engleski

Sorption/Desorption Equilibrium and Thermodynamics of Imidacloprid in Croatian Coastal Region Soils

In Croatia, imidacloprid [1-(6-chloro-3-pyridinylmethyl)-N-nitroimidazolidin-2-ylideneamine, IMI] is most commonly used in olive growing areas against olive fruit fly. Understanding variability’s in pesticide sorption/desorption that can occur among and within the regions, can improve IMI’s applicability. Therefore, sorption/desorption equilibrium, and thermodynamics of IMI in ten coastal Croatian soils were investigated as a function of organic carbon content (OC), cation exchange capacity (CEC), concentration of pesticide solution and temperature. The residues of IMI were analyzed by HPLC using a UV/VIS detector (270 nm). As the experimental data showed the best fit to the Freundlich equation (R2 =0.974-0.999 for sorption and 0.985-0.999 for desorption), this model was used for calculation of sorption/desorption coefficients: equilibrium sorption capacity (KF) and desorption capacity (KFd). Coefficient KF decreased as the temperature increased, while coefficient KFd increased with increasing temperature. Both coefficients correlated significantlly with the OC (R2>0.98 ; R2>0.91 ; P<0.05) and CEC (R2>0.86 ; R2>0.79 ; P<0.05), but according to the multiple regression the OC predominantly influenced IMI sorption. In all soils, a greater sorption occurred at lower concentrations of IMI. After desorption, the percentage of IMI’s desorbed amount decreased as the initial sorbed concentration increased in all tested soils. Sorption/desorption showed extensive hysteretic behavior resulting from discrepancies between sorption and desorption isotherms. The calculated thermodynamic parameters, H, S and G indicated that IMI sorption/desorption on soils was spontaneous and exothermic. However, these results emphasize the importance of temperature on the sorption/desorption processes, especially in greenhouses, where it is necessary to achieve high temperatures for crops cultivation. Within the meaning of IMI’s applicability, it could be a serious problem, because the sorption of IMI was less pronounced at higher temperature than the desorption, which means that IMI in these conditions has a higher mobility in soil, and thus represents a greater risk for environment and groundwater pollution.

desorption; imidacloprid; organic carbon content; soil; sorption; thermodynamics

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