Environmentalists are proud to display the scalps of industrial polluters. One of their most gratifying achievements has been ridding the environment of lead-based pollutants, particularly tetraethyllead, an additive in gasoline to inhibit engine knock. Tetraethyllead production peaked in the 1960s, and then was voluntarily phased out in the 1980s, with a complete ban on leaded gas in the 1990s.
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The controversy over tetraethyllead usage came to a head in 1976 with data from a NHANES national survey which showed elevated levels of lead in the blood of preschool children. The data was concerning to the public and accelerated the phase out of leaded gas by industry. By 1990, lead level in preschool children had decreased by a factor of four from its earlier level in 1976 (see figure below).
Image: Public domain (Source: Blood Lead Levels in U.S. Children Ages 1–11 Years, 1976–2016; Figure 1, page 4)
There appears to be a link between lead in the environment and lead in children’s blood. Beyond that, it gets sketchier. A link between the measured blood lead level and a drop in IQ is weak. The countervailing opinion is that average IQ increased from1950 to 1980. The Flynn effect documented a long-term rise in average scores on IQ tests observed across much of the 20th century, including the period in which leaded gas was sold. It is named after psychologist James Flynn, who documented that people in later generations tended to score higher on the same or comparable intelligence tests than people in earlier generations. A common estimate is roughly 2–3 IQ points per decade over much of the 20th century, with the effect having slowed and even stopped in recent decades.
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Others pounced on the fact that the blood lead of black children was higher than that of white children, and that it accounted for the difference in IQ and academic performance. They are mute, however, in explaining why black IQ and school performance did not rebound with a substantial reduction in the blood lead level of black children by the mid-1990s.
There was always something flimsy in coupling IQ with blood lead, especially at the levels that were being debated. If taken seriously, it implied that the Boomer generation is mentally impaired, which may be true, but not because of lead poisoning.
It is a prime example of the junk science that environmentalists have employed to maintain their chosen narrative. From outlawing DDT to banning CO2 emissions, junk science has been a useful handmaiden for the environmental movement.
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Image generated by ChatGPT.