Formulations of the insecticide imidacloprid were made using a commercially available pine kraft lignin. The release kinetics of imidacloprid from granules with variation in the loadings of the insecticide and granule sizes were evaluated in water under dynamic flow conditions. The release data were fitted to the generalized model M t /M z = kt n + c, where M t /M z is the percentage of insecticide released at time t, k and c are constants, and n is another constant that indicates the mechanism of release. The results indicated that the release of imidacloprid was diffusion-controlled. The time taken for 50% of the active ingredient to be released into water, T 50, was also calculated for the comparison of formulations. The results showed that the formulation with the higher loading of imidacloprid had the higher value of T 50, which means a slower release of the active ingredient. In a related experiment, it was found that as the size of this formulation decreased, the release of the active ingredient was faster. In addition, mobilities of technical and formulated imidacloprid were compared by using soil columns simulating a layered bed system commonly used under a plastic greenhouse. The use of formulated imidacloprid produced a less vertical distribution of the active ingredient compared to the technical product. Sorption capacities of the various soil constituents for imidacloprid molecules were also calculated by using batch experiments. The results obtained were in agreement with those for sorption in dynamic conditions. Keywords: Controlled release; imidacloprid; lignin; leaching

To evaluate the effects of dissolved organic carbon on sorption and mobility of the insecticide imidacloprid [1-(6-chloro-3-pyridinyl) methyl-N-nitro-2-imidazolidinimine] in soils, adsorption and column experiments were performed by using a typical calcareous soil from southeastern Spain and two different types of dissolved organic carbon, that is, dissolved organic carbon extracts from a commercial peat (DOC-PE) and high-purity tannic acid (DOC-TA). The experiments were carried out from a 0.01 M CaCl2 aqueous medium at 25 degrees C. The results obtained from the sorption experiments show that the presence of both DOC-PE and DOC-TA, over a concentration range of 15 to 100 mg L(-1), produces in all cases a decreasing amount of imidacloprid adsorbed in the soil studied. From the column experiments the retardation coefficients (RC) were calculated for imidacloprid by using either 0.01 M CaCl2 aqueous solution (RC = 2.10), 0.01 M CaCl2 DOC-PE solution (RC = 1.65), or 0.01 M CaCl2 DOC-TA solution (RC = 1.87). The results indicate that mobility of imidacloprid is increased 21.4 and 11.0% in the presence of DOC-PE and DOC-TA solutions, respectively. Dissolved organic carbon reduces imidacloprid sorption by competing with the pesticide molecules for sorption sites on the soil surface, allowing enhanced leaching of imidacloprid and potentially increasing ground water contamination.

The leaching processes of the insecticide imidacloprid [1‐(6‐chloro‐3‐pyridinylmethyl)‐N‐nitro‐2‐imidazolidinylideamine] and the fungicide procymidone [N‐(3,5‐dichlorophenyl)‐1,2‐dimethyl‐1,2‐cyclopropanedicarboximide] in a greenhouse soil from the southeastern of Spain were investigated. Four separate pesticide applications were made at dose rates considerably higher than the recommended in normal agronomic practice, representing a worst case scenario. Soils samples were taken to a depth of 40 cm at time intervals after each application and analyzed by high performance liquid chromatography (HPLC). The partition coefficients (Kd) of the samples for imidacloprid and procymidone were calculated by carrying out batch experiments and fitting the experimental data point to the linear isotherm equation. Soil tension, water content, and temperature measurements were also determined during all the experiments. Although the results show a high degree of variability, rapid transport of pesticides through the soil occurred which increases the possibility of groundwater pollution. The leaching of these pesticides, particularly procymidone, generally thought of as immobile, might be possible through formation of stable soluble organic fraction–pesticide interactions in solution, allowing an increased groundwater contamination potential.

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