We've heard a lot about Flint, Michigan, 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.  That's the topic of this week's Healthcare Triage.  

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

Jessica Reyes is a leading expert on the effects of lead exposure in children, was also a classmate of mine at Amherst College.  She's now a professor of economics there.  She found that not only did elevated lead levels correspond to low achievement test scores in 3rd and 4th grade, but also the communities where people managed to lower their lead levels in the 1990s saw increased scores in the 2000s.  

For every 1% increase in their proportion of children with a lead level above 10 micrograms per deciliter, the proportion of those achieving an unsatisfactory test score rose 0.2%.  For every 1% increase in the proportion of children with a lead level above 20 micrograms per deciliter, the proportion receiving an unsatisfactory test score rose 1 full 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 in development.  Even so, they're not perfect.  For a long time, research into the effects of lead was complicated by other factors.  Some theorize that those people who clustered together in places where lead levels were high were different, for instance, more socioeconomically disadvantaged, and they were that way in ways that accounted for the negative cognitive effects associated with higher blood lead levels, but in the early 20th century, lead was so ubiquitous in pipes that peoples' 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 the pipes, (?~2:21), faucet, and water heater.

Some savvy 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 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 in order to have a detrimental effect.  A study published in Pediatricsin 2013 examined more than 3,400 children in Rhode Island.  They found that while 32% of children with a low blood lead level fell below the benchmark for reading readiness in Kindergarten, 38% of those with a blood lead level of only 5-9 micrograms per deciliter fell below it.  More than half with a blood lead level of at least 10 micrograms per deciliter fell below that metric.  These relationships held, even after adjusting for demographic and socioeconomic factors.

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

The damage associated with lead exposure goes far beyond schooling, however.  In a paper published in Economic Inquiry last year, Jessica Reyes used data from the National Longitudinal Survey of Youth to examine the effect of lead exposure in early childhood to 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 lead in our gas and we no longer allow lead in our paint, but we're still a long way from eliminating lead from the environment.  We still haven't removed it from our nation's pipes.  It's thought that between 3 million and 6 million miles of pipes leading from water mains to homes contains 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's old and it's not solved as long as those pipes remain in use.

In Flint, the pipes will remain the main concern for some time.  Jessica e-mailed me and I'm quoting her here, "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."  Further, lead is still around in old paint and 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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