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.

Different ammonium nitrate controlled-release (CR) systems based on ethylcellulose have been investigated to reduce environmental pollution derived from nitrogen-fertilizer use. Coated ammonium nitrate granules were produced in Wurster-type fluidized-bed equipment using two different amounts of ethylcellulose. The highest one was modified by the addition of two plasticizers, dibutyl sebacate, and dibutyl phthalate. Having researched the encapsulation efficiency and the homogeneity of the coated granules, we carried out the kinetic-release experiments in water and soil. The release rate of the active ingredient was related to the thickness of the coating film, granule size, and type of plasticizer used. Using an empirical equation, the time taken for 50% of the active ingredient to be released into water and soil (T 50) was calculated. From the analysis of the T 50 values, we can deduce that the release rate of ammonium nitrate can be controlled, mainly changing the thickness of the coating film and using plasticizer as well. In water experiments, T 50 values for granules prepared without plasticizers ranged between 7.47 h for 1 mm < d < 2 mm granules coated with 10% of ethylcellulose and 24.06 h for 2 mm < d < 3 mm granules coated with 20% of ethylcellulose. For those prepared with plasticizers, T 50 ranged between 22.80 h for 1 mm < d < 2 mm granules containing dibutyl sebacate and 35.74 h for 1 mm < d < 2 mm granules containing dibutyl phthalate. However, in soil experiments T 50 values ranged between 10.24 h for 1 mm < d < 2 mm granules coated with 10% of ethylcellulose and 38.80 h for 1 mm < d < 2 mm granules containing dibutyl sebacate. Finally, a linear regression of the T 50 values was obtained by the results of the study carried out in water and soil. This allows us to predict the behavior of the formulations in soil. This could be useful in the design of systems which control the nitrogen release.

Lignin and ethylcellulose (EC) have been used for the preparation of controlled release (CR) formulations of urea. The lignin matrixes were prepared by mixing the urea with kraft lignin (UL) under melting conditions. They were also crushed and sieved to obtain granules of size between 0.5-1, 1-2, 2-3 and 3-5 mm. The coated urea granules were produced in a Wurster-type fluidized-bed equipment, using an ethanolic solution of EC on two different polymer levels. Having researched the encapsulation efficiency (EE) and the homogeneity of the CR formulations, kinetic-release experiments were carried out in water. A high EE was reached, it oscillated between 95.12% for the system coated with 20% of EC and 97.18% for the 1 mm < d < 2 mm UL system. The rate of urea release from CR granules diminished in all cases in relation to nonformulated urea, being the latter completely dissolved in less than 0.5 h, but it took at least 48 h to release the 90% of urea from the EC coated formulations. Using an empirical equation, the time taken for 50% of the active ingredient to be released into water (T 50 ) was calculated. From the analysis of the T 50 values, we can deduce that the release rate of urea can be controlled mainly by selecting the granule size for lignin CR systems and changing the thickness of the coating film for EC coated granules. The variation order of T 50 values, UL (0.5 mm < d < 1.0 mm) < UL (1.0 mm < d < 2.0 mm) < UL (2.0 mm < d < 3.0 mm) < UL (3.0 mm < d < 5.0 mm) < UEC 10 < UEC 20 , showed that the presence of EC in formulations retarded the release of urea in relation to those prepared with lignin.

In this research, controlled release formulations (CRFs) of the herbicides chloridazon and metribuzin, identified as potential leachers, have been evaluated in soils with different texture. To prepare the CRFs, ethylcellulose (EC) and dibutylsebacate (DBS) have been used as coating agents in lignin-polyethylene glycol based formulations. Mobility experiments have been carried out in two light textured soils (sandy and sandy-loam). Breakthrough curves have shown that the use of CRFs reduces the presence of chloridazon and metribuzin in the leachate compared to technical and commercial products, being the lignin CRF coated with EC and DBS the most efficient to diminish the herbicide leaching. Mass balance study has shown a higher amount of chloridazon and metribuzin recovered in soils when these herbicides were tested as CRFs compared to technical and commercial products. The gradual release of herbicides from the CRFs resulting in a rather available levels of chloridazon and metribuzin in soil for a longer time. A good correlation between percentages of herbicide recovered in leachates and T values (time corresponding to 50% release of herbicide in water) was obtained, which allows to select the most appropriate CRF in each agro-environmental practice to reduce the potential pollution of groundwater by chloridazon and metribuzin.

The mobility of imidacloprid [1-(6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] from alginate-based controlled-release (CR) formulations was investigated in two different soil pro®les. In one, a layered bed system simulating the typical arrangement under a plastic greenhouse, which is composed of sand, peat, amended soil and native soil, was used. In the other, the layer containing amended soil was used in order to determine the mobility of the insecticide in a soil system with a low content of organic matter and a high content of clay. Two CR formulations based on sodium alginate (1.87% wt/wt), imidacloprid (1.21%), natural or acid-treated bentonite (3.28%), and water (93.64%) were compared to technical grade imidacloprid. The use of alginate CR formulations produced less vertical mobility of the active ingredient as compared to the technical product. With the technical grade product treatment, the total amount of imidacloprid leached from columns packed with amended soil was 82.3% of that applied, whereas for the alginate-based CR formulations containing natural or acid-treated bentonite, the leached percentages were 44.7% and 37.1%, respectively. In the column experiments simulating the layered bed system, no insecticide was found in the leachate when the alginate-based CR formulations containing natural bentonite were used. However, 3% of the applied imidacloprid appeared when the treatment was carried out with technical grade material. Sorption-desorption capacities of the various soil layers for imidacloprid molecules were also calculated using batch experiments.