Dirty air may cause cancers

Steve Connor, Science editor Copyright 1998 Financial Times October 27, 1998

Air pollution may be responsible for some childhood cancers, scientists claimed yesterday. They argued that the risk of developing leukaemia increases significantly for children born near industrial centres.

A study of nearly 22,500 children who suffered cancer between 1953 and 1980 found that babies born near to sources of pollution were up to 20 per cent more likely to develop the disease.

Professor George Knox and Estelle Gilman, of the University of Birmingham, believe the results show that early exposure to toxic pollutants, even in the womb, can cause leukaemia later in childhood. Although they are careful not to suggest that they have found the explanation for cancer clusters in Britain, they suggest that airborne contamination may be a significant factor.

"Proximity to several types of industrial source, around the time of birth, were followed by a raised risk of childhood cancer. Combustion products and volatile organic compounds were especially implicated," the researchers conclude in the Journal of Epidemiology and Community Health.

"Among children who moved house between birth and death, the birth addresses were closer to these hazards than were the death addresses, suggesting that the exposures were more effective shortly before or after birth than at later ages," they said. "This matches much other evidence that these diseases are initiated early, and probably pre-natally."

The scientists said the results were difficult to explain with our current understanding of the toxicity of certain airborne pollutants, which have been measured at levels that should not in theory carry a cancer risk.

But they point out that certain industrial toxins, such as polychlorinated biphenyls (PCBs) and dioxins, are known to be extremely toxic in low doses and it is possible that some of the cancer victims may have suffered significant exposure to them in early childhood.

Another possible explanation for the findings is that mothers may have been exposed to low doses of toxins over a long period before they became pregnant. The women could then have subsequently acted as "cumulative filters" which raised the exposure levels of the foetus to cancer-causing substances.

Dr Gilman said that high-temperature industrial processes, such as steel making, and activities such as oil storage and refining were the most likely to be linked with an increased risk of childhood cancers.

The study found that there were "very powerful solid tumour reactions in the near vicinities of major oil-storage facilities and gasworks; and halogenated hydrocarbons showed a particular link with central nervous system tumours".

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