WELLINGTON, March 29 (Xinhua) -- Extremely high levels of lead in New Zealand cities in the 1970s and 1980s appear to have caused a loss of intelligence among today's adults, researchers said Wednesday.
The research showed that among more than 500 children who grew up in the era of leaded petrol in the South Island city of Dunedin, those exposed to lead had a lower IQ (intelligence quotient) and social standing by the age of 38, relative to peers who had less exposure.
New Zealand's lead levels were consistently higher than international standards during the 1970s and 1980s, largely due to motor vehicle exhaust fumes, said a statement from the University of Otago which compiled the data.
The study's participants were part of the life-long examination of more than 1,000 people born in Dunedin in 1972 and 1973.
Blood-lead tests were conducted for 565 of them at age 11.
Participants with more than 10 micrograms of lead per decilitre of blood at age 11 had IQs at age 38 that were, on average, 4.25 points lower than their less lead-exposed peers.
They were also found to have lost IQ points relative to their own childhood scores.
The study showed that for each 5-microgram increase in childhood blood lead, a person lost about 1.5 IQ points by age 38.
About half of the 11-year-olds had blood-lead levels more than 10 micrograms per decilitre of blood, and 94 percent had levels above 5 mg per decilitre, the level at which the United States' Center for Disease Control and Prevention now recommended a public health intervention.
Children who were over 10 micrograms of lead attained occupations with socioeconomic status levels lower than those of their parents.
The paper's senior author, Professor Terrie Moffitt of U.S.-based Duke University, said the data was from an era when such high lead levels were viewed as normal for children and not dangerous.
In 1984, when the Dunedin children were tested, only a lead level in excess of 35 micrograms per decilitre signalled a need for medical investigation.
"This research shows how far-sighted New Zealand was when the country banned leaded petrol in 1996," Moffitt said in the statement.