If hens are kept outside, how does this affect the dioxin levels of their eggs?

Summary

EU regulations have set upper limits to the dioxin content of a wide range of foodstuffs from animal origin. The level in eggs has been set to 3 pg TEQ/ gram of fat. Outdoor access of chickens is known to lead to a higher dioxin content in the eggs. The purpose of this study was to quantify the amount of organic eggs exceeding the proposed dioxin limits, to identify factors that influence dioxin levels in organic eggs and to propose measures to keep these levels below the 3 pg limit.
Eggs, soil, feed, worms and spiders were sampled from 34 organic poultry farms. Dioxin levels were screened by bioassay (CALUX method) and confirmed by gaschromatography and mass spectrometry.
Nine small organic poultry farms (26%) produced eggs that exceeded the 3 pg limit. The highest value was 8.1 pg TEQ/gr fat. Soil dioxin levels in farms exceeding the 3 pg limit were 2.6 pg/gram soil as compared to 1.9 in the low dioxin level farms. No effect was seen concerning the breed of the chickens used. The main factor associated with raised dioxin content was flock size. An explanation is that small flocks spend more time in the outdoor run than large flocks. Based on the fact that most commercially pro-duced organic eggs come from relatively large flocks, one may conclude that the dioxin level of organic eggs from the Netherlands are below the EU limits.