Comparison of Toxic Equivalent Factors for Selected Dioxin and Furan Congeners Derived Using Fish and Mammalian Liver Cell Lines

Toxic equivalent factors (TEFs) for eight polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) congeners were derived with a rainbow trout (Oncorhynchus mykiss) cell line, RTL-W1, and compared with TEFs obtained with a rat hepatoma cell line, H4IIE. Cells were exposed to a range of concentrations of the congeners which included 1,2,3,7,8-pentaCDD, 1,2,3,4,7,8-hexaCDD, 1,2,3,6,7,8-hexaCDD, 1,2,3,4,6,7,8-heptaCDD, 2,3,7,8-tetraCDF, 1,2,3,7,8-pentaCDF, 2,3,4,7,8-pentaCDF, and 1,2,3,4,7,8-hexaCDF. Ethoxyresorufin o-deethylase (EROD) activity was measured and EC50 values calculated from a dose–effect curve newly proposed for this purpose. TEFs were computed using 2,3,7,8-tetraCDD standard curves run concurrently with each assay. With the exception of 1,2,3,6,7,8-hexaCDD and 1,2,3,7,8-pentaCDF, all of the RTL-W1-derived TEFs were significantly higher (two- to eightfold higher) than the respective H4IIE TEFs. Immunoblotting analysis with the monoclonal anti-scup P4501A1 antibody was used to identify basal and induced levels of P4501A1 protein in both the RTL-W1 and H4IIE cells. It was concluded that mammalian-derived TEFs may not accurately predict the potency of PCDDs or PCDFs to fish.