The toxic effects of lead exposure are well-established. Lead serves no useful biologic function in the human body. Once inside, it mimics calcium and builds up in teeth and bones, and causes severe damage to virtually all body systems with major impact on the central and peripheral nervous system, gastrointestinal, cardiovascular, renal, endocrine and immune systems. Brain, heart, liver, bones and kidneys are a few organs that take the maximum hit.
Environmental lead exposure can affect people of every age but it is particularly harmful to children, and even those unborn. As a potential neurotoxin, lead can adversely affect the development of the brain and nervous system. Exposure to lead in early life can result in serious developmental, behavioural and learning disorders. The human brain has only a minor capacity to repair itself, so decline in cognitive abilities and disruption in behavior is believed to be irreversible, lasting a lifetime with some effects and symptoms only appearing later in adulthood.
The impact of lead poisoning on the mental development of young children is well-known. It has been associated with loss of IQ, disabilities in learning, growth issues, hyperactivity, low attention span, memory problems and antisocial behavior. But is there also an association between lead exposure and criminal behavior? It seems there is. We have scientific literature backing the claims that blood lead concentrations are indeed strongly related to subsequent criminal behavior and other socially unwanted trends in adults.    
A recent study published in the journal Environmental Health found a strong relationship between lead levels in the air and the ensuing aggressive criminal behavior in children. Researchers from Macquarie University in Sydney analysed air lead levels and criminal behavior in six NSW suburbs; namely Boolaroo, Earlwood, Lane Cove, Port Kembla, Rozelle and Rydalmere.
The researchers adjusted for socio-demographic factors that are known to contribute toward aggressive criminal behaviour, such as age, education and household income. The researchers found that exposure to environmental lead during childhood resulted in increased likelihood of criminal behavior in later years. In fact, the researchers found that lead exposure in early life is the most solid predictor of assault rates in adulthood.
More specifically, “air lead concentrations accounted for 29.8 % of the variance in assault rates 21 years later, after adjusting for socio-demographic covariates. Lead petrol emissions in the two most populous states accounted for 34.6% and 32.6 % of the variance in death by assault rates 18 years later.” 
Interestingly, the drift for lead exposure appears to be associated with only violent crimes. When it comes to any relationship between the levels of lead and crimes like fraud, which is non-aggressive, non-impulsive and usually pre-meditated in nature, the researchers saw that lead accounted for only 5.5% of the variance.
The findings are not surprising and they align with the results from earlier studies that also suggest that lead exposure during early years is a big risk factor for criminal behaviour in adult life. A big tie-in is that lead exposure increases impulsive actions, commonly associated with aggressive, violent crimes. The researchers believe that the relationship between early lead exposure and the rates of aggressive crime holds significant inferences for global public health. Important collaborative measures need to be taken to bring down the levels of lead, as well as other environmental toxins associated with neurodevelopmental consequences.
Children and Lead Poisoning
The World Health Organization (WHO) released a booklet on Childhood Lead Poisoning describing in detail the lead exposure pathways and the resulting harmful effects in children. It stated “Children are now understood to be at particularly high risk of lead toxicity. From conception onward, children have a greater risk of exposure and greater susceptibility to the toxic effects of lead than do adults. There exist windows of vulnerability to lead in early life – during embryonic, fetal and early postnatal life – that have no counterparts in adult life (American Academy of Paediatrics Committee on Environmental Health, 2003)”
There are many reasons why children are biologically more vulnerable to lead toxicity than adults. One of these reasons apparently is that the brain of a child is under the process of rapid growth, development and differentiation. Lead has the capability to disrupt these extremely intricate and fragile processes in a developing brain. Also, the most common exposure pathway for children is through ingestion and working in tandem is children’s capacity to absorb almost 4 to 5 times as much ingested lead as adults, clearly making them more susceptible to feel the brunt of lead toxicity.
Another risk factor for early lead exposure is in the womb. High levels of lead in the blood of pregnant women can have devastating consequences of the neuro-development and all-inclusive health of a developing baby. Lead from a pregnant woman’s bones passes onto the child. Studies show that the levels of lead in the maternal and fetal blood are practically the same. Once in the fetal circulation, lead easily gains access to the developing brain by penetrating the undeveloped blood–brain barrier. Besides causing damage to the brain, excessive accumulation of lead in an expecting woman can result in stillbirth, premature birth, a baby with low birth weight and even deformities in the baby growing in the womb.
So, is there any safe level below which children don’t suffer any untoward consequences on overall and cognitive health? Research suggests that blood lead concentrations even as low as 5 µg/dl, the levels that were once believed to be safe, have the potential to wreak havoc in learning and behavioral development. This is indeed a dangerous statistic.
On this issue the WHO booklet states, “Recent research indicates that lead is associated with neurobehavioural damage at blood levels of 5 μg/dl and even lower. There appears to be no threshold level below which lead causes no injury to the developing human brain. The Joint FAO/WHO Expert Committee on Food Additives re-evaluated lead in June, 2010 and withdrew the provisional tolerable weekly intake guideline value on the grounds that it was inadequate to protect against IQ loss” 
- Nevin R. Understanding international crime trends: the legacy of preschool lead exposure. Environmental Research 2007
- Wright et al. Association of prenatal and childhood blood lead concentrations with criminal arrests in early adulthood. PLoS Medicine. 2008
- Nevin R. How lead exposure relates to temporal changes in IQ, violent crime, and unwed pregnancy. Environmental Research 2000
- Goodlad JK, Marcus DK, Fulton JJ. Lead and Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms: a meta-analysis. Clinical Psychology Review. 2013
- Taylor MP, Forbes MK, Opeskin B, Parr N, Lanphear BP. The relationship between atmospheric lead emissions and aggressive crime: an ecological study. Environmental Health. 2016.
- Childhood Lead Poisoning. World Health Organization.