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Diesel engine exhaust fumes can cause cancer in humans and belong in the same potentially deadly category as asbestos, arsenic and mustard gas, World Health Organisation (WHO) experts said today.
In an announcement that caused consternation among car and truck makers, the France-based International Agency for Research on Cancer (IARC), part of the WHO, reclassified diesel exhausts from its group 2A of probable carcinogens to its group 1 of substances that have definite links to cancer.
The experts, who said their decision was unanimous and based on "compelling" scientific evidence, urged people across the world to reduce their exposure to diesel fumes as much as possible.
"The (expert) working group found that diesel exhaust is a cause of lung cancer and also noted a positive association with an increased risk of bladder cancer," it said in a statement.
The decision is a result of a week-long meeting of independent experts who assessed the latest scientific evidence on the cancer-causing potential of diesel and gasoline exhausts.
The decision puts diesel fumes in the same risk category as a number of other noxious substances including asbestos, arsenic, mustard gas, alcohol and tobacco.
Christopher Portier, chairman of the IARC working group, said the group's conclusion "was unanimous, that diesel engine exhaust causes lung cancer in humans".
"Given the additional health impacts from diesel particulates, exposure to this mixture of chemicals should be reduced worldwide," he said in a statement.
Diesel cars are mainly popular in western Europe, where tax advantages have encouraged technological advances and a boom in demand.
Outside of Europe and India, diesel engines are almost entirely confined to commercial vehicles - mostly because of the fuel's greater efficiency. German carmakers are trying to raise awareness for diesels in the United States, where the long distances travelled on highways suit diesel engines.
IARC noted that large populations all over the world are exposed to diesel exhaust in everyday life, whether through their jobs or in ambient air.
"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," it said.
IARC's director Christopher Wild said that against this background, Tuesday's conclusion "sends a strong signal that public health action is warranted".
"This emphasis is needed globally, including among the more vulnerable populations in developing countries where new technology and protective measures may otherwise take many years to be adopted," he said in a statement.
For about 20 years, diesel engine exhaust was defined by IARC as probably carcinogenic to humans - group 2A - but an IARC advisory group has repeatedly recommended diesel engine exhaust as a high priority for re-evaluation since 1998.
The global auto industry had argued diesel fumes should be given a less high-risk rating to reflect tighter emissions standards.
Reacting to the decision, Allen Schaeffer, executive director of the Washington-based Diesel Technology Forum said diesel engine and equipment makers, fuel refiners and emissions control technology makers have invested billions of dollars in research into technologies and strategies to reduce emissions.
"New technology diesel engines, which use ultra-low sulphur diesel fuel, advanced engines and emissions control systems, are near zero emissions for nitrogen oxides, hydrocarbons and particulate matter," he said in a statement.
A spokeswoman for the European Automobile Manufacturers' Association said she was surprised by the move and the industry would "have to study the findings in all their details".
"These technologies have been developed to address precisely these concerns," Sigrid de Vries told Reuters. "The latest diesel technology is really very clean."
IARC said it had considered recent advances in technology which had cut levels of particulates and chemicals in exhaust fumes, particularly in developed economies, but said it was not yet clear how these might translate into health effects.
"Research into this question is needed," it said. "In addition, existing fuels and vehicles without these modifications will take many years to be replaced, particularly in less developed countries, where regulatory measures are currently also less stringent."
IARC said gasoline exhaust fumes should be classified as "probably carcinogenic to humans", a finding that was unchanged from its previous assessment in 1989.