Distribution and Persistence of Diflubenzuron within Littoral Enclosure Mesocosms

The insecticide diflubenzuron was applied as Dimilin 25W twice, 32 days apart, to the surfaces of 12 of 18 littoral enclosure mesocosms (5 x 10 m) to study its distribution, persistence, and mass balance in a natural ecosystem. Nominal concentrations were 0.7, 2.5, 7, and 30 mu g/L active ingredient. The residue half-life in the water column ranged from 3.3 to 8.2 days with a mean of 4.3 days and required 14-35 days for 95% dissipation. The half-life in the macrophytes ranged from 2.0 to 5.7 days, and 95% dissipation required 8.6-24.6 days. The half-life in sediment ranged from 6.2 to 10.4 days, and 95% dissipation required 26.9-45.0 days. The water was the major compartment for residues, with amounts ranging from 82.3% of that applied after 3 h to 11.6% after 7 days. The sediment and macrophytes had maximum amounts of 6.3 and 10.2%, respectively. The mass balance ranged from 82.3% after 3 h to nondetectable after 56 days.