Formation and release of residues of the 14C-labelled herbicide isoproturon and its metabolites bound in model polymers and in soil

Abstract

The humic monomer catechol was reacted with 14C-isoproturon and some of its metabolites, including 14C-4-isopropylaniline, in aqueous solution under a stream of oxygen. Only in the case of 14C-4-isopropylaniline, incorporation in oligomers, in fulvic acid-like polymers, and in humic acid-like polymers by covalent bonds was observed. The main oligomer was identified by mass spectrometry as a trimer, 4,5-bis-(4-isopropylphenylamino)-3,5-cyclohexadiene-1,2-dione. Biomineralization of 14C-compounds to 14CO 2 in a loamy soil and release of 14C from soil columns into percolate water decreased in the order: free isoproturon >free 4-isopropylaniline>fulvic acid-like polymers>trimer>humic acid-like polymers. In soil columns, a small but measurable migration of 14C from polymers from upper to deeper soil layers could be detected; most of this 14C was bound again in a non-extractable form. It is concluded that aniline-derived pesticides bound in soil by covalent binding may not be fully undegradable, nor fully immobile.