De kippe-embryo test. Fase III. Beschikbaarheid van 2,3,7,8-TCDD in het kippe-embryo

Abstract

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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.