The stability and persistence of diflubenzuron in marine sediments studied under laboratory conditions and the dispersion to the sediment under a fish farm following medication

A high performance liquid chromatographic ŽHPLC. method was developed to determine the concentration of diflubenzuron, a delousing agent used in fish farming, in marine mud and shell sand. The recovery of diflubenzuron from mud was 100.8 1.1% and 105.5 4.3% for shell sand. The limit of quantitation was found to be 0.1 g g 1. The stability of diflubenzuron was studied under laboratory conditions in marine sediments at different temperatures Ž4 and 14 C.. No degradation of diflubenzuron occurred in the organic rich mud sediment or in the shell sand sediment during the experimental period of 204 days. Increasing the temperature from 4 to 14 C had no effect on the stability. Furthermore, diflubenzuron showed to be persistent in both mud and shell sand sediment since no detectable diffusion from the sediment to the water phase occurred during the experimental period of 204 days. Increasing the water current in the tanks had no effect on the persistence. Under field conditions, the concentrations of diflubenzuron found in the organic material from sediment traps placed 2 m from the bottom under the cage in a fish farm during medication were high and ranged from 71 to 259 g g 1. The concentrations of diflubenzuron in the sediment under the fish farm were, however, low, with a maximum concentration of 5.4 g g 1. The dispersion of diflubenzuron to the sediment was limited to less than 20 m from the edge of the cage in every direction. Fifteen months following the medication, only traces Ž 0.1 g g 1. of diflubenzuron were detected in the sediment under the fish farm. Possible explanations for this decrease are resuspension and redistribution of sediment and or oxic degradation of the drug.