Lead and violence –strong linkages found prior to 2009

By Robert Taylor, Researcher for The LEAD Group Inc, Edited by Zac Gethin-Damon.

Since Herbert L. Needleman’s research on bone lead levels in adjudicated delinquents in 2002 there have been ongoing studies on lead and violent behaviour. Studies have compared lead levels with rates of violence between countries (Nevin 2007) and groups (Stretesky & Lynch 2001, Stretesky & Lynch 2004, Reyes 2007) and established correlations. But the most important studies are of violence within a group, since these are less vulnerable to confounding factors.

In 2008 a team led by John Paul Wright (Wright 2008) studied 250 children from a group with a fairly high arrest rate (66.9% of 125 males and 92.7% of 225 African-Americans) whose blood lead level levels had been tracked from birth to 6.5 years and whose mother’s lead levels had been measured during pregnancy. While there was there was some increase for non-violent crime there was a more significant increase in arrests for violent crimes with rates rising in a predictable manner for every increment above the base with statistical variations apparent at levels above 3µg/dL (less than one third the CDC’s level for concern). The results for violence are summarised in the graphs on the following page.  There was a stronger correlation was with blood lead levels at six years of age (RR (Relative Risk) 1.48 per 5 µg/dl increase) than with average childhood blood lead (RR 1.30 per 5µg/dl increase) and for non violent crime arrests blood lead levels at six years of age were also more important than average childhood blood lead (RR 1.22 to 1.05 per 5 µg/dl increase). Intriguingly the mother’s prenatal blood lead level had more impact on the risk of arrest for non-violent crime (RR 1.4 per 5 µg/dl increase) than for violent crime (RR 1.34 per 5 µg/dl increase) and had much stronger links with non-violent crime than the weak, and probably insignificant, correlation with average childhood lead levels (RR 1.05 per 5 µg/dl increase). For violent crime average childhood blood lead also had a higher threshold level (6µg/dl) before effects became apparent than either prenatal or six year old levels (3 µg/dl).

  This appears to indicate that blood lead has significantly different neurological impact at specific stages of development and that aging alone does not reduce this impact. From these results it would appear that blood lead levels of above 3µ/dL have significant impacts at key developmental stages on the long term violence related behaviour of exposed children. While these impacts are only part of a larger picture exposure to lead is, to a fair degree, avoidable (Rae 2006 p16, Bellinger 2008). Further research is required to determine the mechanisms involved though the balance of probability lies in lead impact on executive function, specifically its ability to impair inhibitory responses that govern impulse control and reduce the levels of serotonin and dopamine in the brain.

Figure 2. Adjusted Relationship between Blood Lead Concentration and Arrest Rate Ratio For Violent Offenses

Shown are data for maternal prenatal blood lead concentration (A), early childhood average blood lead concentration (B), and 6-year blood lead concentration (C). Rate ratios are plotted as a function of increasing blood lead from the 5th to the 95th percentiles of blood lead relative to participants at the 5th percentile. Dashed lines are 95% confidence intervals.

References

David C. Bellinger Neurological and Behavioral Consequences of Childhood Lead Exposure PLoS Med. 2008 May; 5(5): e115. Published online 2008 May 27.

Rick Nevin Understanding international crime trends: The legacy of preschool lead exposure Environmental Research 104 (2007) 315–336

Rae, Mary Nicholas Genetic and Environmental Influences on Criminal Behavior University of Cincinati thesis 

Jessica Wolpaw Reyes (2007) Environmental Policy as Social Policy? The Impact Of Childhood Lead Exposure On Crime National Bureau Of Economic Research Working Paper 13097 May 2007 

Paul B. Stretesky, PhD; Michael J. Lynch, PhD (2001) The Relationship Between Lead Exposure and Homicide Archives of Pediatrics & Adolescent Medicine Vol. 155 No. 5, May 2001

Stretesky, Paul B & Lynch, Michael J. (2004) The Relationship between Lead and Crime  Journal of Health and Social Behavior, Vol.45, No. 2, 1 June 2004, pp. 214-229(16) 

John Paul Wright, Kim N. Dietrich, M. Douglas Ris, Richard W. Hornung, Stephanie D. Wessel, Bruce P. Lanphear, Mona Ho, Mary N. Rae (2008) Association of Prenatal and Childhood Blood Lead Concentrations with Criminal Arrests in Early Adulthood PLoS Med. 2008 May; 5(5): e101. Published online 2008 May 27.