Exposure to car exhaust from leaded gas during childhood altered the balance of mental health in the U.S. population, making generations of Americans more depressed, anxious and inattentive or hyperactive, according to researchers. They estimate that 151 million cases of psychiatric disorder over the past 75 years have resulted from American children's exposure to lead.

Exposure to car exhaust from leaded gas, which was phased out in 1996, resulted in anxiety, depression and ADHD symptoms in generations of people, researchers found.