November 7, 2006
Toxic chemicals may be causing a pandemic of brain disorders because of inadequate regulation, researchers say.
A report in the Lancet identifies over 200 industrial chemicals, including metals, solvents and pesticides, which have potential to damage the brain.
Studies have shown low-level exposure of some can lead to neurobehavioral defects in children, the US and Danish team behind the report said.
UK experts remained divided over the findings.
One in six children worldwide has a development disability such as autism and cerebral palsy.
The causes are unknown, but the researchers trawled through a range of previous studies and data to show how some chemicals can effect the brain.
The team, from the University of South Denmark and New York's Mount Sinai School of Medicine, said pinning down the effects of industrial chemical pollution was extremely difficult because symptoms may not develop for several years.
The report said lead, which was used in petrol from 1960 to 1980, illustrated the risk of even low exposure of industrial chemicals for children.
Based on what is known about the toxic effects of lead, this may have reduced IQ, shortened attention span, slowed motor co-ordination and heightened aggressiveness.
The researchers said developing brains - defined as from foetus to adolescence - were much more susceptible to toxic chemicals than those of adults.
Several other chemicals, including methylmercury, arsenic and polychlorinated biphenyls, were also studied in depth and shown to cause neurobehavioral problems.
The scientists identified 202 industrial chemicals with the potential to damage the human brain, and said they were likely to be the "tip of a very large iceberg".
More than 1,000 chemicals are known to be neurotoxic in animals, and are also likely to be harmful to humans.
Lead researcher Dr Philippe Grandjean said: "The human brain is a precious and vulnerable organ. And because optimal brain function depends on the integrity of the organ, even limited damage may have serious consequences.
"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."
Of the 100,000 chemicals registered for commercial use in the EU in 1981 and the 80,000 in the US, fewer than half had been subjected to even the most basic testing.
Researchers said it was only recently that the tide has started changing with the EU's Reach programme, which will lead to strict regulation of chemicals if there is an early indication of the potential for a serious toxic effect.
Professor Mark Hanson, director of developmental origins of health and disease at Southampton University, said: "The authors have put their finger on something which is important and which will not go away."
But he said the findings were extremely hard to prove as the effect of the chemicals did not seem to lead to gross abnormalities, "but rather change the way that the normal control systems work".
However, Professor Alan Boobis, a toxicology expert at Imperial College London, said: "The authors of this review have raised an issue of significant concern, but some of the evidence in support of the conclusions lacks rigour."
THE HIDDEN DANGERS
Lead - The neurotoxic effects of lead in adults were known in Roman times, but a report from Australia 100 years ago was the first description of epidemic poisoning in children. Source traced to ingestion of lead-based paint.
Methylmercury - The developmental toxicity of this organic mercury compound became evident in the 1960s in Japan where mental illness and blindness was seen in infants born to mothers who had consumed fish from contaminated waters
Polychlorinated biphenyls - PCBs used to be widely applied in electrical equipment insulators. Development toxicity of PCBs was seen in children exposed to high concentrations in Asia where cooking oil had been contaminated during manufacturing