There is no safe level of lead. The naturally occurring metal is so toxic that the Environmental Protection Agency began banning its use in paint and gasoline in the 1970s, following the lead of other countries. Since then, a growing body of research has confirmed the health effects of lead exposure, including heart and kidney diseases. The effects are particularly pronounced in children. Exposure to lead in the first five years of life has been shown to hinder brain development, stunting a child’s ability to learn, focus, and control their impulses. 

A new study from the World Bank tallies the staggering worldwide toll: 5.5 million deaths from heart diseases because of exposure to lead in 2019 alone. Researchers also found that exposure to lead in children under 5 years old led to a loss of more than 750 million IQ points — a standardized measure of intellectual ability. People in low- and middle-income countries, where blood lead levels are higher on average than in high-income countries, were hit hardest. The overall cost of exposure was $6 trillion in 2019, the equivalent of nearly 7 percent of the world’s economic output.  

“There has been this idea that since the phase out of lead in gasoline [in the 1970s], the problem has more or less been solved,” said Bjorn Larsen, a consultant with the World Bank and lead author of the study. “Our estimate indicates that the health effects and the cost of lead exposure is possibly as large as the health effects and costs of fine particulate ambient air pollution and household air pollution combined. That is enormous.”

The study, published in the journal Lancet Public Health on Monday, relied on blood lead level estimates in a 2019 study that aggregated data sources on health and mortality outcomes worldwide. Larsen and his co-author then used existing research on the effects of lead to calculate IQ loss in children and deaths from cardiovascular disease in adults. They also estimated the economic costs of the loss in IQ and deaths. The findings were “surprising,” Larsen said. 

Grist thanks its sponsors. Become one.

IQ losses were about 80 percent higher and the number of deaths from cardiovascular disease was six times higher than previous estimates. Larsen attributed the difference to improvements in our understanding of the effects of lead exposure and a more comprehensive methodology that better captured how exposure could cause cardiovascular diseases. 

Blood lead levels in American children have dropped dramatically in the last few decades. In the 1970s, kids between the ages of one and five years old were found to have 15 micrograms of lead in each deciliter of blood. That figure dropped to 0.6 micrograms in 2017. But in low and middle income countries the researchers found that the average is still about 4.6 micrograms per deciliter, which Larsen said drove the findings on IQ loss and cardiovascular disease.

There are many factors causing higher levels of blood lead levels in lower-income countries. Lead battery recycling units may contaminate the air, water, or soil in and around population centers. Aluminum pots and pans might be tainted with lead that eventually leaches into food. Leaded paint is also still used in many countries, and lead has been found in phosphate fertilizers, which could be contaminating crops. It’s unclear which of these sources are driving elevated levels of blood in lower-income countries. 

Larsen said that governments and aid organizations should routinely test children to get a better understanding of lead exposure. And that, in turn, could help identify hot spots and potential sources of the toxic metal. 

Grist thanks its sponsors. Become one.

“The understanding of these sources is very incomplete,” said Larsen. “We are decades behind on lead, because it has been a neglected area up until now.”