McDonald’s restaurants have recalled 16-ounce glasses sold for about $2 each as part of a promotional campaign for the movie, “Shrek Forever After.”

A cancer-causing agent, cadmium, was discovered in the painted designs on the glasses. Cadmium may also cause bone softening and severe kidney problems.

In the case of the Shrek-themed glassware, the potential danger is long-term exposure to low levels of cadmium, which could leach from the paint onto a child’s hand, then enter the body if the child puts that unwashed hand to his or her mouth.

No incidents have been reported.

The glasses were available in four designs depicting the characters Shrek, Pincess Fiona, Puss in Boots and Donkey.

The U.S. Consumer Product Safety Commission warned consumers today to immediately stop using the glasses.

McDonald’s said it would post instructions on its website next week about refunds.

The glasses were manufactured by ARC International of Millville, N.J. and about 12 million of them sold from May 21 into June.