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Pesticide Trends in Surface and Groundwater in Iowa: 1980 - 1995 M.P. Skopec and B.E. Hoyer In 1991, the Iowa Department of Agriculture and Land Stewardship (IDALS) started the groundwork for a Pesticide State Management Plan. As part of this effort, the Geological Survey Bureau (GSB) of the Iowa Department of Natural Resources began an evaluation of the state’s surface and groundwater quality. This evaluation required the creation of a pesticide database compiled from many different types of datasets ranging from field-scale studies to watershed-scale studies and single- to multi-year monitoring programs. Such a collection increased the amount of data available and was necessary to evaluate various environmental questions for management purposes. The Iowa Pesticide Water Resources Database (IAPEST) is dominated by groundwater analyses (12,375 groundwater samples compared to 5,766 surface water analyses); however, the surface water data has a slightly longer period of record (1980 – 1995) than groundwater (1982 – 1995). Seventy-five different pesticides, pesticide metabolites, or pesticide groups are included in the database. Pesticides are detected in 78.2% of the surface water samples analyzed and 26.4% of the groundwater samples. Temporal trends in surface and groundwater quality were examined. The data were further stratified by groundwater vulnerability regions and major river basins to examine the spatial, as well as the temporal, variability in water quality.     Figure 1. Summary of IAPEST data for the regions defined by the Groundwater Vulnerability Regions of Iowa (GVRI) map (Hoyer and Hallberg, 1991).   Good Bedrock Aquifers include those of Cambrian, Ordovician, Silurian, and Devonian (a selected subset) systems. Generally, they have good natural quality and produce adequate quantities for many purposes. Variable Bedrock Aquifers include those of the Devonian (a selected subset), Mississippian and Cretaceous systems. Generally, the natural quality and yields from these aquifers vary considerably. Thin Drift is defined as less than 100 feet in thickness. Moderate Drift cover is defined to be between 100 and 300 feet in thickness. Bedrock Wells with Thick Drift Cover defines those bedrock wells that occur within the identified drift region. Drift Aquifer – these are not mapped, per se, on the GVRI. Rather, the GVRI identifies regions where drift aquifers are most commonly used. Drift aquifers are potentially available wherever there is glacial drift or loess of reasonable thickness. They are used where bedrock aquifers are not economical, not reliable, or of poor natural quality. Alluvial Aquifer – areas underlain by sand and gravel aquifers situated beneath floodplains along stream valleys and includes alluvial deposits associated with stream terraces and benches, contiguous wind-blown sand deposits, and glacial outwash deposits. The numbers of samples and sites are not evenly distributed across groundwater vulnerability regions. The most vulnerable areas have received the majority of the research and monitoring efforts. Due to the low number of samples, some of the original GVRI regions were combined for trend analyses.     Figure 2. Summary of IAPEST data for the interior river basins.   Seven major surface water basins were identified for Iowa: Northeastern Iowa Rivers basin including Upper Iowa, Maquoketa, Yellow, and the Turkey rivers; Cedar River basin; Iowa River basin; Skunk River basin; Des Moines River basin; Southern Iowa Rivers basin including Chariton, Grand, Nodaway and Nishnabotna rivers; and the Western Iowa Rivers basin including Rock, Little Sioux, Maple, Soldier, and Boyer rivers. The number of samples (and sites) is poorly distributed between and within surface water basins.     Figure 3. Comparison of detection frequency in surface and groundwater for the most commonly found pesticides, 1980 – 1982. *ELISA Triazine category represents the enzyme-linked immunoassay test for the triazine family of compounds.       Figure 4. Precipitation departure from normal for Iowa: 1982 – 1995 (from Climatological Data for Iowa).       Figure 5. Atrazine detection rates in Iowa surface and groundwater: 1982 – 1995.       Figure 6. Alachlor detection rates in Iowa surface and groundwater: 1982 – 1995.       Figure 7. Cyanazine detection rates in Iowa surface and groundwater: 1982 – 1995.       Figure 8. Metolachlor detection rates in Iowa surface and groundwater: 1982 – 1995.   Figures 5 - 8. The bar charts show the frequency of detection for four of the most commonly detected pesticides in Iowa’s waters. Pesticides are detected much more frequently in surface water than in groundwater. All of the detection rates show a decrease in the late 1980s due to the effect of a state-wide drought (see Figure 4). Alachlor detections have dropped in the 1990s as a result of rapidly declining use patterns (see Table 2). Atrazine detection rates also seem to be decreasing despite a relatively stable use pattern. At this time, it appears that management changes in the use of atrazine (including a reduction in maximum use rate, elimination of fall applications, and buffers adjacent to streams and tile intakes) may be responsible for this decrease. Cyanazine detection rates seem to be increasing despite declining use rates. This may be the result of a sampling bias – the database contains several recent studies on reservoirs in the southern part of the state where cyanazine is primarily used. Metolachor detection rates have remained stable reflecting its unchanging use patterns.     Figure 9. Scatterplot of alachlor concentrations in Iowa groundwater.       Figure 10. Scatterplot of atrazine concentrations in Iowa groundwater.   Figures 9 – 10. Both atrazine and alachlor concentrations in Iowa groundwater have shown significant decreases for the period 1982 – 1995 (see Table 3). The decreases in alachlor concentrations are most likely due to declining use rates. The atrazine decreases appear to be related to management changes and are not the result of reductions in use.   Table 1. Pesticides found in Iowa’s surface and groundwater (data from IAPEST). Groundwater Surface Water -------------------------------------------- ------------------------------------------- Alachlor Acetochlor Atrazine Alachlor Butylate Alachlor – immunoassay test Carbofuran v Aldrin v Carbofuran 3 hydroxy @ Ametryn Chloramben Atrazine Chlordane v BHC alpha form v Chlorpyrifos v Butylate Cyanazine Carbofuran v Dacthal Chloramben Deisopropyl Atrazine @ Chlordane v Deethyl Atrazine @ Cyanazine Diazinon v DDD v Dicamba Deisopropyl Atrazine @ Dimethoate v Deethyl Atrazine @ Endosulfan sulfate @ Dicamba Endrin aldehyde @ Dieldrin v Ethoprop v Endosulfan 1 v Fonofos v Endosulfan 2 v Heptachlor epoxide @ Endosulfan sulfate @ Hydroxy alachlor @ Endrin aldehyde @ Malathion v EPTC Metolachlor Fonofos v Metribuzin Heptachlor v Parathion v Lindane v Pendimethalin Metolachlor Phorate v Metribuzin Picloram Pendimethalin Prometon Prometon Propachlor Propachlor Simazine Propazine Sulprofos v Silvex Terbufos v Simazine Toxaphene v Terbufos v Triazines – immunoassay test Triazines – immunoassay test Trifluralin Trifluralin 2,4-D 2,4-D v= insecticides @=metabolites   The same number of products (37) are found in Iowa’s surface and groundwater, however composition of the list varies slightly. Iowa groundwater has been studied much more extensively with 12,375 samples as compared to surface water with only 5,766 samples.   Table 2. Herbicide use rates in the state of Iowa: 1979 – 1995. (Pest Management in Iowa: Planning for the Future, 1996, Iowa State University publication). Use rates are given in 1,000 pounds of active ingredient (a.i.) per year. Rank is based on the number of pounds used in any given year (e.g., the pesticide with the greatest number of pounds used is assigned a rank of "1").   Alachlor (Lasso) Atrazine (Aatrex) Cyanazine (Bladex) Metolachlor (Dual) Year 1,000 lbs a.i. rank 1,000 lbs a.i. rank 1,000 lbs a.i. rank 1,000 lbs a.i. rank 1979 15,581 1 6,642 4 8,513 3 1,674 7 1985 12,019 1 9,716 4 10,366 3 11,815 2 1990 7,802 2 7,548 3 5,120 5 9,981 1 1991 8,689 2 7,354 3 6,583 4 11,839 1 1992 9,223 2 8,160 3 6,943 4 12,204 1 1993 6,223 4 6,659 3 7,947 2 10,288 1 1994 4,507 4 7,471 3 7,768 2 10,664 1 1995 766 12 6,490 2 5,296 4 8,374 1     Table 3. Trends in herbicide concentrations for Iowa groundwater (1982 – 1995).   Linear Regression F-Statistics   Groundwater Region Atrazine Alachlor Cyanazine Metolachlor All Bedrock Wells 54.57 D 21.95 D 4.40 I 0.90 -- Alluvial Wells 18.29 D 2.12 -- 1.65 -- 1.97 -- Drift Wells 2.35 -- 0.63 -- 6.03 I 0.40 -- Good Bedrock/Thin Cover 5.88 D 12.71 D 11.18 D 13.06 I Good Bedrock/Moderate, Shale Cover 1.67 -- 1.03 -- 0.17 -- 5.09 I Variable Bedrock/Thin Cover 21.26 D 20.54 D 14.67 D 6.05 I Variable Bedrock/Moderate, Shale, and Thick Cover 378.14 D 5.69 D 74.80 D 14.71 I   I = Significant Increase (0.05 level) shown in red D = Significant Decrease (0.05 level) shown in blue -- = no change     Table 4. Trends in herbicide concentrations for Iowa surface water (1980 – 1995).   Linear Regression F - Statistics   Major Interior River Basins Atrazine Alachlor Cyanazine Metolachlor All Surface Water 13.55 D 3.2 -- 12.29 D 0.21 -- Northeastern Iowa Rivers 7.78 D 2.00 -- 20.72 D 0.35 -- Cedar River 1.99 -- 9.42 D 8.83 D 0.59 -- Iowa River 0.07 -- 0.38 -- 0.49 -- 0.18 -- Skunk River 7.91 D 14.26 D 0.62 -- 7.91 D Des Moines River 1.15 -- 80.19 D 1.53 -- 6.80 D Southern Iowa Rivers 6.71 D 0.27 -- 7.05 D 0.32 -- Western Iowa Rivers 9.91 D 6.52 D 3.34 -- 0.15 --   D = Significant Decrease (0.05 level) shown in blue -- = no change   In Tables 3 and 4, linear regression techniques were used to test for significant increases or decreases in herbicide concentrations through time for the various groundwater regions and surface water basins. Acknowledgements The development of the IAPEST database has been supported financially through cooperative agreements with the Iowa Department of Agriculture and Land Stewardship: Laboratory Division, Pesticide Bureau and grants from the U.S. Environmental Protection Agency, Region VII: Water, Wetlands, & Pesticides Division. Reference Hoyer, B.E., and Hallberg, G.H., 1991, Groundwater Vulnerability Regions of Iowa: Department of Natural Resources, Special Map Series 11. Mayerfeld, D., Hallberg, G., Miller, G., Wintersteen, W., Hartzler, R., Brown, S., Duffy, M., and DeWitt, J., 1996, Pest Management in Iowa: Planning for the Future: Iowa State University publication IFM 17, University Extension, Iowa State University, Ames, IA, 89 p.. Presented as a poster at the Sixth National Nonpoint-Source Monitoring Workshop, September 21-24, 1998, Sheraton Four Points Hotel, Cedar Rapids, Iowa.