The purpose of this study is to elucidate the degradation kinetics and byproducts of several chemicals with 1-benzopyran-2-one (coumarin) base structure in soil. The degradation kinetics follows a bi-phasic pattern, where a fast initial dissipation is followed by a decrease in the dissipation rate, and this pattern can be described by a sum of two first-order expressions. All other experimental data sets can be fitted well in terms of goodness-of-fit criteria demonstrating the general suitability of the model to describe the biotransformation kinetics of coumarin derivatives in soil. It was found that the degradation kinetics depends on the initial doses applied to the soil, where the toxic impact of coumarin on the microbial population could be significantly relevant to the total effect observed in the rate of biotransformation. Studies of structure biodegradability relationships (SBR) indicate that the presence of hydroxyl groups in the chemical structure of coumarin yields a higher rate of biotransformation. Methyl and methoxyl groups increase resistance to biotransformation. The correlation between structural parameters and rate constants show a significant relationship only with K1, as structural features could only affect the first process. This process would consist more of physical processes (adsorption and diffusion) than of biochemical processes such as bacterial biotransformation. In the case of the hydrophobicity, there is an exponential decay rate constant K1 with increasing cLogP. By the analysis of the time course experiments, the extracts obtained from the harvested samples permitted the detection of a diversity of new compounds. According to analyzes by Gas Chromatography-Mass Spectrometry (GC-MS), the main reaction is the conversion of coumarin (C) to dihydrocoumarin (DHC). However, the analysis of DHC biotransformation products allowed to detect C. This would suggest the presence of a mixture of C and DHC as biodegradation products coming from both C and DHC as independent starting chemicals.
Buy this Article