Exposure to atmospheric lead during childhood results in lifelong mental health deficits, a 30-year study has found.

Researchers led by Aaron Reuben from Duke University in North Carolina, US, followed a cohort of 579 people born between 1 April 1972 and 31 March 1973, in the small New Zealand city of Dunedin.

The location was chosen as the target for the investigation because during the 1970s it had one of the highest atmospheric lead levels in the world – caused entirely by motor vehicle exhausts. There were no other contributing sources, such as lead pipes or paint.

Levels of lead in the blood were measured when the cohort turned 11, providing a baseline standard. Almost all of them had levels that were above what today is considered concerning enough to warrant clinical attention.

Each of the participants was given a clinical interview at 18, 21, 26, 32 and 38 years of age. The interviews were designed to assess mental health wellbeing in line with what is known as the Big Five Personality Inventory, which measures neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness.{%recommended 6407%}

Other psychopathological assessments, of internalising, externalising, and thought disorder symptoms were also made.

The results of the study, published in the journal JAMA Psychiatry, are believed to represent the largest and longest investigation into the adult effects of childhood blood lead levels (BLLs) ever conducted.

Reuben and colleagues found that the entire exposed cohort showed personality and psychological outcomes that were cause for concern.

“Across nearly three decades of follow-up, childhood BLLs were associated with higher levels of general psychopathology, driven primarily by greater rates of internalising and thought disorder symptoms,” they write.

“Second, childhood BLLs were associated with higher neuroticism, lower agreeableness, and lower conscientiousness.”

The cohort spanned a wide range of economic, social and cultural positions, meaning that many aspects that can influence outcomes – such as poverty or poor education – could be taken into account.

Doing so did not affect the outcome.

“Each of these findings remained significant after adjusting for members’ social class backgrounds, their mothers’ IQs, and their family histories of mental illness,” the authors report.