A model for the formation and degradation of bound residues of the herbicide ¹⁴C-isoproturon in soil

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 was observed. The main oligomer was identified by mass spectrometry as 4,5-bis-(4-isopropylphenylamino)-3,5-cyclohexadiene-1,2-dione. Oligomers and polymers containing bound ¹⁴C-4-isopropylaniline were subjected to biodegradation studies in a loamy agricultural soil during 55 days by quantifying ¹⁴CO₂ evolved. In all cases, significant mineralization rates could be determined, which, however, were much smaller than those of free ¹⁴C-isoproturon and free ¹⁴C-4-isopropylaniline in the same soil.