You can use them as coasters or bird-scarers or even a high-tech alternative to wallpaper, but eventually a large proportion of the billions of CDs produced each year end up on landfill sites.

And there they stay, because they are made of polycarbonate that doesn't degrade. There are currently some 26 billion CDs already in circulation, enough to cover the surface of the U.K. 194 times.

But now Sanyo and Mitsui Chemicals have a developed MildDisc, a CD and jewel case made from polyactic acid derived from corn resin that is entirely biodegradable, breaking down into water and carbon dioxide over about 50 years.

Currently MildDiscs are about three-times the price of conventional polycarbonate CDs, but Sanyo expects the price to approach parity as demand grows. It takes about 42 grams of dried corn to make a CD and worldwide production of corn is some 600 million tons a year.

Unfortunately label printing, coating and the reflective materials used for the MildDisc are the same as those used for conventional CDs. "These materials are only around one to three percent of the entire disc by weight, and we consider that its impact to the environment will be extremely small," said a Sanyo spokesperson.

Sanyo has already received orders for MildDiscs and has applied for GreenPla status, a kitemark given to environmentally sound products by the Biodegradable Plastics Society.