Figure | Pixabay
Source | Research Circle (ID:keyanquan)
Written by | Wei Xiao
In 1923, leaded gasoline, which could improve the efficiency of automobile engines, was introduced and quickly became popular around the world. In the United States, leaded gasoline peaked in sales in the 1970s, but it also emitted large amounts of lead into the air and the environment through the exhaust of automobiles. Lead contamination can not only cause heart disease, cancer and stroke, but also damage the human brain and reduce cognitive abilities, which children are particularly sensitive to. A new study published March 7 in the Proceedings of the National Academy of Sciences (PNAS) shows that more than half of Americans now experience excessive blood lead levels in early childhood, with millions of them having more than five times the level of blood lead in childhood. This led to impaired cognitive abilities and a decline in IQ, and pulled the average IQ of all Americans down by nearly 3 points. Some middle-aged Americans born in the 1960s and 1970s even dropped their IQ by 6 to 7 points.
The birth of toxic fuels
At the beginning of the last century, the American Ford Company realized the assembly line mass production of automobiles, and driving travel gradually became a daily routine. In 1923, Thomas Midgley Jr., a chemist working at General Motors in the United States, successfully added lead (tetraethyl lead) to gasoline. This improved the operational efficiency of the car engine, which brought great economic benefits to the company, and leaded gasoline (then known as Ethyl) was quickly promoted.
Posters promoting leaded gasoline | dok1, CC BY 2.0
The United States thus became a "nation on wheels," and the price came with it. The lead in leaded gasoline will enter the atmospheric environment with the exhaust of the car, it can enter the human body through breathing, and even penetrate the blood-brain barrier to invade the central nervous system and harm the brain. This toxic fuel not only caused multiple deaths from poisoning of refinery workers, but also caused the rate of lead poisoning among children in the United States in the 1960s to climb to a staggering 85%. But manufacturers have insisted that their products are non-toxic and harmless.
Turning this around was the American geochemist Clair Cameron Patterson. He was exposed to lead contamination during sampling since the 1940s and spent the rest of his research career with his colleagues. They found that the amount of lead in the snow in modern Greenland increased hundreds of times more than 100 years ago, and the amount of lead in modern human bones was 700 to 1200 times that of Peruvians 1600 years ago. Under the impetus of all parties, the U.S. Congress passed the Clean Air Act in 1970, which began to limit exhaust emissions from motor vehicles. Automakers began designing and producing unleaded gasoline engines in large numbers. In 1996, the United States stopped selling leaded gasoline, and the blood lead content of Americans fell sharply, reaching 80%.
But the consequences of leaded gasoline don't end there, leaving a lasting mark on generations or even generations. A new study from PNAS shows that 170 million Americans currently have more lead in their blood in early childhood than the warning value. According to estimates, the cognitive damage caused by lead has reduced the per capita IQ of the United States by 2.6 points.
More lead, less intelligence
The new study used blood-lead level data from nearly 12,000 young children collected by the National Health and Nutrition Survey (NHANES) from 1976 to 2016, combined with demographic and U.S. lead gasoline consumption data to estimate blood lead levels among children aged 1-5 years in the United States between 1940 and 2015.
Blood lead levels are one of the important indicators for assessing whether a child is contaminated with lead. The U.S. Centers for Disease Control and Prevention (CDC) introduced the pediatric blood lead reference value in 2012 based on NHANES census data, defining it as 5 micrograms per dL (μg/dL), which was downgraded to 3.5 micrograms/dL in 2021. Reference values are primarily used to measure whether children's blood lead levels are high and whether their exposure to lead requires the vigilance and intervention of parents, doctors, or the community. The researchers' calculations show that only 131 million of the current 318 million Americans have blood lead concentrations below 5 μg/dL in childhood; Americans who exceed the standard make up the majority of the country's population, accounting for 54%. In this group, nearly 100 million people have blood lead values in early childhood exceeding 10 μg/dL — which meets the lead poisoning standards defined by authorities such as the American Academy of Pediatrics — and about 10 million people have blood lead values in early childhood that exceed 25 μg/dL, which is 7 times the current reference value.
Among the American population, middle-aged people aged 40 to 50 have the most severe lead exposure in early childhood| thesis
Leaded gasoline consumption in the United States rose rapidly in the early 1960s and peaked in the 1970s. The researchers found that nearly every American born in both decades was poisoned by lead-laden car exhaust — the paper showed that 100 percent of U.S. young children had blood lead concentrations of more than 5 μg/dL between 1966 and 1975. Americans born during this time period are now middle-aged, with at least 70 percent of them having blood lead values above 15 g/dL in early childhood, and 7 percent having blood lead values above 30 g/dL. The latter is a rather dangerous number. When blood lead concentrations enter the range of 25 to 60 micrograms/dL, neuropsychiatric effects such as delayed response, irritability, and inattention may occur, as well as slowing of motor nerve conduction and headache.
From 1940 to 2015, the relationship between leaded gasoline consumption in the United States (black line) and the proportion of blood lead in young children that did not exceed the standard (red line) (solid line is actual data, dotted line is estimated data) | thesis
"I was really shocked," said Michael McFarland, a paper's first and corresponding author and associate professor of sociology at Florida State University, "and even if I'm ready, I'm still shocked by the numbers." ”
Even more surprising is the effect of lead on intelligence. Using international standards for IQ impairment caused by different levels of lead exposure in children, the authors estimated cognitive impairment in the United States at different levels of lead exposure, and found that lead exposure in early childhood affected the IQ of Americans to varying degrees, with per capita IQ values dropping by 2.6 points. In the worst case scenario, people born in the mid-to-late 1960s could have their IQ drop by nearly 6 points. In 3 million people with blood lead concentrations above 30 g/dL in early childhood, IQ values may be reduced by more than 7 points.
For most people, the impact of a few points lowering the IQ value may be negligible. But the authors note that this change is enough to make people with lower-than-average cognitive abilities (IQ). IQ and the cognitive abilities it represents can predict a person's educational achievement and health wealth status, and can also predict to some extent how happy they will be. So on an individual level, even a small amount of IQ loss can have a meaningful impact on life.
Influence a generation
Thankfully, since 1980, blood lead concentrations in young children in the United States have begun to decline dramatically. The researchers pointed out that after 2000, the blood lead value greater than 5 g/dL of the population has become rare in the young group of the United States, and the proportion has dropped from 6% in 2001 to 2005 to 1% in 2011-2015. But lead pollution, which has been experienced over the past few decades, will continue to leave its mark on the U.S. population for the foreseeable future.
It is predicted that by 2030, more than 40% of Americans will still have blood lead concentrations above 5 g/dL in childhood, and more than 20% will have experienced lead poisoning (blood lead concentrations greater than 10 g/dL) in early childhood. And this will continue to drive down the IQ of Americans, with IQ values per capita or dropping by 2.03 points.
"Once lead is inhaled, ingested or enters the digestive tract through drinking water, it can enter the bloodstream." Aaron Reuben, a co-author and a doctoral student in clinical psychology at Duke University in the United States, said, "Millions of us have a history of lead exposure, which is not like you are healthy after a car accident when your wounds heal." This is a completely different kind of physical damage. ”
Next, the researchers hope to analyze the long-term effects of former lead exposure on brain health in older adults. Previous studies have found that adults with high lead exposure in childhood may also age their brains faster.
Thomas Mitchley Jr., who created leaded gasoline, later invented Freon, a refrigerant that was once widely used. Decades later, Freon's role as the "Ozone Killer" was discovered and banned by countries around the world in 1996. Mitchley obtained hundreds of patents for inventions in his lifetime, but because of these two inventions, he was evaluated by later media as "a person who brought environmental disasters with his own strength". The talented chemist was elected president of the American Chemical Society in 1944, but died of his own invention the same year: he suffered from polio in his later years, was paralyzed and invented a pulley device to help him get out of bed, and was accidentally strangled by one of the ropes.
In July 2021, the Algerian government in North Africa announced the suspension of leaded gasoline at all gas stations in the country. Since then, the world has officially got rid of leaded gasoline (Note: The General Office of the State Council of the Mainland issued a document in February 1998 stipulating that from July 1, 2000, all gas stations in the country will stop selling leaded gasoline for vehicles, and all cars will stop using leaded gasoline). But lead will continue to coexist with us in aviation fuels, car batteries, radiation-protected materials and building materials.
bibliography
Thesis information
Half of US population exposed to adverse lead levels in early childhood. Michael J. McFarland, Matt E. Hauer and Aaron Reuben. PNAS. March 7, 2022. https://doi.org/10.1073/pnas.2118631119
Other References:
[1] https://www.eurekalert.org/news-releases/945202
[2]https://www.bbc.com/zhongwen/simp/world-58408671
[3]https://www.cdc.gov/nceh/lead/prevention/blood-lead-levels.htm
[4]https://www.eia.gov/energyexplained/gasoline/gasoline-and-the-environment-leaded-gasoline.php
[5]https://en.wikipedia.org/wiki/Thomas_Midgley_Jr.
[6]https://en.wikipedia.org/wiki/Clair_Cameron_Patterson
This article is authorized to be reproduced from the scientific research circle (ID: keyanquan), if you need to reprint for a second time, please contact the original author.