Michael F. Jacobson, executive director of the Center for Science in the Public Interest, said the group collected samples of Coca-Cola, Pepsi, Diet Coke, Diet Pepsi, Dr Pepper, Diet Dr Pepper and Whole Foods 365 Cola from Washington-area stores.
The analysis found Pepsi's products had 145 to 153 micrograms of 4-methylimidazole in two 12-ounce cans. Regular Coca-Cola had 142 micrograms per 12 ounces in one sample and 146 micrograms in another. Diet Coke had 103 micrograms per 12 ounces in one sample and 113 micrograms in another. In California, levels of 29-microgram of 4-methylimidazole and above in a food serving or beverage may be required have a warning notice, Jacobson said.
The carcinogen forms when ammonia or ammonia and sulfites are used to manufacture the "caramel coloring" that gives those sodas their distinctive brown colors, Jacobson said.
"Coke and Pepsi, with the acquiescence of the U.S. Food and Drug Administration, are needlessly exposing millions of Americans to a chemical that causes cancer," Jacobson said in a statement. "The coloring is completely cosmetic, adding nothing to the flavor of the product. If companies can make brown food coloring that is carcinogen-free, the industry should use that. And industry seems to be moving in that direction. Otherwise, the FDA needs to protect consumers from this risk by banning the coloring."
Pepsi told CSPI it switched to a coloring in California that contains much less 4-methylimidazole and plans to do the same in the rest of the country.
A Coca-Cola spokesman disputed the health concerns raised by CSPI.
"Unlike CSPI, the Coca-Cola Co. deals in hard facts," company spokesman Ben Sheidler said. "Fact: The body of science about 4-MEI in foods or beverages does not support the erroneous allegations that CSPI would like the public to believe. The 4-MEI levels in our products pose no health or safety risks. Outside of California, no regulatory agency concerned with protecting the public's health has stated that 4-MEI is a human carcinogen.
"The caramel color in all of our ingredients has been, is and always will be safe. That is a fact."