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

The humic monomer catechol was reacted with C-14-isoproturon and some of its metabolites, including C-14-4-isopropylaniline, in aqueous solution under a stream of oxygen. Only in the case of C-14-4-isopropylaniline: incorporation in oligomers, in fulvic acidlike 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 C-14-compounds to (CO2)-C-14 in a loamy soil and release of C-14 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 C-14 from polymers from upper to deeper soil layers could be detected; most of this C-14 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. (C) 2000 Elsevier Science Ltd. All rights reserved.