The burger giant said early Friday that it wants customers to stop using the 16-ounce glasses, which have been sold for about $2 each and were available in four designs depicting the main characters from the hit animated franchise.
Cadmium is a known carcinogen that research shows also can cause bone softening and severe kidney problems.
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In the case of the Shrek glasses, the concern 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.
The collectibles were manufactured by ARC International in Millville, N.J.