title: Effects of temperature on sorption-desorption processes of imidacloprid in soils of Croatian coastal regions.
abstract: Sorption-desorption behavior of imidacloprid in six soils collected from five coastal regions in Croatia at 20, 30 and 40°C was investigated using batch equilibrium technique. Isothermal data were applied to Freundlich, Langmuir and Temkin equations, and the thermodynamic parameters ΔH°, ΔG°, ΔS° were calculated. The sorption isotherm curves were non-linear and may be classified as L-type, suggesting a relatively high sorption capacity for imidacloprid. Our results showed that the K( sor ) ( F )  values decreased for all the tested soils as the temperature increased, indicating that the temperature strongly influences the sorption. Values of ΔG° were negative (-4.65 to -2.00 kJ/mol) indicating that at all experimental temperatures the interactions of imidacloprid with soils were spontaneous processes. The negative and small ΔH° values (-19.79 to -8.89 kJ/mol) were in the range of weak forces, such as H-bonds, consistent with interactions and partitioning of the imidacloprid molecules into soil organic matter. The ΔS° values followed the range of -57.12 to -14.51 J/molK, suggesting that imidacloprid molecules lose entropy during transition from the solution phase to soil surface. It was found that imidacloprid desorption from soil was concentration and temperature-dependent, i.e. at lower imidacloprid concentrations and temperature, lower desorption percentage occurred. Desorption studies revealed that hysteretic behavior under different temperature treatments existed, and it was more pronounced at 20°C in the soils with higher OC content. The study results emphasize the importance of thermodynamic parameters in controlling soil pesticide mobility in different geographical locations, seasons and greenhouse conditions.
authors.affiliation: Department of Chemistry and Biochemistry, School of Medicine, University of Rijeka, Rijeka, Croatia. dbroznic@medri.hr
authors.forename: Dalibor
authors.initials: D
authors.lastname: Broznić
authors.forename: Cedomila
authors.initials: C
authors.lastname: Milin
mesh_terms: D000327:Adsorption; D017523:Croatia; D006540:Herbicides / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D013696:Temperature
chemical_list: D006540:Herbicides; D007093:Imidazoles; D000073943:Neonicotinoids; D009574:Nitro Compounds; D012989:Soil Pollutants; C082359:imidacloprid