When readers of this newsletter think about lead, it is likely that two things come to mind.
The first is Flint, Michigan. In 2014 the city of Flint changed the source of its municipal drinking water in an attempt to save money. Inadequate testing and treatment of the water supply resulted in contaminated water. The contaminants included lead, and by the time action was taken to fix the problem (which didn’t start until 2015), blood lead levels were seriously elevated in children and health problems plagued the city in general. This episode is appalling, an example of incredible environmental injustice and terrible policymaking.
The second reason you may think about lead, as a parent, is that all children in the U.S. are screened for blood levels in early childhood. And if your child’s test returns an elevated blood lead level, it is likely you’ll find yourself taking a serious look at lead sources around your home — water, paint, soil, that weird old bathtub that the neighbors left on their porch. This is time-consuming, potentially expensive, and scary. And it can be hard to figure out a straight answer to how worried you should be and why.
Today’s newsletter is all about those questions: what we know about lead, how much is bad, and what to do about it.
What are the risks of lead?
Lead is toxic. In high concentrations it can cause serious illness and death. Those levels of concentration wouldn’t be a result of household exposures, though. The questions here are about the impacts of lower levels of lead, in particular on brain development.
Much of the work on this subject focuses on exposure in children (who may be evaluated either in childhood or adulthood). A typical example is this paper, published in the New England Journal of Medicine in 1990, which related lead levels in a cohort of children to outcomes at age 18. The authors use lost teeth in primary school as a way to measure lead levels.
They found that kids with higher teeth lead levels had worse school outcomes and performed worse on many cognitive tests. I’ve inserted one of their graphs below. In it, we see the relationship between lead levels and high school graduation rates. Higher lead levels correlate with lower graduation rates.
In this paper, as in much of the literature, it is difficult to separate correlation from causality. Exposure is more common in lower-income children, largely because of worse housing quality, and it is not obvious how much of the association is due to that factor.
We have, however, better evidence of causality from policy changes. A wonderful colleague of mine, Anna Aizer, along with several co-authors, published an excellent paper in 2018 that used data from Rhode Island to address the relationship between lead levels and test scores in school. Rhode Island is unusual in having both consistent childhood lead testing and a change in housing policy regulation that led to significant decreases in lead exposure for children.
Using the change in housing policy, along with data on lead levels and test scores, Anna and her co-authors argue that decreasing lead levels increases test scores. In particular, a 1-unit reduction in blood lead levels led to a decrease of 1 percentage point in the risk of being below proficient in reading and a 0.79 percentage point decrease in such risk in math. These numbers are large (the overall risks are 12% in reading, 16% in math), but they are also striking because the lead levels in the study are not that high to begin with. Only 2% of the children have levels above 10, so most of the variation is in lower levels than what we see in the graph above.
A broad takeaway is that higher lead levels seem to be problematic, and especially affect cognitive functioning. Anna and her co-author Janet Currie also have a later paper where they show higher lead levels causing greater risk of juvenile delinquency.
The follow-on question: When should we worry? Is there a safe level?
What lead level Is too high? Is there a “safe level”?
Historically — I’m talking going back to Roman times and lasting through the mid-20th century — people knew that acute lead poisoning was bad but did not suspect that lower-level exposure was an issue. This changed in the 1960s, when it was discovered that ongoing lead exposure could also be very dangerous, especially for babies, children, and fetuses in utero.
This realization led to significant changes in the 1970s in regulations about lead in household paint and gasoline (it was removed from both). Lead levels dropped in kids.
Over the period from the 1960s on, the “trigger” level to consider a child at high risk for lead has changed. Prior to 1971, the figure was 60 micrograms per deciliter. That is, a child wasn’t flagged as at risk of lead exposure unless their level was above 60. This gradually dropped. In the 1990s, the high-risk level was lowered from 25 mcg/dL to 10. Most recently, in 2010, it was lowered to 5.
This latest change implies that many more kids are screening positive for lead. In the paper about Rhode Island I cited above, only 2% of children had levels over 10, but 17% had levels over 5. This number was even higher (up to 40%) when researchers looked at a single measure rather than an average across several measures.
What is behind this continual lowering?
The main reason for the changes is increasing evidence, like that in Rhode Island, implying that lead exposure matters even at low levels. Another paper, published in the NEJM in 2003, linked average blood lead levels over childhood to IQ test scores. The authors’ data is shown in the graph below. They make the point that IQ looks like it is responsive to lead level changes even at low levels.
Not all of these results are easy to understand. The finding (shared in several papers) that the effect on IQ per unit of lead is larger at low levels than high levels is somewhat puzzling; usually we would expect the effect to be similar or larger at high levels. And most of these papers don’t have an ideal strategy to separate differences across family background from the effect of lead.
However, over many papers we get the general sense that increases in blood lead levels seem problematic over almost any range. This is why the high-risk screening cutoff has changed, but it’s also worth saying that there isn’t anything magic about the screening cutoff we have now. The broad message of “decreasing lead exposure is good across any levels” is probably a more accurate message than “6 is bad, 4 is fine.”
Given this: What to do?
What to do
This is somewhat scary. But on the promising and reassuring side, lead exposure isn’t all or nothing. It builds up over time. So changes that we make — either as individuals or as policy — will impact kids now, not just in some distant future.
The biggest changes in lead exposure for kids will come as a result of policy. There have been huge reductions in lead levels in children as a result of removal of lead in gasoline and paint and from regulations on its use in food production. Lead risks remain higher among lower-income children and children of color, as a result of residual lead paint in older housing stock, possible lead contamination in water, and lead contamination in soil, which may be more significant in urban areas.
So the first point is: lead is still a policy problem, and is still contributing to learning deficits in kids and to inequality. Mobilizing policymakers to (for example) ensure that municipal water supplies are free of lead, consider soil testing, or write better regulations on residual lead paint in housing would be for the good.
But what about as an individual parent or pregnant person?
If you’re pregnant, get screened. Lead passes through the placenta, so there are fetal risks to high lead levels in pregnant women. If you’re pregnant or thinking about getting pregnant, testing your own lead level is likely a good idea (especially if you have known exposure risks). If you have a high lead level, you can look for exposures and lower them, and this will likely help with your baby also.
Deal with it before the testing. The most common lead exposures for kids are household water (more for infants, because of formula), paint chips, and soil. You can test all of these before you have kids, or right now even if you have them. You do not need to wait until your kids are tested for lead to think about these exposures. There are various companies that will do lead testing, and some cities will also help. You can DIY your water testing with resources like this.
A final point. Don’t panic. Yes, there are concerns about lead. However: The reason we test kids for lead and then work to look for exposures is that lead builds up over time. A test showing elevated lead levels is a reason to look for possible exposure sources, precisely because lowering exposure can lower levels in your kids. So be proactive, but don’t panic.
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