Adsorption and Desorption of Atrazine, Hydroxyatrazine, andS-Glutathione Atrazine on Two Soils

Abstract

Adsorption and desorption isotherms for atrazine and two metabolites, hydroxyatrazine (HA) andS-glutathione atrazine (GSHA), were determined by batch equilibration on Plano and Waukegan silt loam soils at two soil pH levels (Plano, 6.1 and 4.5; Waukegan, 6.1 and 4.0). Freundlich adsorption isotherms were not affected by soil type except for GSHA at pH 4.0 to 4.5. When averaged over both soils, the order of adsorption at pH 6.1 was atrazine (Kf= 3.7) < GSHA (Kf= 7.3) << HA (Kf= 25) and at pH 4.0–4.5 was atrazine (Kf= 6.1) << HA (Kf= 58) ≤ GSHA (Kf: Plano = 35; Waukegan = 78). The average slope of the adsorption isotherms (1/nads) was 0.81. The slopes of all desorption isotherms (1/ndes) were less than their respective 1/nads, indicating hysteresis. Atrazine desorbed into soil solution (1/ndes> 0.0). With the exception of GSHA which desorbed from the pH 6.1 Plano silt loam (1/ndes= 0.15), desorption of HA and GSHA from other treatments was negligible (1/ndes= 0.0). Consequently, leaching of HA and GSHA in these and similar soils is not likely, due to high adsorption and low desorption.