A new study of colas has found varying levels of a chemical compound classified as a possible human carcinogen in many popular brands. The study, from Consumer Reports, has resulted in the Food and Drug Administration taking a closer look at the compound, known as 4-methylimidazole — 4-MEI, for short. CR detected low levels of 4-MEI in Coca-Cola, Coke Zero and Diet Coke. But it found higher levels in some Pepsi products, particularly in Pepsi One.