A CLAIM that childhood cancer is strongly linked to traffic pollution has been contested by research groups.

George Knox, a retired Professor of Epidemiology at the University of Birmingham, reports today in the Journal of Epidemiology and Community Health that a range of air pollutants caused by burning oil or petrol increase the risk of childhood cancer.

But other experts, including the Leukaemia Research Fund and Cancer Research UK, said that Professor Knox’s evidence did not justify such a conclusion. He compared data on 22,500 children who died from cancer in Britain between 1955 and 1980 with modern pollution maps, based on data collected in 2001.

The maps, which show pollution hot spots, include chemicals such as carbon monoxide, nitrogen oxides, 1,3-butadiene, benzene and dioxins. Professor Knox compared the birth and death address of the children with the location of the hot spots to work out the excess risks, comparing the number of deaths from childhood cancer that would be expected in a particular area with the actual number of deaths.

His calculations suggest that children have a higher risk of cancer if they live within 300 metres (1,000ft) of a chemical emissions hot spot.

They were also at increased risk, he calculated, if they live within a kilometre of major emission sources such as hospitals, bus stations, heavy transport centres, railways and oil installations. The two chemicals with the strongest link were 1,3-butadiene and carbon monoxide, derived mostly from motor vehicle exhausts.

“Childhood cancers are strongly determined by prenatal or early postnatal exposures to oil-based combustion gases, especially from engine exhausts,” he concludes.

The paper is the latest in a series from Professor Knox, and comes after one published in the same journal in January that said that most childhood cancers were “probably” caused by exposure to pollutants while babies were still in the womb.

But other cancer experts are critical of the conclusions. The Leukaemia Research Trust said that the recent UK Childhood Cancer Study found no link between cancer and pollution exposure. Furthermore the group said that a large number of studies of leukaemia in relation to traffic gave conflicting results.

Ruth Yates, of Cancer Research UK, said: “The results of this latest study should be interpreted with considerable caution and people should not be alarmed by its claims.

“Research needs to include much more detailed information on people’s levels of exposure than this study provides.”

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