Risk From Diesel Fumes Estimated : Pollution: State board says the exhaust could cause up to 1,000 cases of lung cancer a year. Study could increase pressure for more stringent regulations.

The California Air Resources Board has tentatively concluded that diesel exhaust could be responsible for more than 1,000 cases of lung cancer a year, which increases pressure on the state to tighten its stringent regulations on buses, trucks and other vehicles that run on diesel fuel.

As part of its efforts to control smog, California, since 1988, has imposed the nation’s strictest program for controlling diesel exhaust. In the process, according to ARB officials, the state has substantially reduced components of diesel exhaust, such as benzene, butadiene and formaldehyde, which are potential carcinogens.

“We have identified and regulated some components of diesel exhaust in the past,” said William Sessa, an ARB spokesman.

For the first time, however, the state has sought to gauge the health risks of everything that comes out of the exhaust pipe of diesel engines.

“This is an assessment of the health risk of all components combined,” Sessa said.

The study estimates that “from 300 additional cancer cases a year to 1,100 or 1,200” could be caused by diesel exhaust, Sessa said.

The findings are contained in a preliminary draft of an ARB risk assessment study that will be undergoing review and modification for more than a year. At the end of that process, the ARB will decide whether to impose additional regulations on diesel emissions.

The ARB study echoes research by the federal government that concluded in 1990 that diesel exhaust probably causes cancer in people.

Factored into the California study, however, is the amount of diesel exhaust in the air that people in this state are exposed to. The exposure level in Southern California is significantly higher than it is statewide.

Statewide, 58,000 tons of diesel exhaust go into the air each year, more than a third of it in Southern California, according to the study. The concentration level ranges from 3.7 micrograms per cubic meter statewide to 5 micrograms per cubic meter in Southern California.

The results of the study prompted one environmental group, the Natural Resources Defense Council, to call Thursday for new regulations “which will phase out diesel trucks, school buses, locomotives and (diesel powered) construction equipment from California cities.”

Sessa emphasized that the study is a first draft.

“This is the first cut at a risk assessment to determine the risk of diesel emissions, and there is still some uncertainty about the risk level.”

He said the risk assessment is based on the results of 40 studies on animals and humans, but he cautioned that it does not take into account how much diesel pollution will be reduced as some of the state’s regulations on fuel reformulation and emissions “go more fully into effect.”

“As more new vehicles are introduced, the emission levels will go down,” he said. “We have estimated that diesel emissions will be reduced by 50% over the next 16 years.” Whether the ARB’s latest study will lead to more regulation “is premature at this stage in the process to speculate about.”

Up to now, the state has attempted to reduce toxic diesel emissions by mandating reformulated fuels. And its emission standards require a reduction of particulate matter by 90%. That regulation went into effect for buses last year and will apply to trucks beginning next year.