DEGRADATION IF ISOPROTURON ON AND AVAILABILITY OF RESIDUES IN SOIL

The availability and degradation of C-14-ring-labelled isoproturon in soil was investigated over 140 days under controlled laboratory conditions. Degradation of the active ingredient followed and 65 days later only a minor fraction (0.6%) of the parent molecule remained extractable. A demethylated-isoproturon metabolite was detectable in soil from day 15 (2.6%). The amount of (CO2)-C-14 derived from the C-14 benzene ring label and liberated over time indicated that a total of 13.6% isoproturon was mineralized during the incubation period. In parallel, the amount of C-14 residue extracted from the soil by water followed by methanol or remaining within the soil-analysed by combustion-was also determined at intervals. After 140 days, 72% of the radiolabel added remained in the soil as non-extractable residue. The degradation half-life of extractable isoproturon was an estimated 14 days.