Lower IQs linked to leaded petrol use, says Kiwi study

Exhaust fumes from the era of leaded petrol could be to blame for Kiwis with lower IQs and social standing, according to the latest Dunedin Study findings.

Researchers at the longrunning University of Otago project said that high levels of lead in New Zealand cities during the 1970s and 1980s appeared to be responsible for a loss of intelligence and occupational standing among adults in the country today.

Until now, the long-term effects of lead exposure were unknown due to a lack of research, said Dunedin Study associate director Professor Terrie Moffitt, of Duke University.

‘‘In the 1980s, the Dunedin Study – guided by Professor Phil Silva – was influential in making New Zealanders aware that lead might be harmful to children,’’ Moffitt explained.

Just over half of the 1000 participants, all born in 1972 or 1973, had a blood-lead test when they were 11 years old. Those with more than 10 micrograms (mcg) of lead per decilitre of blood had IQs more than 4 points lower than their peers with less lead by the age of 38.

The same group also had lower IQs when aged 38 than they had done as children.

Moffitt said the data came from an era when high levels of lead were viewed as normal, and not dangerous, for children.

Lead is a powerful neurotoxin that can build up in children’s bloodstreams and settle into bones, teeth and soft tissue.

According to the research, the highest levels of lead particles were found in roadside soil, due to cars emitting lead-laden exhaust as they drove by.

Children playing outside near roads either inhaled lead-laden dust or swallowed small amounts of leaded soil.

‘‘Lead exposure is very rare in Kiwi children today. But the findings suggest the importance of keeping up our vigilance against other environmental pollutants,’’ she said.

‘‘This research shows how farsighted New Zealand was when the country banned leaded petrol in 1996.’’

The effects of lead on the participants was ‘‘slight, but significant’’, particularly as lead levels here during the 1970s and 1980s were higher than international standards.

The main author of the paper, Duke University PhD candidate Aaron Reuben, said the lower social standing of participants exposed to lead was ‘‘partially, but significantly explained by the loss of IQ’’.

‘‘The cognitive deficits associated with lead persisted for decades and showed in the kinds of occupations people got,’’ he added.

Using the New Zealand socioeconomic index, children with more than 10mcg of lead per decilitre of blood were in jobs of a lower socioeconomic status than their parents.