Toxicity Assessment upon Thermal Treatments of Chlorpyrifos and 3,5,6-Trichloro-2-Pyridinol (a Potential Precursor of the Pyridine Analogue of 2,3,7,8-T4CDD) Using the Early Developmental Stage Medaka Embryos (Oryzias latipes)

Abstract

Chlorpyrifos is one of the major pesticides used today which has a chlorinated aromatic moiety of a pyridine analogue of 2,4,5-trichlorophenol and can be a potential direct precursor of another pyridine analogue of 2,3,7,8-T4CDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). In the recent study, PCDF compounds have been detected in chlorpyrifos samples, however, the presence of this analogue of 2,3,7,8-T4CDD has not been assessed yet to our knowledge. Here, we analyzed the ecotoxicities of this dioxin-like compound in the early developmental stage embryos (Oryzias latipes). Chlorpyrifos and its analogue, 3,5,6-trichloro-2-pyridinol, were thermally treated in closed glass ampoules at 300, 340, and 380°C for 10 minutes and exposed to medaka embryos in early developmental stage for 48 hours, to assess the response of the 20 biomarker gene expressions. The thermally treated 3,5,6-trichloro-2-pyridinol enhanced the expression of CYP1A1 (Cytochrome P450 1A1) and AhRR (aryl hydrocarbon receptor repressor) as 2,3,7,8-T4CDD and PCBs, suggesting that the potentially ecotoxic compounds like 2,3,7,8-T4CDD is newly produced during the thermal treatment of 3,5,6-trichloro-2-pyridinol. The expression profiles of the 20 biomarker genes in the embryos exposed to 2,3,7,8-T4CDD and 3,5,6-trichloro-2-pyridinol were almost the same, strongly suggesting that the thermally treated 3,5,6-trichloro-2-pyridinol sample contained 2,3,7,8-T4CDD-like ecotoxic compounds.