▎ WuXi AppTec content team editor
In 1923, a "small change" in the automobile manufacturing industry had a profound impact in the century that followed.
At that time, the car engine often had a "knocking" phenomenon, causing the power to drop. An American engineer found that adding tetraethyl lead to gasoline was effective in avoiding this problem. As a result, from 1923, leaded gasoline entered the historical stage and gradually spread to the world. But with the spread of leaded gasoline, a health catastrophe spread and still leaves a clear mark today.
The multiple harms of lead to human health have long been confirmed by a large number of studies. Lead enters the atmosphere, soil and water sources with car exhaust. When this element enters the human body through the respiratory or digestive tract, it increases the risk of many diseases such as cardiovascular disease. What's more, lead is also neurotoxic, and at any point in life, there is no safe intake of lead — as long as it is ingested, it can cause harm. Among them, young children are extremely sensitive to the consequences of lead hindering brain development and reducing cognitive ability.
Image credit: 123RF
"Once lead is inhaled in the form of dust, or as water is ingested by the body, it can enter the bloodstream," said Aaron Reuben, one of the authors of the paper and a doctoral student at Duke University. The blood-brain barrier blocks a large number of toxins and pathogens, but it is not enough to block all harmful substances. ”
Finally, at the end of the 20th century and the beginning of this century, countries began to ban the use of leaded gasoline, but the harm of lead to generations has long been engraved in their bodies.
Now, a study published in the Proceedings of the National Academy of Sciences has looked at how lead in gasoline affects American health. The findings are striking: About half (170 million) of Americans today were exposed to high concentrations of lead in childhood, with high blood lead levels, and this group of people has experienced a cumulative IQ decline of more than 800 million due to lead-bearing exhaust. In other words, the equivalent of the average IQ value of all Americans today has been pulled down by 2.6.
To analyze how leaded gasoline can cause long-term health effects, the research team employed a relatively simple research strategy. They collected sets of publicly available information, including data on blood lead concentrations of U.S. children over time, leaded gasoline use, and the U.S. population, and calculated the lifetime burden of lead exposure for all Americans in 2015. Subsequently, using the relationship between lead exposure levels and IQ values established by previous studies, the research team deduced the health hazards caused by leaded gasoline in the United States.
Looking back at the history of leaded gasoline in the United States, the use of leaded gasoline rose sharply in the early 1960s, eventually peaking in the 1970s. As a result, those born in the 1960s and 1970s experienced more severe lead exposure during childhood. This is also supported by statistics: the average blood lead level of people born during this period is 3 to 5 times the current clinical warning value (5 μg/dL), and almost all of them exceed this warning value.
▲The ratio of leaded gasoline use (black) to lower blood lead levels in children (red) over time (Image source: Reference[1])
Based on the correspondence between blood lead levels and IQ levels, the team speculated that lead exposure in childhood caused a total iq value drop of 824 million in the United States. Of these, people born in the mid-to-late '60s were the most severely affected: in the worst case, these people may have lost an average of 6 pips of IQ.
If the study also shows a positive side, it is the improvement in lead exposure in the half century. In 1996, the United States banned the use of leaded gasoline. Correspondingly, Americans born in the 21st century have significantly lower blood lead levels and a reduced risk of lead-related health problems.
▲ Blood lead levels in children change with age or time (Image source: Reference[1])
The study focused on the impact of lead in the United States, but in fact, because leaded gasoline was widely used worldwide, lead exposure was undoubtedly a global risk factor in the 20th century, and the findings of this study are also of cautionary and guiding significance for other countries.
In 2021, the United Nations Environment Programme announced that gas stations in Algeria would stop supplying leaded gasoline, which means that after nearly a hundred years, leaded gasoline has completely withdrawn from the historical stage. However, the health hazards posed by lead are not over. Reuben says they next plan to examine how the long-term effects of former lead exposure on their brain health are for older adults.
The emergence of leaded gasoline is a tragedy in the history of modern science and technology. The health hazards it has caused cannot be withdrawn, but for us, only a deep understanding of this history and the science in it can prevent the recurrence of similar tragedies.
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[2] Lead exposure in last century shrunk IQ scores of half of Americans. Retrieved Mar 7th, 2022 from https://www.eurekalert.org/news-releases/945202
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