Atrazine sorption in field-moist soils: Supercritical carbon dioxide density effects

Supercritical carbon dioxide (SF-CO2) has been recently introduced for use in determining sorption coefficients of atrazine (6-chloro-N-ethyl-N′-(1-methyl)-1,3,5-triazine-2,4-diamine) in field-moist soils. In this study we determined the effects of SF-CO2 density modification on atrazine-soil sorption coefficients. As the density of SF-CO2 increased, the SF-CO2 soil/water partition coefficient (Kd) decreased. Kd values for the first desorption equilibration (KdD1) obtained with the SF-CO2 technique at an SF-CO2 density of 0.25 g mL−1 were linearly related to soil organic carbon content, clay content, and batch Freundlich coefficients (Kf values). The log of Kd for each soil was linearly related to the log of the SF-CO2 density for densities 0.25 through 0.45 g mL−1. The SF-CO2 Kd value predicted using the batch Kf / SF-CO2 Kd relationship obtained in this study, and an experimental batch Kf value for a Minnesota (USA) soil from the literature, was consistent with the SF-CO2 Kd values predicted using organic carbon and clay content relationships obtained from this study.