A long-term study of 565 children who grew up in the era of leaded gasoline has shown that their exposure to the powerful neurotoxin may have led to a loss of intelligence and occupational standing by the time they reached age 38. Ninety-four percent of the children exceeded today’s reference value of 5 micrograms of lead per deciliter of blood. For each 5-microgram increase in blood lead, a person lost about 1.5 IQ points.