From PNAS:

Half of US population exposed to adverse lead levels in early childhood

Michael J. McFarland, Matt E. Hauer, and Aaron Reuben

March 7, 2022 | 119 (11) e2118631119 | https://doi.org/10.1073/pnas.2118631119
Vol. 119 | No. 11

Significance
Considerable effort is expended to protect today’s children from lead exposure, but there is little evidence on the harms past lead exposures continue to hold for yesterday’s children, who are victims of what we term legacy lead exposures. We estimate that over 170 million Americans alive today were exposed to high-lead levels in early childhood, several million of whom were exposed to five-plus times the current reference level. Our estimates allow future work to plan for the health needs of these Americans and to inform estimation of the true contributions of lead exposure to population health. We estimate population-level effects on IQ loss and find that lead is responsible for the loss of 824,097,690 IQ points as of 2015.

Abstract
Lead is a developmental neurotoxicant in wide industrial use that was once broadly distributed in the environment. The extent of the US population exposed in early life to high levels of lead is unknown, as are the consequences for population IQ. Serial, cross-sectional blood–lead level (BLL) data from National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of US children aged 1 to 5 (n = 11,616) from 1976 to 1980 to 2015 to 2016 was combined with population estimates from the US Census, the Human Mortality Database, and the United Nations. NHANES and leaded gasoline consumption data were used to estimate BLLs from 1940 to 1975. We estimated the number and proportion of people that fall within seven BLL categories (<4.99; 5 to 0.9.99; 10 to 14.9: 15 to 19.9; 20.24.9; 25 to 29.9; and ≥30 µg/dL), by year and birth cohort, and calculated IQ points lost because of lead exposure. In 2015, over 170 million people (>53%) had BLLs above 5 µg/dL in early life (±2.84 million [80% CI]), over 54 million (>17%) above 15 µg/dL, and over 4.5 million (>1%) above 30 µg/dL (±0.28 million [80% CI]). BLLs greater than 5 µg/dL were nearly universal (>90%) among those born 1951 to 1980, while BLLs were considerably lower than 5 µg/dL among those born since 2001. The average lead-linked loss in cognitive ability was 2.6 IQ points per person as of 2015. This amounted to a total loss of 824,097,690 IQ points, disproportionately endured by those born between 1951 and 1980.

During the peak era of leaded gasoline in the United States, which ran from the late 1960s to the early 1980s, the average blood–lead level (BLL) for the general US population was routinely three to five times higher than the current reference value for clinical concern and case management referral (3.5 micrograms of lead per deciliter of blood) (3–5). Consequently, millions of adults alive today were exposed to high levels of lead as children. While these exposures were deemed harmless at the time, animal studies and epidemiological evidence accrued in the intervening years reveal that such exposures likely disrupted healthy development across multiple organ systems (particularly the brain, bone, and cardiovascular systems), resulting in subtle deficits to important outcomes, such as cognitive ability, fine motor skills, and emotional regulation (6), that may influence the trajectory of a person’s life (e.g., their educational attainment, health, wealth, and happiness). These deficits largely persist across time and, in some cases, worsen (7, 8) and are now hypothesized to put individuals at risk for difficult-to-treat chronic and age-related diseases, including cardiovascular disease and dementia (9–11).

The black line is leaded-gasoline consumption in the U.S. The red line is percent of children age 1-5 in the safe zone of minimal blood lead levels.

One implication of this logic is that rural children should have lost fewer IQ points than city children due to less exposure to leaded gasoline. Is this true?

Another implication is that children born in rural Mexico should be smarter than their younger siblings born in Los Angeles. That seems testable.

Understanding racial disparities in BLLs across the time—particularly Black/White disparities—are an additional, essential next step for legacy lead-related research. Existing work shows that African Americans have disproportionately higher BLLs at the national level (3). There is no indication that these disparities were smaller in the past. For instance, NHANES identified the average BLL among 3- to 5-y-old children between 1976 to 1980 was 14.9 µg/dL for White children and 20.8 µg/dL for Black children (30). Our own calculations using 1976 to 2015 NHANES data consequently show that most Black adults now under age 45 y experienced considerably higher levels of BLLs in early life than their White counterparts (SI Appendix, Fig. S2), not just those born between 1976 and 1980. Future research should evaluate racial disparities in legacy lead exposure pre-1976. This will inform understanding of lead contributions to health disparities across a multitude of outcomes (e.g., kidney disease, coronary heart disease, and dementia).

Blacks born in the rural South should be smarter than blacks born in the big cities. Is this true?

I would think the worst place to be a child would be an auto-intensive area that had freeways very early and little wind to dispel the lead pollution. Off the top of my head, an example of the worst place to grow up would be, say, in the San Fernando Valley in the auto-intensive postwar era, such as … well, me.

So, if you can’t understand why I can’t understand your completely obvious arguments, well, there you go: I lost a massive number of IQ points by growing up next to the Ventura Freeway, which opened when I was 16 months old.

[Comment at Unz.com]