e s i n Hagerstown s i l t y c l a y loam s o i l t h i n - l a y e r p l a t e s ; Henry's law constant (H) i s a measure of the escaping tendency of d i l u t e s o l u t e s from water and i s approximated by the r a t i o of the vapor pressure to the water s o l u b i l i t y at the same temperature ( 11). The s i g n i f i c a n c e of H values to environmental s i t u a t i o n s i s presented i n the D i s c u s s i o n s e c t i o n . Whenever p o s s i b l e , f i e l d d i s s i p a t i o n h a l f l i v e s are given, which include l o s s e s due to h y d r o l y s i s , mic r o b i a l a c t i v i t y , v o l a t i l i z a t i o n , e t c . , i n a lumped, pseudof i r s t - o r d e r process. I t i s r e a l i z e d that t h i s i s o f t e n an o v e r s i m p l i f i c a t i o n , s i n c e many mechanisms f o r l o s s of p e s t i c i d e s o c
In Treatment and Disposal of Pesticide Wastes; Krueger, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
Downloaded by UNIV LAVAL on October 1, 2015 | http://pubs.acs.org Publication Date: August 15, 1984 | doi: 10.1021/bk-1984-0259.ch018
18.
C O H E N ET A L .
Pesticide Contamination from Agricultural Uses
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i n the environment are not f i r s t - o r d e r . The environmental f a t e summaries presented should only be considered as capsule sum maries r a t h e r than extensive c r i t i c a l reviews. The w e l l con tamination i n c i d e n t s discussed are considered to be due to nor mal a g r i c u l t u r a l use of the p e s t i c i d e and g e n e r a l i z a t i o n s presented on p e s t i c i d e l e a c h i n g based on a g r i c u l t u r a l l y r e l a t e d Kjj values, r a t e s of degradation, e t c . , a r e not always a p p l i c a b l e to waste d i s p o s a l s i t e s . For example, i t has been demonstrated that adsorption i s l e s s than a n t i c i p a t e d , r e s u l t i n g i n i n c r e a s e d l e a c h i n g , when p e s t i c i d e s are present at very high s o i l concen t r a t i o n s such as might e x i s t a t waste dump s i t e s (12,13). Thus, the adsorption isotherms are not l i n e a r . T h i s occurs even though the p e s t i c i d e a d s o r p t i o n s i t e s are not s a t u r a t e d as manifested by the f a c t that the data f i t the F r e u n d l i c h equation up t o the s o l u b i l i t y l i m i t s of the p e s t i c i d e s s t u d i e d ( 1 3 ) . There i s a l s o evidence that m i c r o b i a l degradation of high s o i l concentrations of p e s t i c i d e s i s slower than lower s o i l concen t r a t i o n s (14,15). The impact of organic s o l v e n t s on values i s less clear. Recent work (16) has demonstrated that organic solvents such as methanol, when present at h i g h concentrations i n hazardous waste s i t e s , can s i g n i f i c a n t l y i n c r e a s e the l e a c h i n g p o t e n t i a l of organic s o l u t e s . However, i t i s not known whether organic s o l v e n t s are u s u a l l y present at high concentra tions i n l a n d f i l l leachates. For example, recent analyses of leachates from above and below the l i n e r s of 11 l a n d f i l l s i n d i cate that organic solvents were present at only ppm l e v e l s ( 17). It i s important t o note that much of the monitoring data presented below r e s u l t s from s t u d i e s which were not designed f o r s t a t i s t i c a l treatment of the r e s u l t s . Therefore, i t i s o f t e n d i f f i c u l t or n e a r l y impossible to draw s t a t i s t i c a l l y reliable conclusions about the r e s u l t s from these s t u d i e s . A l s o , key i n f o r m a t i o n such as depth to the water t a b l e and w e l l c o n s t r u c t i o n are sometimes u n a v a i l a b l e . S o i l core data are a v a i l a b l e f o r only s i x of the p e s t i c i d e s discussed i n t h i s paper. The s i x p e s t i c i d e s a r e : a l d i c a r b ; a t r a z i n e ; 1,2-dibromo-3-chloropropane (DBCP); 1,2-dichloropropane (DCP); 1,2-dibromoethane (EDB); and simazine. Cores were always sampled at depths greater than one meter and the s o i l was c h a r a c t e r i z e d p h y s i c a l l y and c h e m i c a l l y . The importance of s o i l core sampling i n p e s t i c i d e l e a c h i n g assessments i s presented i n the D i s c u s s i o n s e c t i o n . A l a c h l o r . A l a c h l o r i s an a c e t a n i l i d e h e r b i c i d e with a water s o l u b i l i t y of 242 ppm (18) and a 2.2 χ 10"^ t o r r vapor pressure (18). The approximated Henry's law constant (H) i s 3.2 X 10~ atm-m /mol. K j values range from 0.6-8.1 i n various types of s o i l ( 19). However, most K
