Identification of chloro‐nitro‐trifluoromethyl‐substituted dibenzo‐p‐dioxins in lampricide formulations of 3‐trifluoromethyl‐4‐nitrophenol: Assessment to induce mixed function oxidase activity

Abstract

AbstractThe contamination of field formulations of the lampricide 3‐trifluoromethyl‐4‐nitrophenol (TFM) bya dibenzo‐p‐dioxin containing ‐chloro, ‐nitro, and ‐trifluoromethyl substituents was suspected from chemical fractionations of a TFM formulation that were directed by mixed function oxidase (MFO) induction in rainbow trout. Three dioxin isomers containing these substituents in field formulations were identified by gas chromatography–mass spectrometry (GC‐MS). Short‐term waterborne exposures to a mixture of two isomers, 2‐trifluoromethyl‐3‐nitro‐7‐ (and 8)‐chloro‐dibenzo‐p‐dioxin, elevated MFO activity in trout, with a threshold between 0.148 and 0.745 nM (4.1–20.5 ng/L). Synthetic preparations of other dioxins related to formulation impurities enabled characterizations of this previously unknown family of dioxin congeners by GC‐MS. The elution order of the isomers followed those established for halogenated dioxins except where there was a lone ‐nitro substitution on one ring. The average concentration of these compounds in TFM formulations spanning more than a decade was 288 ± 47 μg/L, which translates into an annual loading of approximately 40 g to the Great Lakes Basin. Using mammalian (H4IIE) and fish (PLHC‐1) in vitro assays, a 2,3,7‐substituted chloro‐nitro‐trifluoromethyl isomer was a four to five times more potent inducer of MFO activity than 2,3,7‐trichlorodibenzo‐p‐dioxin. Characterizations of the synthetic isomers indicate that the isomers present in the formulation are not substituted in the 2,3,7‐ positions and are relatively weak inducers of MFO activity.