Characterization of the Interaction between Xenobiotic Residues and Humic Substances

TL;DRAbstract

Organic xenobiotics can be immobilized in soil through various mechanisms involving either covalent binding or sequestration. In this study, 13C-nuclear magnetic resonance (NMR) spectroscopy was applied to evaluate soil-bound residues of the 13C-labeled fungicide cyprodinil (4-cyclopropyl-6-methyl-2-phenylamino-pyrimidine). To facilitate NMR analysis, the isolated humic acid and humin fractions were derivatized by silylation with trimethylchlorosilane. The 13C-NMR spectra of the silylated samples revealed that the formation of soil-bound residues of cyprodinil involved: (i) cleavage of the cyprodinil molecule between the aromatic rings followed by covalent binding of the separated moieties to humic acid, and (ii) sequestration of the unaltered or slightly altered fungicide in the humin fraction. The results obtained confirm the great potential of 13C-NMR spectrometry for the investigation of xenobiotics immobilized in soil.

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