May 02, 2025

By Phoebe Cykosky, Staff Editor

“A superpredator is a young juvenile criminal who is so impulsive, so remorseless, that he can kill, rape, maim, without giving it a second thought.”^[1] Or so John J. DiIulio Jr., a Princeton professor and criminologist, thought. The superpredator myth DiIulio sparked had lasting impacts on the juvenile justice system. Had DiIulio looked to other sources, like lead paint, mass incarceration of juveniles could have been prevented.

Understanding the juvenile brain is key to understanding how lead impacts it. The United States Supreme Court even recognizes the differences in youth brain development and criminal culpability.[2] And if an outside force impacts that development, harms can occur imminently or down the road. Research indicates many individuals who are abused early in life turn to criminality in adolescence.^[3] Factors in a child’s environment impact their wellbeing—from family structure to toxins, like lead.

            As the areas within the brain expand, their functions to the child develop as well. The amygdala, part of the limbic system, develops first within juvenile brains.^[4] This area is “responsible for immediate reactions including fear and aggressive behavior.”^[5] The limbic system’s hippocampus development aids in memory and cognitive function.^[6] The anterior cingulate cortex (ACC) provides error processing, conflict monitoring, response selection, and avoidance learning.^[7] The ACC communicates error information from the inferior frontal cortex to motor areas, and the motor areas communicate behavioral plans back to the cortex.^[8] The prefrontal cortex develops later. The prefrontal cortex holds the decision-making and impulse control functions, but because this develops later, juveniles notoriously lack impulse control.^[9]

Lead exposure deteriorates crucial parts of the brain during development, like the prefrontal cortex, ACC, and amygdala. According to the World Health Organization, youth are “particularly vulnerable” to lead’s effects and may suffer “permanent adverse health impacts.”^[10] Likewise, lead exposure impacts the ACC by decreasing its volume.^[11] Lead attacks the ACC and reduces frontal gray matter, leading to difficulties with mood regulation and decision making.^[12] Lead exposure impairs the amygdala and suggests a long lasting but not totally irreversible effect of early exposure.^[13] Researchers used rats split them into two groups: a group experimentally exposed to lead and a group never exposed.[14] The study found that permanent and maternal lead exposure caused three results.^[15] First, lead exposure had no effect on locomotor activity. Second, lead exposure impaired the acquisition phase of the radial maze. Third, lead exposure impaired passive avoidance in the brain.^[16] Further research on rats demonstrates how even low levels of lead destructs important memory functions within the hippocampus.^[17]

            In the 1960s to 80s, lead paint exposed youth to these development abnormalities, and those youth grew into teenagers during the era of increased criminality rates. Lead impacted the United States during the 1900s. In the 1920s, the vehicle industry added lead to gas to aid in vehicle efficiency. In the 1960s and 1970s, manufacturers utilized lead in paint and petroleum gas.^[18] Likewise, individuals in lead-painted homes and around car exhaust were susceptible to lead’s dangerous effects. Lead can still be found in various products, like ceramic glazes, jewelry, toys, lead crystal glassware, and ammunition, but countries began to phase it out in the 1970s.^[19] Blood tests in the 1970s showed high blood-lead levels across the country, which led to the Lead-Based Paint Poisoning Prevention Act of 1971.^[20] The Centers for Disease Control established the Childhood Lead Poisoning Program to combat exposure.^[21] Children received chelation therapy to treat severe lead poisoning when their blood-lead levels were greater than 70 micrograms per deciliter (µg/dL).^[22] Even though lead use in paints ended, the damage had already been done, and the impacts marinated in youth exposed over the subsequent decades.

By the 1980s and 1990s, lead use phased out, but crime rates sprung up.^[23] Young adults had the highest homicide victimization and offending rates during the late 1980s and 1990s.^[24] Teen offending rates (14 to 17 years old) and young adults (18 to 24 years old) increased dramatically in the late 1980s while older age group rates declined.^[25] 1993 peaked criminal homicide behavior, but since then, the young adult category declined to 24.6 offenders per 100,000 by 2008.^[26]

Research already shows how lead affects the brain, but criminologists have conducted studies highlighting the criminality correlation. A long-term study from Cincinnati Children’s Research Horizons connected criminal behavior in adulthood and brain damage from childhood lead exposure.^[27] Lead exposure deteriorated important areas in individuals’ brains, such as regions responsible for “cognition, decision making, impulse control, socially driven behaviors, emotional regulation, and risky behaviors.”^[28] The study followed women, who were children in inner cities between 1979 to 1984, throughout their lives. 78% of the lead-impacted youth were later arrested for crimes.^[29] Adults suffered deficiencies in social behaviors, executive functions, and cognition when lead exposure decreased their brains’ volumes.^[30] A unique 2016 study showed that 20th century cities utilizing lead water pipes had 14–36% higher murder rates compared to cities using iron pipes over a twenty-year span.^[31]

Additionally, lead decreased gray matter more so in men than in women.^[32] In subsequent studies, researchers performed high resolution volumetric magnetic resonance imaging on 157 adults around the age of 20 who were exposed to lead in youth.^[33] Results showed that adults exposed later in childhood to lead had greater loss in gray matter.[34] Male frontal lobes deteriorated more significantly, and the study found that blood lead levels do not fully capture gray matter deterioration.^[35] With the deterioration of these crucial developmental functioning areas, criminal behavior significantly increased.^[36] Further, research in 2016 from St. Louis determined that lead invokes “violent” behavior over time.^[37]

Various ecological studies yield the same results—lead poisoning enables criminal behavior. DiIulio’s narrow-minded approach, however, neglected an entire subsection of what may have led to increased criminality during his time: lead poisoning.

^[1] Priyanka Boghani, They Were Sentenced as “Predators.” Who Were They Really?, PBS (May 2, 2017), https://www.pbs.org/wgbh/frontline/article/they-were-sentenced-as-superpredators-who-were-they-really/.

[2] See Roper v. Simmons, 542 U.S. 551 (2005) (abolishing the juvenile death penalty) and Graham v. Florida, 560 U.S. 48 (2010) (abolishing life without parole for juveniles).

^[3] Boghani, supra note 1.

^[4] Teen Brain: Behavior, Problem Solving, and Decision Making, American Academy of Child & Adolescent Psychiatry (Sept. 2017), https://www.aacap.org/AACAP/Families_and_Youth/Facts_for_Families/FFF-Guide/The-Teen-Brain-Behavior-Problem-Solving-and-Decision-Making-095.aspx.

^[5] Id.

^[6] John Lisman, et. al., Viewpoints: How the Hippocampus Contributes to Memory, Navigation, and Cognition, 11 Nat Neurosci 1434–1447 (Oct. 26, 2017), https://pmc.ncbi.nlm.nih.gov/articles/PMC5943637/.

^[7] Eyal Aharoni, et. al., Neuroprediction of Future Arrest, 110 PNAS 6223–6228 (Mar. 27, 2013), https://www.pnas.org/doi/10.1073/pnas.1219302110.

^[8] CB Holroyd & MGH Coles, The neural basis of human error processing: Reinforcement learning, dopamine, and the error-related negativity, 109 Psychol Rev. 679–709 (2002).

^[9] SOS Project, Adolescent Brain Development Section 1.2, Coalition for Juvenile Justice https://www.juvjustice.org/our-work/safety-opportunity-and-success-project/national-standards/section-i-principles-respondin-10.

^[10] World Health Organization, Lead Poisoning, WHO (Sept. 27, 2024), https://www.who.int/news-room/fact-sheets/detail/lead-poisoning-and-health.

^[11] Kim Cecil, et. al., Decreased Brain Volume in Adults with Childhood Lead Exposure, 5 PLoS Med. 112 (May 27, 2008), https://pmc.ncbi.nlm.nih.gov/articles/PMC2689675/.

^[12] Id.

^[13] C Munoz, et. al., Neuronal Depletion of the Amygdala Resembles the Learning Deficits Induced by Low Level Lead Exposure in Rats, 11 Neurotoxicol Teratol 257–64 (May–June 1989), https://pubmed.ncbi.nlm.nih.gov/2755422/.

[14] Id.

^[15] Id.

^[16] Id.

^[17] C Munoz, et. al., Significance of Hippocampal Dysfunction in Low Level Lead Exposure of Rats, 10 Neurotoxicol Teratol 245–53 (May–June 1988), https://pubmed.ncbi.nlm.nih.gov/3211103/.

^[18] Hannah Ritchie, How the World Eliminated Lead from Gasoline, Our World in Data (Jan. 11, 2022), https://ourworldindata.org/leaded-gasoline-phase-out.

^[19]World Health Organization, supra note 10.

^[20] Paul B. Allwood, et. al., A Historical Perspective on the CDC Childhood Lead Poisoning Prevention Program, Amer. J. Pub. Health (Sept. 30, 2022), https://ajph.aphapublications.org/doi/10.2105/AJPH.2022.307005.

^[21] Id.

^[22] Id.

^[23] Alexia Cooper & Erica L. Smith, Homicide Trends in the United States, U.S. Dept. of Just. (Nov. 2011), https://bjs.ojp.gov/content/pub/pdf/htus8008.pdf.

^[24] Id.

^[25] Id.

^[26] Id.

^[27] Travis J. Beckwith, et. al., Criminal Arrests Associated with Reduced Regional Brain Volumes in an Adult Population with Documented Childhood Lead Exposure, 201 Env’t. Research (Oct. 2021), https://www.sciencedirect.com/science/article/abs/pii/S0013935121008537; see also Kim Cecil, Long-Term Study Documents Link Between Adult Crime and Brain Damage from Childhood Lead Exposure, Cincinnati Children’s Research Horizons (Oct. 25, 2021), https://scienceblog.cincinnatichildrens.org/long-term-study-documents-link-between-adult-crime-and-brain-damage-from-childhood-lead-exposure/.

^[28] Id.

^[29] Cecil, supra note 11.

^[30] Id.

^[31] James J. Feigenbaum & Christopher Muller, Lead Exposure and Violent Crime in the Twentieth Century, 62 Explorations in Econ. Hist. 51–86 (Oct. 2016), https://www.sciencedirect.com/science/article/abs/pii/S0014498316300109.

^[32] Cecil, supra note 11.

^[33] Christopher Brubaker, et. al., The Influence of Age of Lead Exposure on Adult Gray Matter Volume, 31 Neurotoxicology 259–66 (June 2010), https://pubmed.ncbi.nlm.nih.gov/20226811/.

[34] Id.

^[35] Id.

^[36] Cooper, supra note 22.

^[37] Brian Boutwell, et. al., The Intersection of Aggregate-Level Lead Exposure and Crime, 148 Env’t Research 79–85 (July 2016), https://www.sciencedirect.com/science/article/abs/pii/S0013935116301037.