Adsorption and desorption processes of the organophosphorus pesticides, dimethoate and fenthion, onto three Greek agricultural soils

Laboratory studies were conducted to determine the sorption and desorption behaviour of two commonly used organophosphorus pesticides dimethoate and fenthion, which are widely used in the studied area to treat the olivetrees. Three Greek soils from the region of Mytilene island (denoted M, KT and P) which differed with respect to pH (pH 5.45-6.90), clay content (6-26%), organic matter content (1.0-4.2%), cation exchange capacity (4.8-24.4 meq/100 g) and specific surface (10.79-109.22 m(2) g(-1)) were selected for the experimental section that was conducted using the batch equilibrium technique. The sorption isotherms could be described by Freundlich and Langmuir equations for both compounds with correlation regression coefficients for fit of the isotherms to that models R-2 >= 0.9666 and R-2 >= 0.8117, respectively. Freundlich sorption coefficients K-f were normalised to soil organic matter content and K-OM estimated values for M, KT and P soils respectively were 60.19, 163.58 and 663.43 for dimethoate and 1365.84, 820.73 and 2902.52 for fenthion. Desorption studies revealed that dimethoate was adsorbed very weakly on soils tested and easily desorbed with water, while on the contrary fenthion was adsorbed very strongly on studied matrices with acetone extractable amounts.