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Comparative studies to model bioavailability of pesticides in distinctive soil types
Published February 23, 2008
17-23

Bioavailability of pesticides is determined by two major factors: soil characteristics and pesticides’ chemical feature. These factors result in a definite adsorption capability whose extent varies on a large scale. By revealing interactions between pesticides and soils it is of high interest to model bioavailability of widely used pesticides..., as it is a key element in terms of prospective toxicological aspects. Our work signifies steps forward improving pesticide soil mobility prediction models as we created model systems representing correctly natural relations. Comparison of different solvent extraction methods proved to be an efficient tool to gain information on the bioavailability of some widely used pesticides as well as to model actual environmental processes.
Comprehensive comparison has been made between different experimental methods by applying 5 extraction models showing diverse efficiency in extracting capability of pesticides. In some cases chloroform excelled in mobilizing pesticides from soil, however mostly application of humic acid solution as extraction model was found to be at least as efficient as methanol, chloroform or CaCl2-solution.
Four chemically much different pesticide (simazine, acetochlor, chlorpyrifos and diuron) were applied to two soil types (both sandy and brown forest). The extracted amounts were determined by GC/MS technique. Adsorption coefficients (Kd) were also calculated for the examined samples.
Obtained results for Kd indicated that chemical feature of pesticides seemed to be of utmost importance in terms of soil binding capability preceding the relevance of soil characteristics. Adsorption capability of chlorpyrifos proved to be the most pronounced preceding simazine and the least prone to bind to soil acetochlor and diuron

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GC-MS studies to map mechanistic aspects of photolytic decomposition of pesticides
Published February 23, 2008
11-16

Transformation of pesticides in the environment is a highly complex process affected by different factors. Both biological and physical-chemical factors may play a role in the degradation, whose ratio depends on the actual environmental conditions.
Our study aims to reveal specific details of photolytic degradation of pesticides as important... soil contaminants. Significance of these studies is enhanced by the fact that pesticide decomposition may contribute to soil degradation, and have harmful biological effects by degrading to toxic products. The toxicity of the examined pesticides is well known, however very little information is available regarding their natural degradation processes, the quality, structure and biological impact of the degradation products.
The photolytic degradation of frequently applied pesticides of distinctive types (acetochlor – acetanilide, simazine – triazine, chlorpyrifos – organophosphate, carbendazim – benzimidazole) was investigated. A special, immerseable UV-light source was applied in order to carry out photodegradation. The degradation processes were followed by thin layer chromatography (TLC) and mass spectrometry coupled with gas chromatography (GC/MS). EI mass spectrometry was used to identify the degradation species.
Each of the studied pesticides underwent photolytic decomposition, and the detailed mechanism of photolytic transformation was established. At least four degradation species were detected and identified in each case. Loss of alkyl, alkyloxy, amino-alkyl and chloro groups might be regarded as typical decomposition patterns. Deamination occurred at the last stage of decomposition.

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