English Abstract Chicken embryos were used to develop an experimental
bioassay to investigate the Toxicological Equivalency Factors (TEF) of
dioxines and furans, and mixtures using the TEF principle for risk
assessment of dioxins related compunds in reference to the public health.
The animals were exposed to the chemicals by a single injection in the air
sac of the egg. After incubation, liver microsomes were isolated from the
chicken-embryo, in which activity of ethoxyresorufine-o-dealkylase (EROD),
and the amount of cytochrome P-450 and protein were determined. The
objective of the first phase, reported here, was to optimize the amount of
vehicle, the method of isolation, the time of injection and the duration of
incubation and exposure. The best suitable vehicle appeared to be 25 mul
dioxane, mixed with 25 mul of an isotonic salt solution per egg. Isolation
of microsomes by ultracentrifugation turned out to be the mostly effective
isolated method, compared to gelfiltration. Injection at the 17th day of
incubation and an exposure time of 24 hours, prior to dissection, resulted
in the highest EROD induction. The ED50 for EROD induction by 2, 3, 7, 8-
tetrachlorodibenzodioxin determined was 10.8 ng/egg. In a second
experiment the result was 9.2 ng/egg. For
2,3,4,7,8-pentachlorodibenzofuran the ED50 was assigned to 8.7
ng/egg.
