More than half of the people who were perpetrators or victims of gun violence in Milwaukee in recent years had elevated blood lead levels as children, according to a study released Friday by the University of Wisconsin-Milwaukee.

The study of nearly 90,000 residents, conducted at the University's Joseph J. Zilber School of Public Health, suggests a link between early childhood lead exposure and gun violence in later years.

Lindsay R. Emer, the study's lead author, said it was conducted using public health, education and criminal justice data.

After reviewing the records of 89,129 people who were born in Milwaukee between June 1, 1986, and Dec. 31, 2003, and given blood lead tests before the age of 6, Emer and other researchers found a correlation between elevated blood lead levels and the risk of being involved in gun violence.

Emer said that while the study was not able to definitively prove cause and effect, the link is striking:

According to their findings, 56% of the shooters and 51% of the victims were found to have blood lead levels equal to or greater than the recommended limit of lead exposure of 5 micrograms per deciliter.

The study

The study originated from a dissertation Emer started she while still a doctoral student at UWM.

Since then, she has earned and defended her Ph.D., worked with the Medical College of Wisconsin and is currently a senior research consultant at the National Center for State Court.

The publication of her study, "Association of childhood blood lead levels with firearm violence perpetration and victimization in Milwaukee," is a culmination of years of work.

Emer said she and other researchers gathered their sample size from people who had consistent Milwaukee addresses for their lead test(s) and were documented in the Milwaukee Public Schools system.

They then compared that group with those who were listed as gun violence victims or perpetrators in Milwaukee Homicide Review Commission data. The commission — created by Mallory O'Brien, also listed as an author in this study — gathered data only between 2005 and 2015.

Because of that, Emer said, she chose birth years from 1986 to 2003 because that would make her sample size young adults by the time the review commission was active.

During those years, deteriorating lead paint and household dust were contaminating children, many of whom were more likely to be poor and/or African American.

RELATED:A battle is brewing between Milwaukee and paint industry over lead poisoning of Milwaukee children

Those same racial and socioeconomic disparities were reflected in the racial and socioeconomic disparity of people overrepresented in the review commission as perpetrators or victims of gun violence.

The study follows a consistent vein of prior research connecting lead exposure and violence:

Researchers at Harvard University and the University of California Berkeley published a study in 2016 that concluded that cities that used lead water pipes had homicide rates that were 24% higher than cities that did not.

Two researchers published a paper in 2017 for the National Bureau of Economic Research that studied the link between lead exposure and juvenile delinquency and found that as blood lead levels increased, so did the probability of suspension from school.

That trend is highlighted by this latest study, which concluded, "In Milwaukee, during a period of high lead exposures, childhood levels may have substantially contributed to adult firearm violence."

The implications

This more localized study comes as Milwaukee children continue to experience elevated blood lead levels; an average of 3,000 of the 25,000 Milwaukee children tested for lead each year have elevated levels, the Journal Sentinel has reported.

Childhood lead exposure has been proven to reduce IQ scores and increase attention disorders, both of which put children at risk for increased delinquency.

Bruce Lanphear, professor of health sciences and epidemiology at Simon Fraser University in British Columbia, described lead exposure in children as insidious.

"If it's not overt poison, one of the challenges is you don't really see acute symptoms," he said. "You do see symptoms more like acting-out type behaviors: ADHD type behaviors, problems with schoolwork, risk-taking behaviors, impulsive behaviors in kids, delinquency in kids."

Those behavioral challenges, he noted, don't just disappear once someone turns 18.

"Conduct disorder in children matures into delinquent and sometimes even criminal behavior," he said.

Robert Miranda, a spokesperson for the Freshwater for Life Act Coalition, said the study confirms a long line of research that has several implications.

For example, he said the city should consider testing prisoners' blood lead levels and seeing if certain treatments targeting the effects of lead exposure can help reduce recidivism.

Moreover, he said more conclusive evidence of what lead poisoning can do should encourage the city to move urgently — more urgently, he said, than what its current plan calls for.

"Replacing 1,000 lead service lines a year isn't going to cut it," he said. "The damage done by lead poisoning is irreversible. So those children who have been harmed today are pretty much damaged for the rest of their lives.

"What we need to get focused on is treating those children who have been harmed today, but to remove this toxic poison from our environment completely so more children can be saved."

Lead abatement in Milwaukee

Earlier this month, the city received a grant of nearly $6 million for lead abatement, in addition to the $21 million Mayor Tom Barrett earmarked in his 2020 budget.

At recent budget hearings, residents have demanded that more funding go toward speeding up the city's process on lead abatement.

Last month, lead-free activists at Hephatha Lutheran Church gathered pledges from local politicians to support a $240,000 program to provide lead-education kits to new mothers in the hospital.

Supporters of that pledge included Aldermen Ashanti Hamilton, Russell Stamper, Jose Perez, Nik Kovac and Mark Borkowski and Milwaukee Health Commissioner Jeanette Kowalik.

Contact Talis Shelbourne at (414) 223-5261 or tshelbourn@jrn.com. Follow her on Twitter at @talisseer and Facebook at @talisseer.

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