Persistence and fate of 2,3,4,6-tetrachlorophenol and pentachlorophenol in limnocorrals

Abstract

Three separate limnocorral experiments were conducted to assess the fate and effects of a commercial 2,3,4,6-tetrachlorophenol (TeCP) formulation (DIATOX®; 19.4% TeCP, 4.8% pentachlorophenol [PCP], 75.8% “inert” buffers) in an aquatic ecosystem. Nominal treatment concentrations 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®, 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, unreplicated concentrations of 0.1, 0.25, 0.5, 1.0, 2.0, 4.0, and 7.3 mg a.i./L DIATOX® were chosen; pesticide was applied in the evening. In all three experiments, the pesticide was applied as a single, uniform surface treatment. Both TeCP and PCP dissipated rapidly from the water of treated limnocorrals. Times to 50% dissipation for TeCP and PCP in the integrated water column were generally similar within experiments 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 experiments 2 and 3. The faster initial dissipation of TeCP and PCP from the water following the morning application implicated photolysis as the primary degradation mechanism, as did the faster dissipation of chlorophenols from the surface layer than from other water depths during experiment 2. Aqueous dissipation rates for both compounds from the integrated water column were similar in all three experiments after the initial mixing period (1–4 d); the three-experiment average first-order rate coefficient for either compound after day 4 was 0.09/d. From a mass balance perspective, the majority of the chlorophenols remained in the water column. Neither compound accumulated in the sediments to any significant extent ( 99% of the applied chlorophenols had dissipated from the water of treated enclosures by the end of the various experiments (42–63 d).