Effect of Flock Size on Dioxin Levels in Eggs from Chickens Kept Outside

To decrease dioxin uptake by the general population the European Union (EU) has set limits to the dioxin content of many foodstuffs including eggs. Eggs from free foraging chickens are known to have a higher dioxin content as compared to confined laying hens and it is the question whether these eggs can adhere to current EU regulations. The aim of the study was to investigate parameters that are involved in the contamination of eggs from chickens raised under “organic” conditions. Samples from 34 organic farms including soil and earth worm samples were collected between September and December of the year 2003. Dioxin levels were assayed by GC/MS. Various parameters were collected by on farm interviews. Egg dioxin content varied between 0.4 and 8.1 pg Toxic Equivalents (TEQ)/g egg fat with a mean of 2.2 pg TEQ/g egg fat. Nine out of 34 farms exceeded the EU limit of 3 pg TEQ/g egg fat. In addition dioxin-like (dl) PCBs were measured and 8 samples exceeded the limit for the sum of dioxins and dl-PCBs. Overall, egg samples from 10 farms were non-compliant with either the dioxin or total TEQ limits. No statistically significant relation could be observed between egg dioxin levels and the concentration observed in soil or earth worms. A statistically significant association was observed between flock size and egg dioxin and dl-PCB content. This effect is most likely attributable to the fact that flock size is related to the time chickens spend outside. Restricting outdoor run use on one of the farms resulted in a decrease of the egg dioxin content to a level that was within the EU limits. This demonstrates that the most likely contamination source is the soil or soil organisms but that the behaviour of the hens determines the extent of the contamination. Following the completion of this study, a dioxin monitoring protocol has been set up in The Netherlands to prevent marketing of eggs with raised dioxin levels.