Contrary to popular belief, paying a premium price for free-range eggs may not be healthier than eating regular eggs, a new study reports. Scientists found that free-range eggs in Taiwan contain at least five times higher levels of certain pollutants（污染物） than regular eggs. Their findings appear in ACS' bi-weekly Journal of Agricultural and Food Chemistry.

In the new study, Pao-Chi Liao and colleagues note that free-range chickens are those that have continuous access to fresh air, sunshine, and exercise, in contrast to chickens that are confined to（限制，禁闭） cages. Demand for eggs from free-range chickens has increased steadily due to their supposed better nutrition（营养） qualities, including higher levels of certain healthy fats.

But scientists suspect that free-range chickens may risk getting higher levels of exposure to environmental pollutants, particularly PCDDs and PCDFs, potentially toxic substances（有毒物质） that are produced as by-products of burning waste.

Also known as dioxins（二恶英） , these substances may cause a wide range of health problems in humans, including reproductive and developmental problems and cancer.

The scientists collected six free-range eggs and 12 regular eggs from farms and markets in Taiwan and analyzed the eggs for their content of dioxins.

Taiwan, they note, is a heavily populated, industrialized island with many of the municipal（市政的） incinerators（焚化炉） that release PCDDs and PCDFs.

They found that the free-range eggs contained 5.7 times higher levels of PCDDs and PCDFs than the regular eggs.

The scientists suggest that the findings raise concern about the safety of eating free-range chicken eggs.