PERSISTENCE AND FATE OF 2,3,4,6-TETRACHLOROPHENOL AND PENTACHLOROPHENOL IN LIMNOCORRALS

Three separate limnocorral experiments were conducted to assess the fa te and effects of a commercial 2,3,4,6-tetrachlorophenol (TeCP) formul ation (DIATOX(R); 19.4% TeCP 4.8% pentachlorophenol [PCP], 75.8% ''ine rt'' buffers) in an aquatic ecosystem. Nominal treatment concentration s for experiments 1 and 2 were 0.075 and 0.75 mg active ingredient (a. i.)/L and 0.75 and 1.50 mg a.i./L DIATOX(R), respectively, with three replicates of each treatment. Pesticide was applied in the morning for experiment 1 and in the evening for experiment 2. For Experiment 3, u nreplicated concentrations of 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, and 7.3 m g a.i./L DIATOX(R) were chosen; pesticide was applied in the evening. In all three experiments, the pesticide was applied as a single, unifo rm surface treatment. Both TeCP and PCP dissipated rapidly from the wa ter of treated limnocorrals. Times to 50% dissipation for TeCP and PCP in the integrated water column were generally similar within experime nts but ranged from 0.4 to 1.1 d following the morning application of experiment 1 to 3.4 to 7.3 d following the evening applications of exp eriments 2 and 3. The faster initial dissipation of TeCP and PCP from the water following the morning application implicated photolysis as t he primary degradation mechanism, as did the faster dissipation of chl orophenols from the surface layer than from other water depths during experiment 2. Aqueous dissipation rates for both compounds from the in tegrated water column were similar in all three experiments after the initial mixing period (1-4 d); the three-experiment average first-orde r rate coefficient for either compound after day 4 was 0.09/d. From a mass balance perspective, the majority of the chlorophenols remained i n the water column. Neither compound accumulated in the sediments to a ny significant extent (<0.1% of applied mass), but sediment-associated residues did dissipate at a considerably slower rate than residues in the water column. From 97 to >99% of the applied chlorophenols had di ssipated from the water of treated enclosures by the end of the variou s experiments (42-63 d).