Adsorption and Desorption of Atrazine, Desethylatrazine, Deisopropylatrazine, and Hydroxyatrazine in Vegetated Filter Strip and Cultivated Soil LARRY JASON KRUTZ,* ,† SCOTT ALLEN SENSEMAN, † KEVIN JOSEPH MCINNES, † DAVID ALLEN ZUBERER, † AND DENNIS PATRICK TIERNEY § Department of Soil and Crop Sciences, Texas Agricultural Experiment Station, Texas A&M University, College Station, Texas 77843-2474, and Environmental Stewardship and Regulatory Policy, Syngenta Crop Protection, P.O. 18300, Greensboro, North Carolina 27409 Adsorption and desorption of atrazine and its metabolites in vegetated filter strip soil (VFS) has not been evaluated, yet these data are needed to predict the transport of these compounds through the VFS. Adsorption and desorption parameters for atrazine, desethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA) were compared between a cultivated Houston Black clay (CS) and an adjacent 12-year-old VFS established in a mixed stand of bermudagrass [Cynodon dactylon (L.) Pers.] and buffalograss [Buchloe dactyloides (Nutt. Engelm)]. Adsorption and desorption isotherms were determined by batch equilibrium. The evaluated chemical and physical properties of the VFS and CS were similar with the exception of a 1.7-fold increase in the organic carbon content of the VFS. Adsorption and desorption coefficients for atrazine were at least 59% higher in VFS than in CS. The adsorption coefficient for HA was 48% higher in VFS compared with CS, but desorption was not statistically different between soils. Adsorption and desorption coefficients for DEA and DIA were not statistically different between soils. The predicted order of mobility in CS is HA < atrazine ) DIA ) DEA. In VFS, the predicted order of mobility is HA < atrazine ) DIA < DEA. These data indicate that the higher organic carbon in VFS will likely retard the transport of atrazine and HA to surface and ground waters; however, the transport rates of DEA and DIA will be similar between soils. KEYWORDS: Vegetated filter strip; adsorption; desorption; mobility; atrazine; desethylatrazine; deiso- propylatrazine; hydroxyatrazine; hysteresis INTRODUCTION Atrazine [2-chloro-4-(ethylamino)-6-isopropylamino)-s-tri- azine] is used to control annual grasses and broadleaf weeds primarily in corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] (1). In soil, atrazine is transformed into several products including desethylatrazine [2-amino-4-chloro- 6-(isopropylamino)-s-triazine; DEA], deisopropylatrazine [2- amino-4-chloro-6-(ethylamino)-s-triazine; DIA], and hydroxyatra- zine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine; HA] (2)(Figure 1). The formation of DEA and DIA occurs through N-dealkylation of atrazine, a microbially mediated process (3, 4). Formation of HA occurs through both biological (5) and nonbiological (6) pathways. Atrazine and its metabolites have been detected in surface and ground waters. The maximum concentrations in 95 Mid- western streams were 136 μgL -1 for atrazine, 7.5 μgL -1 for DEA, 7.4 μgL -1 for DIA, and 3.7 μgL -1 for HA (7). Similar maximum concentrations for atrazine and its metabolites have been reported for the lower Mississippi River (8), various Midwestern streams (9, 10), and the Playa Lakes of West Texas (11). In groundwater, Kolpin et al. (12) reported that the maximum concentrations in 131 Iowa wells were 2.1 μgL -1 for atrazine, 0.6 μgL -1 for DEA, 1.1 μgL -1 for DIA, and 1.3 μgL -1 for HA. Similar results have been reported for near- surface aquifers of the Midwestern United States (13). Conse- quently, means for limiting the transport of atrazine and its metabolites from application zones are desirable. Vegetated filter strips are bands of indigenous or planted vegetation below cultivated fields or animal production facilities that are intended to reduce the transport of sediment and agricultural chemicals. Vegetated filter strips have been reported to reduce atrazine and atrazine metabolite losses from application zones by facilitating the deposition of sediment-adsorbed compounds (14), increasing infiltration (14-23), and adsorbing compounds to vegetated filter strip grass, grass thatch, or soil surfaces (14-16, 19, 22). Although these processes reduce * Corresponding author [e-mail lkrutz@ag.tamu.edu; telephone (979) 845-5384; fax (979) 845-0456]. † Texas A&M University. § Syngenta Crop Protection. J. Agric. Food Chem. 2003, 51, 7379-7384 7379 10.1021/jf0348572 CCC: $25.00 © 2003 American Chemical Society Published on Web 11/11/2003