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How do you measure exposure to lead? The usual—and most accurate—way is a blood test. The problem is that lead disappears from the bloodstream pretty quickly, so this only tells us about lead exposure in the past few months. What if you want to know about lead exposure several years ago?

Well, lead builds up in teeth, so you can take a look at that. For example, if you measure lead levels in the teeth of prisoners locked up for violent crimes, you find that their lead buildup is higher than average. This is useful, but it still doesn’t tell you when the lead exposure occurred.

But what if you could measure lead like tree rings? Then you get this:

Baby teeth from children with autism contain more toxic lead and less of the essential nutrients zinc and manganese, compared to teeth from children without autism, according to an innovative study funded by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health. ….The differences in metal uptake between children with and without autism were especially notable during the months just before and after the children were born. The scientists determined this by using lasers to map the growth rings in baby teeth generated during different developmental periods. The researchers observed higher levels of lead in children with autism throughout development, with the greatest disparity observed during the period following birth.

This is similar to the way lead exposure produces more crime-prone individuals. Basically, lead takes the place of calcium in the brain, which is crucial to normal development. In the autism study, they discovered that lead takes the place of zinc and manganese.

This was a small study. On the bright side, the researchers looked at twins so they could isolate environmental factors. On the not-so-bright side, they only studied 32 pairs of twins. So this study is suggestive, but far from conclusive. For one thing, if lead poisoning really is a factor in autism, then rates of autism should have gone up during the 50s to the late 70s, and then declined since then. That hasn’t been the case, though there are all sorts of measurement problems that get in the way here. Or, it might be the case that lead has only a small effect and gets drowned out in the historical data by other things.

But if this turns out to be right, it means that lead poisoning is now implicated in reducing intelligence and increasing the rates of violent behavior, ADHD, and autism. Has one element ever caused so much damage? What does it take for us to make the decision to finally get rid of it once and for all?