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Are School Bus Diesel Fumes Fueling Kids' Cancer Risk?

Can your child's bus ride to school be hazardous to her health?
By: Katy Abel

Are School Bus Diesel Fumes Fueling Kids' Cancer Risk?

Study Questions Air Quality Inside Buses
Those bright yellow school buses that transport millions of kids to school each day may be among the safest vehicles on the road, but a recent report suggests they may not be the healthiest.

A study by the Natural Resources Defense Council (NRDC) found that levels of diesel exhaust on four Los Angeles school buses were eight and a half times higher than average levels found in California's smoggy air. This was four times higher than the fumes from inside a car driven directly in front of the buses. NRDC researchers measured diesel exhaust levels during five hours of tests conducted on actual bus routes in the city.

"Diesel exhaust has been identified as a likely or known carcinogen," says Julie Masters, project attorney for the NRDC. "We don't want parents to begin pulling children off school buses because of our report, but the bad news is children are being exposed to (much more) diesel exhaust inside the bus than outside."

Based on an estimate of the amount of time an average child spends riding a bus to and from school, NRDC researchers estimated that the exposure to diesel exhaust would result in 23 to 46 more cancer cases per million children exposed. The researchers said the calculated cancer risk is long-term, not immediate. Earlier studies done at UCLA have shown that diesel soot is also linked to allergic and asthmatic reactions.

"Diesel particles don't just cause someone who is allergic to have worse symptoms, they cause people who are not normally allergic to some agents to become allergic," David Diaz-Sanchez, UCLA immunologist, told The Los Angeles Times.

Study's Sample Size, Conclusions Questioned
Although the adverse health effects of diesel are well-documented, some critics question the NRDC's testing of only four buses.

"On a scale of one to ten, I'd give (the report) a minus four," says Doug Freeman, director of quality and product safety for Blue Bird Buses, the largest supplier of school buses in the United States. "Our buses meet or exceed all standards set by local, state, and federal agencies, including the U.S. Environmental Protection Agency."

The study has also come under fire for using older buses, dating to the mid-80s. Julie Masters, lawyer for the NRDC, concedes that newer diesel buses are environmentally safer, but notes that one-third of California's buses are 13 years or older.

Some public-health officials caution parents against panicking about the findings, noting that other types of environmental pollution, especially second-hand cigarette smoke, pose a greater health risk to children than diesel exhaust. In general, children are considered more susceptible than adults to air pollution because their lungs and immune systems are still developing.

What To Do? Recommendations for School Districts, Parents
The NRDC makes the following suggestions, based on its findings:

  • Parents should press school districts and legislative officials to set aside or seek funding to upgrade their bus fleets.

  • While newer diesel buses are better than older models, buses that run on alternative fuels such as propane or natural gas are the best choice (although currently, an alternative fuel bus costs $30,000 more than a diesel bus).

  • In the short term, school buses should be retrofitted with "particulate traps," a device expected to be on the market later this year that will reduce children's exposure to toxic air contaminants.

  • Children should be encouraged to sit at the front of the bus, where diesel fumes are considerably lower.

  • Bus windows should be kept open during rides, weather permitting.
The full text of the Natural Resources Defense Council Report is available at More information on school bus safety information can be found at

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