Understanding herbicide sorption within soil profiles is the first step to predicting their behavior and leaching potential. Laboratory studies were conducted to determine the influence of surface and subsurface soil properties on acetochlor, atrazine, and S-metolachlor sorption. Soil samples were taken from horizons A, B, and C of two loamy soils of the humid pampas of Argentina under no-till management; horizon A was divided into two layers, A0 (0-5cm) and A1 (5cm to the full thickness of an A horizon). Sorption isotherms were determined from each sampled horizon using the batch equilibrium method and seven concentrations (0, 0.1, 0.5, 2.0, 5.0, 10.0, and 20.0mgL-1). Sorption affinity of herbicides was approximated by the Freundlich equation. The sorption strength Kf (mg1 - 1/n kg-1 L1/n) over the soils and horizons studied followed the order S-metolachlor (16.51-29.19)>atrazine (4.85-12.34) ≥ acetochlor (5.17-11.97), which was closely related to the hydrophobicity of herbicides expressed as octanol-water partition coefficient (KOW). The Kf values of the three herbicides were positively correlated with soil organic carbon, with a significance of p<0.01. Values of Kf for the three herbicides decreased with depth in the two soils, indicating greater sorption onto surficial soil horizons and possibly a delayed transport toward subsurface soils and subsequent pollution of groundwater.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Health, Toxicology and Mutagenesis
- Soil profile
- Surface/subsurface horizons