Articles Scientific Papers

Neurological Effects

Why Are Young Children Most Susceptible?
The body accepts lead as a substitute for the calcium ions needed in developing brains.  Because of this, lead is able to pass through the blood-brain barrier (endothelial cells) that normally protect this critical organ from toxic metals.1 This is particularly problematic for young children whose brains and nervous systems are in stages of rapid development.2

What are the Neurological Effects of Lead?
Lead decreases neuronal growth, diminishes neurochemical development, impedes organization of ion channels,3 interferes with synapse formation, reduces the numbers of neurons,4 interferes with neurotransmission, degenerates nerve cells and causes loss of the myelin (sheaths protecting neurons).  Each of these physiological effects can cause cognitive, behavioral and motor skill disabilities.

What Disabilities are Associated with Lead?
The effects of lead poisoning can cause emotional instability, attention deficit disorder, hyperactivity, anxiety, irritability, insomnia, excess lethargy or hyperactivity, pervasive developmental delay and loss of milestones such as language.  In extreme cases there can be seizure, coma and even death.

Lead exposure in young children has been linked to learning disabilities.5 Children with blood lead concentrations greater than 10 μg/dL are also in danger of developmental disabilities,6 decreases in intelligence, nonverbal reasoning, short-term memory, attention, reading and arithmetic ability, emotional regulation, and social engagement.7

The effect of lead on children’s cognitive abilities takes place at very low levels.8 Reduced academic performance is commonly associated with lead exposure even when blood lead levels are lower than 5 μg/dL.9

Blood lead levels below 10 μg/dL have been reported to be associated with lower IQ and behavior problems such as aggression.10

Figure 1. From www.ricknevin.com

 

Unlike other heavy metals, there is apparently no lower threshold such that lead does not have an impact on a child’s development.11

Since lead poisoning harms the central and peripheral nervous systems, victims can also experience decreased nerve conduction, a painless wristdrop (weakness of the extensor muscles of hand) and reductions in fine motor skills.

Can Lead Poisoning Generate Violent Behavior?
Neuropsychiatric disorders such as attention deficit hyperactivity disorder and antisocial behavior have been linked with lead exposure.12 Children with elevated lead levels correlated with higher scores on aggression and delinquency measures13 and violent criminal activities in adulthood.14

Countries with the highest air lead levels have been found to have the highest murder rates (after adjusting for confounding factors).13  A May 2000 study by economic consultant Rick Nevin theorizes that lead exposure explains 65% to 90% of the variation in violent crime rates in the US.15  Nevin’s 2007 paper seems to show a strong association between preschool blood lead and subsequent crime rate trends over several decades across nine countries.15,16

Do Adults Experience Lead Poisoning?
High blood lead levels in adults are also associated with decreases in cognitive performance and with psychiatric symptoms such as depression and anxiety.17 It was found in a large group of current and former inorganic lead workers in Korea that blood lead levels in the range of 20–50 μg/dL were correlated with neuro-cognitive defects in the adult workers.18 Increases in blood lead levels from about 50 to about 100 μg/dL in adults are associated with persistent, and possibly permanent, impairment of central nervous system function,19

Neurological damage can generate a number of cognitive developmental disabilities.

References
  1. Lead Neurotoxicity in Children: Basic Mechanisms and Clinical Correlates, Theodore Lidsky, Brain 126 (Pt 1): 5–19
  2. Decreased Brain Volume in Adults with Childhood Lead Exposure, Cecil, Brubaker, Adler, Dietrich Altaye, Egelhoff, Wesse, Elangovan et al, PLoS medicine 5 (5): e112.
  3. Pediatric Toxicology: Diagnosis and Management of the Poisoned Child, Mycyk, Hryhorczuk, Amitai, McGraw-Hill Professional, 2005, p. 462
  4. Lead / Rudolph’s Pediatrics (21st ed.), Pearson & Schonfeld, McGraw-Hill Professional, 2003, p. 369
  5. A Global Approach to Childhood Lead Poisoning Prevention, Meyer, McGeehin & Falk, International Journal of Hygiene and Environmental Health, 2006 206 (4–5): 363–9
  6. Principles of Toxicology / Goodman and Gilman’s Manual of Pharmacology and Therapeutic, Brunton, Goodman, Blumenthal, Buxton & Parker,  McGraw-Hill Professional, 2007, p. 1131
  7. Lead Bullet Fragments in Venison from Rifle-Killed Deer: Potential for Human Dietary Exposure, W.G. Hunt, R.T. Watson, J.L Oaks, C.N Parish, K.K. Burnham, R.L. Tucker, J.R. Belthoff, G. Hart PLoS ONE 4 (4): e5330, (2009). Zhang, Baohong, ed.
  8. Low-Level Environmental Lead Exposure and Children’s Intellectual Function: An International Pooled Analysis, Lanphear et al, Environmental health perspectives 113 (7): 894–9.
  9. Metals / Principles and Methods of Toxicology (5th ed.), Merrill, Morton & Soileau, CRC Press, 2007, p. 861
  10. Protecting Children From Toxic Exposure: Three Strategies, Guidotti & Ragain, Pediatric Clinics of North America 54 (2): 227–35, vii, 2007
  11. The Long-Term Effects of Exposure to Low Doses of Lead in Childhood (An 11-Year Follow-Up Report),  Needleman, Schell, Bellinger, Leviton & Allred, The New England Journal of Medicine 322 (2): 83–8.
  12. Very Low Lead Exposures and Children’s Neurodevelopment, Bellinger, Current Opinion in Pediatrics 20 (2): 172–7, 2008
  13. Lead Poisoning, Needleman, Annual Review of Medicine 55: 209–22, 2004.
  14. Lead Hazards for Pregnant Women and Children: Part 1: Immigrants and the Poor Shoulder Most of the Burden of Lead Exposure in this Country, Cleveland, Minter, Cobb, Scott and German, The American journal of nursing 108 (10): 40–9, 2008.
  15. How Lead Exposure Relates to Temporal Changes in IQ, Violent Crime, and Unwed Pregnancy, Nevin, Environmental Research 83 (1): 1–22, 2000.
  16. Understanding International Crime Trends: the Legacy of Preschool Lead Exposure, Nevin, Environmental Research 104 (3): 315–36, 2007.
  17. Cumulative Lead Dose and Cognitive Function in Adults: A Review of Studies That Measured Both Blood Lead and Bone Lead, Shih, Hu, Weisskopf & Schwartz, Environmental health perspectives 115 (3): 483–92, 2007.
  18. Recommendations for Medical Management of Adult Lead Exposure, Kosnett, Wedeen, Rothenberg, Hipkins, Materna, Schwartz,; Hu & Woolf,  Environmental health perspectives 115 (3): 463–71, 2007.
  19. Lead and Compounds / Environmental Toxicants: Human Exposures and Their Health Effects (3rd ed.), Lippmann, Wiley-Interscience, 2009.