Quantitative and Enantioselective Analyses Following Enzyme Assisted Processes in Soil: Degradation and Non-extractable Residue Formation of the Fungicide Metalaxyl

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In this study the chiral fungicide metalaxyl was used as an exemplary pesticide to investigate/its (the) degradation and NER formation including incorporation mode into soil surfaces and interfaces. The fate of the fungicide was determined in separate incubation experiments with organo-mineral subfractions of soil as well, as they depict significant binding capacities with their numerous functional groups and high surface areas. The transformation of the parent compound is predominantly biotically induced. Therefore, the metabolism mediated by microbial activities, including intra- as well as extracellular enzymes, was analyzed. Additionally the transformation of the fungicide solely catalyzed by extracellular enzymes was analyzed as well. Especially, extracellular enzymes are assumed to be strongly involved in the process of xenobiotic NER formation. The discrimination between microbial assistance and extracellular assistance was achieved through specific sterilization methods. The potential influence of these biotic agents in the NER formation could thus be monitored. As a chiral compound the stereochemical interaction and specificity is of high interest especially in an asymmetrical surrounding like the soil system. Hence, enantioselective processes during the degradation and NER formation were investigated. The elucidation of reversibly bound non-extractable metalaxyl fraction was realized through chemical degradation by alkaline hydrolysis. In soil, the main metabolite was the acid derivative metalaxyl acid, therefore, the incorporation was assumed to be via covalent ester or amide linkage. This bond type can be cleaved by hydrolysis. To assess a temporal evaluation for short- and long-term development, processes of metalaxyl degradation and NER formation was followed for 10 and 92 days. Quantitative analyses were carried out for extractable fractions (water, solvent, dilute acid) and hydrolysis releasable NER fraction by the means of GC/MS. Furthermore, stereochemical analyses of these extracts were performed on a chiral capillary column on a GC/MS-system.

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Roschni Kalathoor

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Fungicides Metalaxyl NER formation

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