Study claims leaded petrol lowered the IQ of more than half of Americans via fumes

Historic emissions suggest ‘several million’ people were exposed to five times current levels

Some 117 million Americans were thought to have suffered from leaded petrol use (Getty Images)

As many as half of Americans may have had their IQs lowered after inhaling leaded petrol fumes, a new study has found.

Although small, the drop in intelligence and brain functionality was thought to affect more than half of Americans who grew up in the 1960s and 70s when leaded petrol use was widespread, or about 117 million Americans in all.

People who breathed in exhaust fumes from leaded petrol were found to be somewhere between 2.6 and 5.9 points lower on the IQ scale on average, according to the researchers at Florida’s state university (FSU) and North Carolina’s Duke University.

The study looked at millions of Americans who were potentially exposed to leaded petrol as children, “several million of whom were exposed to five-plus times the current reference level” of lead in the environment, researchers said.

Blood samples taken from children aged between one and five in 1976 to 1980 and from 2015 to 2016 were combined with estimates of historic leaded petrol consumption in the US to figure out how widespread exposure to lead was.

The FSU-Duke study, which was published in the journal PNAS (Proceedings of the National Academy of Sciences of the United States of America) this month, found that the consequences of breathing in leaded petrol were both bad for the brain and long lasting.

The data was put into an established formula that links lead exposure to changes in a person’s IQ, with the FSU-Duke study finding that “170 million Americans alive today were exposed to high-lead levels in early childhood”.

An average drop of 2.6 IQ points was observed across the US, with people born in the mid-to-late 1960s believed to have lost as many as 5.9 points.

Duke University’s Aaron Reuben, an author of the recent study, said levels of leaded petrol use “were very similar across developed countries” before the fuel was banned by the US in 1996 and 2000 in the UK amid concerns for public and environmental health.

According to the University of Michigan. about one in 40 children in the US aged one to five still have unsafe levels of lead in their blood however.

Higher levels of lead in a person’s bloodstream have historically been associated with lower brain functionality, among other health issues including an “impaired cognitive function” and “attention and behavioural problems, another study found last year.