by Clark Engelbert


1. - 2007 study on lead and crime.


Some highlights – “The elasticity of violent crime with respect to childhood lead exposure is estimated to be approximately 0.8. This implies that, between 1992 and 2002, the phase-out of lead from gasoline was responsible for approximately a 56% decline in violent crime.”


“This paper shows that childhood lead exposure can increase the likelihood of violent criminal behavior, and that this effect is large enough to significantly affect national crime trends. It provides a surprising explanation for rising and declining crime rates, and predicts continuing declines in the future. Lastly, this paper shows that environmental regulations such as the Clean Air Act can have large and unexpected societal benefits.”


“The association between low-level lead exposure during early development and subsequent deficits in cognitive development and behavior is widely accepted. A large and diverse literature in epidemiology, psychology, and neuroscience reaches the consensus that early childhood lead exposure negatively affects cognitive development and behavior in ways that increase the likelihood of aggressive and antisocial acts.12”


“Lead can also disrupt neurotransmitter function in ways that impair cognition and reduce impulse control.”


“Lead has also been associated directly with delinquent, criminal, and aggressive behavior. Denno [1990] finds that lead poisoning is the most significant predictor of disciplinary problems and one of the most significant predictors of delinquency, adult criminality, and the number and severity of offenses. Needleman et al. [1996] find a significant relationship between the amount of lead in bone (a good measure of past exposure) and antisocial, delinquent, and aggressive behaviors. Dietrich et al. [2001] followed a cohort of 195 inner-city youths from birth through adolescence, and found a clear linear relationship between childhood blood lead levels and the number of delinquent acts. In addition, Needleman et al [2002] showed that adjudicated delinquents were four times as likely to have high lead levels than non-delinquents, and several studies have shown that violent criminals exhibit higher levels of lead in their bodies than nonviolent criminals or the general population.25”


“Thus, the current results imply that lead exposure was likely an important factor in both the rise and the decline of violent crime in the last 30 years. At the same time, the recent history of violent crime is not fully understood: a sustained rise in crime of about 3-5% annually remains unexplained.”


2. - 2012 study on heavy metals and crime.


Some highlights -  “Individuals exposed to heavy metals, generally at a young age, are more at risk of developing a lower IQ and other neurobehavioral effects because the metals replace the nutrients that their brains need to fully develop.2”


“It has been found that various environmental toxicants have also been linked to abnormalities in brain chemistry that lead to the loss of impulse control and increased aggressive behavior.17 Over the years many environmental hazards have been linked to subclinical effects on brain biochemistry, including lead, manganese and mercury (Tables 1-3).”


“Early life exposure to these environmental toxicants is a leading factor for criminal behavior because they cause irreversible alterations to the brain; resulting in the individuals taking more risks and less able to deal with the frustrations of life.3


 “In Philadelphia, PA a longitudinal biosocial study was conducted on 1,000 Black residents from birth until 22 years of age.23 The study found that lead intoxication and anemia at the age of 7 were significant predictors of juvenile offenses and adult offenses for the males within the study.”


“Children are more susceptible than adults to develop neurotoxicity from lead because they absorb up to 50% of the lead they ingest compared to the 8% adults ingest.28 Also lead is more likely to form in the bones of children than adults, resulting in a more long term exposure.28  Exposure to lead can negatively impact both adults and children’s cognitive function such as decreased IQ, but early life exposures tend to have a greater impact and predispose an individual to a life of violence and other criminal offending.3”


Other behavioral deficits, such as Attention Deficit Disorder (ADD) and Attention Deficit Hyperactive Disorder (ADHD), which are commonly diagnosed in children today, are associated with significantly higher blood lead concentrations.3 Those conditions are also frequently associated with juvenile delinquency.30 In general, the highest levels of lead uptake have been reported within the demographic group that is most likely to commit violent crimes.31”


“Manganese is another environmental toxicant that has been linked to neurotoxicity and increased crime rates. Manganese affects the brain by lowering the levels of essential neurotransmitters in the brain.16 With fewer neurotransmitters, there is a decrease in both the levels of essential minerals in brain cells, and the levels of serotonin in the brain. 32 Low levels of serotonin is caused by chronic exposure to about 10 mg of manganese per day, and is associated with mood disturbances, impulse control, aggressive behavior and outbursts of violent behavior.16, 33”


“Another mode of toxicity is through lifestyle and diet.  If an individual is calcium, zinc or vitamin D deficient, to name a few, the body will take up higher levels of manganese, making the chemical more toxic.16 This is apparent in a study conducted showing manganese uptake in animals who are raised on formula compared to animals raised on mother’s milk. The results concluded that animals raised on formula retained more manganese than animals raised on mother’s milk because mother’s milk has more nutrients than the formula.34 The study was then conducted on humans and again the babies raised on formula retained 5x more manganese than the babies raised on mother’s milk.35 When an individual has sufficient vitamins, manganese is not as toxic and has minimal impact on those exposed. The poor and low income populations tend to be malnourished, and in those populations manganese may have a greater impact on development and aggressive behavior outbursts.”


“Lead, manganese and mercury are three main neurotoxins that alter brain biochemistry commonly resulting in lowering IQ; and increasing antisocial behavior, poor impulse control and the risk of aggressive behavior.”


“A Danish study provided weight to this hypothesis by showing that a high IQ was protective against serious criminal activity in high risk individuals.41 The study looked at the mean IQ’s of four different cohorts; those at high risk for serious criminal involvement but avoided criminal behavior, those at high risk who committed serious criminal behavior, those at low risk and avoided criminal behavior; and those at low risk who committed serious criminal behavior. The results showed that the mean IQ of the groups where individuals did not commit a serious crime were much higher than the groups that committed serious crimes.41”

3. - this is a chapter from a book called Pediatric Neurotoxicology. Only the abstract is available, the entire chapter is behind a paywall. Although this is a good chapter to use to search through more references.

4. - December 2019 study on the links between heavy metals in the topsoil of Spanish provinces and mental health.


Some highlights – “Whereas most research has been focused on the effect of acute intoxications by metals, the long-term impact of low-dose exposure is understudied. Authors have argued that continuous exposure to heavy metals could give rise to a “silent pandemic” in modern society, one responsible for a subclinical and permanent decrease in the IQ, an increase in school failure, a reduction in productivity (Grandjean and Landrigan, 2006), and an increased risk of antisocial and criminal behavior (Rodríguez-Barranco et al., 2013).”


5. – 2013 review and meta-analysis of many studies linking heavy metals and behavioral disorders.


Some highlights – “Grandjean and Landrigan (2006) suggested that continued exposure to these neurotoxic compounds could be creating a “silent pandemic” in modern society, being responsible for a subclinical, permanent decrease in IQ, leading to increased school failure, diminished economic productivity and increased risk of criminal and antisocial behavior.”


“With regard to behavioural disorders, all reviewed articles showed a positive association between manganese exposure and behavioural disorders in children aged between 5 and 15 years (Table 4). Three of the five studies (Yousef et al., 2011; Farias et al., 2010; Ericson et al., 2007) found a higher risk of attention deficit hyperactive disorder (ADHD) associated with manganese exposure, measured through levels in blood (in the first two studies) or in teeth (in the third). Khan et al. (2011) observed higher scores on internalising and externalising behaviour associated with higher levels of manganese in the regular drinking water of children aged 8–11, while Bouchard et al. (2007) found a similar result associated with oppositional and hyperactivity subscale scores of Conner's scales when they measured manganese levels in hair of children aged 6–15 (Table 4).”


6. – 2008 study on lead and criminality in adulthood.


Some highlights – “Prenatal and postnatal blood lead concentrations are associated with higher rates of total arrests and/or arrests for offenses involving violence. This is the first prospective study to demonstrate an association between developmental exposure to lead and adult criminal behavior.”


“These findings provide strong evidence that early lead exposure is a risk factor for criminal behavior, including violent crime, in adulthood. One possibility, which the authors were unable to assess in this study, is that lead exposure impairs intelligence, which in turn makes it more likely that a criminal offender will be caught (i.e., arrested). “


7. – 2012 study on lead and societal violence.


Some highlights – “The 1950–1985 fluctuation of Pb emissions explains 90% of the aggravated assault variation. Each 1% tonnage Pb increase 22 years prior raised aggravated assault by 0.46% (95% CI, 0.28 to 0.64). Childhood Pb prevention may yield numerous benefits in two decades, including less violence.”


8. – 2007 study on preschool lead exposure and future murders.


Some highlights – “This study shows a very strong association between preschool blood lead and subsequent crime rate trends over several decades in the USA, Britain, Canada, France, Australia, Finland, Italy, West Germany, and New Zealand. The relationship is characterized by best-fit lags (highest R2 and t-value for blood lead) consistent with neurobehavioral damage in the first year of life and the peak age of offending for index crime, burglary, and violent crime. The impact of blood lead is also evident in age-specific arrest and incarceration trends. Regression analysis of average 1985–1994 murder rates across USA cities suggests that murder could be especially associated with more severe cases of childhood lead poisoning.”


9. – 2014 study on the link between lead and crime.


Some highlights – “People with higher levels of lead during childhood are more likely to partake in delinquent acts later in life than those with normal levels of lead during childhood (Dietrich et al., 2001; Needleman et al., 2002; Needleman et al., 1996; Wright et al., 2008). This relationship to delinquency is likely due to the neuropsychological deficits that lead causes and how society responds to children with the behavioral and learning problems created by these deficits (Moffitt, 1993; Raine, 2002).”