engleski

Mathematical Description of Imidacloprid Degradation in Two Coastal Croatian Soils

Introduction: The ability of soils to degrade pesticides strongly influences their environmental fate and is often used as a key parameter in pesticide risk assessment. The aim of this study was to investigate the persistence of imidacloprid [1-(6-chloro-3-pyridinylmethyl)-N-nitroimidazolidin-2-ylideneamine] in two coastal Croatian soils (Krk and Istria) during six months and to identify mathematical models that adequately describe imidacloprid persistence in the soil. Material and Methods: The persistence of imidacloprid was studied at two concentration levels (CL), 0.5 and 5 mg/kg. Experimental degradation data were fitted by five models: a monophasic first-order model (Model 1) and four biphasic models, a first-order double exponential model (Model 2), a first-order two-compartment model (Model 3), a first-order discontinuous biphasic model (Model 4) and the Hoerl function (Model 5). Results and Discussion: Model 1 adequately described imidacloprid persistence in Krk soil (sandy clay loam soil) at the high CL, but biphasic models better described imidacloprid persistence at the low CL. The time for 50% (DT50) of initial imidacloprid loss was approximately 45 days, and 131 days at low and high CL, respectively. The more complex Models 2 through 5 also better described the biphasic degradation of imidacloprid in Istrian soil (clay soil) than Model 1. The DT50 values were 32 days and 65 days at low and high CL, respectively. Conclusion: Faster imidacloprid loss in the Istrian soil possibly resulted from the higher soil organic carbon content that retained more imidacloprid near the soil surface where higher temperature and photolysis accelerated the loss.

Croatia; imidacloprid; insecticide; persistence; kinetics; soil

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