When you let go of a helium balloon and it floats away in Tucson, where does it end up?

Erin Zylstra, a University of Arizona biologist, has a pretty good idea after taking the first-ever inventory of balloon waste in federal parkland surrounding the city.

Shriveled latex in rainbow colors is ubiquitous in the Rincon and Tucson mountains sections of Saguaro National Park, where the air-filled orbs often land due to local wind patterns, Zylstra found.

Some hang from trees with ribbons still attached. Others are in various states of decomposition, many half-melted onto rocks like rubberized lichens.

To Zylstra's amazement, balloons greatly outnumbered desert tortoises and Western diamondback rattlesnakes in the 120 square kilometers - roughly 75 miles - of parkland she studied to collect the data.

In the Rincons, for example, a square kilometer of land had an estimated density of 62 balloons, 30 tortoises, 26 rattlers and 29 plastic bags, which Zylstra also counted.

The impact of such trash on local wildlife isn't clear, though it poses potential threats if animals eat it or get tangled in it, Zylstra said. Scarce water sources also could become clogged by such debris.

"I was surprised by how many balloons were out there. I don't think many people realize where they end up," said Zylstra, 36, who has a UA master's degree in wildlife ecology and now is studying for a Ph.D.

Her findings, which recently ran in the peer-reviewed Journal of Arid Environments, appear to be the first time published research has tackled the topic of wind-borne trash dispersal in an inland environment.

All sorts of similar studies have been done in coastal regions, spawning public awareness and in some cases legislation, to keep balloons, plastics and other flotsam from soiling beaches and harming marine life.

At least six states and five U.S cities now have laws that ban or restrict the mass release of balloons. The tradition often has been replaced by green events such as butterfly or dove releases or bubble-blowing.

In Tucson, balloon releases are common and often organized by charities, such as one held Monday outside City Hall to highlight the problem of addiction.

Janice Harris, a local nurse, the mother of an addict and founder of the There Is No Hero in Heroin Foundation, said she can sympathize with potential harm to wildlife from balloons. But that's not as important, in her view, as the human suffering caused by addiction.

"If I could come up with something more eco-friendly, sure. But we're doing this for a very good cause," she said.

Zylstra's research, which employed a computer modeling program commonly used to estimate wildlife populations, was done in 2005 and 2006 but was published only recently after she finished her master's degree.

The problem she detected hasn't gone away, said Don Swann, a biologist with the National Park Service, who hopes Zylstra's findings will make Tucsonans think twice about releasing balloons.

The study shows "how the decisions we make at home can affect our wilderness areas," he said.

Contact reporter Carol Ann Alaimo at calaimo@azstarnet.com or at 573-4 138.