Using 13 C‐nmr spectroscopy to evaluate the binding mechanism of bound pesticide residues in soils

Soil‐bound residues of organochemicals and their metabolites can be extracted together with the humic acid fraction. These residues are only detectable by using radioactive labelling, e.g. 14C (or 3H). An analysis of the character of the bonding can be achieved by means of 13C‐NMR spectroscopy. A prerequisite is a 13C‐enrichment of the observed molecule and, if possible, a 13C‐depletion of the humic substances. The fungicide anilazine is known to form high amounts of soil‐bound residues within a few days. 13C‐NMR spectra of extracted humic acids of two different orthic luvisols (Parabraunerde), a gleyic cambisol (Pseudogley Braunerde) and of an artificially prepared soil from humified, 13C‐depleted maize straw show ester or ether bonds of anilazine to the humic acids. Line broadening of ≤ 20 Hz yields a group of signals which indicate that different functional groups of the humic acids are responsible for the bondings.