Submitted to: Geological Society of America Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/3/1996
Publication Date: N/A
Technical Abstract: Atrazine is a widely used herbicide which is found in shallow groundwater throughout the American Midwest and elsewhere. Knowledge of adsorption and desorption reactions are necessary for modeling atrazine transport, but this information is generally lacking for most geologic materials. We investigated the adsorption and desorption of atrazine to surface soil (A horizon), subsoil (B horizon) and geologic sediments at four locations in Iowa. The sediment types included sandy alluvium from a shallow aquifer near Ames, an oxidized loess from near Treynor, late Wisconsinan till materials from near Ames, and Pre-Illinoian till from near Nashua. Adsorption was measured by batch equilibrium techniques with initial concentrations of 0.05, 0.1, 1, 5, 10 and 20 mg atrazine L**-1. Adsorption isotherms for all of the surface soils were constructed with the nonlinear Freundlich model. The Freundlich exponent (1/n) values were generally < 0.90 for the surface soils, but the majority of isotherms for the subsurface sediments were linear. The partition coefficient (Kf) varied between 0.75 and 10.67 for the surface soils (0-25 cm depth). Sorption generally declined with the depth of sediment. In the alluvial and loess sediments below 100 cm depth, Kf values ranged from 0.29 to 0.86. The Kf values for shallow oxidized till samples were similar, but the deeper unoxidized till adsorbed more atrazine (Kf of 2.1 to 15.7) than other subsurface sediments. Shallow subsoils of 25 to 100 cm depth were generally intermediate in sorption between the surface and deeper subsurface sediments. High sorption of atrazine by unoxidized till units may retard potential atrazine transport.