Toxic cadmium has been discovered in the painted design on "Shrek"-themed drinking glasses being sold nationwide at McDonald's, forcing the fast food company to recall 13.4 million of the collectibles in the U.S. and Canada.

The U.S. Consumer Product Safety Commission, 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, 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.

Known carcinogen

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."

Wolfson said the glasses have "far less cadmium than the children's metal jewelry that CPSC has previously recalled."

Concerns about cadmium exposure emerged in January, when The Associated Press reported that some items of children's jewelry sold at major national chains contained up to 91 percent of the metal. Federal regulators worry that kids could ingest cadmium by biting, sucking or even swallowing contaminated pendants and bracelets.

The consumer protection agency has issued three recalls this spring for jewelry highlighted in the AP stories, including products sold at Wal-Mart, the world's largest retailer; at Claire's, a major jewelry and accessories chain in North America and Europe; and at discount and dollar stores.

Those recalls all involved children's metal jewelry — and all of that jewelry was made in China.

Manufactured by ARC International of Millville, N.J., the glasses were to be sold from May 21 into June. Roughly seven million of the glasses had been sold so far.

Associated Press reporters tried unsuccessfully to buy the glasses late Thursday at McDonald's in New York, Los Angeles and northern New Jersey but were alternately told the merchandise was sold out, no longer available or "there'll be more tomorrow."

E-mails sent after business hours to two spokesmen for ARC International seeking comment were not immediately returned.

McDonald's said it was asking customers to stop using the glasses "out of an abundance of caution."

"We believe the Shrek glassware is safe for consumer use," Whitman said. "However, again to ensure that our customers receive safe products from us, we made the decision to stop selling them and voluntarily recall these products effective immediately."

Whitman said that as the CPSC develops new protocols and standards for cadmium in consumer products, "we adjust as necessary to ensure that our customers can continue to trust what they receive from McDonald's."