It's true that ethoxyquin can be used as a pesticide and rubber hardener, Trish. However, it also has important antioxidant functions, and has been used as a preservative in pet foods for more than 35 years to protect fats, fatty acids and fat-soluble vitamins from spoiling. Ethoxyquin has been approved by the Food and Drug Administration (FDA) and is considered safe when added to pet foods at a maximum of 150 parts per million.
A 1982 literature study conducted by the FDA resulted in no evidence of cancer-causing properties in ethoxyquin. However, if you prefer not to serve your pet a food that contains this ingredient, there are many pet food products on the market you can switch to that contain natural antioxidants such as vitamin E, rosemary, and citric acid.