Democrats want their convention in Denver to be as biodegradable and reusable as possible: Their goal is to reuse, reduce or compost 85 percent of the waste and debris. One signature commodity of political conventions, though, is proving more difficult to dispose of than expected: balloons.

The party will need at least 100,000 balloons to properly nominate Barack Obama and his running mate — roughly the same number that cascaded down onto John Kerryand John Edwards at the end of the 2004 convention in Boston. That’s a lot of latex to get rid of afterward.

Technically, latex rubber balloons are biodegradable, because they are made from tree sap. The industry’s trade association, the Balloon Council, makes that point over and over in response to environmental groups’ efforts to ban the release of balloons as a hazard to wildlife, and particularly to marine life. Balloons, the council says, decompose at about the same rate as oak leaves.

Oak leaves, though, as any gardener knows, are pretty durable and can linger on the forest floor or flower bed for eight months or more. That’s kind of what staff members of the Democratic National Convention Committee found after stuffing balloons into compost heaps and waiting for something to happen. Nothing has.

Committee spokeswoman Natalie Wyeth said the staff has been tinkering with different temperatures, liquids and time periods in an effort to coax the balloons to rot properly. Does she think it will work? “Only time will tell,” she says.

This durability has prompted Connecticut, Florida, Tennessee, Virginia and California to limit the mass release of balloons. New Hampshire’s legislature last year thought about banning the release of lighter-than-air balloons, but it didn’t. (It was just months before the state’s first-in-the-nation primary, after all.) The California Legislature is now considering banning foil balloons, which utility companies blame for some power failures.

The director of the Balloon Council, Lorna O’Hara, says such environmental and power line hazards haven’t been substantiated and that the industry advocates the safe use of balloons. Manufacturers and distributors offer guidelines to properly handle and dispose of both latex and foil balloons, she says, such as releasing only hand-tied latex balloons and attaching weights to those that are helium-filled.

At Democratic convention headquarters, meanwhile, Wyeth and her colleagues have their work cut out to reach their 85 percent goal. “We’re trying to do the absolute best with the tools and resources available,” she said.