A new study has shown New Zealand children exposed to high levels of lead in the 1970s and 1980s now have a lower IQ as adults.
It's the latest finding from Dunedin's world-acclaimed Dunedin Longitudinal Study, which has tracked the health and social progress of more than 1000 children born in Dunedin in 1972/73.
Half the study cohort were lead-tested at age 11. Those who were more exposed to lead from car exhaust fumes at this age were later found, at age 38, to have a lower IQ and social standing, compared to those who had less exposure.
The higher the blood-lead level was in childhood, the greater the loss of IQ points and occupational status in adulthood.
Participants with more than 10 micrograms of lead per decilitre of blood at age 11 had IQs, at age 38, which were 4.25 points on average lower than their less-exposed peers.
In all, 94 per cent of the tested children were found to have blood-lead levels greater than five micrograms per decilitre, the level at which the United States' Centre for Disease Control and Prevention (CDC) now recommends a public health intervention.
Research author, Associate Professor Terrie Moffitt of Duke University, says the data was from an era when such high lead levels were viewed as normal for children and not dangerous.
New Zealand's lead levels were consistently higher than international standards during the 1970s and 1980s with leaded petrol not banned here until 1996.
"Lead exposure is very rare in children today," says Associate Professor Moffitt. "But the findings suggest the importance of keeping up our vigilance against environmental pollutants."
Lead is a powerful neurotoxin that can accumulate in a child's bloodstream and settle in the bones, teeth and soft tissues.