Diesel engine exhaust fumes can cause cancer in humans, the World Health Organisation (WHO) declared.
Further, the fumes belong in the same deadly category as smoking, asbestos, ultraviolet radiation, arsenic and mustard gas, the WHO reportedly said.
They caused lung cancer and increased the risk of bladder cancer, and the WHO experts, cited by the New York Times, said they were more carcinogenic than secondhand cigarette smoke.
The reclassification of diesel exhausts from its group of probable carcinogens to its group of substances that have definite links to cancer came after a week-long meeting of the France-based International Agency for Research on Cancer (IARC).
The decision was reportedly unanimous and based on "compelling" scientific evidence.
Reuters quoted the IARC as saying: "People are exposed not only to motor vehicle exhausts but also to exhausts from other diesel engines...[such as diesel trains and ships] and from power generators."
Bloomberg cited Kurt Straif, director of the IARC department that evaluates cancer risks, as saying diesel fumes affected not only pedestrians on the street, but passengers and crew on ships, railroad workers, truck drivers, mechanics, miners and people operating heavy machinery."
The director of New York's Clean Fuels and Vehicles Project, Rich Kassel, meantime told CNN the WHO simply confirmed what has been suspected for some time.
"Anybody who lives in Beijing, Mexico, New York or any congested city has probably felt the feeling of holding their breath when the bus pulls away from the curb leaving you in a ... puff of black smoke," he said.
"This study basically confirms that we're right to hold our breath when the bus pulls away."
He said that while exhaust from buses, trucks and other diesel engines was technically called particulate matter: "We all know it is soot. It's fine, fine particles that are small enough to get past our throat, past our lungs into the deepest part, the deepest of our lungs, where they trigger asthma attacks, bronchitis, emphysema, heart disease and now of course we've learned cancer."
The WHO decision to elevate diesel to the “known carcinogen” level is particularly relevant to poor countries, where trucks and other machinery are outdated or poorly serviced, the Times wrote.
The US and other wealthy nations legislate for cleaner-burning diesel engines.
And Bloomberg cited diesel engine makers and car companies as being quick to point out emissions from trucks and buses have been slashed by more than 95 percent for nitrogen oxides, particulate and sulfur emissions.
However, Christopher Portier, chairman of the IARC working group, said in a statement: "Given the additional health impacts from diesel particulates, exposure to this mixture of chemicals should be reduced worldwide."
Diesel vehicles are popular in western Europe and India, but outside of those countries are almost entirely confined to commercial vehicles, Reuters wrote.
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It cited the European Automobile Manufacturers' Association expressing surprise at the WHO announcement and saying that the industry would "have to study the findings in all their details."
Meanwhile, the Times quoted the medical director of the American Cancer Society, Dr. Otis W. Brawley, as praising the ruling, saying the society had "for a long time had concerns about diesel."
"I don’t think it’s bad to have a diesel car," Brawley added. "I don’t think it’s good to breathe its exhaust. I’m not concerned about people who walk past a diesel vehicle, I’m a little concerned about people like toll collectors, and I’m very concerned about people like miners, who work where exhaust is concentrated."