Beginning tomorrow, McDonald's will refund $3 for each recalled Shrek-themed glass returned to one of the chain's restaurants, the company announced today.

The glasses, found to contain more cadmium than proposed federal guidelines would allow, came in four designs illustrating characters from the movie Shrek Forever After - Shrek, Princess Fiona, Puss in Boots and Donkey.

Customers purchased at least seven million of the glasses, which were manufactured in Millville, N.J., by ARC International.

No receipt is required, but each customer will have to fill out a slip, McDonald's announced on its website Tuesday.

No other promotional glassware or any Happy Meal toys are part of the recall.

Why $3 is being refunded when each glass reportedly cost $2 was unexplained, so clarification is being sought from McDonald's.

Meanwhile, on eBay, the glasses seem to be fetching more than $5 apiece, especially for full sets of four. The website might soon pull all the listings, though, at the request of the Consumer Product Safety Commission, according to a report.

McDonald's stated that the glasses comply with current safety limits, and that "the CPSC has said the glassware is not toxic," but the company agreed to the recall "in an abundance of caution."

"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," explained CPSC spokesman Scott Wolfson after the agency's recall announcement last week.

"Long-term exposure to cadmium can cause adverse health effects," the agency noted at the time.

Exposure to high levels of cadmium has been linked to cancer, weak bones and severe kidney problems.

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

Some China-made jewelry items, recalled in January, contained up to 91 percent of the metal, which could enter the body through biting, sucking or swallowing, as well as touching contaminated fingers to lips or mouth. Those products were sold at Wal-Mart, Claire's, and discount and dollar stores.