Childhood cancers are strongly linked to engine exhausts from cars and factories, it was claimed yesterday.

Scientists made the link by linking pollution “hotspots” on a map of Britain to a higher risk of childhood cancer.

Exposure soon after birth, or even before, to combustion gases and particularly engine exhaust, is strongly linked to the development of childhood cancers like Leukemia, according to a report from the UK.

“These results confirm the relative proximities of child cancer births to substance-specific hotspots from oil-based emissions, and to industrial sites known to discharge such materials,” Dr. E. G. Knox, from the University of Birmingham, reports in the Journal of Epidemiology and Community Health.

In the study, Dr. Knox linked emission hotspots for specific chemicals, from maps available on the Internet maps, to the birth addresses of children who later died from leukemia or other cancers before their 16th birthday.

An excess risk of childhood cancer was noted in hotspots for a variety of chemicals, including carbon monoxide, nitrogen oxides and 1,3-butadiene.

Although many of the associations seemed to be artifactual, an independent link with 1,3-butadiene and carbon monoxide remained.

Knox notes that these chemicals, which are largely produced by engine exhausts, were powerful predictors of childhood cancer. For example, joint exposure to a nearby bus station and 1,3-butadiene raised the risk of cancer 12.6-fold.

In terms of policy implications, the findings suggest that current atmospheric standards for 1,3-butadiene in workplaces may not be low enough to protect from childhood cancer, Knox points out.

Chemical emission included carbon monoxide, particulate matter, nitrogen oxides, 1,3-butadiene, benzene and volatile organic compounds.

Prof Knox then looked at the postal addresses of 22,500 children who died of cancer in Britain between 1955 and 1980. To calculate the risk of cancer near particular hotspots, he looked at where the children who later died of cancer were born.

The study in the Journal of Epidemiology and Community Health found there was excess risk for children living within 0.3km of a chemical emission hotspot.

In a breakdown of emissions, 1,3-butadiene and carbon monoxide - both of which are produced by vehicle exhausts, and particularly diesel engines - were among the primary culprits, the study suggested.

Prof Knox said: “Within a short range of installations that emit these chemicals, that is within 300 metres, the risk is at least doubled and in some cases more than doubled. Not enough to worry the individual, but enough from a public health point of view.”

Proximity of up to a kilometre of an emissions hotspot, such as a transport hub, also increased risk.

The combination of proximity to an emissions source in a pollution hotspot increased the child’s risk by up to 12 times, the study said.

Prof Knox said his study showed a need for a realisation of the risk of pollutants in public health.

He said he accepted that atmospheric safety levels for 1,3-butadiene should be lowered so as not to harm the health of children in the womb and soon after birth - when they are most at risk.

He also said all vehicles should be fitted with catalytic converters, including lorries and public transport like buses and trains should have stricter guidelines to avoid leaving the engine running unnecessarily.

Prof Knox said parents should not be worried as the risk of childhood cancer is so low - one in 800 - that the relative increase would not necessarily mean a very high risk.

But he defended his study.

“People ask: Do you think you are worrying people? But I think there is less worrying in knowing where the disease comes from.”

However, Freda Alexander, emeritus professor of cancer epidemiology at the University of Edinburgh, said the study was not convincing.

She said the study did not have a control group of healthy children to compare the birth and death rates to and said no account was taken of factors other than pollutants, such as social status.

Prof Alexander said the study was “interesting” but more research was needed.

Recent research includes a theory that children who develop cancer have a fairly common chromosome defect that occurs in the womb. Then at some point later in life, something else happens to trigger the cancer.

Prof Alexander continued: “The sad thing is we do not know what causes childhood cancer. The study is right that cancer takes hold very early in life but we do not know what causes this.”

Ken Campbell of the Leukaemia Research Fund was also unconvinced.

He pointed out that the map used by Prof Knox shows the emissions from 2001. But the cancer deaths compared to the map are over a period from 1955 to 1980.

He also said the map used by Prof Knox did not give an accurate picture of which addresses are close to pollutants because they are broken down into such large areas.

Mr Campbell said the recent UK Childhood Cancer Study had ruled out pollutants as a cause. It also ruled out links with power lines, breast feeding, parental smoking and background radiation as possible causes of the disease.

He said: “A recent high-quality study has found no evidence to support this hypothesis. And we would be concerned there is a very large mismatch between the time of the data and the time of deaths of the children. Also, it is our understanding from NAEI that the scale of the maps would not permit extraction of data at this level.”

SOURCE: Journal of Epidemiology and Community Health, September 2005.