Millions of children throughout the world may have suffered brain damage as a result of industrial pollution, researchers say.

Common pollutants may be causing a “silent pandemic” of neurodevelopmental disorders by impairing the brain development of foetuses and infants, scientists writing today in The Lancet medical journal say.

Potential effects of exposure to even tiny amounts of toxic chemicals include lower IQ scores and conditions such as autism, attention deficit disorder, and cerebral palsy.

One in six children is thought to have some kind of developmental disability, but the exact causes are largely unknown.

The American and Danish researchers say that lead, methylmercury, arsenic and solvents such as ethanol and toluene are among 202 industrial and agricultural chemicals with potential to damage the brain. But these are likely to be the “tip of a very large iceberg” of potentially noxious chemicals, they write.

More than 1,000 chemicals are known to be neurotoxic in animals, and are also likely to be harmful to humans, especially during the vulnerable phases of development that begin during pregnancy and can extend as late as the onset of adolesence.

Other substances that could prove to be toxic in excessive amounts include fluoride, a common additive in drinking water and toothpaste, the researchers say.

In the EU, 100,000 chemicals were registered for commercial use in 1981, and in the US, 80,000 are registered.Yet fewer than half have been subjected to even token laboratory testing, the researchers say, and in 80 per cent of cases there was no information about the danger to children.

Although new chemicals are more rigorously tested, access to data could be restricted for commercial reasons.

The researchers are calling for much tighter worldwide controls on chemicals, and a “precautionary approach” to testing. In the EU, a new testing programme called Reach is planned that will enforce tighter controls. But the scientists say that this does not go far enough, since it fails to emphasise the importance of testing chemicals for damage that they may cause to the developing brain.

Philippe Grandjean, from the University of Southern Denmark in Winslowparken, who co-wrote the study said: “Only a few substances, such as lead and mercury, are controlled with the purpose of protecting children.

“The 200 other chemicals that are known to be toxic to the human brain are not regulated to prevent adverse effects on the foetus or a small child.”

Dr Grandjean and his co-author, Philip Landrigan, from the Mount Sinai School of Medicine in New York, trawled a range of scientific data sources to compile their evidence. Five substances for which sufficient toxicity evidence exist were examined in detail — lead, methylmercury, arsenic, polychlorinated biphenyls (PCBs) and toluene.

For example, virtually all children born in industrialised countries between 1960 and 1980 must have been exposed to lead from petrol, the researchers say. Based on what is known about lead’s toxic effects, this may have reduced the number of people with IQ scores of 130 and above by more than half, and increased the number of those with scores of less than 70.

Other results of lead exposure included shortened attention span, slowed motor co-ordination and heightened aggressiveness. In later life, early damage from lead can increase the risk of Parkinson’s and other neurodegenerative diseases.

Pinning down the effects of industrial chemical pollution is extremely difficult because they may not produce symptoms for several years or even decades, the scientists say.

Writing in the online version of The Lancet, the scientists conclude: “The combined evidence suggests that neurodevelopmental disorders caused by industrial chemicals has created a silent pandemic in modern society.”

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