Fate of 1,3,6,8‐tetrachlorodibenzo‐ p ‐dioxin in an outdoor aquatic system

Three outdoor pools (5.5 m 3 ) were treated with [ 14 C]1,3,6,8‐tetrachloridibenzo‐ p ‐dioxin (1,3,6,8‐T 4 CDD) at concentrations of 98, 245 and 980 ng/L, and the movements and accumulation of the compound were monitored in air, water, sediment and vegetation over a 426‐d period. The concentrations of 1,3,6,8‐T 4 CDD in the air above the treated pools ranged from 8.4 to 18.8 ng/m 3 during the first day after treatment. Total 14 C concentration in the water column declined rapidly, with more than 90% lost from the water phase within 96 h (t 1/2 = 14.0 to 28.5 h). The sediments were the major reservoir for the compound, accounting for 34 to 80% of the added compound at 34 d and 5 to 14% at 426 d. Total [ 14 C]T 4 CDD concentrations in the sediments increased at 90 d, in part because of the end‐of‐season deposition of rooted vegetation. 1,3,6,8‐T 4 CDD degraded in natural water in Pyrex flasks at similar rates in sterile and nonsterile waters (t 1/2 = 6.3 to 8.0 d) in sunlight, but not under darkened conditions. A single, polar photodegradation product (retention time 0.82 relative to 1,3,6,8‐T 4 CDD) was detected by HPLC, and 20% of the 14 C was unextractable within 10 d. Similar degradation products were noted in the water and sediments (90 and 426 d). In duckweed ( Lemna sp.) and ( Potamogeton sp.), concentration factors for 1,3,6,8‐T 4 CDD ranged from 2.5 to 3.4 × 10 4 and from 0.27 to 2.0 × 10 5 , respectively. At 426 d posttreatment, 5 to 8% of the applied 1,3,6,8‐T 4 CDD could be accounted for in all aquatic compartments, with an additional 4 to 6% of 14 C present as unidentified polar products and unextractable residue.