Lost amid the anxiety surrounding the tainted U.S. pet food supply is this sobering reality: It's not just pet owners who should be worried. The uncontrolled distribution of low-quality imported food ingredients, mainly from China, poses a grave threat to public health worldwide.Essential ingredients, such as vitamins used in many packaged foods, arrive at U.S. ports from China and, as recent news reports have underscored, are shipped without inspection to food and beverage distributors and manufacturers. Although they are used in relatively small quantities, these ingredients carry enormous risks for American consumers. One pound of tainted wheat gluten could, if...