High levels of lead show less intelligence
Children in New Zealand who were exposed to high levels of lead have grown up to be less intelligent adults than their counterparts who were not as affected, researchers said last week.
The decades-long study published in the Journal Of The American Medical Association (Jama) shows that the effects of lead, a metal and potent neurotoxin, can be long-lasting.
The research involved more than 500 people living in the southeastern city of Dunedin in the 1970s and 1980s, an era when leaded gasoline (petrol) was common and the exhaust from vehicles meant most people were exposed to high levels of lead. New Zealand’s lead levels were consistently higher than international standards during this time.
A full 94% of children in the area had blood-lead levels that were higher than 5 microgrammes per decilitre, the level at which the US Centers for Disease Control and Prevention now recommends a public-health intervention.
On average, kids’ blood level was 11 microgrammes of lead per decilitre — twice today’s warning level. Children with this high amount of lead in their blood were given IQ tests as 38-year-old adults, and their IQ was on average 4.25 points lower than peers who had been exposed to less lead.
This is a “slight but significant” difference” that also affected their ability to gain well-paying jobs, said the study.
“The cognitive deficits associated with lead persisted for decades, and showed in the kinds of occupations people got,” said lead author Aaron Reuben, a researcher at Duke University in North Carolina.
New Zealand eventually banned leaded gasoline in 1996, and it has also been phased out elsewhere in the world. However, experts say there is no safe level of lead exposure, and the recent water crisis in Flint, Michigan — where lead in pipes leeched into drinking water — shows that risks remain.
Researchers say the Dunedin study is particularly useful because it tracked people for four decades. Also, it showed “high blood lead levels were observed among children from all socioeconomic status levels”, allowing a clearer look at the longterm effects of lead exposure.