Characterizing the biotransformation of hexachlorocyclohexanes in wheat using compound-specific stable isotope analysis and enantiomer fraction analysis

摘要

Hexachlorocyclohexane isomers (HCHs) are persistent organic pollutants being responsible for environmental contamination worldwide. In order to characterize transformation of HCHs in different plant compartments during uptake, a hydroponic experimental setup was designed using wheat as the test plant. The extent of transformation was determined by using compound-specific isotope analysis (CSIA) and enantiomer fraction (EF) analysis. In nutrient solutions, no change of carbon (delta C-13) and chlorine isotope ratios (delta Cl-37) of alpha-HCH and beta-HCH was detected throughout the experiment indicating no transformation there. In wheat leaves, stems and roots, however, transformation of alpha-HCH due to a C-Cl bond cleavage was indicated by increasing delta C-13 and delta Cl-37 compared to the nutrient solution. In addition, 1,3,4,5,6-pentachlorocyclohexene (PCCH) was identified as the major metabolite of alpha-HCH transformation. For beta-HCH, in contrast, no transformation was detected. The evaluation of enantiomer fraction analysis revealed no change of the EF(-) in the nutrient solution or on root surface but a decrease in the wheat compartments, providing an evidence for the preferential biological transformation of (-)alpha -HCH in wheat. The current study provides the first experimental evidence for biotransformation of alpha-HCH in wheat using CSIA and EF and provides a concept to evaluate processes during phytoremediation.