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Identification of chloro-nitro-trifluoromethyl-substituted dibenzo-P-dioxins in lampricide formulations of 3-trifluoromethyl-4-nitrophenol: assessment to induce mixed function oxidase activity

Hewitt, L.M., Carey, J.H., Munkittrick, K.R., Parrott, J.L., Solomon, K.R., Servos, M.R.
Environmental toxicology and chemistry 1998 v.17 no.5 pp. 941-950
Oncorhynchus mykiss, basins, dioxins, gas chromatography-mass spectrometry, in vitro studies, isomers, mammals, mixed function oxidase, trout, Great Lakes
The contamination of field formulations of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) by a 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 microgram/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.