Atrazine surface runoff water

In recent years, the effect of buffers on the major metabolites of herbicides has begun to receive attention. Gay et al. (2006) monitored atrazine and three major degradation products in groundwater, soil, and runoff water for 11 months after application to a 0.1 ha strip immediately upslope from a restored forested riparian buffer in southern Georgia. Removal efficiency from groundwater (84.2-99.5%), surface runoff water (92-100%), and surface runoff sediment (67.4-92.0%) was significant for all four compounds (ranges in parentheses). 

The documented occurrence of pesticides in surface water is indicative that runoff is an important pathway for transport of pesticide away from the site of appHcation. An estimated 160 t of atrazine, 71 t of simazine, 56 t of metolachlor, and 181 of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of mnoff (47). Field appHcation of pesticides inevitably leads to pesticide contamination of surface runoff water unless runoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in runoff varies from site to site. It is controlled by the timing of mnoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the appHed pesticide can leave the edge of the field where it was appHed. 

Deethylatrazine (DEA) and deisopropylatrazine (DIA) also have been detected in shallow, unsaturated surface-water runoff from a Eudora silt loam soil with DEA present at higher concentrations (Mills and Thurman, 1994a). Dissolved atrazine, DEA, and DIA concentrations in water samples from two closely spaced lakes indicated large differences in input from watershed nonpoint sources. Levels of these chemicals increased in response to spring and early summer runoff events (Spalding et al., 1994). In studies conducted by Gaynor el al. (1992, 1995), DEA was found in surface runoff samples that contained atrazine. Hydroxyatrazine (HA), deethyl hydroxyatrazine (DEHA), and deisopropyl hydroxyatrazine (DIHA) have also been identified in surface water (Lerch et al., 1995). 

The three major pathways for atrazine to enter the Chesapeake Bay are surface runoff, groundwater inflow, and wet and dry atmospheric deposition. Processes such as hydraulic flushing, air-water transfer and chemiod reactions will then influence the final concentration and distribution of atrazine in the Bay. 

Three tributaries, the Susquehanna, the Potomac, and the James Rivers account for approximately 80 to 85 percent of the fresh water flow into the Bay from the northern and western regions. These three tributaries also dominate herbicide input to the Bay (8). Foster and Lippa (8) present the most comprehensive data sets available. They estimated that 2,700 kg of atrazine were loaded into the Bay in the period 1992-1993 1,700 kg via the Susquehamia, 780 kg via the Potomac, and 220 kg via the James. Similar estimates of atrazine loading were reported by the U. S. Enviromnental Protection Agency (USEPA) 15, 24) for the Susquehanna and the James Rivers. Godfrey et cd. 25) showed that the relative error in the estimation method used by Foster and Lippa (8) was less than 40%. The Chester and Choptank Rivers are the major pathways of atrazine input fix)m the Eastern Shore of the Bay. Based on concentration and flow rate, fliese rivers accoimt for a combined mass load of approximately 100 kg. The total input of atrazine via surface runoff is thus 2,800 kg/yr. 

The adoption of best management practices can reduce the storm-related runoff of atrazine, simazine, and other moderately soluble herbicides from fields into bodies of surface water. Several papers (Fawcett et al., 1994 Hirsch et al, 1997 USDA-NRCS, 2000 Krutz et al., 2005) note how these in-field practices can be beneficial to water quality. 

Preferential removal of an ethyl versus an isopropyl moiety is a concept that has been suggested by Leonard (1988). DIA occurs in surface water that has received parent atrazine, simazine, or cyanazine. DEA occurs in surface water that has received atrazine or propazine. The concentrations of DEA and DIA in surface water vary with the hydrologic conditions of the basin and the timing of runoff (Mills and Thurman, 1994 Thurman et al, 1994,1998a). 

Significant progress in the adoption of BMPs has been made by the farming community. Setbacks from waterways added to herbicide product labels such as atrazine-containing products have contributed significantly to buffers being established on corn and sorghum farmland. Continued emphasis on the reduction of erosion and surface water runoff,... 

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