By Anton Caputo

That old yellow school bus might look kid-friendly, but its diesel engine spews pollutants that could be harmful to the precious cargo inside, an environmental group charges.

Some 35,000 Texas school buses transport 1 million students a day. Most run on diesel fuel, and more than one-third were built before 1994, according to the report released today by the Environmental Defense advocacy group. The older buses can emit 25 to 60 times the fine particle pollution produced by cleaner models mandated in 2007. Such pollution can trigger asthma attacks, cause dizziness and coughing, and — with long-term exposure — has been linked to heart disease and premature death, according to the Environmental Protection Agency.

Some research suggests it collects inside school buses at far higher levels than can be found on the side of roads or highways. One study by Yale University researchers that used a monitor in a child's backpack found levels five to 10 times higher.

"It's not just much higher, but it goes up very rapidly as soon as they enter the bus, and goes down very rapidly as soon as they leave the bus," said Dr. Bonnie New, a Houston occupational and environmental health specialist.

Many Texas school districts have instituted programs to run cleaner buses. For example, Northside and Judson independent school districts use clean-burning propane buses for at least half their fleets. Northeast Independent School District uses a grade of clean-burning diesel fuel for three-quarters of its fleet, and plans to buy 20 or 30 of the new 2007 models this year at a cost of $60,000 to $65,000 a bus.

But Environmental Defense thinks the state should take the lead in phasing in cleaner buses. The group wants buses built before 1994 replaced, and those built in 1994 and after retrofitted with pollution-control equipment to put them on par with the 2007 models. That pollution control costs about $7,300 a bus, said Betin Santos, who helped write the report.

"The schools are facing so many challenges in just paying their teachers or putting books in the classrooms," she said. "We don't think the fix should come from education money."

Environmental Defense has targeted a $50 million surplus in the Texas Emissions Reduction Program fund projected by the end of 2007. The money is collected from fees on commercial vehicle inspections, registrations, title transfers and sales tax on certain vehicles. Most is used for projects to reduce nitrogen oxide pollution to help the state meet the federal government's new ground-level ozone standards.

Diane Mazuca, the Texas Commission on Environmental Quality legislative liaison, said the money can't be used for clean school buses unless approved by the Legislature. There is a caveat in the fund that would allow it to pay for such a project if the state was meeting its federal ozone pollution standards. But, with Houston and Dallas failing those standards and San Antonio and the Longview-Tyler area in danger of failing, she doesn't see that happening soon.

New hopes political pressure forces the Legislature's hand. In the meantime, while she doesn't recommend parents keep their kids off school buses, she suggested they urge their school districts to provide the cleanest fleets possible.

"I want people to understand the risk to themselves and their kids," she said. "It is very frustrating for us to keep treating symptoms. Without real change in air quality, we're just committed to treating symptoms."