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PARIS - The World Health Organization's cancer research agency on Tuesday classified diesel engine exhaust as cancer-causing, and urged action to reduce human exposure to it.
"Diesel engine exhaust causes lung cancer in humans," Christopher Portier, chairman of a working group at the WHO's International Agency for Research on Cancer (IARC), said in a statement.
There was also a "positive association" with an increased risk of bladder cancer, the UN body said.
"Large populations are exposed to diesel exhaust in everyday life, whether through their occupation or through the ambient air," it said a statement.
People are exposed to the emissions of diesel cars, trains, ships and power generators, as are workers in fields such as underground mining.
"Given the additional health impacts from diesel particulates, exposure to this mixture of chemicals should be reduced worldwide," said Portier.
In 1988, the IARC had classified diesel exhaust as "probably" carcinogenic.
Portier's group on Tuesday also concluded that petrol, or gasoline, exhaust was possibly carcinogenic, a finding unchanged from its previous assessment in 1989.
The agency said environmental concerns had given rise to new regulations in the last two decades, notably in North America and Europe -- resulting in a lower sulphur content for diesel, engine changes that burn fuel more efficiently and emission reductions through exhaust control technology.
However, existing fuels and vehicles without the modifications will take years to be replaced, particularly in less-developed countries where regulatory measures are also less stringent.
The agency urged policy makers to work with engine and fuel manufacturers.
IARC said it decided to issue the warning after finding "sufficient evidence" that diesel exhaust caused lung cancer and "limited evidence" that it caused bladder cander.
"The main studies that led to this conclusion were in highly exposed workers," said the IARC's Kurt Straif.
"However, we have learned from other carcinogens, such as radon, that initial studies showing a risk in heavily exposed occupational groups were followed by positive findings for the general population.
"Therefore actions to reduce exposures should encompass workers and the general population."