Toxicokinetics of selenium in the avian egg: Comparisons between species differing in embryonic tolerance

Wild eggs from selenium-contaminated habitats were analyzed for Se content in distinct egg compartments at different developmental stages. To identify the influence of the variables upon gross egg partitioning, an experiment was designed using the domestic chicken and selenized yeast as a surrogate for natural dietary Se.; The reproductive performance in these hens was monitored, along with specific measures to quantitatively determine if delays in embryogenesis are a valid endpoint with respect to Se toxicosis. Observations are consistent with the interpretation that embryogenesis can effectively be delayed in-ovo below doses capable of producing overt terata or those that lead to embryo death. However, this finding was not that embryos were behind in developmental stage, but instead that overtly normal chicken embryos were underweight. Evidence is also presented that indicates a separate class of eggs (early-deads)—which are a relevant endpoint of selenium toxicosis distinct from terata, and contribute to reduced hatching success.; Quantitative data were analyzed to define critical variables influencing toxicokinetics in the avian egg, and to direct further statistical analyses to discern differences between species. Egg toxicokinetics are influenced by variable selenium dose. Albumen is enriched with selenium in a manner proportional to dose; while yolk and embryo Se is apparently bioaccumulated in proportion to dose until some constraining influence manifests at highly teratogenic concentrations. Egg toxicokinetics are also influenced by the variables of form and embryogenesis itself.; Selenium toxicokinetics in the avian egg are complex and multivariate. A model was developed to test whether species differences in egg Se partitioning are detectable using the broad measure of total recoverable [Se]. Evidence for toxicokinetic phenomena consistent with embryonic depuration are suggested. While this process seems more pronounced in the Se tolerant species up to teratogenic doses, surviving embryos in the sensitive species nevertheless express significant depuration potential. Sensitive species have the potential to remove significant amounts of egg-borne Se from the embryonic compartment, so this ability in itself is insufficient to explain differences between species in Se tolerance. Indications are that other factors are involved allowing tolerant species to withstand higher realized [Se] in-vivo before expressing toxic effects.