An industrial chemical that led to the nationwide recall of more than 100 brands of cat and dog food has turned up in a second pet food ingredient imported from China. The discovery expands the month-long cascade of recalls to include more brands and varieties of pet foods and treats tainted by the chemical. The chemical, melamine, is believed to have contaminated rice protein concentrate used to make a variety of Natural Balance Pet Foods products for both dogs and cats, the Food and Drug Administration said Wednesday. The FDA has there is no evidence so far to suggest any of the rice protein went to companies that make human food, said Michael Rogers, director of the agency's division of field investigations. But the FDA, which is continuing to update its list of pet food recalls, has not yet accounted for all of the imported ingredients.