Lead is a handy metal for making pipes, but unfortunately people didn't grasp its brain-destroying power when American waterworks were constructed a century ago.
Now, new research shows that American cities with lead water pipes had higher murder rates in the first half of the 20th century.
James J. Feigenbaum of Harvard and Christopher Muller of the University of California, Berkeley, report that on average, "cities that used lead water pipes had homicide rates that were twenty-four percent higher than cities that did not."
The paper, which will be published in the journal Explorations in Economic History, builds on a growing body of research linking lead exposure to various criminal behaviors, amounting to a plausible explanation for rising and falling crime rates in the United States over the past several decades. Most of that research to date has focused on lead exposure from air pollution caused by leaded gasoline, not water.
The water crisis in Flint, Michigan brought national attention to the fact that millions of American homes receive water from pipes made from the poisonous metal -- pipes that were installed a century ago. Starting in 2014, the government in Michigan failed to make sure the water wouldn't leach too much lead out of the pipes, eventually resulting in higher blood lead levels in Flint kids.
State officials initially blamed Flint kids' high blood lead on paint chips and dust, which public health experts say are usually the main sources of lead exposure. That fact has always made it difficult to pin lead poisoning on water, even when water systems are caught making mistakes. To this day, the water utility in Washington, D.C. refuses to admit anyone might have ingested dangerous levels of lead from the water during a lead crisis in the early 2000s, even after peer-reviewed research said they had.
Back in the 1920s, before wider use of lead in gasoline, water pipes were a primary source of exposure. Feigenbaum and Muller compiled historical information on pipe materials in 545 cities from 1921 to 1936, and after controlling for a variety of demographic factors, found that "cities that used lead pipes had between 14 and 36 percent higher homicide rates than cities that did not."
How much lead a city's water might contain can change based on the acidity of the water, because more acidic water is more corrosive to pipes, resulting in more dissolved lead and lead flakes flowing through household taps. Flint's water, for instance, became more corrosive when the city started pumping water from the Flint River in 2014, having previously bought treated water from Detroit. The city and state failed to treat the river water with anti-corrosion chemicals.
The city-to-city variations in water chemistry served as a way for Feigenbaum and Muller to further confirm the link between lead pipes and murder. "As the water in a city becomes more acidic," they found, "homicide rates rise accordingly."
As epidemiologists have become more familiar with the dangers of lead, the U.S. government banished it from gasoline, paint and new plumbing materials -- but lead pipes are still carrying water to millions of American homes. The difference is that today, engineers better understand how to reduce leaching from the pipes. Federal law requires water systems to keep the lead beneath a level that would have been considered negligible at the turn of the century.
In an interview, Feigenbaum cautioned that the lead levels in municipal water supplies 100 years ago were much, much higher than they are now, which "makes it hard to extrapolate from our research to what's going on today."
Back then, cities measured lead levels in parts per million, whereas today they're tallied in parts per billion. In some towns in the early 1900s, a single glass of water could contain as much lead as a black market abortion pill, as Werner Troesken reported in his 2006 book The Great Lead Water Pipe Disaster. The dangers of water lead were masked, however, by the overall public health benefits when new waterworks replaced contaminated wells. "Infectious diseases, which killed and sickened people quickly and in easily identifiable ways, often blinded observers to the problem of lead-contaminated water, which undermined adult health more slowly and subtly," Troesken wrote.
Feigenbaum and Muller stressed that they're not trying to say they've proven, once and for all, that lead causes crime -- and that even if it does, it's one cause among many. But they said getting rid of lead pipes is probably a good idea.
"Even if lead removal will not reduce crime, it will remove a dangerous toxin from the environment," the paper says. "Other strategies to reduce crime may not have similarly positive side effects."