Cadmium discovered in the painted design on “Shrek”-themed drinking glasses being sold nationwide at McDonald’s, have forced the burger giant to recall 12 million of the cheap U.S.-made collectibles.The glasses were sold locally at the Demopolis McDonalds.

The U.S. Consumer Product Safety Commission (CPSC), which announced the voluntary recall early Friday, warned consumers to immediately stop using the glasses; McDonald’s said it would post instructions on its website next week regarding refunds.

The 16-ounce glasses, which were being sold for about $2 each as part of a promotional campaign for the movie “Shrek Forever After,” were available in four designs depicting the characters Shrek, Princess Fiona, Puss in Boots and Donkey.

The CPSC noted in its recall notice that “long-term exposure to cadmium can cause adverse health effects.” Cadmium is a known carcinogen that research shows also can cause bone softening and severe kidney problems.

In the case of the Shrek-themed glassware, the potential danger would be 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.

Cadmium can be used to create reds and yellows in paint. McDonald’s USA spokesman Bill Whitman said a pigment in paint on the glasses contained cadmium.

“A very small amount of cadmium can come to the surface of the glass, and in order to be as protective as possible of children, CPSC and McDonald’s worked together on this recall,” said CPSC spokesman Scott Wolfson. He would not specify the amounts of cadmium that leached from the paint in tests, but said the amounts were “slightly above the protective level currently being developed by the agency.”