New chemical analyses have found that Coca-Cola, Pepsi, Diet Coke, and Diet Pepsi contain high levels of 4-methylimidazole (4-MI), a known animal carcinogen. The carcinogen forms when ammonia or ammonia and sulfites are used to manufacture the caramel coloring used in those sodas, according to the Center for Science in the Public Interest, the nonprofit watchdog group that commissioned the tests. CSPI first petitioned the FDA to ban ammonia-sulfite caramel coloring in February 2011. The FDA is reviewing the groups claims, while reassuring consumers that sodas are safe. "A consumer would have to consume well over a thousand cans of soda a day to reach the doses administered in the studies that have shown links to cancer in rodents," said Doug Karas, an FDA spokesman, in a statement.