DERIVATION OF 2,3,7,8-TCDD TOXIC EQUIVALENT FACTORS (TEFS) FOR SELECTED DIOXINS, FURANS AND PCBS WITH RAINBOW-TROUT AND RAT-LIVER CELL-LINES AND THE INFLUENCE OF EXPOSURE TIME

The effect of exposure time on the induction of 7-ethoxyresorufin O-de ethylase (EROD) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2, 3,7, 8-tetrachlorodibenzofuran (TCDF), and 3,3',4,4'-tetrachlorobiphenyl ( PCB 77) was examined in two liver cell lines: rainbow trout RTL-W1 and rat H4IIE. In RTL-W1, exposure time had no effect on induction EC50s and derivation of TCDD- toxic equivalency factors (TEFs). In H4IIE, EC 50s for TCDD also were unchanged. However, for TCDF and PCB 77 in H4II E, EC50s increased and TEFs decreased as exposure time increased from 6 to 72 h. These results suggest that metabolism of TCDF and PCB 77 ca n account for some of the previously observed differences between RTL- W1 and H4IIE TEFs. (C) 1997 Elsevier Science Ltd.