Thermodynamic behavior of atrazine sorption–desorption on three soil types from sugarcane fields: a case study in Suphan Buri Province, Thailand

This study examines the sorption and desorption behavior of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) across different soil types to assess its environmental risks in tropical agricultural systems. Three soil series—Chantuk (Cu), Ladya (Ly), and Doembang (Db)—were collected from sugarcane fields in Suphan Buri, Thailand. The objective is to clarify how specific soil properties influence the mobility and persistence of atrazine. Sorption and desorption isotherms were evaluated for 24 soil samples using the Freundlich and Langmuir models at four temperatures (15–45 °C). Key parameters, such as Freundlich sorption and desorption coefficients ( $${K}_{F,sorp}$$ and $${K}_{F,des})$$ , were analyzed, along with thermodynamic properties including Gibbs free energy ( $$\Delta G$$ ) and enthalpy ( $$\Delta H$$ ). Additionally, soil leachability was assessed using the Soil Leaching Potential Index (SLPi) and Retardation Factor (RF). The Freundlich isotherm model best fit for both sorption (coefficient of determination, R2 = 0.970 to 0.979) and desorption data (R2 = 0.984 to 0.987) compared to the Langmuir model. Sorption capacity was primarily influenced by soil organic carbon (SOC) content, while desorption coefficients ( $${K}_{F,des}$$ ) consistently exceeded sorption coefficients, indicating partial irreversibility. Under laboratory conditions across the tested temperature range (15–45 °C), the desorption process exhibited spontaneous and exothermic behavior, with Gibbs free energy ( $$\Delta G$$ ) values becoming increasingly negative at higher temperatures. Ly showing the highest average KF,des (10.24 ± 2.48), suggesting stronger retention of atrazine compared to Cu (9.58 ± 1.79) and Db soils (8.87 ± 1.42) mg1-n Ln kg−1. The low atrazine desorption was Ly<Cu<Db soils. Calculated SLPi values correlated with estimated mobility parameters, suggesting potential relationships that warrant field validation. The findings highlight the influence of thermodynamic parameters and soil-specific Soil Leaching Potential Index (SLPi) and Retardation Factor (RF) values on atrazine mobility. These factors provide insights for assessing atrazine behavior in similar soil systems and may inform risk evaluation approaches.