“Lead damages brain health. We know what it does,” said study co-author Aaron Reuben, a graduate student in clinical psychology at Duke University. “What we didn’t know until this study was, how long do those effects last? … There’s no reason to believe they ever go away.”

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Public health officials have repeatedly said that there is no safe level of lead in a child’s blood and that lead exposure can seriously affect the IQ and attention span of children, as well as cause other problems. But the new study adds another layer of evidence to what many scientists have long suspected — that environmental exposures to lead not only risk an array of physical, behavioral and cognitive problems but can change the very trajectory of a child’s life.

It also raises questions about how best to respond to catastrophes such as the water crisis in Flint, Mich., in which thousands of young children were exposed for months to lead-tainted water. Although many of those children are eligible for a range of interventions, including nutritional and educational programs, Reuben and his co-authors note that short-lived public responses may not be enough given the potential lifelong effects.

“The thing that surprised me is that the impairment you experience once exposed to lead doesn’t go away,” Reuben said. “Even mild cognitive impairment really seemed to have a knock-on effect to the social trajectories people’s lives took. We know from other studies that even small changes in IQ can have large implications for earnings potential and wealth over time.”

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Flint is not New Zealand, of course. And the 1970s were a different era for widespread lead exposures. At the time, for instance, New Zealand had among the highest lead-in-gasoline levels in the developed world, meaning children at all levels of society, rich and poor, were likely to be exposed through emissions into the air.

“This cohort in New Zealand, unlike the United States, itself didn’t have a correlation with lead levels and socioeconomic status at the beginning. It was a much more uniform population, a homogeneous population racially, socioeconomically,” said Maitreyi Mazumdar, an assistant professor of neurology at Harvard Medical School, who was not involved in the study.

That meant the correlation between lead and long-term cognitive and socioeconomic consequences was much clearer, she said. In studies in the United States and elsewhere, she noted, it has been difficult to separate out the effects of lead from the effects of poverty, given that lead exposures tend to be more prevalent in poor communities.

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The latest research “underscores the story of lead is not over,” she said, adding that although lead has long been banned in gasoline, paint and most plumbing fixtures, plenty of threats remain in the United States and particularly in other parts of the world. “This is still a continuing story. There are health effects we need to prepare for.”

The study has clear limitations. The children growing up in 1970s New Zealand likely experienced ongoing lead exposures during childhood, mainly from emissions in the air. The way that affected them over an extended period could differ from the consequences of relatively short but severe exposures, as happened in Flint.

Researchers also had only a snapshot of lead levels from the tests taken when the children were 11, and there was no way to measure their cumulative lead exposures by the time they were 38, Reuben said. In addition, the conclusions were based on only one group of primarily white children in one city, so generalizing the findings to other populations and settings could be problematic.

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Still, the findings were stark enough to prompt David C. Bellinger, a professor of environmental health at Harvard, to write in an accompanying JAMA editorial that much more needs to be done to eliminate lead exposures in every form. That includes more stringent lead-abatement efforts, more rigorous screening, more determined cleanup of the “vast reservoirs of lead that remain” in the environment, in everything from paint to plumbing, he said. Bellinger also argues for finding educational interventions to help improve outcomes for lead-exposed children, in the hope that their futures won’t be defined by the environmental threats of their childhood.

“Until these steps are taken, problems such as those in Flint are almost certain to occur periodically,” Bellinger warns. “Children will continue to experience the greatest harm from lead exposure, and disadvantaged children will bear a disproportionate share of the burden.”