The numbers are startling. According to the U.S. Centers for Disease Control and Prevention, about 1.8 million more children in the U.S. were diagnosed with developmental disabilities between 2006 and 2008 than a decade earlier. During this time, the prevalence of autism climbed nearly 300 percent, while that of attention deficit hyperactivity disorder increased 33 percent. CDC figures also show that 10 to 15 percent of all babies born in the U.S. have some type of neurobehavorial development disorder. Still more are affected by neurological disorders that don’t rise to the level of clinical diagnosis.

And it’s not just the U.S. Such impairments affect millions of children worldwide. The numbers are so large that Philippe Grandjean of the University of Southern Denmark and Harvard T.H. Chan School of Public Health and Philip Landrigan of the Icahn School of Medicine at Mount Sinai in New York — both physicians and preeminent researchers in this field — describe the situation as a “pandemic.”

While earlier and more assiduous diagnosis accounts for some of the documented increase, it doesn’t explain all of it, says Irva Hertz-Piccioto, professor of environmental and occupational health and chief of the University of California, Davis, MIND Institute. Grandjean and Landrigan credit genetic factors for 30 to 40 percent of the cases. But a significant and growing body of research suggests that exposure to environmental pollutants is implicated in the disturbing rise in children’s neurological disorders.

What, exactly is going on? And what can we do about it?

Chemicals and the Brain

Some chemicals — lead, mercury and organophosphate pesticides, for example — have long been recognized as toxic substances that can have lasting effects on children’s neurological health, says Bruce Lanphear, health sciences professor at Simon Fraser University. While leaded paint is now banned in the U.S., it is still present in many homes and remains in use elsewhere around the world. Children can also be exposed to lead from paints, colorings and metals used in toys, even though these uses are prohibited by U.S. law (remember Thomas the Tank Engine), and through contaminated soil or other environmental exposure as well as from plastics in which lead is used as a softener. Mercury exposure sources include some fish, air pollution and old mercury-containing thermometers and thermostats. While a great many efforts have gone into reducing and eliminating these exposures, concerns continue, particularly because we now recognize that adverse effects can occur at exceptionally low levels.