A study on the relationship between iridium concentration in hen eggshell and iridium-enriched feed by NAA

Abstract

Four hens were fed by adding ammonium hexachloroiridate into their forage. After two weeks, we measured the Ir concentration in three fractions (eggshell, albumen, egg yolk) of their eggs by instrumental neutron activation analysis (INAA). Ir was present in all the three parts of the eggs. Further, the highest concentration of Ir was found in the egg yolk fraction, about 10 times higher than that in the eggshell and albumen. Moreover, the longer the Ir-containing feed was used, the higher the Ir concentration in the egg fractions was. After 4-6 day feeding, the Ir concentration became stable. The experimental results indicated that the Ir concentration was about 2-7·10^-10 g/g in the eggshell fraction compared to 5.6·10^-7 g/g in feed. Therefore, we can estimate the ratio from the feed over the eggshell via gastrointestinal pathway to be about 0.08%. The new result is useful to evaluate the iridium-enriched eggshell fossils of dinosauria and to interpret the origin of the mass extinction of dinosauria at the end of Cretaceous.