Diesel Exhaust Found to Pose Strong Cancer Risk

Capping nearly a decade of debate, a state panel of scientists Wednesday decided that diesel exhaust poses a serious cancer danger and urged state environmental officials to take steps to protect public health.

The implications of the long-awaited decision are great, not only in terms of people’s health, but also the economy. State environmental officials must wrestle with how to reduce the hazards posed by diesel-powered vehicles, which are so commonplace that they transport virtually every product that Californians consume.

Because of that, how to handle diesel pollution is now among the biggest issues facing the California Air Resources Board, which must start deciding this summer how to respond to the scientists’ recommendation.

The scientists estimated that 14,850 Californians now living could eventually die of disease caused by diesel exhaust. Over a lifetime, exposure to diesel pollution will cause 450 lung cancers among every 1 million people exposed, the scientists estimate, making diesel exhaust a highly potent carcinogen.

Residents of the Los Angeles Basin are breathing the worst diesel fumes in the state, about 60% more than the average level the scientists used to estimate the cancer risk.

UCLA toxicologist John Froines, who chairs the group of nine scientists, called Wednesday’s decision the “most important” public health issue that the scientific panel has addressed since it was formed by the Legislature 15 years ago.

“If you believe these risk numbers at all, diesel has a significant impact on the health of Californians,” Froines said. “This [exhaust] is without a doubt the most toxic set of constituents that you could ever find.”

Diesel exhaust is a brew of thousands of gases and particles, including more than 40 compounds, such as benzene, dioxins and formaldehyde, that have already been declared carcinogenic.

But the economic implications of protecting the public against diesel pollution are also great.

California industries fear that the recommendation could be the first step toward elimination of diesel engines, which power not only heavy-duty trucks and buses but also trains, ships, construction and farm equipment, and industrial generators.

Air board officials say they have no intention of banning diesel. But they may consider tighter standards that would force more engine modifications and encourage use of natural gas and other alternatives. They also have the option of deciding that existing measures already do enough to safeguard the public.

Diesel engines are already substantially cleaner than a decade ago--emissions are scheduled to decline 85% between 1990 and 2010--so the Air Resources Board faces a dilemma of how to cut additional pollution.

The board is expected to decide in July whether to act on the scientists’ recommendations and declare diesel fumes a toxic threat. Board members are expected to accept the scientists’ advice. If so, the state will need to devise a strategy to safeguard Californians from the tons of hazardous compounds spewed by trucks, buses, ships and other diesel equipment.

The state Scientific Review Panel’s unanimous decision was a major defeat for the trucking industry and the California Chamber of Commerce, which orchestrated a high-profile campaign to keep diesel off the state’s list of cancer-causing air pollutants.

Alan Zaremberg, president of the California Chamber of Commerce, called diesel “the backbone of our nation’s transportation infrastructure and our economy.”

Complicating matters, auto makers and the U.S. Department of Energy recently began developing new sport utility vehicles that run on diesel fuel instead of gasoline, because diesel has better fuel efficiency and emits lower amounts of gases linked to global warming.

The scientists and state environmental officials have spent an inordinate length of time--nine years--reviewing diesel exhaust. The first report recommending action against diesel came in 1994. But, under fire from industry groups, the state staff and scientific panel revised it twice, each time toning down the language in describing the cancer threat.

Froines said it has been the longest and most hotly contested review even though there is more scientific evidence linking diesel to disease than any of the other 19 contaminants already declared toxic.

“There are big stakes in this, so we want to do it right,” Froines said. “But the science very clearly shows that diesel exhaust should be identified as a toxic air contaminant.”

The scientists said more than 30 human health studies provide strong support for concluding that diesel causes lung cancer. The studies show that railroad crews and other workers regularly exposed to the fumes suffered a 40% average increase in lung cancer, the panel concluded. Also, in laboratory tests, the exhaust causes gene mutations, cell damage and lung tumors.

Among scientists, the debate focuses not on whether diesel exhaust causes cancer--most agree that it probably does--but on how big a threat it poses to the general population.

The panel of academics struggled to assess the cancer danger that Californians are exposed to driving down freeways, waiting at bus stops and doing other routine activities. Using the cancers suffered by workers breathing large amounts of fumes to extrapolate the risk for people who breathe far less is a highly uncertain scientific endeavor.

Industry groups attacked the estimated number of cancers linked to diesel as “junk” science, especially since the numbers kept changing. Some scientists have also questioned the estimate because of the great uncertainty.

Trucking company owners worry that identifying diesel as a carcinogen will increase their liability in lawsuits filed by people who contract cancer.

“We’re suggesting that the science they used is extremely flawed,” said Beau Biller of the California Trucking Assn. “This is an advocacy document. This is not pure science.”

Biller said the state has refused to reveal all the raw scientific data, adding that there is no data showing that the amount of exhaust people breathe “in the ambient air, as they walk down the street” causes cancer. “This obviously isn’t fully cooked, and it’s just bizarre that this is going to have such an impact on our industry. . . . There really is no alternative to diesel right now.”

In addition to lung cancer, workers exposed to diesel exhaust can suffer allergies, asthma, loss of lung function and bronchitis, health studies show.