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Source: Washington Post

Over the past 50 years, after scientists realized that even minute doses of lead can have harmful effects, policymakers have been steadily pushing to eradicate the stuff from the environment. In the United States, no one uses lead-based paint or fills up their cars with leaded gasoline anymore—those were phased out back in the 1970s and 1980s. Lead levels in the air have dropped 92 percent since then. 

By most accounts, this was a savvy investment. There’s ample evidence that lead exposure is extremely damaging for young children. Kids with higher lead levels in their blood tend to act more aggressively and perform more poorly in school. Economists have pegged the value of the leaded gasoline phase-out in the billions or even trillions of dollars. Some criminologists have even argued that the crackdown on lead was a major reason why U.S. crime rates plunged so sharply during the 1990s. 

Yet there’s arguably still more clean-up that could be done. Childhood lead levels have been falling steadily in the past decade, according to the Centers on Disease Control, but there’s room to fall further. There are still older houses with deteriorating lead paint. Soils in urban areas contain lead deposits from old vehicle emissions. And thousands of miles of lead water pipe are still in service around the country. It would take money to strip that lead out. But a new NBER paper from economist Jessica Wolpaw Reyes suggests that even modest reductions can have out-sized benefits.

Reyes took a look at what happened in Massachusetts during the 1990s, when the state took aggressive steps to strip old paint from homes with children under the age of six — and closely monitored students for lead levels. By scrutinizing state standardized test scores before and after the policies were enacted, Reyes found suggestive evidence that lead abatement had a major impact on school performance:

The paper finds that elevated levels of blood lead in early childhood adversely impact standardized test performance, even when controlling for community and school characteristics. The results imply that public health policy that reduced childhood lead levels in the 1990s was responsible for modest but statistically significant improvements in test performance in the 2000s, lowering the share of children scoring unsatisfactory on standardized tests by 1 to 2 percentage points.

It’s worth spelling this out a bit. Massachusetts managed to reduce the fraction of students who scored poorly on their exams by 1 to 2 percentage points. (It appears that the gains largely came from low-income children, who were more likely to have come in contact with lead in the first place.)

That may not sound like a lot, but as Reyes explains, it’s about what one would expect to happen if Massachusetts had managed to close 22 percent of the income gap between low- and middle-income communities in the state. In other words, Massachusetts officials spent just $5 million on lead abatement and saw the same improvement in their schools that they would’ve seen from a sizable push to reduce income inequality.

That’s hardly an argument against reducing income inequality. But it does give a sense for how significant lead-abatement policies can be. Reyes concludes that policymakers in other states “may want to broaden their view” and pay more attention to environmental factors in their attempts to boost school performance. That’s especially true since there’s evidence that even tiny doses of lead can have large marginal effects on small children. (That is, the benefits of reducing lead exposure levels from 10 micrograms per deciliter of blood down to 5 can be even greater than going from 15 to 10.) Over time, a few million dollars on lead abatement can look like quite the bargain.