Commonly-used industrial chemicals damage developing brains, according to recent studies.

It is estimated that currently one in six children has some kind of developmental disability such as autism, attention deficit hyperactivity disorder (ADHD), and cerebral palsy.

Researchers identified 202 potentially harmful industrial chemicals, including metals, solvents, and pesticides, that may be contributing to the dramatically rising pandemic of irreversible neurological disorders.

Roughly half of the chemicals are in common use, but very few have been tested to determine their impact on brain development.

Of the industrial chemicals known to be toxic to the human brain, only five -- lead, mercury, arsenic, PCBs, and toluene -- have been proven to cause damage to the developing brain, note lead author Philippe Grandjean, chair of environmental medicine at the University of Southern Denmark, and co-author Philip Landrigan of New York's Mount Sinai School of Medicine. These chemicals have been identified not because they are necessarily more dangerous than the others, but because they have been studied the most, they suggest.

Developing brains are much more susceptible to toxic chemicals than those of adults, according to the researchers, and developing fetuses are at the highest risk.

During the nine months of prenatal life, the human brain is developing from a small number of very sensitive cells. The blood-brain barrier, which protects the adult brain from many toxic chemicals, is not fully formed until an infant is six months old.

Toxic exposure can also have delayed consequences as well, causing Parkinson's disease or other neurodegenerative diseases in adults.

"The few substances proven to be toxic to human neurodevelopment should be viewed as the tip of a very large iceberg," the researchers caution.

They estimate that there are more than 1,000 chemicals that are known to be neurotoxic in animals, and are also likely to be harmful to humans.