Behind the headlines: Do chemicals harm children's brains?

Children's brains may be at risk from chemicals. Sanjay Tanday reports

What is the story?

Toxic chemicals may harm the brains of millions of children around the world triggering a ‘silent pandemic’ of brain disorders, according to media reports.

The press said that one in six children has a developmental disability, such as autism, cerebral palsy or attention deficit disorder, and that up until adolescence, the brain is much more susceptible to toxic chemicals than in adulthood.

The problem with lead, which was used in petrol from 1960 to 1980, illustrated the risk of low exposure of industrial chemicals for children, the papers said.

At least 202 industrial chemicals, including metals, solvents and pesticides, are known to have the capacity to damage the brain and their effects at low levels of exposure are unknown. Household goods were included on the list.

What is the research?

The media reports are based on a joint US and Danish study that involved a systematic examination of the hazardous substances data bank of the US National Library of Medicine and the integrated risk information system of the US Environmental Protection Agency in order to identify the industrial chemicals that are the most likely to damage the developing brain.

Of the 202 chemicals identified, sufficient documentation of toxicity to the developing human brain was found for only five substances, which were lead, methylmercury, arsenic, polychlorinated biphenyls and toluene.

Analysis showed that the toxicity of these substances was noted in a similar way. It was normally initiated by recognition of adult toxicity and episodes of poisoning among children.

This was followed by a growing body of epidemiological evidence showing that exposure to low levels of the substances led to neurobehavioural deficits in children.

The researchers concluded that industrial chemicals are responsible for a silent pandemic that has caused impaired brain development in millions of children. It is silent because the subclinical effects of individual toxic chemicals are not apparent in available health statistics.

What does the researcher say?

Lead researcher Dr Philippe Grandjean, from the department of environmental health at the Harvard School of Public Health, said it is vital to protect the developing brain from toxic chemicals.

‘The human brain is a precious and vulnerable organ and because optimal brain function depends on integrity of the organ, even limited damage may have serious consequences,’ he said. ‘We used the term silent pandemic because in the short term the effect is disease.

‘In the long term, however, it will lead to functional problems that will cause children to struggle at school. This will result in many children failing to complete education, resulting in a less economically productive society.’

He added that only a few chemicals, such as lead and mercury, were currently controlled with the purpose of protecting children.

The other 200 chemicals, identified in the review, are known to be toxic to the human brain but are not regulated in the same way.

‘Testing new chemicals before allowing them to be marketed is a highly efficient means of preventing toxicity. Tests to show the effect of chemicals on brain function are urgently needed,’ he said, adding that it would cost  $150,000 (about £80,000) to determine the toxicity of each chemical.

What do the experts say?

Other toxicologists are doubtful of the conclusions. Professor Alan Boobis, a toxicologist at Imperial College London, said: ‘The authors have raised an issue of significant importance, but they have produced some far reaching conclusions that are less secure than they suggest.

The evidence for the silent pandemic, which they refer to, is completely missing. It is an extrapolation of the data.’

Professor Nigel Brown, dean of medicine at St Georges’s School of Medicine, University of London, an expert in developmental toxicology, said: ‘The review does not present any new information. The authors are explicit about the idea that there is a pandemic, but there is not a shred of evidence to support this.’

Informing patients

  • A joint US and Danish review has found that toxic chemicals may cause neurodevelopmental disorders in children.
  • Researchers say they have identified at least 202 industrial chemicals that could be harmful to the brain.
  • Other experts have cast doubt on the review’s findings.
  • No firm evidence to back claims of a silent pandemic.

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