Chapter 18
Groundwater Contamination by Atrazine and Its Metabolites
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Risk Assessment, Policy, and Legal Implications D. A. Belluck1, S. L. Benjamin1, and T. Dawson2 1Minnesota Pollution Control Agency, 520 Lafayette Road, St. Paul, MN 55155 2Wisconsin Department of Justice, Madison, WI 53707 Atrazine can degrade in s o i l to metabolites that can enter groundwater. Principal metabolites are currently assumed to be at least of equal toxicity to atrazine, a possible human carcinogen. Recent groundwater sampling indicates that atrazine and its metabolites can occur alone or i n combination. Total residues, atrazine plus i t s metabolites, can exceed atrazine regulatory limits even though atrazine does not. Atrazine metabolites themselves can exceed these limits. Routine monitoring of parent and metabolites w i l l enable total resource degradation and potential human health risks to be appropriately evaluated. Options to regulate atrazine metabolites i n groundwater include increasing the stringency of current regulatory limits for atrazine to account for the potential toxicity of the unmeasured metabolites. Groundwater contamination by p e s t i c i d e s i s of great and growing concern i n the United States (1, 2 ) . Widespread p u b l i c concern e x i s t s that a g r i c u l t u r a l a c t i v i t i e s are c o n t r i b u t i n g to the contamination of United States groundwater and surface water Q ) . For instance, r u r a l Americans rank groundwater and drinking water contamination at the top of t h e i r environmental concerns ( 4 ) . Approximately 70% o f a l l p e s t i c i d e s used i n the United States are applied to a g r i c u l t u r a l lands and more than $4 b i l l i o n worth of a g r i c u l t u r a l p e s t i c i d e s are s o l d each year ( 5 ) . An estimated 4 E+8 kg o f p e s t i c i d e s were applied to a g r i c u l t u r a l lands i n 1985. Less than 0.1% o f applied p e s t i c i d e a c t u a l l y reaches targeted pests. About 99.9% o f applied p e s t i c i d e , therefore, has the p o t e n t i a l t o move i n t o other environmental compartments including groundwater ( 6 ) . Although c e r t a i n p e s t i c i d e s have been removed from the market because o f environmental or human health r i s k s , these actions have not slowed the growth of p e s t i c i d e use i n the United States ( 2 ) . Contamination can occur by normal a g r i c u l t u r a l a c t i v i t i e s or v i a s p i l l s , improper storage, backflushing during chemigation, and other accidents ( 8 ) . A recent review (£) states that "many p e s t i c i d e s are
0097-6156791A)459-0254$06.00/0 © 1991 American Chemical Society In Pesticide Transformation Products; Somasundaram, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
18. BELLUCK ET AL
Groundwater Contamination by Atrazine255
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leaching to groundwater from routine, nonpoint source use." Nonpoint source p o l l u t i o n of groundwater by a g r i c u l t u r a l chemicals i s an increasing environmental problem (Ifi). According to the Congressional Research Service ( 8 ) , a g r i c u l t u r a l a c t i v i t i e s are the most pervasive contributors to nonpoint source p o l l u t i o n o f groundwater. USDA states that the p o t e n t i a l f o r groundwater contamination by a g r i c u l t u r a l chemicals i s high i n many major crop and l i v e s t o c k producing areas of the United States Q ) . A g r i c u l t u r a l a c t i v i t i e s , i r r i g a t i o n and l i v e s t o c k usage account f o r approximately two-thirds o f groundwater used d a i l y i n the United States ( 8 ) . P e s t i c i d e Contamination o f Groundwater i n the United States Several reports have recently been published on the extent of contamination o f the nation's groundwater. The U.S. Environmental P r o t e c t i o n Agency's (U.S. EPA) "Pesticides I n Ground Water Data Base, 1988 Interim Report" ( H ) found 74 p e s t i c i d e s i n the groundwater o f 38 states. A t o t a l of 46 p e s t i c i d e s detected i n the groundwater of 26 states were a t t r i b u t e d to normal a g r i c u l t u r a l use, while 32 p e s t i c i d e s i n groundwater o f 12 states were a t t r i b u t e d t o point sources or misuse. A 1986 paper from the U.S. EPA's O f f i c e of P e s t i c i d e Programs noted that a t l e a s t 17 p e s t i c i d e s have been found i n a t o t a l o f 23 states as a r e s u l t o f a g r i c u l t u r a l p r a c t i c e s (12). A 1989 review reported that a t o t a l of 39 p e s t i c i d e s have been detected i n groundwater from 34 states or provinces ( 9 ) . Another 1989 report found 67 p e s t i c i d e s i n a t o t a l o f 33 states (12). A recent s p e c i a l report i n Chemical and Engineering News (14) stated that groundwater o f more than h a l f the states i n the United States contains a g r i c u l t u r a l p e s t i c i d e s . A recent State of Iowa groundwater monitoring study exemplifies the types o f information being generated by states on the extent of groundwater contamination by p e s t i c i d e s and the magnitude of human exposure. Iowa's State-Wide Rural Well-Water Survey (SWRL) checked p r i v a t e d r i n k i n g water supplies used by r u r a l Iowans and found parent pesticides (atrazine, metribuzin, pendamethalin, metolachlor, cyanazine, a l a c h l o r , picloram, 2,4-D, dacthal, propachlor and trifluralin) as w e l l as degradation products of atrazine (deethylatrazine and deisopropylatrazine) , a l a c h l o r (hydroxy-alachlor) and carbofuran (3-hydroxy-carbofuran and 3-keto-carbofuran) . State o f f i c i a l s estimate that, based on SWRL f i n d i n g s , approximately 13.6% of p r i v a t e , r u r a l drinking water wells (both shallow and deep) i n the state are contaminated with one or more p e s t i c i d e s . Approximately 1.2% of the p r i v a t e r u r a l drinking water w e l l s , serving about 5,400 r u r a l residents (about 0.7% of the r u r a l population), may be contaminated with p e s t i c i d e l e v e l s exceeding drinking water advisory l e v e l s and about 94,000 r u r a l Iowans (about 13.1% o f the r u r a l population) are consuming d r i n k i n g water containing one or more p e s t i c i d e s (15). Despite debate i n the l i t e r a t u r e concerning the absolute number of states reporting groundwater contamination by p e s t i c i d e s and the number o f p e s t i c i d e s found per state, the number o f w e l l s w i t h reports of p e s t i c i d e contamination increase each year. "Pesticides are leaching through the s o i l and into groundwater f a r more commonly than the preconceptions o f a decade ago would have predicted" (9).
In Pesticide Transformation Products; Somasundaram, L., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
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PESTICIDE TRANSFORMATION PRODUCTS
Atrazine Use and Groundwater Contamination. Atrazine, a t r i a z i n e h e r b i c i d e , accounts f o r 12% of a l l p e s t i c i d e s used i n the United States (1). Atrazine use i n the U.S. i s heaviest i n the midwest with s i g n i f i c a n t use i n the eastern states and l e s s e r amounts used throughout the r e s t of the country . I t has been the most h e a v i l y used herbicide over the past 30 years i n the United States f o r nonselective weed c o n t r o l on i n d u s t r i a l o r noncropped land and s e l e c t i v e weed c o n t r o l i n corn, sorghum, sugar cane, pineapple and c e r t a i n other plants (12). Annual use i s estimated at 75 to 90 m i l l i o n pounds (18). Following f i e l d a p p l i c a t i o n , atrazine may eventually enter ground and surface waters (10). "Atrazine shares the c h a r a c t e r i s t i c s of other t r i a z i n e herbicides which make i t a ground water contaminant: high leaching p o t e n t i a l , higb persistence i n s o i l s , slow h y d r o l y s i s , low vapor pressure, moderate s o l u b i l i t y i n water, and moderate adsorption to organic matter and c l a y , " according to U.S. EPA (18). Others have described atrazine's propensity to leach to groundwater as high (12), s l i g h t (20), moderate ( l i ) and as a leacher (21)· C e r t a i n metabolites o f atrazine appear to be more water soluble than parent atrazine and could, therefore, be expected to have higher m o b i l i t y t o groundwater than e x h i b i t e d by the parent compound. I n f a c t , a recent study indicates that s o i l m o b i l i t y p r o f i l e s correspond w e l l to soil-water p a r t i t i o n i n g c o e f f i c i e n t s and that desethylatrazine i s more mobile than atrazine i n both P l a i n f i e l d sand and Honeywood s i l t loam (22). In Quebec, Canada, s o i l s are c o l d f o r a greater part of the year than i n many areas of the United States where atrazine i s used. The r a p i d movement of the water table from close to the surface i n spring to around 3 meters i n summer, reported i n Quebec, could enhance leaching of atrazine and i t s phytotoxic dealkylated metabolites which have been shown to p e r s i s t , i n some cases, beyond the growing season
(22). Atrazine Groundwater Monitoring Data. Atrazine groundwater are commonly 10 t o 20 times more frequent most frequently detected p e s t i c i d e (2) · Atrazine i s the detected compound " i n nearly a l l corn-belt areas" i n the
detections i n than the next most commonly United States
