Diesel exhaust can cause cancer, World Health Organization says

In this 2006 photo, California Air Resources Board inspector Paul Leon prepares to test the emissions of a diesel truck. This week the World Health Organization classified diesel exhaust as a carcinogen, linking it to lung and other cancers.
(Bob Chamberlin / Los Angeles Times)

Diesel engines power commerce and transportation around the world, but the exhaust they produce can prove deadly. The World Health Organization (WHO) announced on Tuesday that it now classifies diesel exhaust as a cause of cancer. While major advances in technology have helped clean up some diesel pollution in the United States, the findings could have serious implications for developing countries still relying on dirty diesel power.

Following a week-long meeting of experts, the WHO’s International Agency for Research on Cancer concluded there was sufficient evidence that diesel exhaust can cause lung cancer, and noted it may also increase the risk of bladder cancer. Gasoline exhaust remains classified as a “possible” carcinogen, a WHO status that has not changed since a 1989 evaluation.

California’s Air Resources Board classified diesel as cancer-causing in 1998, and passed a number of regulations to reduce the public’s diesel pollution exposure from sources like trucks, ports and agricultural equipment.


The WHO’s announcement validates California’s efforts, said Diane Bailey, a senior scientist with the Natural Resources Defense Council in San Francisco. “It’s a signal to the international community that we really need to take diesel pollution seriously,” Bailey said. “It’s a major global health threat to people throughout the world.” She added that tens of thousands of people die from exposure to diesel exhaust every year.

Diesel exhaust contains tiny soot particles that can pass through the lungs into the bloodstream, carrying heavy metals, sulfates and other chemicals. “The health risks of diesel exhaust are a little like smoking a couple of cigarettes a day, the difference being that you don’t choose” to be exposed, Bailey said.

However, these risks are largely preventable, thanks to low-sulfur diesel and more efficient engines with improved filtration. “We really have diesel that’s near zero emissions for fine particles and nitrogen oxides,” said Allen Schaeffer, the executive director of the Diesel Technology Forum. A recent study by the Health Effects Institute found that exhaust from diesel engines meeting the 2007 EPA standards, which reduce particle emissions by 90%, only slightly decreased lung function in rats.

California’s trucking industry has already taken many steps to comply with Air Resources Board regulations, such as installing particle filters, said Michael Shaw, a spokesperson for the California Trucking Assn. However, the costs of such upgrades get passed on to consumers buying items like a gallon of milk or a loaf of bread, he said.

The trucking industry is currently experiencing a “renaissance” in terms of alternative fuels, Shaw said, “everything from liquified natural gas, to hybrid trucks and all-electric trucks.” But he added that these alternatives comprise just a small percentage of fuel used by the trucking industry, which is projected to rely predominantly on diesel well into this century.

Although the United States has made progress to clean up diesel pollution, exposure is a serious issue in the developing world, Bailey said. “We’re starting to see the sales of diesel vehicles skyrocket.”


In order to take advantage of cleaner diesel technology, developing countries first need to adopt cleaner fuel standards, Schaeffer said. The low-emission engines won’t work properly on diesel high in sulfur.

A June 2012 United National Environment Programme map of sulfur content standards in diesel fuel around the world shows that North America, Europe and Australia have the highest standards, but that the sulfur problem is worse – and sometimes much worse – in large parts of the globe. To see more, click here.

“It’s the challenge of getting the clean equipment and the clean fuel together,” he said. “That becomes a big problem in a hurry outside of the U.S.”


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