Adsorption and Desorption of Atrazine in Soils and Subsurface Sediments

Prediction of herbicide movement in the subsurface environment requires accurate estimates of herbicide sorption in soils and geologic materials. This information is often lacking for materials below the soil surface. We describe adsorption and desorption of atrazine in surface soils, subsoils, and sediments from different geologic settings with the Freundlich equation. Average adsorption partition coefficients (K f) for the C horizon materials were 0.43 ± 0.25 for oxidized till, 0.51 ± 0.02 for loess, and 0.55 ± 0.24 for alluvium. Adsorption of atrazine was controlled principally by organic C. Samples of unoxidized tills adsorbed atrazine at levels equivalent to surface soils. All subsurface sediments retained atrazine during desorption to a greater relative extent than that predicted from adsorption isotherms. Although sorption of atrazine in subsurface sediments is generally low, there is sufficient retention to warrant consideration of sorption processes in the assessment of atrazine transport in the subsurface environment.