After decades of increasing

crime In ordinary language, a crime is an unlawful act punishable by a State (polity), state or other authority. The term ''crime'' does not, in modern criminal law, have any simple and universally accepted definition,Farmer, Lindsay: "Crime, definiti ...

across the industrialised world, crime rates started to decline sharply in the 1990s, a trend that continued into the new millennium. Many explanations have been proposed, including situational crime prevention and interactions between many other factors with complex, multifactorial causation.

Lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

is widely understood to be toxic to multiple organs of the human body, particularly the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

. Concerns about even low levels of exposure began in the 1970s; in the decades since, scientists have concluded that no safe threshold for lead exposure exists. The major source of lead exposure during the 20th century was leaded gasoline. Proponents of the lead–crime hypothesis argue that the removal of lead additives from motor fuel, and the consequent decline in children's lead exposure, explains the fall in crime rates in the United States beginning in the 1990s. This hypothesis also offers an explanation of the in crime in the preceding decades as the result of increased lead exposure throughout the mid-20th century. The lead–crime hypothesis is not mutually exclusive with other explanations of the drop in US crime rates, which includes analysis of the hypothesized legalized abortion and crime effect. The difficulty in measuring the effect of lead exposure on crime rates is in separating the effect from other indicators of

poverty Poverty is a state or condition in which an individual lacks the financial resources and essentials for a basic standard of living. Poverty can have diverse Biophysical environmen ...

such as poorer schools, nutrition, and medical care, exposure to other pollutants, and other variables that may lead to crime.

Background and research

Usage of lead in modern history

, a naturally occurring

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

of bluish-grey color, has been used for multiple purposes in the history of human

civilization A civilization (also spelled civilisation in British English) is any complex society characterized by the development of state (polity), the state, social stratification, urban area, urbanization, and symbolic systems of communication beyon ...

. Advantages include being somewhat soft and pliable as well as resistant to

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

compared to other metals. The widespread substance is also able to function as a shield against various forms of

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

. Expanded scientific investigation into

organolead chemistry Organolead chemistry is the scientific study of the synthesis and properties of organolead compounds, which are organometallic compounds containing a chemical bond between carbon and lead. The first organolead compound was hexaethyldilead (Pb2(C2 ...

and the varied ways in which human biology changes due to lead exposure took place throughout the 20th century. Although it has continued to be in wide use even into the 21st century, greater understanding of

blood lead levels Blood lead level (BLL), is a measure of the amount of lead in the blood. Lead is a toxic heavy metal and can cause neurological damage, especially among children, at any detectable level. High lead levels cause decreased vitamin D and haemoglo ...

(BLLs) and other factors have meant that a new scientific consensus has emerged. No 'safe' level of lead in the human bloodstream exists as such; any amount can contribute to

neurological Neurology (from , "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the s ...

problems and other health issues. Medical analyses of the role of lead exposure in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

note increases in impulsive actions and social aggression as well as the possibility of developing

attention deficit hyperactivity disorder Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by symptoms of inattention, hyperactivity, impulsivity, and emotional dysregulation that are excessive and pervasive, impairing in multiple con ...

(ADHD). Those conditions likely influence

personality Personality is any person's collection of interrelated behavioral, cognitive, and emotional patterns that comprise a person’s unique adjustment to life. These interrelated patterns are relatively stable, but can change over long time per ...

traits and behavioral choices, with examples including having poor

job performance Job performance assesses whether a person performs a job well. Job performance, studied academically as part of industrial and organizational psychology, also forms a part of human resources management. Performance is an important criterion for o ...

, beginning a pattern of

substance abuse Substance misuse, also known as drug misuse or, in older vernacular, substance abuse, is the use of a drug in amounts or by methods that are harmful to the individual or others. It is a form of substance-related disorder, differing definition ...

, and undergoing

teenage pregnancy Teenage pregnancy, also known as adolescent pregnancy, is pregnancy in a female under the age of 20. Worldwide, pregnancy complications are the leading cause of death for women and girls 15 to 19 years old. The definition of teenage pregnancy i ...

. Evidence that lead exposure contributes to lower

intelligence quotient An intelligence quotient (IQ) is a total score derived from a set of standardized tests or subtests designed to assess human intelligence. Originally, IQ was a score obtained by dividing a person's mental age score, obtained by administering ...

(IQ) scores goes back to a seminal 1979 study in ''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'', with later analysis finding the link particularly robust. The international process of trying to lower the prevalence of lead has been largely spearheaded by the Partnership for Clean Fuels and Vehicles (PCFV). The

non-governmental organization A non-governmental organization (NGO) is an independent, typically nonprofit organization that operates outside government control, though it may get a significant percentage of its funding from government or corporate sources. NGOs often focus ...

partners with major

oil companies The following is a list of notable companies in the petroleum industry that are engaged in petroleum exploration and production. The list is in alphabetical order by continent and then by country. This list does not include companies only involved ...

, various governmental departments, multiple

civil society Civil society can be understood as the "third sector" of society, distinct from government and business, and including the family and the private sphere.2002 'Earth Summit', institutions under the umbrella of the

United Nations The United Nations (UN) is the Earth, global intergovernmental organization established by the signing of the Charter of the United Nations, UN Charter on 26 June 1945 with the stated purpose of maintaining international peace and internationa ...

vowed to emphasize public–private partnerships (PPPs) in order to help developing and transitional countries go unleaded.

Correlation between lead exposure and crime

In terms of

, multiple commentators and researchers have noted that, after decades of relatively steady increases, crime rates in the United States started to sharply decline in the 1990s. The trend continued even into the new millennium. Multiple possible explanations have been suggested, with academic studies pointing to complex, multifactorial causation concurrent with various social trends. The

economist An economist is a professional and practitioner in the social sciences, social science discipline of economics. The individual may also study, develop, and apply theories and concepts from economics and write about economic policy. Within this ...

s Steven D. Levitt and John J. Donohue III, of the

University of Chicago The University of Chicago (UChicago, Chicago, or UChi) is a Private university, private research university in Chicago, Illinois, United States. Its main campus is in the Hyde Park, Chicago, Hyde Park neighborhood on Chicago's South Side, Chic ...

and

Stanford University Leland Stanford Junior University, commonly referred to as Stanford University, is a Private university, private research university in Stanford, California, United States. It was founded in 1885 by railroad magnate Leland Stanford (the eighth ...

, respectively, have argued that the decline in U.S. crime rates was the combined result of an increase in the number of police, hikes in size of the prison population, waning of the spread of

crack cocaine Crack cocaine, commonly known simply as crack, and also known as rock, is a free base form of the stimulant cocaine that can be Smoking, smoked. Crack offers a short, intense Euphoria (emotion), high to smokers. The ''Manual of Adolescent Sub ...

, and the widespread legalization of

abortion Abortion is the early termination of a pregnancy by removal or expulsion of an embryo or fetus. Abortions that occur without intervention are known as miscarriages or "spontaneous abortions", and occur in roughly 30–40% of all pregnan ...

from the 1970s onward. Possible other factors include changes in

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

consumption. Later studies have upheld many of these findings while disputing others. While noting that

correlation does not imply causation The phrase "correlation does not imply causation" refers to the inability to legitimately deduce a cause-and-effect relationship between two events or variables solely on the basis of an observed association or correlation between them. The id ...

, the fact that in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

anti-lead efforts took place simultaneously alongside falls in violent crime rates attracted attention from researchers. Changes were not uniform across the country, even while increasingly stringent

Environmental Protection Agency Environmental Protection Agency may refer to the following government organizations: * Environmental Protection Agency (Queensland), Australia * Environmental Protection Agency (Ghana) * Environmental Protection Agency (Ireland) * Environmenta ...

rules went into force from the 1970s onward. Several areas had far greater lead exposure compared to others for years. A 2007 report published by ''The B.E. Journal of Economic Analysis & Policy'', authored by Jessica Wolpaw Reyes of

Amherst College Amherst College ( ) is a Private college, private Liberal arts colleges in the United States, liberal arts college in Amherst, Massachusetts, United States. Founded in 1821 as an attempt to relocate Williams College by its then-president Zepha ...

, found that between 1992 and 2002 the phase-out of lead from gasoline in the U.S. "was responsible for approximately a 56% decline in violent crime". While cautioning that the findings relating to "murder are not robust if New York and the District of Columbia are included," the author concluded that " erall, the phase-out of lead and the legalization of abortion appear to have been responsible for significant reductions in violent crime rates." She additionally speculated that by "2020, all adults in their 20s and 30s will have grown up without any direct exposure to gasoline lead during childhood, and their crime rates could be correspondingly lower." In 2011, a report published by the official United Nations News Centre remarked, "Ridding the world of leaded petrol ..has resulted in $2.4 trillion in annual benefits, 1.2 million fewer premature deaths, higher overall intelligence and 58 million fewer crimes". The

California State University The California State University (Cal State or CSU) is a Public university, public university system in California, and the List of largest universities and university networks by enrollment, largest public university system in the United States ...

did the specific study. Then U.N. Environment Programme (UNEP) executive director

Achim Steiner Achim Steiner (born 17 May 1961) is a Brazilian-German environmentalist who currently serves as the administrator of the United Nations Development Programme and vice-chair of United Nations Sustainable Development Group. Before joining UNDP, ...

argued, "Although this global effort has often flown below the radar of media and global leaders, it is clear that the elimination of leaded petrol is an immense achievement on par with the global elimination of major deadly diseases." In a 2013 article, '' Mother Jones'' ran a report by Kevin Drum arguing: Drum writes: According to Reyes, "Childhood lead exposure increases the likelihood of behavioral and cognitive traits such as impulsivity, aggressivity, and low IQ that are strongly associated with criminal behavior". A May 2017 study by Anna Aizer and Janet Currie found that lead exposure in childhood substantially increased school suspensions and juvenile detention among boys in

Rhode Island Rhode Island ( ) is a state in the New England region of the Northeastern United States. It borders Connecticut to its west; Massachusetts to its north and east; and the Atlantic Ocean to its south via Rhode Island Sound and Block Is ...

, suggesting that the phasing out of leaded gasoline may explain a significant part of the decline in crime in the United States beginning in the 1990s.

Systematic reviews / meta-analysis

The first meta-analysis of the lead-crime hypothesis was published in 2022. "The Lead-Crime Hypothesis: A Meta-Analysis", authored by Anthony Higney, Nick Hanley, and Mirko Moro consolidates findings of 24 studies on the subject. It found that there is substantial evidence linking lead exposure to a heightened risk of criminal behavior, particularly violent crimes. This aligns with earlier research suggesting lead exposure may foster impulsive and aggressive tendencies, potential precursors to violent offenses. The study concluded that, while a correlation between declining lead pollution and declining criminality is supported by research, it is likely not a significant factor in reduced crime rates, and that the link is generally overstated in lead-crime literature. The study's implications point towards the potential benefits of reducing lead exposure to decrease crime rates. Such reductions could be achieved through initiatives like removing lead from products like gasoline and paint, water pipes and enhancing lead abatement measures in schools and residences.

Background and research

Usage of lead in modern history

Correlation between lead exposure and crime

Systematic reviews / meta-analysis

See also

References

Further reading