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 The 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.