According to a new report toxic chemicals may be causing a pandemic of brain disorders because of inadequate regulation.
Researchers from Denmark and the U.S. say that there are over 200 industrial chemicals, including metals, solvents and pesticides, which have the potential to damage the brain.
Scientists believe fetal and early childhood exposures to industrial chemicals in the environment can damage the developing brain and can lead to neurodevelopmental disorders such autism, attention deficit disorder (ADHD), and mental retardation.
Studies have already shown, say the team, that low-level exposure of some can lead to neurobehavioral defects in children.
Although experts remain divided over the findings, nevertheless one in six children worldwide has a development disability such as autism and cerebral palsy, which raises the possibility that the authors may have an argument.
The team of researchers from the University of South Denmark and New York's Mount Sinai School of Medicine, scrutinised a range of previous studies and data in order to show how some chemicals can effect the brain.
The team, say pinning down the effects of industrial chemical pollution was extremely difficult because symptoms may not develop for several years, but lead, which was used in petrol from 1960 to 1980, provides a good illustration of the risk of even low exposure of industrial chemicals for children.
The toxic effects of lead, are thought by some scientists to be guilty of causing reduced IQ levels, shortened attention spans, slowed motor co-ordination and heightened aggressiveness.
The researchers say developing brains, from foetus to adolescence, were much more susceptible to toxic chemicals than those of adults.
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" as 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 says the human brain is a precious and vulnerable organ and optimal brain function depends on the integrity of the organ, so even limited damage may have serious consequences.
Grandjean says only a few substances, such as lead and mercury, are controlled with the purpose of protecting children, while 200 others known to be toxic to the human brain are not regulated to prevent adverse effects on the foetus or a small child.
Testing chemicals for toxicity is a highly efficient public health measure, however, less than half of the thousands of chemicals currently used in commerce have been tested to assess acute toxicity.
Although new chemicals undergo more thorough testing, access to the data may be restricted because companies fear exposing proprietary information.
Also, current toxicity testing rarely includes neurobehavioral functions.
Of the 100,000 chemicals registered for commercial use in the EU in 1981 and the 80,000 in the U.S., fewer than half had been subjected to even the most basic testing.
The study is published online in The Lancet on November 8, 2006.