EFFECT OF THE INPUT PATHWAY ON THE DISTRIBUTION OF 1,2,3,4,7-PENTACHLORODIBENZO-p-DIOXIN IN AN AQUATIC MESOCOSM

摘要

The effect of the input pathway on the distribution of 1,2,3,4,7-pentachlorodibenzo-p-dioxin (P_5CDD) in small-pond mesocosms was determined by introducing ~(14)C-labeled dioxin (468 μg) into the water sorbed to sediment particles and by a surface sprayover in a water-miscible organic solvent. Rates of clearance from the water column were rapid and unrelated to the input method in either case, with pseudo-first-order half-lives (t_(1/2)) of 0.38 ± 0.19 d (r~2 = 0.81) and 0.57 ± 0.08 d (r~2 = 0.98) for the particle-sorbed and sprayover applications, respectively, over the first 24 h after input. However, redistribution pathways were strongly influenced by the route of entry of P_5CDD into the ecosystem. Ponds receiving a sprayover of P_5CDD showed higher concentrations of the dioxin in surface microlayers with larger amounts also collected in air above these ponds. Concentrations of P_5CDD in the bottom sediments of these ponds were significantly lower (0.6 ng/g dry weight) compared to concentrations in sediments of ponds receiving a sediment slurry input (1.2 ng/g dry weight). Evaluation of the results using several fugacity-based aquatic-fate models indicated that when P_5CDD entered the aquatic ecosystem in the sorbed state, sedimentation dominated its redistribution. However, with a sprayover input, film-to-water transfer, partitioning and deposition to bottom sediment, volatilization, and photolytic degradation in surface microlayers were important processes affecting the fate of P_5CDD in the mesocosm.