When I was a kid, adults told me that the Roman Empire fell because they used lead plumbing. Lead poisoning made them all go crazy, after which they surrendered the keys to the Visigoth conquerors. It was years before I learned that the grown-ups were pulling my leg. And yet now, in a “truth is stranger than historical fiction” sort of way, I’m discovering that lead pollution is actually an important issue in our modern Rome, the U.S.

The basic reason for lead’s importance comes from biology -- when the heavy metal gets in your body, it wrecks your brain. It lowers your IQ for your entire life. In children, just a little lead in the blood can cause intellectual impairment. Of course, IQ is just one simple, convenient measure of mental ability, but it’s a good bet that whatever lead does to make us dumber also impairs functions like self-control, attention, judgment and rationality.

If this is the case, it stands to reason that lead might play an important role in contributing to crime. Kevin Drum, a writer for Mother Jones, has been unearthing some fairly compelling evidence to this effect. For example, Drum highlights a paper by economist Jessica Reyes and another by environmental researcher Rick Nevin, finding an association between lead and crime. A couple of decades after each state started to reduce leaded gasoline from cars (to comply with the Clean Air Act of 1970), crime in that state started to fall. Those papers were only the beginning, as Drum found -- study after study linked lead to crime.

That means lead abatement could have been responsible for part of the stunning drop in crime that started in the early 1990s, which has defied most explanations. The early ’90s was when the generation born after the Clean Air Act began to come of age. If lead really did cause a substantial piece of the fall in crime, then the Clean Air Act has been saving not just our lives, but a lot of money as well. Crime is estimated to cost the U.S. almost $200 billion a year and it has dropped by about half since its peak.

Of course, that’s not the only way lead abatement might be boosting our economy. A less mentally impaired workforce is probably more productive.

So if even a small amount of lead wreaks havoc on kids’ brains, we should be looking to repeat the feat we accomplished in 1970. Our air has much less lead -- now it’s time to get it out of our water.

Most people by now have heard about the lead crisis in Flint, Michigan, which led President Barack Obama to declare a state of emergency in that city. Like the Romans, we use lots of lead pipes to move our water. Those pipes corrode. And in poor places such as Flint, there is less money to maintain the pipes. Flint’s pipes got corroded by chlorinated river water and protecting against chlorine costs money.

But it isn’t just Flint that’s in danger -- Washington, for example, had a major lead cover-up scandal back in 2004. Philadelphia and New Jersey may be even worse than Flint. Portland, Oregon -- a city renowned for its educated, civic-minded populace and good city government -- recently discovered high levels of lead in its schools’ drinking water. If Portland is in trouble, it’s a good bet that many cities around the country are equally at risk. Yes, this means your own children might be getting their brains subtly damaged by lead from corroded water pipes.

The reason these lead problems go undiscovered goes far beyond poverty. It’s a matter of incentives. Under a 1991 Environmental Protection Agency rule, utility companies are supposed to monitor local water levels for lead and copper. If the heavy metals reach unsafe levels, the company is supposed to take action. Action, of course, is expensive, so the companies have every incentive not to obey the rule, and to let high lead levels go unnoticed.

When incentives fail, dedicated public servants can only fill part of the gap. Wired magazine had a good story recently about a Virginia Tech environmental engineer named Marc Edwards who goes around testing cities’ water for lead, after he was fired by a consulting firm for demanding that Washington test its entire tainted water supply. People like this are doing heroic work, but without a change in the incentive system, they will not be enough.

And note that I haven’t even talked about the issue of lead paint in soil, which is enormous in their own right. If you live in a house that was painted before 1978 and it’s been sanded, scraped and repainted, there might be too much lead in the soil where you walk, your pets frolic and your kids play.

What we really need is a better system. The EPA could send independent inspectors to monitor lead levels and impose harsh penalties on utility companies that fail their tests. In addition, a permit system might be used to encourage lead abatement as we do for acid rain. Strong action at the national level can dramatically reduce the lead in our water, saving our children’s brains. We may not be facing the fall of Rome just yet, but eliminating lead is one of the easiest ways to make durable improvements in our economy and society.

By Noah Smith

Noah Smith is an assistant professor of finance at Stony Brook University and a freelance writer for a number of finance and business publications. He maintains a personal blog called Noahpinion. -- Ed.

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