LOS ANGELES — The noxious smoke plumes that wafted over the military base in Balad, Iraq, alarmed Lt. Col. Michelle Franco. The stench from a huge burn pit clung to her clothing, skin and hair.

"I remember thinking: This doesn't look good, smell good or taste good," Franco said recently. "I knew it couldn't be good for anybody."

She wheezed and coughed constantly. When Franco returned to the U.S., she was diagnosed with reactive airway dysfunction syndrome. She is no longer able to serve as an Air Force nurse.

Other returning veterans have reported leukemia, lymphoma, congestive heart problems, neurological conditions, bronchitis, skin rashes and sleep disorders — all of which they attribute to burn pits on dozens of U.S. bases in Afghanistan and Iraq.

"The military needs to step up and address this problem," said John Wilson of the advocacy group Disabled American Veterans, which maintains a registry of more than 500 veterans with disorders they blame on burn pits. The fumes emanating from the pits, he warned, could become the Agent Orange of the current war zone.

Items burned in the pits have included medical waste, plastics, computer parts, oil, lubricants, paint, tires and foam cups, according to soldiers and contractors. Some say amputated body parts from Iraqi patients were burned in Balad, site of a large U.S. military hospital.

A military environmental agency that tested air samples from Balad in 2007 found dioxins, metals, volatile organic compounds and other toxic substances in the smoke. But in its report — titled "Just the Facts" — the U.S. Army Center for Health Promotion and Preventive Medicine said the substances "were within acceptable standards." It also blamed particulate matter found at levels above military exposure guidelines on the blowing sand and dust that is common at bases across the region.

"Although no chemical concerns or significant health risks have been identified, smoke from any source, including burning trash, can still cause temporary irritation effects," the report said.

Last year, the center recommended moving burn pits downwind from areas where service members live and work, and minimizing the burning of plastics and cooking grease.

According to Lt. Cmdr. Bill Speaks, a military spokesman, the burning of medical waste, fuels, oils, lubricants, tires, most metals, electronics, batteries and other hazardous items is prohibited. More environmental sampling and independent reviews are planned "to ensure ... an improved understanding of burn-pit smoke and any resulting health risks," Speaks said.