English Abstract At the Institute are chicken embryos used to develop an
experimental bioassay to investigate the Toxicological Equivalency factors
(TEF) of individual dioxins and furans, and mixtures of congeners using the
TEF principle. The bioassay should be used to determine the toxic potency
of a mixture with dioxin related compounds, within the objective of future
risk assessment of these compounds for the public health. In this study,
the concentration 2,3,7,8-TCDD within the egg had to be determined after a
single injection of 101 ng 2,3,7,8-TCDD, or 505 ng 2,3,7,8-TCDD per egg.
That was achieved by analyzing the various samples, using gas
chromatography, with an ECD (Electron Capture Detector). The clean up of
these samples was done by a extraction of total fat with toluene, and a
additional purification with active carbon (Carbosphere) and alumina. The
recovery of the seventeen 2,3,7,8-chlorine substituted dioxins and furans
was in a range of 60 to 120% with a mean value of 79%. The total amount of
2,3,7,8-TCDD, that was regained from the egg, 48 hours after exposure, was
in a range of 17 to 123% of the total dose injected. That revovery appeared
to be dose related. It was concluded, that the manual method of exposure by
a single injection is not very accurate, and needs improvement. The
retention of 2,3,7,8-TCDD in the chicken embryo's liver was not dose
related, nor affected by a injection in the air sac or egg fluid. It was
between 4 and 8% of the retrieved quantity. Furthermore, the analysis
showed a retention in the yolk, of 75% of the retrieved quantity. So, it
can be seen, that the major amount of (lipophilic) chemical is absorbed by
the yolk, that containsa rather high concentration of fat. That has its
consequences for the lowest external dose possible, that will cause a
detectable EROD induction, that is used as the marker for the toxic potency
of the dioxin related compounds in this test system. The high absorption
will may be aslo cause problems for the interpretation of the results of the
chicken embryo assay for risk assessment in reference to the public
health.
