Prepare to fume.

Leaded gasoline was extensively used as a car fuel in the United States from the 1920s until its phase-out in the 1970s due to its detrimental effects on the environment and human health.

It took years to fully comprehend the toxicity of lead. A recent study brings more concerning news — people who lived in areas with high atmospheric lead levels between 1960 and 1974, a period when leaded gasoline usage was at its peak, are 20% more likely to experience memory issues later in life.

“Research indicates that half of the US population — over 170 million individuals — were exposed to elevated lead levels during early childhood,” stated Maria C. Carrillo, the chief science officer and medical affairs leader at the Alzheimer’s Association.

“This research sheds more light on the toxicity of lead related to brain health in older adults today.”

Lead was initially added to gas in the early 1920s to improve engine performance and prevent a knocking or rattling sound that occurs when fuel burns unevenly in the engine’s cylinders.

It was eventually deemed dangerous to the maturing brains and nervous systems of young children, who experienced developmental, learning and behavioral difficulties.

Adults faced neurological and reproductive issues, and soil and water contamination persisted.

The sale of leaded fuel for on-road vehicles was gradually reduced in the US over two decades, with a full ban taking effect in 1996.

For the new study, University of Toronto researchers mapped historic atmospheric lead levels in the US.

They compared this data to the memory difficulties that more than 600,000 residents 65 and over described from 2012 to 2021. Residents were only included in the analysis if they lived in their birth state.

The study authors calculated that 17% to 22% of people in places with moderate, high or extremely high atmospheric lead levels reported memory problems.

“When I was a child in 1976, our blood carried 15 times more lead than children’s blood today,” said Esme Fuller-Thomson, senior author of the study and director of the Institute for Life Course and Aging at the University of Toronto.

“An astonishing 88% of us had levels higher than 10 micrograms per deciliter, which are now considered dangerously high.”

The researchers — who are presenting their work this week at the Alzheimer’s Association International Conference (AAIC) in Toronto — recommend that those concerned about decades-old lead exposure focus on reducing other dementia risk factors, such as high blood pressure, smoking and loneliness.

Over 6 million Americans have dementia, which gradually destroys memory, concentration and judgment skills. It’s responsible for more than 100,000 deaths each year.

Unfortunately, there’s no easy way to measure long-term lead exposure.

Lead levels in the blood primarily reflect recent or ongoing exposure.

Lead is stored in the bones for significantly longer than in the blood — but that marker presents challenges.

“Some research studies have measured lead in the bone,” Dr. Eric Brown, lead study author, told The Post.

“This is done by using a technology called K-X-ray fluorescence, however, it is not available to the general public and is primarily a research tool, not a clinical tool.”

What’s more, leaded gas is still used in some aircraft and race cars — and lead pipes and paint remain a significant public health concern in many areas.

A separate study shared at AAIC revealed that lead exposure — even at low levels — can contribute to the accumulation of abnormal tau and amyloid beta, proteins associated with Alzheimer’s disease, in brain cells.

And finally, another AAIC study found that older adults living about 3 miles from a lead-releasing facility — such as glass, ready-mixed concrete or computer and electronics manufacturers — face greater odds of memory and thinking problems than those living farther away.

“Our results indicate that lead exposure in adulthood could contribute to worse cognitive performance within a few years,” said Kathryn Conlon, senior study author and an associate professor of environmental epidemiology at UC Davis.

“Despite tremendous progress on lead abatement,” she added, “studies have shown there is no safe level of exposure, and half of US children have detectable levels of lead in their blood.”