'Childhood cancers are strongly determined by prenatal or early postnatal exposures to oil based combustion gases, especially from engine exhausts.'

And the highest risk of cancer for children is caused by living within 0.3 kilometers of a chemical emissions hotspot and within 1km of an emissions source -- such as a transport hub.

It is thought that exposure to such pollution while in the womb could cause cancers to develop in childhood.

Professor George Knox from the University of Birmingham compared the postal addresses of 22,500 children who had died of cancer in Britain between 1955 and 1980 to emissions hotspots for specific chemicals, identified from maps of atmospheric pollution levels.

The chemicals included carbon monoxide, particulate matter, nitrogen oxides, 1,3-butadiene, benzene, dioxins, benzo(a)pyrene and volatile organic compounds.

Emission sources, including hospitals, bus and train stations, heavy transport hubs, and oil installations, were also located using maps and information downloaded from the internet.

Vehicle Emissions Primary Culprits

The expected deaths from childhood cancer were plotted against the actual deaths, and the postcodes where they had been born, lived and died were used to calculate distances from the particular hotspots and emissions sources.

Emissions from vehicle exhausts, particularly diesel engines, were among the primary culprits, the findings suggested.

When combined with close proximity to an emissions source, such as a bus or coach station, a child was at 12 times the risk of dying from cancer.

Prof Knox said that the exposure of a child in the womb and soon after birth to atmospheric pollutants is likely to be the critical period.

And, writing in the Journal of Epidemiology and Community Health, he added that accepted atmospheric safety levels for 1.3-butadiene in the workplace are probably unlikely to protect unborn children from developing cancer.

Prof. Knox concluded, "Childhood cancers are strongly determined by prenatal or early postnatal exposures to oil based combustion gases, especially from engine exhausts. 1,3 butadiene, a known carcinogen, may be directly causal."

He is calling for more controls to be placed on the sources of emissions.

Prenatal Exposure

Earlier this year, Prof. Knox published research saying that most childhood cancers are "probably" caused by exposure to pollutants while babies are still in the womb. He said that prenatal exposure to industrial and environmental pollutants, most likely to have been inhaled by the mother during pregnancy, were probably to blame for the majority of cancers in under-16s.

Prof. Knox said the most dangerous pollutants were produced by industry or transport and these should be targeted in attempts to reduce childhood cancers.

About 1,500 new cases of childhood cancer are diagnosed each year in the UK, accounting for about 300 deaths annually.

Geoff Thaxter, director of Services for CLIC Sargent -- the UK's children's cancer charity -- said, "We want to see conclusive research, but not reports which simply raise alarm without offering solutions to the public.

"This study is based on information that is 25 years old and as we understand it makes a statistical but not evidenced link between two events."