Occurrence of Selected Pesticides and Their Metabolites in Near- Surface Aquifers of the Midwestern United States
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by DigitalCommons@University of Nebraska University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- Published Research US Geological Survey 1996 Occurrence of Selected Pesticides and Their Metabolites in Near- Surface Aquifers of the Midwestern United States Dana Kolpin U.S. Geological Survey E. Michael Thurman U.S. Geological Survey Donald Goolsby U.S. Geological Survey Follow this and additional works at: https://digitalcommons.unl.edu/usgsstaffpub Part of the Earth Sciences Commons Kolpin, Dana; Thurman, E. Michael; and Goolsby, Donald, "Occurrence of Selected Pesticides and Their Metabolites in Near-Surface Aquifers of the Midwestern United States" (1996). USGS Staff -- Published Research. 72. https://digitalcommons.unl.edu/usgsstaffpub/72 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- Published Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Environ. Sci. Technol. 1996, 30, 335-340 Occurrence of Selected Introduction Nonpoint source contamination of water resources from Pesticides and Their Metabolites agriculturally applied pesticides in the United States has been a topic of increased environmental concern over the in Near-Surface Aquifers of the last decade (1, 2). However, even more recently awareness has been growing that pesticide metabolites could also be Midwestern United States contaminating the nation's water resources (3-8). Al- though many of the commonly used pesticides in the United DANAW.KOLPIN* States have either a maximum contaminant level (MCL) or U.S. Geological Survey, 400 South Clinton Street, Box 1230, a health advisory level set for drinking water, very few of Iowa City, Iowa 52244 the corresponding metabolites have had such levels de- termined (9). E.MICHAELTHURMAN To better understand the occurrence of pesticides and U.S. Geological Survey, 4821 Quail Crest Place, pesticide metabolites in groundwater, the U.S. Geological Lawrence, Kansas 66049 Survey (USGS) designed a monitoring network that was DONALDA.GOOLSBY geographically and hydrogeologically representative of near-surface aquifers in the corn (Zea mays L.) and soybean U.S. Geological Survey, Denver Federal Center, Building 25, [Glycine max (L.) Merr.] producing region of the midwestern Lakewood, Colorado 80225 United States (5). Near-surface aquifers are defined as those having their aquifer materials being within about 15 m of the land surface. The occurrence and distribution of selected pesticides In 1991, a strategy was developed to select a recon- and their metabolites were investigated through the naissance network of 303 sampling sites distributed through- collection of 837 water-quality samples from 303 out 12 midwestern states (Figure 1). The results of samples collected from this network were used to compare spatial wells across the Midwest. Results of this study showed and statistical differences of pesticides and pesticide that five of the six most frequently detected metabolites in groundwater. The consistency of the site compounds were pesticide metabolites. Thus, it was selection, sampling protocol, laboratory methods, time of common for a metabolite to be found more frequently sampling, and ancillary data collection for this study allowed in groundwater than its parent compound. The for a unique investigation of the regional hydrogeologic, metabolite alachlor ethanesulfonic acid (alachlor- spatial, and seasonal distributions of pesticides and pes- ESA; 2-[(2,6-diethylphenyl)(methoxymethyl)amino]-2- ticide metabolites in near-surface aquifers of the Midwest. Other companion reports were published elsewhere (5, 10- oxoethanesulfonic acid) was detected almost 10 15). The purpose of this paper is to summarize all available times as frequently and at much higher concentrations analytical results obtained from samples collected during than its parent compound alachlor (2-chloro-2′,6′- 1991-1994 for selected metabolites of alachlor, atrazine, diethyl-N-(methoxymethyl)acetamide). The median cyanazine, dacthal (dimethyl tetrachloroterephthalate), detectable atrazine (2-chloro-4-ethylamino-6- DDT (dichloro diphenyl trichloroethane), and simazine isopropylamino-s-triazine) concentration was almost [2-chloro-4,6-bis(ethylamino)-s-triazine] and discuss their half that of atrazine residue (atrazine plus the two occurrence in groundwater. These parent compounds atrazine metabolites analyzed). Cyanazine amide represent those where at least one of the corresponding metabolites were also analyzed for this study. [2-chloro-4-(1-carbamoyl-1-methylethylamino)-6- ethylamino-s-triazine] was detected almost twice as Methods frequently as cyanazine (2-chloro-4-ethylamino-6- The groundwater reconnaissance network consisted of 303 methylpropionitrileamino-s-triazine). Results show that wells distributed across 12 States (Figure 1), with the entire information on pesticide metabolites is necessary network being sampled twice during 1991 (299 wells to understand the environmental fate of pesticides. March-April and 290 wells July-August) (5). Additional Consequently, if pesticide metabolites are not water samples were collected from 100 randomly selected quantified, the effects of chemical use on groundwater wells from the network during July-August 1992 (15), from 110 wells completed in unconsolidated aquifers during quality would be substantially underestimated. Thus, September-October 1993 (14), and from 38 wells completed continued research is needed to identify major in unconsolidated aquifers during July-August 1994. degradation pathways for all pesticides and to develop All samples were collected by USGS personnel using analytical methods to determine their concentrations equipment constructed of materials, such as glass and in water and other environmental media. stainless steel, that would not leach or adsorb pesticides (10). Decontamination procedures, which included the thorough rinsing and cleaning of all equipment, were * Corresponding author e-mail address: [email protected]; (319)- 358-3614 (voice); (319)-358-3606 (fax). This article not subject to U.S. Copyright. VOL. 30, NO. 1, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 335 Published 1995 by the American Chemical Society. dacthal f DCPA acid metabolite (2,3,5,6-tetrachloro- 1,4-benzenedicarboxylic acid) (27, 28) DDT f DDE (dichlorodephenyldichloroethylene) (29, 30) simazine f DIA (31) Results To determine the occurrence of pesticides and metabolites in water in near-surface aquifers of the Midwest, 837 samples from 303 wells were collected for analysis from March 1991 to August 1994. The frequency of detection for the selected pesticides and their metabolites is given in Table 1. However, because the analytical reporting limits between these compounds are not consistent, this table FIGURE 1. Location of wells in Midwestern groundwater recon- may be somewhat misleading. Research has documented naissance network. an inverse relation between analytical reporting limits and the frequency of pesticide detection (15, 32-34). To implemented to prevent cross-contamination between compensate for this inconsistency, Figure 2 presents the wells and samples. Wells were purged before sampling frequencies of chemical detection after adjusting to a until pH, water temperature, and specific conductance common reporting limit of 0.05 µg/L. Other factors that stabilized. The pumping time to reach chemical stability may be affecting the frequency of detection in Table 1 are for each well varied, but required a minimum of 15 minutes. the amounts of chemical applications being used in crop All water samples were stored in amber, baked-glass bottles production in the Midwest (35) and their environmental and chilled upon collection. No other preservation tech- fate (36). niques were required. A quality-control program using a At least one of the five parent compounds examined series of field blanks, field duplicates, and spikes verified (Table 1) were reported above 0.05 µg/L in 24.4% of the 303 effectiveness of the sampling protocol and the analytical wells sampled. However, when selected metabolites for procedures. these five pesticides are considered, the frequency of Several analytical methods were used during this study detection increases to 39.6%. This detection frequency to determine concentrations of pesticides and pesticide would likely have increased even further if concentrations metabolites in the groundwater samples. All samples were of all the metabolites examined were obtained for every analyzed for 11 herbicides and two triazine metabolites by well. Five of the six most frequently detected compounds gas chromatography/mass spectrometry (GC/MS) following for this study were pesticide metabolites (Figure 2). Thus, solid-phase extraction on C-18 cartridges (16, 17). The it was common for a metabolite to be found more frequently analytical reporting limit for this method was 0.05 µg/L for in groundwater than the parent compound. all compounds. To quantify concentrations of pesticides Alachlor. Alachlor is used as a pre-emergent herbicide and pesticide metabolites at reporting limits as low as 0.002 to kill grasses and broadleaf weeds primarily in corn and µg/L in selected samples, analytes were extracted by a solid- soybeans. Although alachlor has historically been one of phase extraction