What the Science Says About Long-Term Damage From Lead

The following originally appeared on The Upshot (copyright 2016, The New York Times Company).

Many eyes are now focused on Flint, Mich., where government failures have resulted in elevated lead levels in the city’s drinking water. But the effects on Flint’s residents, particularly its children, may not show up until long after the cameras have left town.

Lead intoxication or poisoning is somewhat of a misnomer. The levels of lead in the water in Flint in the last year or so will probably not lead to many seizures, hospitalizations or medical events. But doctors still become alarmed when lead levels in the blood reach 5 micrograms per deciliter, or µg/dL.

The percentage of children under age 5 in Flint with lead levels that high has been estimated to have doubled, from 2.4 percent to 4.9 percent, according to recently published work in the American Journal of Public Health. In the areas with the highest levels of lead, more than 10 percent of children have now had a blood lead level at least that high.

Jessica Wolpaw Reyes, a leading expert on the effects of lead exposure in children, found that not only did elevated lead levels correspond to low achievement test scores in third and fourth grade, but also that communities where people managed to lower their lead levels in the 1990s saw increased scores in the 2000s.

For every 1 percent increase in the proportion of children with a lead level above 10 µg/dL, the proportion of those achieving an unsatisfactory test score rose 0.2 percent.

And for every 1 percent increase in the proportion of children with a lead level above 20 µg/dL, the proportion achieving an unsatisfactory test score rose 1 percent. In the absence of randomized controlled trials, which would be unethical, these studies are often the best available evidence to show what kind of causal effects lead can have on development.

Even so, they’re not perfect. For a long time, research into the effects of lead was complicated by other factors. Some theorized that those people who clustered together in places where lead levels were high were different (i.e., more socioeconomically disadvantaged) in ways that accounted for the negative cognitive effects associated with higher blood lead levels.

In the early 20th century, lead was so common in pipes that people’s exposure to it was related not to the quality of their housing but to the acidity of their water. More acidic water liberates more lead from pipes, solder, faucets and water heaters.

Economists examined data on a cohort of more than 5,500 World War II soldiers who took the Army General Classification Test, used to assess the intellectual capacity of enlistees. They found that, after controlling for other factors, growing up in a city with water with a pH (a measure of acidity) of 5.5, versus a pH of 6.0, was associated with a five-point drop in the intelligence test. For those who were exposed to more acidic water, and therefore to more lead, there was an even greater negative effect.

Blood lead levels don’t have to reach spectacularly high levels in children to have a detrimental effect. A study published in Pediatrics in 2013 examined more than 3,400 children in Rhode Island. Researchers found that while 32 percent of children with a low lead level in their blood (0 to 4 µg/dL) fell below the benchmark for reading readiness in kindergarten, 38 percent of those with a blood lead level of 5 to 9 µg/dL fell below it. More than half with a blood lead level of at least 10 µg/dL fell below it. These relationships held even after adjusting for demographic and socioeconomic factors.

Similar work in Connecticut showed that even lead levels between 3 and 4 µg/dL are associated with reduced reading scores, and levels between 4 and 5 µg/dL are associated with reduced math scores. Levels as low as 4 µg/dL were linked to higher chances of being classified as learning disabled in elementary school.

The damage associated with lead exposure goes far beyond schooling. In a paper published in Economic Inquiry last year, Ms. Reyes used data from the National Longitudinal Survey of Youth to examine the possible link between lead exposure in early childhood and later behavioral outcomes. She found that, even after controlling for other factors, high blood lead levels were associated with increased oppositional, hyperactive and bullying behaviors in children.

Teenagers who had high lead levels in childhood were more likely to have had sex by 13, be pregnant by age 17 and smoke or drink while in their early teens. There is even some evidence of a connection to crime.

We no longer allow leaded gasoline, and we no longer allow lead in our paint. But there’s still a long way to go. It’s thought that between 3 million and 6 million miles of pipe leading from water mains to homes contain lead. If water isn’t treated properly, it can corrode those pipes enough to free up the lead. That’s what happened in Flint; it’s also what happened with the World War II enlistees. This problem is old, and it won’t be solved as long as those pipes remain in use.

In Flint, the pipes will remain the main concern for some time. Ms. Reyes emailed me: “Once the lead has been mobilized from the pipes, it’s not so easy to put it back: Lead may continue leaching into the water for some time. Further, water filters have finite capacity, and filters dealing with heavily contaminated water may need to be changed more often than every three months.”

Moreover, too much lead is still around in old paint in deteriorating housing. It’s still in the soil from when lead was commonly airborne from exhaust. Until we solve the lead problem for good, we may be condemning children to a lifetime of problems. Flint is just the latest example.


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