DIESEL engine exhaust fumes cause cancer, the World Health Organisation says - and classes them alongside passive smoking as a cancer risk.
Research by WHO's Lyon-based scientists at the International Agency for Research on Cancer (IARC) showed fumes "caused lung cancer in humans", said study leader Dr Christopher Portier, and he urged urgent moves to reduce exposure. It also highlighted a "positive association" with bladder cancer.
Diesel is the most widely used fuel in France, making up 80% of the total consumption and Dr Portier said: "Given the additional health impacts from diesel particulates, exposure to this mixture of chemicals should be reduced worldwide."
He said that the proof that diesel fumes were carcinogenic was "irrefutable" and called for for more efficient engines "to burn diesel fuel more efficiently" and to cut the sulphur content.
In its statement, the IARC said: "Large populations are exposed to diesel exhaust in everyday life, whether through their occupation or through the ambient air. People are exposed not only to motor vehicle exhausts but also to exhausts from other diesel engines, including from other modes of transport (e.g. diesel trains and ships) and from power generators."
The risks from diesel fumes are now the same as for passive smoking, alcohol, asbestos and ultraviolet radiation.
Diesel engines have been promoted because they produce less CO2 than petrol engines and fuel tax reductions have helped them make up 60% of cars in France against less than 25% in 1995.
However they produce fine particulates - microscopic particles given off in diesel exhaust fumes - which are known to be responsible for high rates of breathing and heart problems and are blamed for 42,000 deaths a year.
Last year the European Court started a case against France for not taking urgent action to improve air quality.
The scientists have been meeting for a week and reaffirmed their previous findings in 1989 that petrol exhaust fumes were possibly carcinogenic. The previous year the IARC had said that diesel fumes were "probably" carcinogenic.
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