From Wikipedia:
Ethoxyquin is a
quinoline-based
antioxidant used as a
food preservative and a
pesticide (under commercial names such as "Stop-Scald"). It is commonly used as a preservative in pet foods to prevent the
rancidification of fats. There has been some speculation that ethoxyquin in pet foods might be responsible for multiple health problems. To date, the
U.S. Food and Drug Administration (FDA) has only found a verifiable connection between ethoxyquin and buildup of
protoporphyrin IX in the liver, as well as elevations in liver-related enzymes in some animals, but there are no known health consequences from these effects.
[2] Until further evidence is reported, the FDA has asked pet food manufacturers to voluntarily limit ethoxyquin levels to 75
ppm.
[2] However, most pet foods that contain ethoxyquin have never exceeded this amount.
[2]
Ethoxyquin has been shown to cause mortality in fish.
[3]
Ethoxyquin is also commonly used in spices to prevent color loss due to oxidation of the natural
carotenoid pigments.
The FDA Center for Veterinary Medicine (CVM) in 1997 requested a voluntary reduction of ethoxyquin from 150 ppm to 75 ppm in complete dog foods. The work used to make the reduction request was never published in peer reviewed journals or made readily available to public or scientific scrutiny.