FDA says it will launch an investigation of the safety of caramel coloring used in soda after a Consumer Reports study found varying levels of 4-methylimidazole in 12 brands of soda from five companies. The chemical is an impurity formed in some caramel coloring at low levels in the manufacturing process, and it is listed by the state of California as a carcinogen. Other studies of 4-methylimidazole's carcinogenic potential have not been conclusive.

There are no federal limits on the chemical, but California law now requires products containing over 29 micrograms of 4-methylimidazole to carry a cancer warning label. As a result, Coca Cola, Pepsi and others have directed caramel-color suppliers to reduce levels of 4-methylimidazole, according to the Associated Press.