The Link Between Lead Exposure and Serial Killers
The “lead-crime hypothesis” suggests that widespread exposure to lead—from things like leaded gasoline, paint and industrial pollution—contributed to higher rates of violent crime in the U.S. in the 20th century.
Proponents of this theory highlight a striking overlap: As lead levels began to climb in America after World War II, the national crime rate also began to tick upward. And when lead levels started to fall in the early 1990s, the national crime rate also began to decline. By the early 2000s, homicide rates alone had plunged by more than 40%.
This is hardly the first time lead has been cast as a culprit. Scholars have linked lead poisoning, also known as “plumbism,” to everything from the fall of the Roman Empire to the ailments that tormented famed German composer Ludwig van Beethoven.
Lead is a naturally occurring heavy metal present in Earth’s crust. But human activities—such as mining, smelting and industrial manufacturing—have dispersed it into the air, soil and water at levels far beyond the natural background concentrations.
Historically, lead was used in a variety of everyday products, from household paint to water pipes. Over the last 60 years or so, however, those uses have been restricted or banned as public health experts have come to recognize the serious risks of lead exposure, particularly among children. Experts now agree there is no safe level of lead for kids.
When ingested or inhaled, lead accumulates in the body and contributes to an array of health issues. In children, lead exposure can cause permanent damage to the still-developing brain and nervous system. It can also cause learning and behavior problems, lower IQ and aggression—traits that, on a population level, might increase the likelihood of criminal behavior in adulthood.
In her book, Fraser examines this theory through the lens of ‘70s and ‘80s serial killers, particularly in the Pacific Northwest. “More lead, more murder,” she writes.
She points out that both Bundy and "Green River Killer" Ridgway grew up near a long-running metal smelter in Tacoma, Wash., where industrial pollution was once so common that the city has its own distinctive smell, known as the “aroma of Tacoma.” Similarly, she notes that Kansas-based serial killer Dennis Rader and California’s Richard Ramirez also grew up around smelting. Lead exposure might even be responsible for London’s infamous Jack the Ripper, she writes, noting the popularity of white lead paint and bituminous coal, which releases lead and other impurities into the air when burned, in the 1800s.
Anecdotal evidence aside, some research appears to support the lead-crime hypothesis, too. A 2019 study found a link between lead exposure and delinquency among boys born between 1990 and 2004 in Rhode Island. Boys with higher blood lead levels were more likely to be suspended from school or sent to detention.
Similarly, a 2020 study conducted in Sweden found that “even a low exposure [to lead] affects long-run outcomes, that boys are more affected and that changes in noncognitive skills explain a sizable share of the impact on crime and human capital.” A 2023 review of studies exploring the link between lead exposure and criminal behavior at the individual level also concluded that an “excess risk for criminal behavior in adulthood exists when an individual is exposed to lead in utero or in the early years of childhood.”
Another study, however, determined that the effects are probably overstated in the scientific literature because of a publication bias toward studies that find a clear link between lead and criminal activity.
“Lead increases crime, but does not explain the majority of the fall in crime observed … in the 20th century,” the researchers write in the 2022 paper. “Additional explanations are needed.”
What Makes a Serial Killer?
Are serial killers born or made? And if they are made, what specific factors contribute to—or even cause—their violent tendencies? Criminologists have been asking these and other related questions for years and, still, “there is no clear-cut answer,” Dr. AJ Marsden, an associate professor and chair of psychology at Beacon College, tells A&E Crime + Investigation. “It is not just nature, nor is it just nurture.”
Many criminologists believe serial killers emerge from a complex blend of biological and environmental factors, many of which remain poorly understood. Scientists have linked certain genetic variations with extremely violent behavior, for example. But these so-called “serial killer genes” alone do not make people become murderers. Instead, they likely interact with other risk factors—such as early exposure to violence, social awkwardness and peer rejection, abuse or neglect, inconsistent parental discipline—to create a dangerous combination.
It’s possible that lead exposure is one of those factors, according to Rod Hoevet, an assistant professor of forensic psychology at Maryville University in St. Louis, who calls it an “interesting theory.”
“We’ve long known that toxic elements, including lead, create all sorts of problems,” he tells A&E Crime + Investigation. “It tracks, at least conceptually, that lead exposure could play a role in the development of a psychopath or serial killer.”
However, he adds, this explanation also raises more questions. Chief among them: Why does lead exposure push some people toward a dark, violent path, but not others? Only additional research will be able to someday answer that question.
“Most people want to believe that psychopaths are just born bad, as if they have some genetic combination that made them that way,” Hoevet says. “In reality, this issue—and the issue of violent crime in general—is much more complex than we like to think.”
