An environmental watchdog group has released a study claiming that PepsiCo Inc. (NYSE:PEP) has not removed high levels of a carcinogen from its formula, more than a year after pledging to do so.

In an independent study released last March, the Center for Environmental Health (CEH) found that the ingredients in both PepsiCo and Coca-Cola Co (NYSE:KO) contained a known carcinogen -- a cancer-causing chemical -- called 4-methylimidazole, or 4-Mel, which forms during the caramel coloring process.

Both companies announced they would institute a nationwide reformulation in their caramel coloring due to a California law which required that products containing the carcinogen be labeled with a cancer warning.

In a follow-up study, CEH found that both companies reformulated in California. But while Coca-Cola Co has also altered their formula outside the state, PepsiCo has not. In fact, 10 products tested outside of California each contained caramel coloring with the same high levels of 4-methylimidazole.

“This shows how California’s Proposition 65 law can make products safer for all Californians, and in some cases for all Americans,” said Michael Green, Executive Director of CEH. “We applaud Coke for taking this health protective action for consumers nationwide. Pepsi’s delay is inexplicable. We urge the company to take swift action to provide all Americans with the same safer product they’re selling in California.”

According to UPI, the 10 Pepsi products tested were: Pepsi, Diet Pepsi, Pepsi Throwback Made with Real Sugar, Pepsi Max Zero Calories, Pepsi One-Zero Calories, and Miniature Pepsi.

After receiving word of the study, Pepsi issued a response. “Our caramel coloring suppliers have been working on modifying the manufacturing process to reduce the amount of 4-MEI,” said PepsiCo Senior Director Aurora Gonzalez. “As you know, 4-MEI levels in our products in California are below Prop 65 levels. The rest of the U.S. will be completed by February 2014. In fact, we’ll be starting the process and shipping concentrate end of this year.”

In light of the news, shares of Coca-Cola Co went up 0.3 percent, while Pepsi shares dipped 1.16 percent on Wednesday.