DISTRIBUTION AND PERSISTENCE OF DIFLUBENZURON WITHIN LITTORAL ENCLOSURE MESOCOSMS

The insecticide diflubenzuron was applied as Dimilin 25W twice, 32 day s 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 n atural 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 require d 26.9-45.0 days. The water was the major compartment for residues, wi th 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 1 0.2%, respectively. The mass balance ranged from 82.3% after 3 h to no ndetectable after 56 days.