Availability and persistence of isoproturon under field and laboratory conditions.

Field and laboratory tests were conducted to investigate the disappearance and decrease in availability of the herbicide isoproturon in soil with time. Monitoring the fate of 14C-labeled isoproturon gave the persistence of the herbicide under different conditions. The calculated half-life (DT50) of the extractable parent product was close to 19 days for the two experiments, whereas half-lives of exhaustive extractable 14C-residues averaged 22 days under controlled conditions versus 48 days in the field. Moreover, if nonextractable 14C-residues were taken into account in estimating isoproturon fate, the DT50 of radioactive residues in soil (extractable parent and degradation products + nonextractable residues) reached 1 to 1.4 years under field and controlled conditions, respectively. The variability of disappearance rates for the different kinds of residues is discussed within a wider definition of persistence.