To Örebro University

A technique for studying 7-ethoxyresorufin O-deethylase (EROD) induction in chick embryo liver in vitro was developed. Livers from 8-d-old embryos were cultured in rotating vials at 37 degrees C for 48 h in a medium to which DMSO-dissolved test compounds had been added. This bioassay proved to be highly sensitive to dioxin-like compounds, and its usefulness for assessing the toxic potency of such compounds in environmental samples was demonstrated. Concentration-response curves were determined for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3',4,4',5-penlachlorobiphenyl (PCB IUPAC no. 126), 3,3',4,4'-tetrachlorobiphenyl (PCB 77), 2,3,3',4,4'-pentachlorobiphenyl (PCB 105), and benzo[k]fluoranthene (BkF). TCDD induced EROD in a concentration-dependent manner, having an EC50 of 5.0 x 10(-12) M. The cultured embryo livers were extremely sensitive to TCDD, and about 30 fg of this compound per liver (2 x 10(-13) M) was enough to significantly induce EROD. The EC50 values obtained for PCBs 126, 77, 105, and BkF were 4,4 x 10(-11) M, 9.2 x 10(-9) M, 1.6 x 10(-8) M, and 6.2 x 10(-7) M, respectively. The maximal induction levels obtained for three different preparations of polychlorinated naphthalenes (PCNs) were less than those of the other compounds tested. When the technical PCN mixture Halowax 1014 was coadministered with TCDD, the induction was lower than that caused by TCDD alone. An organic extract of fly ash from a municipal waste combustion plant was very potent. Considering its contents of polychlorinated dibenzo-p-dioxins/furans, expressed as TCDD equivalents, the EC50 obtained was close to that for TCDD.