by Casey J. Bastian

Is there an identifiable and preventable cause of crime? Experts have related trends in criminal activity to the economy, law enforcement-related activity and presence, societal demographics, and certain cultural issues. Causation has allegedly been linked to fatherless homes or a lack of education, both presumed to result in increases in crime. Conversely, surges in community law enforcement activity have frequently been associated with decreases in crime. But no firm set of data or statistics confirms any of the hypotheses derived from such factors.

In fact, a very sharp decline in U.S. crime rates during the 1990s was not accurately predicted by any experts’ models using these theories. Experts had actually warned that the period between 1995-2005 would see a rise in teen murders as a result of an expected increase in the teen population—specifically, Black teens.

The experts were stunned when the teen population increased as projected but was actually matched by a 77% decrease in the murder arrest rate of juveniles between 1993-2003. These statistics were documented in 2004 by the Office of Juvenile Justice and Delinquency Prevention.

Experts attempted to explain the decline in 1990s crime rates as being due to trends of increasing police per capita and incarceration rates. Some even argued that the abortion rates of the early 1970s had eliminated “unwanted” children “presumed more likely to offend.” Not only did their models fail to explain the 1973-1991 crime trends, the models were absolutely unable to correlate what became huge surges in arrest and incarceration rates while police per capita remained flat. The surges were not the result of more policing.

While these U.S. trends were perplexing, it appears the international trends in criminal activity are just as vexing. Statistics compiled during this period demonstrate that violent crime in Britain, and across most of Europe, also trended significantly upward during the 1990s. That uptick in crime occurred despite trends in those areas of increased incarceration rates, rising police per capita, and a decline in the population of juveniles aged 15-19 years-old. A trifecta of factors that, based on experts’ models, should have resulted in decreases in criminal activity. So, if none of these models or hypotheses was accurately predicting crime trends or their causation, what other theories are being considered by the world’s experts?

In 2007, economist and researcher Rick Nevin authored a report titled: “Understanding international crime trends: The legacy of preschool lead exposure.”

Nevin initially analyzed crime data through 2002, but in November 2020, he posted results of a follow-up study on his website ricknevin.com, asking this question: “Has any other crime theory predicted trends with so much accuracy, over so many years, in so many nations?”

In his recent assessment, he provided charts illustrating his evidence of “the predictive power of this causal relationship” from 2002-2018, regarding burglary and robbery trends in Canada, Australia, Britain, and the U.S.

Burglary rates fell 50% or more from 2002-2018 in all four nations. Robbery rates in Britain and Australia peaked in 2001, but Canada and U.S. robbery rates peaked 10 years earlier, reflecting the earlier phase-out of leaded gasoline in Canada and the U.S. Australia’s robbery rate fell 62% from 2002-2018. The Canadian robbery rate fell almost 50% from 1991-2018, including a 39% decline from 2002-2018. The U.S. robbery rate fell 68% from 1991-2018, including a 41% decline from 2002-2018.

Except for what Nevin calls “an anomalous 2014-2018 robbery trend in Britain,” the 2002-2018 burglary and robbery trends for Canada, Australia, Britain, and the U.S. have “all tracked earlier preschool blood lead trends reported for each nation.”

Nevin was not the first or the only researcher to draw a conclusion about the correlation between health impacts from lead exposure and crime. Experts have posited that there may be a causation between certain types of damage to the brain and criminal offending. There is ample evidence to support the inference that brain damage can cause neurobehavioral disorders leading to a subsequent propensity to engage in criminal activity. An idea known as the “lead-crime hypothesis” has received significant attention and study. Several decades of scientific research have thoroughly documented a consistent association between juvenile exposure to toxic levels of lead matter, particularly during the early, formative years, and subsequent delinquency or criminal behavior. Researchers have found that the consequences of elevated blood-lead levels is also evidenced in age-specific arrest and incarceration trends.

While Nevin is primarily an economist, he is most renowned for his research on the issue of lead exposure in children, particularly in the U.S. He authored the Economic Analysis of the 1999 Department of Housing and Urban Development rule on evaluating and reducing lead paint hazards. He also developed methodology for the Federal Strategy for Eliminating Childhood Lead Poisoning and assisted the President’s Task Force on Environmental Health and Safety Risks to Children.

In a previous study which Nevin published in 2000, he found that on a nationwide level, 90% of the U.S. violent crime rate variance from 1960-1998 is paralleled by trends in leaded gasoline emissions.

Independent studies in 2007 and 2012, concerning state and city crime statistics, confirmed Nevin’s findings in the 2000 study at local levels. While Nevin was not the first published study on the matter of the lead-crime hypothesis, his 2007 study is widely regarded as the most comprehensive on juvenile exposure to toxic lead levels. The report provided an examination of international data that recorded blood-lead levels in preschool-age children and documented trends in crime rates of several decades from nine countries: Australia, Britain, Canada, Finland, France, Italy, New Zealand, the U.S., and West Germany.

Nevin’s 2007 study sought to determine if there was more than a simple correlation between blood-lead levels and crime in juvenile and young-adult populations. If it is to be demonstrated that one theory is more viable than another, there must be more than a correlation between factors. The relationship between factors must demonstrate causation, i.e., cause and effect. Not just the coincidental existence of two factors existing in an environment simultaneously.

Experts believe the most reliable indicator of causation is to establish consistency in an association between at least two quantifiable factors. In this case, that would be juvenile exposure to toxic levels of lead and later criminal activity. An observed association between two factors is determined to be consistent once the association has been “repeatedly observed by different persons, in different places, circumstances and times.”

A considerable challenge to further ensuring the viability of the blood-lead hypothesis based on the examined factors is evaluating the impact of additional aggravating factors typically associated with poverty, which is also thought to affect crime and is frequently existing in areas where exposure to lead is more likely. Such poverty factors include inadequate nutrition, deficient healthcare, inferior educational institutions, environmental exposure to toxins other than lead, etc. Nevin’s findings cement what has been observed and confirmed by multiple qualified experts from around the world. Exposure to toxic levels of lead—whether from lead paints, leaded gasoline, lead pipes, or any other source—is consistently linked to neurobehavioral issues caused by damage to the brain. This is especially true when that exposure is at the early stages of development. These data reveal the effects of the world’s misuse of lead and lead-based products and its grave damage done to generations of children around the globe.

A 1990 study of Philadelphia youth by D.W. Denno, “Biology and Violence,” was the first to reveal a consistent association between these two factors. The association was subsequently confirmed by additional studies in Pittsburgh (H. Needleman, et al, 1996, “Bone lead levels and delinquent behavior” and 2003, “Bone lead levels and adjudicated delinquents: A case control study”) and Cincinnati (K. Dietrich, et al, 2001, “Early exposure to lead and juvenile delinquency”).  

A nationwide study published in 2001 by P. Stretesky and M. Lynch entitled “The relationship between lead exposure and homicide” found that U.S. counties with elevated air-lead levels had an increase in murder rates of up to 400% compared to those cities with air-lead considered to be at low levels. James Feigenbaum and Christopher Muller authored another national report on a study of the cumulative effects of exposure from drinking water pumped through lead pipes. That study used U.S. city-level crime rate data spanning the 20th century. The report concluded that exposure to lead on juvenile populations through drinking contaminated water does cause increased homicide rates after the typical two-decade lag between initial exposure and offense when compared to populations lacking any such exposure.

The oft cited two-decade lag accounts for the period of growth from exposure at pre-natal/preschool age to the peak ages of offending, which is approximately late teens or very young adult ages. Critics identified one main problem with the Feigenbaum/Muller study. Data accumulated across multiple communities are susceptible to indeterminate influence from aggravating factors. It is believed to be more revealing when the study is of multiple children in only one area.

Anna Aizar and Janet Currie did just that when they studied 1990-2004 data concerning children in Rhode Island. This study linked data that evidences elevated blood-lead levels in preschool age children and ensuing correlative increases in suspensions and incarcerations. The data showed that those children who lived near busy roads are more susceptible to toxic levels of lead exposure saturation in the blood. This appears to be the result of soil contamination derived from the past use of leaded gasoline.

It appears that the peak of this man-made natural disaster was in the 1970s. This was observed particularly in the data on older children as leaded gasoline has been disused since that period. Data show that as the use of leaded gasoline declined, measured blood-lead levels fell sharply in near diametric proportion. These observations also track the two-decade lag. The Aizar/Currie study compared both kids subjected to elevated lead exposure and similarly situated kids living near less used roads and children from the same roads but after many more years had elapsed.

Lead emissions from busier roads, especially in urban settings, obviously caused greater lead exposure to the kids studied. The results are dramatic and intriguing. These data firmly suggest true causation between the discontinued use of leaded gasolines in the 1970s, resulting in decreased environmental pollution, and the significant decline during the 1990s of crime rates 20 years later. The children from Rhode Island who had been exposed to the most lead toxins were statistically more likely to be incarcerated.

These multiple studies are just a fraction of those that have demonstrated a consistent association between lead exposure and crime at the individual, census tract, city, suburb, county, state, national, and international levels. These findings support a causal link between lead toxins causing brain damage in the first years of life and the neurobehavioral disorders manifesting during the peak age of offending, which consistently lags around two decades.

This is precisely what Nevin’s 2007 comprehensive international study had examined, assembled, and offered for consideration. The blood-lead hypothesis seems to now in fact be a well-supported theory. When lead is introduced into the blood it acts as a degenerative neurotoxin. Elevated pre-natal and preschool blood-lead levels typically impairs formative brain growth.

Prior to age two, critical growth of white and gray brain matter occurs. The 2007 Nevin study cited a publication of the Agency for Toxic Substances and Disease Registry from 2000, which found, “[I]ncomplete development of the blood-brain barrier in fetuses and in very young children (up to 36 months of age) increases the risk of lead’s entry into the developing nervous system, which can result in prolonged or permanent neurobehavioral disorders.” Elevated maternal (causing prenatal exposure) and preschool blood-lead levels increase detrimental neurological effects establishing impairment in learning, behavior, and IQ.

A mere 10 micrograms (one-millionth of one gram) per deciliter (0.1 liter) of blood-lead is harmful to learning and behavior, and there is no low-end threshold for diminishment of IQ.  Levels approaching 70 micrograms per deciliter can cause seizures and death. The previous use of lead in products such as paint and gasoline caused a global increase in exposure to this neurotoxin. Elevated blood-lead was often caused by lead paint ingestion or inhalation of air-lead toxins. Exposure to this toxin caused an especially pervasive effect on young children as they crawled through settled lead dust or engaged in typical hand to mouth behavior.

An indirect effect of lowered IQ is often exhibited in behavioral problems. Clinical observations as early as 1998 found that youth with IQs in the 75-90 range are an astounding seven times more likely to be incarcerated than ones with an IQ of 110-125. The author of those findings wrote, “[N]o other trait or circumstance yet studied is so deeply implicated in the nexus of bad social outcomes” as a low IQ. Intelligence quotient, or “IQ”, is an assessment tool developed in 1920 in which a derivative test score represented as a scaled number is used to express what is believed to be the relative intelligence of a person. However, observations concerning IQ do not completely explain a property crime arrest rate of 15-17 year-olds that was nine times higher than that of those aged over-25 between 1970-2003.

Another direct effect of damage to the developing brain is later impairment of impulse control. One must also take into account the developmental effects of early lead exposure on, and its direct destruction of, the myelin sheath and decreased production of the enzyme integral to myelin synthesis. Myelin is the soft white fatty material that forms as a thick layer insulating the axons of neurons. A more progressed myelin sheath increases the speed of signals that travel from neuron to neuron allowing the brain to work in concert while diminishing impulsive behaviors.

A NIH study from a different perspective used magnetic resonance imaging of the frontal lobes. The study revealed that within the frontal lobe a second surge in gray matter growth occurs just before puberty. The frontal lobes are the “seat of ‘executive function’—planning, impulse control and reasoning.” This incomplete myelination becomes a form of developmental disorder attributed to impulsive teen behavior. Trends in crime repeatedly reflect that most criminal activity is committed by people aged between their early teens and early 20s. Youth are naturally impulsive: when you add in a neurobehavioral disorder, the results are predictable.

Regardless of the form in which it is manifested, researchers can confirm the general observation that irreversible brain damage is caused by exposure to lead during critical periods of developmental vulnerability. The resultant neurobehavioral issues and diminished cognitive functioning clearly are influential factors in criminal activity trends. Is appreciating the full impact of damage to the brain the solution to understanding crime enough to eliminate it?

We already see a continued reduction in crime since its world-wide surge that peaked in the 1990s. While the extensive minutia of these studies is beyond the purview of this article, the expansive data make it abundantly clear that the global use of lead-based products caused tremendous increases in criminal activity during the last century—a true man-made disaster with incalculable costs. World-wide crime trends across both property and violent crimes appear to now be entirely detached form the pernicious effects of the former global use of lead-based products.

In a 2017 study, “Life After Lead: Effects of Early Interventions for Children Exposed to Lead,” economists Stephen B. Billings and Kevin T. Schnepel measured potential economic effects of applying CDC-recommended interventions, i.e., lead abatement and nutritional counseling, for data from kids born near Charlotte, North Carolina, from 1990- 1997. They estimated that for every $1 invested in the intervention, society yields a return of nearly $1.80.  

Realizing the legacy of preschool blood-lead exposure is a great start. Now, we must examine other causes of damage to the brain, particularly in youth, because it also seems certain that the resultant neurological issues must be influential factors in current crime trends—particularly in America, where leading the world in incarceration rates is a clear sign of an unhealthy society. 

Sources: Sciencedirect.com; elsevier.com; ricknevin.com; brookings.edu; Hill A.B. “The environment and disease: association or causation.” Proceedings of the Royal Society of Medicine, 1965, 58, 295-300

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