Leaded fuel might be a thing of the past, but a new report from The World Bank reveals the chemical's toxic legacy continues to take a toll worldwide.

What's worse, the ongoing harmful impacts of lead exposure are far greater than we thought, especially in low- and middle-income countries (LMICs) where lead contamination is more common in food, soils, paint, battery recycling, metal mining, and agricultural products.

We've been aware of the dangers of lead since Ancient Rome, when it was known to cause neurological damage and even death at high levels. But while acute lead poisoning is certainly something to avoid, even very low levels of regular lead exposure can have chronic detrimental effects.

These include cardiovascular disease in adults, and neuropsychological problems – including lower IQ scores and increased behavioral issues – in children.

In the 20th century, leaded fuels were the main source of exposure. The UN began a campaign to phase them out in 2002, and by 2021 they were officially off the market.

While this international effort has significantly reduced blood lead levels across the world, a recent modelling study by environmental specialists Bjorn Larsen and Ernesto Sánchez-Triana shows the heavy burden of lead exposure is far from lifted.

Conservative estimates suggest that in 2019, 5.5 million adults died from cardiovascular disease related to lead exposure – that's six times higher than previously estimated. The researchers also estimated that in 2019, 765 million IQ points were lost from the population of children aged 5 or younger, as a result of exposure to lead.

These impacts were greatest in LMICs, where 95 percent of the total global IQ in young children was lost, and 90 percent of the cardiovascular disease deaths occurred.

IQ losses in these countries were nearly 80 percent higher than previously thought.

"The highest cost of IQ loss as a share of GDP [gross domestic product] was in low-income countries and sub-Saharan Africa due to a combination of high blood lead levels and high birth rates," Larsen and Sánchez-Triana write.

The LMICs of Europe and central Asia experienced the greatest impacts of cardiovascular disease mortality from lead exposure.

"The high cost and mortality rate is due to the high susceptibility to cardiovascular disease and cardiovascular mortality in these countries' aging populations," Larsen and Sánchez-Triana say, "whereas the main reason for the low cardiovascular disease mortality rate in sub-Saharan Africa is a young population and low baseline cardiovascular disease rate."

The global cost of lead exposure was US$6 trillion in 2019 – around 6.9 percent of global GDP. Of this total amount, 77 percent was due to the welfare cost of cardiovascular disease mortality, and 23 percent was the estimated present value of future income losses from IQ loss.

"The estimate of the global health burden of lead exposure in this study places lead exposure as an environmental risk factor at par with PM2.5 ambient and household air pollution combined, and ahead of unsafe household drinking water, sanitation, and handwashing," write Larsen and Sánchez-Triana.

The authors say more comprehensive national blood lead level measurements are needed worldwide, and that it's important for nations to identify and remove sources of lead exposure. They also note that the global health effects and costs of other chemicals need to be quantified in similar ways.

The research was published in The Lancet Planetary Health.